Design For Manufacturing, (DFM)

1

1 Introduction

New Product Design concept starts with conceptualization of ‘Product Idea’. The product

idea typically takes into consideration of customer requirements.

Design for manufacture (DFM) has evolved over the past decade or so from a general

awareness of the need to consider more thoroughly the ease and economics of manufacture

into a set of structured strategies, methodologies, and tools for evaluating a strategies,

methodologies, and tools for evaluating a design for its manufacturability. Spiraling costs and

the emergence of global competition have put an emphasis on design-to-cost strategies,

where cost is elevated to the same level of concern as performance and function, from the

moment the new product is conceived. 1 Design-to cost strategies require cost estimates at

each stage in the product development process. However, the average engineering designer

knows little about the cost of materials and processes implied and specified through the

design drawings. Manufacturing options even for simple parts are numerous, and the effects

on both recurring costs (piece-part costs) and nonrecurring costs (tooling costs) are dramatic.

Rapid cost estimating systems are necessary to enable product designers and product

development teams to make sound decisions early in the conceptual design phase and not, as

is often the case, provide fodder for later value-analysis teams) The conscientious design

engineer is interested in the existence of any design tradeoffs that can be made to help

converge on the most economical approach. Many product manufacturers outsource much of

their primary manufacturing. In some cases, they will only carry out the final assembly

process or even just final distribution and marketing. The product with designing the highest

quality product for the lowest cost manufacture by local, national, or offshore lowest cost

manufacture by local, national, or offshore contractors. Access and understanding of cost

even at the conceptual design stage of the product development process is key to the

realization of competitive world-class products.

A manufacturing system is composed of a large number of distinct processes which all

influence product cost, product quality and productivity of the system. The interactions

2

between these various facets of a manufacturing system are complex, and decisions made

concerning one aspect have ramifications which extend to the others.

A product is usually created by design engineers who may not be familiar with

manufacturing and assembly processes of the product. With insufficient communication with

other engineers and manufacturing functions, design engineers may design a product that will

lead to severe problems during manufacturing and assembly operations. These problems

include failures of meeting dimensions and tolerance requirements, or difficulty in producing

the product in a cost effective way.

Contrary to the traditional sequential approach to design, the distinct processes in a

concurrent product development environment are accomplished simultaneously. Concurrent

design involves the simultaneous consideration and integration of various engineering

activities throughout the product life cycle. By bringing downstream expertise of processes to

the design stage, concurrent engineering will result in fewer design changes and hence lower

cycle time and production cost. According to the experience of Ford Motors Co.,

approximately 70% of the manufacturing cost is dictated by decisions made at the design

stage, although design only accounts for 5% of the total product development expenses

(Plastics World, 1988). This clearly indicates the need of an increased effort on design by

considering the products’ requirements of manufacturing and assembly processes. To avoid

the drawbacks of the conventional product development approach and to take advantage of

the concurrent engineering approach, a framework of concurrent engineering, which models

the engineering design procedure, is developed. The framework consists of four design steps:

design formation, product modeling and representation, Design for Assembly and

Manufacture (DFA and DFM) critique and evaluation, and design optimization. Feature-

based design provides the advantage of using features, which are high level entities closely

related to their manufacturing and assembly operations, for representing products.

The principles of design for manufacturability (DFM) and its application are not really new.

Awareness of the importance of designing products for easy manufacture has existed in

clever design and manufacturing engineers since product design and manufacturing activities

3

originated. However, use of the term design for manufacturability, recognition of it as a

worthwhile engineering approach, and development of an organized DFM methodology are

more recent. The following are some highlights from the history of designing products for

easier manufacture. It is entirely possible for a design engineer, aware of the advantages of

designing for manufacturability to work independently in optimizing the product design for

ease of manufacture. However, most current DFM specialists advocate a team approach in

applying DFM. Essentially, this means that the design and manufacturing people work

together to gain the benefits of manufacturing knowledge and experience that the designer

may not have and to ensure that the product is both functional and manufacturable.

DFM is not a fixed system. This system is continually being developed, both in

university research projects and by a number of consultants and within companies. The

objectives of almost all developments are to make guidelines more accessible to designers

and more easily applied. Additionally, and more important, evaluations are put on each

guideline so that the designer can determine how much cost gain can be achieved if the

guideline is incorporated. All these advances depend on the use of computers.

Computerization is the developing movement in DFM.

The following principles, applicable to virtually all manufacturing processes, will aid

designers in specifying components and products that can be manufactured at minimum cost.

1. Simplicity. Other factors being equal, the product with the fewest parts, the least

intricate shape, the fewest precision adjustments, and the shortest manufacturing

sequence will be the least costly to produce. Additionally, it usually will be the most

reliable and the easiest to service.

2. Standard materials and components. Use of widely available materials and off-the-

shelf parts enables the benefits of mass production to be realized by even low-

unitquantity products. Use of such standard components also simplifies inventory

management, eases purchasing, avoids tooling and equipment investments, and speeds

the manufacturing cycle.

4

3. Standardized design of the product itself. When several similar products are to be

produced, specify the same materials, parts, and subassemblies for each as much as

possible. This procedure will provide economies of scale for component production,

simplify process control and operator training, and reduce the investment required for

tooling and equipment.

4. Liberal tolerances. Although the extra cost of producing too tight tolerances has

been well documented, this fact is often not appreciated well enough by product

designers. The higher costs of tight tolerances stem from factors such as (a) extra

operations such as grinding, honing, or lapping after primary machining operations,

(b) higher tooling costs from the greater precision needed initially when the tools are

made and the more frequent and more careful maintenance needed as they wear, (c)

longer operating cycles, (d) higher scrap and rework costs, (e) the need for more

skilled and highly trained workers, (f) higher materials costs, and (g) more sizable

investments for precision equipment.

5. Use of the most processible materials. Use the most processible materials available

as long as their functional characteristics and cost are suitable. There are often

significant differences in processibility (cycle time, optimal cutting speed, flow

ability, etc.) between conventional material grades and those developed for easy

processibility. However, in the long run, the most economical material is the one with

the lowest combined cost of materials, processing, and warranty and service charges

over the designed life of the product.

6. Teamwork with manufacturing personnel. The most producible designs are

provided when the designer and manufacturing personnel, particularly manufacturing

engineers, work closely together as a team or otherwise collaborate from the outset.

7. Avoidance of secondary operations. Consider the cost of operations, and design in

order to eliminate or simplify them whenever possible. Such operations as deburring,

inspection, plating and painting, heat treating, material handling, and others may

prove to be as expensive as the primary manufacturing operation and should be

considered as the design is developed. For example, firm, nonambiguous gauging

5

points should be provided; shapes that require special protective trays for handling

should be avoided.

8. Design appropriate to the expected level of production. The design should be

suitable for a production method that is economical for the quantity forecast. For

example, a product should not be designed to utilize a thin-walled die casting if

anticipated production quantities are so low that the cost of the die cannot be

amortized. Conversely, it also may be incorrect to specify a sand-mold aluminum

casting for a mass-produced part because this may fail to take advantage of the labor

and materials savings possible with die castings.

9. Utilizing special process characteristics. Wise designers will learn the special

capabilities of the manufacturing processes that are applicable to their products and

take advantage of them. For example, they will know that injection-molded plastic

parts can have color and surface texture incorporated in them as they come from the

mold, that some plastics can provide “living hinges,” that powder-metal parts

normally have a porous nature that allows lubrication retention and obviates the need

for separate bushing inserts, etc. Utilizing these special capabilities can eliminate

many operations and the need for separate, costly components.

10. Avoiding process restrictiveness. On parts drawings, specify only the final

characteristics needed; do not specify the process to be used. Allow manufacturing

engineers as much latitude as possible in choosing a process that produces the needed

dimensions, surface finish, or other characteristics required.

The advantages of DFM are included:

a) Reduce Time to Market

b) Reduce manufacturing time

c) Reduce rework

d) Improve design efficiency

e) Helps in Rapid Prototyping

f) Better cost control

g) Less time in product testing

6

2 Product Specification

The product that has been chosen for this study is Toaster. The function of this product is to

Toast breads by transport the heat to the breads with the heated element made from Tungsten

to change the electricity energy to the heat.

Toaster is typically a small Mechanic-electric kitchen appliance designed to toast multiple

types of Bread products. A typical modern two-slice toaster draws from 600 to 1200 Watts

and makes toast in 1 to 3 minutes. There are also non-electrical toasters that can be used to

toast bread products over an open fire or flame.

Figure 2.0: Isometric view from New Designed Toaster

Specification:

• Metallic body

• Plastic bottom cover

• Environment protective

• Overall parts = 32 parts

• Different parts = 23 parts

7

2.1 Illustration the main parts of product in an exploded/disassembly view

As it is obvious in the figure 2.0, the main components of Toaster has been exhibited.

Figure 2.1: Exploded view of toaster and illustration of main components.

The detailed and some fasteners has been omitted.

2.2 Objectives

In this project we intend to first, detect the best material and process for five components of

our product. By Appling the Boothroyd-Dewhurst DFM methodology; Determine what type

of materials are used in the new design of the product and the cause of that. How they are

made and why those particular manufacturing processes are used, by which the parts can be

made economically. The goal of selection materials are to minimize the cost of

manufacturing and materials and also to minimize waste in manufacturing furthermore to

maximize the performance of the part and safety of the product and also to maximize in the

product life cycle.

8

2.3 Selection of product’s components

2.3.1 Total number of parts

The Toaster contains of 23 different parts which is introduced in the table below.

Table 3.1: Introduction of Toaster Components

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

1

Front plate

2

Small Fire proof plate

3

Cylindrical Guide

4

Spring

9

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

5

moving system

6

U shape

7

Plastic part of U plate female

8

Plastic part of U plate male

10

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

9

Heater board left (Standard Part)

10

Heater board middle (Standard Part)

11

Heater board right (Standard Part)

12

Back plate

11

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

13

connector

14

Electrical kit (Standard Part)

15

Timer regulator

16

Stopper switch

12

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

17

Switch (Standard part)

18

wire of plug

19

Electrical connection snap-fit

20

Bottom cover

13

Par

t ID

NO

.

pict

ure

Nam

e of

par

t

21

Top Cover

22

Handling plastic part

23

Holder of wire

14

2.3.2 Introduction of redesigned parts

Based on product chosen in our Design for Assembly (DFA) assignment we need to select 5

different parts from the product and illustrate them in a detail manner:

1. Front plate

2. Moving system

3. Electrical connection snap-fit

4. Bottom cover

5. Top Cover

Front plate

Easy to manipulate.

Thickness = 10 mm

Size = 120 mm

Justification: The process of this part

has been changed and it has combined

two functions with each other. Before the

changes this part just guided the moving

system. Also it had 3 more punching

processes which is eliminated in this

new design.

Function: Main role of front plate is

Holding the heater board and moving

system. The other role is to guide the

moving system and cover the inner side

of toaster.

15

Moving system

Easy to manipulate.

Thickness = 100 mm

Size = 150 mm

Justification: this part have been

contained from 4 deferent part but same

material, in new design all the parts have

been design by bending process with just

one sheet metal.

Function: Holding the handling plate,

Magnet, Bread’s Holder. Also sliding

movement to move the breads down and

return it up after toasting Operation.


Easy to manipulate.

Thickness = 4 mm

Size = 12 mm

Justification: The previous process for

this part was soldering the wire to the

switch, by designing the snap fit

connector and manufacturing it. It would

be beneficial in cost and time wastage.

Function: Fastening the wire of plug to

the switch.

16

Bottom cover

Easy to manipulate.

Thickness = 15 mm

Size = 250 mm

Justification: The bottom cover in new

design, has some snap fits instead of

using screws for fastening, also its

material has been changed from metallic

to the plastic to improve the time and

cost of manufacturing by improving the

time of manufacturing

Function: To cover and maintain all

assembled parts and the main cover

Top Cover

Easy to manipulate.

Thickness = 300 mm

Size = 250 mm

Justification: The Top cover also has

been changed from the premier design

by changing the material and design

also. This part changed from

combination of plastic and metallic of 4

parts to one plastic part.

Function: Covering all Sub assembly

parts.

17

3 Suitable materials for each par

3.1 Type of material

3.1.1 Cast Iron: Cast irons represent the largest quantity of all metals cast, and they can be cast easily into

intricate shapes. They generally possess several desirable properties, such as wear resistance,

high hardness, and good machinability.

3.1.2 Carbon Steels

Improvement hardening, strength, hardness, and wear resistance; it reduces ductility, ability

to weld, and toughness.

• Low Carbon Steels (Mild Steel):

Mild steel (<0.25% carbon) is the most commonly used, readily welded construction

material, and has the following typical mechanical properties (Grade 43A in BS4360; ability

to weld structural steel):

• Tensile strength, 430 N/mrn2

• Yield strength, 230 N/m2

• Elongation, 20%

• Tensile modulus, 210 KN/mm2

• Hardness, 130 DPN

None steel exceeds the tensile modulus of mild steel. Therefore, in applications in which

rigidity is a limiting factor for design (e.g., for storage tanks and distillation columns), high-

strength steels have no advantage over mild steel. Stress concentrations in mild steel

structures are relieved by plastic flow and are not as critical in other, less-ductile steels. Low-

carbon plate and sheet are made in three qualities: fully killed with silicon and aluminum,

semikilled (or balanced), and rimmed steel. Fully killed steels are used for pressure vessels.

Most general-purpose structural mild steels are semikilled steels. Rimming steels have

minimum amounts of deoxidation and are used mainly as thin sheet for consumer

applications.

The strength of mild steel can be improved by adding small amounts (not exceeding 0.1 %)

of niobium, which permits the manufacture of semikilled steels with yield points up to 280

18

N/mm. By increasing the manganese content to about 1.5% the yield point can be increased

up to 400 N/mm2. Thus provides better retention of strength at elevated temperatures and

better toughness at low temperatures.

• Corrosion Resistance:

Equipment from mild steel usually is suitable for handling organic solvents, with the

exception of those that are chlorinated, cold alkaline solutions (even when concentrated),

sulfuric acid at concentrations greater than 88% and nitric acid at concentrations greater than

65% at ambient temperatures.

Mild steels are rapidly corroded by mineral acids even when they are very dilute (pH less

than 5). However, it is often more economical to use mild

steel and include a considerable corrosion allowance on the thickness of the apparatus. Mild

steel is not acceptable in situations in which metallic contamination of the product is not

permissible.

• Heat Resistance:

The maximum temperature at which mild steel can be usedis 550°C. Above this temperature

the formation of iron oxides and rapid scaling makes the use of mild steels uneconomical. For

equipment subjected to high loadings at elevated temperatures, it is not economical to use

carbon steel in cases above 450°C because of its poor creep strength. (Creep strength is time-

dependent, with strain occurring under stress.)

• Low Temperatures

At temperatures below 10°C the mild steels may lose ductility, causing failure by brittle

fracture at points of stress concentrations (especially at welds) [8,9]. The temperatures at

which the transition occurs from ductile to

brittle fraction depends not only on the steel composition, but also on thickness.

Stress relieving at 600-7OO'C for steels decreases operation at temperatures some 20°C

lower. Unfortunately, suitable furnaces generally are not available, and local stress relieving

of welds, etc., is often not successful because further stresses develop on cooling.

19

3.1.3 High-Carbon Steels

High carbon steels containing more than 0.3% are difficult to weld, and nearly all production

of this steel is as bar and forgings for such items as shafts, bolts, etc Theseitems can be

fabricated without welding.

• Low-Temperature Ductility:

Nickel is the alloying element used for improving low-temperature ductility. The addition of

1 .5% nickel to 0.25% Cr/0.25% Mo steels provides satisfactory application for moderately

low temperatures down to about -50°C.

20

Heat treatment by quenching and tempering improves the low temperature ductility of steels

such as 0.5 Cr, 0.5% Mo, 1% Ni Type V. For lower- temperature application (below -

196"C), up to 9% nickel is used as the sole alloying element.

3.1.4 High-Carbon, Low-Alloy Steels:

High-carbon (about 0.4%), low-alloy steels that are not weldable usually are produced as

bars and forging for such items as shafting, high-temperature bolts and gears and ball bearing

components. These steels can be less drastically quenched and tempered to obtain tensile

strengths of at least 1500 N/mm2, thus minimizing the danger of cracking.

• Properties of High-Alloy Steels:

Stainless and heat-resisting steels containing at least 18% by weight chromium and 8%

nickel are in widespread use in industry. The structure of these steels is changed from

magnetic body centered cubic or ferritic crystal structure to a nonmagnetic, facecentered

cubic or austenitic crystal structure. 3.5.1 Chromium Steels (400 Series), Low-Carbon

Ferritic (Type 405): 12-13% Chromium. The main use of this type steel is for situations in

which the process material may not be corrosive to mild steel, yet contamination due to

rusting is not tolerable and temperatures or conditions are unsuitable for aluminum. However,

prolonged use of these steels in the temperature range of 450 to 550°C causes low-

temperature embrittlement of most ferritic steels with more than 12% chromium.

3.1.5 Alloy Steel

Steel classification is important in understanding what types are used in certain

applications and which are used for others. For example, most commercial steels are

classified into one of three groups: plain carbon, low-alloy, and high-alloy. Steel

classification systems are set up and updated frequently for this type of information.

Generally, carbon is the most important commercial steel alloy. Increasing carbon

content increases hardness and strength andimproves hardenability. But carbon also increases

brittleness and reduces weldability because of its tendency to form martensite. This means

carbon content can be both a blessing and a curse when it comes to commercial steel.

21

And while there are steels that have up to 2 percent carbon content, they are the exception.

Most steel contains less than 0.35 percent carbon. To put this in perspective, keep in mind

that’s 35/100 of 1 percent.

Now, any steel in the 0.35 to 1.86 percent carbon content range can be hardened using a heat-

quench-temper cycle. Most commercial steels are classified into one of three groups:

• Plain carbon steels

• Low-alloy steels

• High-alloy steels

3.1.6 Low-alloy Steels

When these steels are designed for welded applications, their carbon content is usually below

0.25 percent and often below 0.15 percent. Typical alloys include nickel, chromium,

molybdenum, manganese, and silicon, which add strength at room temperatures and increase

low-temperature notch toughness.

These alloys can, in the right combination, improve corrosion resistance and influence

the steel’s response to heat treatment. But the alloys added can also negatively influence

crack susceptibility, so it’s a good idea to use low-hydrogen welding processes with them.

Preheating might also prove necessary. This can be determined by using the carbon

equivalent formula, which we’ll cover in a later issue.

3.1.7 High-alloy Steels

For the most part, we’re talking about stainless steel here, the most important commercial

high-alloy steel. Stainless steels are at least 12 percent chromium and many have high nickel

contents. The three basic types of stainless are:

• Austenitic

• Ferritic

• Martensitic

22

Martensitic stainless steels make up the cutlery grades. They have the least amount of

chromium, offer high hardenability, and require both pre- and postheating when welding to

prevent cracking in the heat-affected zone (HAZ).

Ferritic stainless steels have 12 to 27 percent chromium with small amounts of austenite-

forming alloys.

Austenitic stainless steels offer excellent weldability, but austenite isn’t stable at room

temperature. Consequently, specific alloys must be added to stabilize austenite. The most

important austenite stabilizer is nickel, and others include carbon, manganese, and nitrogen.

3.1.8 Stainless Steels

They primarily are characterised by their corrosion resistance, high strength and

ductility, and high chromium content. They are called stainless because, in the presence of

oxygen (air), they develop a thin, hard, adherent film of chromium oxide that protects the

metal from corrosion. This protective film builds up again in the event that the surface is

scratched.

3.1.9 Tool and Die Steels

Tool and die steels are specially alloyed steels designed for high strength, impact

toughness, and wear resistance at room and elevated temperature. They commonly are used

in the forming and machining of metals.

Aluminum and its’ alloys

Aluminum is the world’s most abundant metal and does the third most common

element comprise 8% of the earth’s crust. The versatility of aluminum makes it the most

widely used metal after steel.

23

Aluminum is derived from the mineral bauxite. Bauxite is converted to aluminum oxide

(alumina) via the Bayer Process. The alumina is then converted to aluminum metal using

electrolytic cells and the Hall-Heroult Process.

Pure aluminum is soft, ductile, and corrosion resistant and has a high electrical

conductivity. It is widely used for foil and conductor cables, but alloying with other elements

is necessary to provide the higher strengths needed for other applications. Aluminum is one

of the lightest engineering metals, having strength to weight ratio superior to steel. By

utilizing various combinations of its advantageous properties such as strength, lightness,

corrosion resistance, recyclability and formability, aluminum is being employed in an ever-

increasing number of applications. This array of products ranges from structural materials

through to thin packaging foils.

Aluminum is most commonly alloyed with copper, zinc, magnesium, silicon,

manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and

nickel are also made and iron is invariably present in small quantities.

There are over 300 wrought alloys with 50 in common use. They are normally

identified by a four figure system which originated in the USA and is now universally

accepted.

Aluminum has a density around one third that of steel or copper making it one of the

lightest commercially available metals. The resultant high strength to weight ratio makes it an

important structural material allowing increased payloads or fuel savings for transport

industries in particular.

Pure aluminum doesn’t have a high tensile strength. However, the addition of alloying

elements like manganese, silicon, copper and magnesium can increase the strength properties

of aluminum and produce an alloy with properties tailored to particular applications.

Aluminum is well suited to cold environments. It has the advantage over steel in that

its’ tensile strength increases with decreasing temperature while retaining its toughness. Steel

on the other hand becomes brittle at low temperatures

24

When exposed to air, a layer of aluminum oxide forms almost instantaneously on the

surface of aluminum. This layer has excellent resistance to corrosion. It is fairly resistant to

most acids but less resistant to alkalis.

The thermal conductivity of aluminum is about three times greater than that of steel.

This makes aluminum an important material for both cooling and heating applications such as

heat-exchangers. Combined with it being non-toxic this property means aluminum is used

extensively in cooking utensils and kitchenware.

Along with copper, aluminums has an electrical conductivity high enough for use as an

electrical conductor. Although the conductivity of the commonly used conducting alloy

(1350) is only around 62% of annealed copper, it is only one third the weights and can

therefore conduct twice as much electricity when compared with copper of the same weight.

From UV to infra-red, aluminums is an excellent reflector of radiant energy. Visible

light reflectivity of around 80% means it is widely used in light fixtures. The same properties

of reflectivity makes aluminums ideal as an insulating material to protect against the sun’s

rays in summer, while insulating against heat loss in winter.

Aluminum can be severely deformed without failure. This allows aluminums to be

formed by rolling, extruding, drawing, machining and other mechanical processes. It can also

be cast to a high tolerance.

Alloying, cold working and heat-treating can all be utilised to tailor the properties of

aluminum.

The tensile strength of pure aluminum is around 90 MPa but this can be increased to

over 690 MPa for some heat-treatable alloys

3.1.10 Copper and its’ alloys:

Copper is an excellent electrical conductor. Most of its uses are based on this property

or the fact that it is also a good thermal conductor. However, many of its applications also

rely on one or more of its other properties. For example, it wouldn't make very good water

and gas pipes if it were highly reactive. On this page, we look at these other properties:

25

• a good electrical conductor

• a good thermal conductor

• corrosion resistant

• antibacterial

• easily joined

• ductile

• tough

• non magnetic

• attractive colour

• easy to alloy

• recyclable

• catalytic

Copper is low in the reactivity series. This means that it doesn't tend to corrode. Again,

this is important for its use for pipes, electrical cables, saucepans and radiators. However, it

also means that it is well suited to decorative use. Jewellery, statues and parts of buildings

can be made from copper, brass or bronze and remain attractive for thousands of years.

Copper is a ductile metal. This means that it can easily be shaped into pipes and drawn

into wires. Copper pipes are lightweight because they can have thin walls. They don't corrode

and they can be bent to fit around corners. The pipes can be joined by soldering and they are

safe in fires because they don't burn or support combustion.

Copper and copper alloys are tough. This means that they were well suited to being

used for tools and weapons. Imagine the joy of ancient man when he discovered that his

carefully formed arrowheads no longer shattered on impact. The property of toughness is

vital for copper and copper alloys in the modern world. They do not shatter when they are

dropped or become brittle when cooled below 0 °C.

Copper can be recycled without any loss of quality. 40% of the world's demand is met

by recycled copper.

26

3.1.11 Zinc and Alloys:

Zinc is a metal that is fourth most utilized industrially, after iron, aluminum, and copper. It

uses for galvanizing iron, steel sheet, and wire. And also it applies as a material in casting.

Zinc based alloys are used extensively in die casting for making such products as fuel pumps

and grills for automobiles, components for household appliances such as vacuum cleaners

and washing machines, kitchen equipment, various machinery parts, and photoengraving

equipment. Another use for zinc is in superplastic alloys that can be formed by methods used

for forming plastics or metals.

3.1.12 Magnesium Alloys:

Controls the shape of inclusions and improves toughness in high strength, low-alloy steels; it

deoxidizes steels. And it has the same effects as Cerium.

3.1.13 Titanium and its’ Alloys

Titanium does not occur free in Nature. However, when combined with other

elements, it is quite abundant, occurring in small amounts in most of the

volcanic,sedimentary and metamorphic rocks. Its more important minerals are ilmenite,

rutile, arizonite (iron titanate), brookite, anatase, leucochene (titanium dioxide), perovskite

(calcium titanate), and others. The first two have commercial importance, and can be found

in deposits spread all over the world. There are important rutile and limonite deposits in

Australia, Argentina, USA, Central Africa, Brazil, Canada, Egypt, India and Norway. The

largest well-known deposits of rutile are located in Australia.

Titanium and its alloys are relatively new engineering metals since they have been in use

only since about 1952. They are extremely attractive materials for engineers because they

have a high strength to weight ratio, high elevated temperature properties to about 550oC,

and excellent corrosion resistance particularly in oxidising acids and chloride media. This

metal is being increasingly used for marine applications. Its resistance to seawater attack

combined with its mechanical properties make it a prime choice for equipment operating

within the sea or transferring seawater.

27

Titanium is not an 'exotic' metal; it is the fourth most abundant structural metal in

the earth's crust, and the ninth industrial metal. This metal has become the prime selection

for a wide range of critical and demanding applications.

Titanium Alloys are generally divided into three groups (Alpha, Alpha-Beta and

Beta). The Alpha group contain most importantly aluminum and tin. They can also contain

molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon. Alpha alloys

are not suitable for heat treatment. Alpha alloys are used for aircraft parts and cryogenic

equipment. The Alpha-Beta group can be strengthened by heat treatment. The alloys are used

in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware. The

Beta Alloys have good hardenability. Beta alloys are slightly more dense than other titanium

alloys, having densities ranging from 4800 to 5050 kg/m3. They are the least creep resistant

alloys, they are weldable, and can have yield strengths up to 1345 x 106 Pa.(Solution treated

and age hardened) Beta alloys are the smallest group. They are used for heavier duty

purposes on aircraft.

3.1.14 Nickel Alloys

Improves strength, toughness, corrosion resistance and hardenability. Nickel alloys

are used in high temperature applications (such as jet engine components, rockets, and

nuclear power plants), in coins, and in marine applications.

3.1.15 Refractory Alloys

There are four refractory metals: Molybdenum, Niobium, Tungsten, and Tantalum.

These metals are called refractory because of their high melting points. More than most other

metals and alloys, the refractory metals maintain their strength at elevated temperatures.

Therefore, they are of great importance in rocket engines, gas turbines, and various other

aerospace applications; in the electronic, nuclear-power, and chemical industries; and as tool

and die materials.

28

3.1.16 Thermoplastics

Thermoplastics soften when heated and harden again to their original state when

cooled. This allows them to be molded to complex shapes. Most accept coloring

agents and fillers, and many can be blended to give a wide range of physical, visual

and tactile effects. Their sensitivity to sunlight is decreased by adding UV filters, and

their flammability is decreased by adding flame retardants. The common

thermoplastics are listed in the adjacent table. They include polyolefin (polyethylene,

polypropylene), PVCS, polystyrenes, acrylics and certain polyesters (PET and PBT).

Some are crystalline, some amorphous, some a mixture of both. The properties of

thermoplastics can be controlled by chain length (measured by molecular weight), by

degree of crystallinity and by blending and plasticizing. As the molecular weight

increases, the resin becomes stiffer, tougher, and more resistant to chemicals, but it is

more difficult to mold to thin-wall sections. For thin-walls, choose a low molecular

weight resin; for higher performance, choose one with higher molecular weight.

Crystalline polymers tend to have better chemical resistance, greater stability at high

temperature and better creep resistance than those that are amorphous. For

transparency the polymer must be amorphous; partial crystallinity gives translucency.

The most transparent polymers are Acrylics, PC, PS and PET.

Some polymers crystallize faster than others: polyethylene crystallizes quickly

but polyesters do so more slowly – they remain amorphous under normal cooling

rates. Crystalline polymers have a more or less sharp melting point, which must be

exceeded for molding. Amorphous polymers do not; instead they progressively soften

and become more fluid as temperature increases above the glass transition

temperature; they must be heated above this temperature for extrusion and injection

molding. The processing force required to generate flow decreases slowly as

temperature rises above the glass transition temperature. Amorphous polymers have

greater impact strength and relatively low mold shrinkage. Semi-crystalline polymers

have higher shrinkage because of the volume change on crystallization.

29

Holes and ribs reduce the effect of shrinkage in a thermoplastic part. Areas near

the filling gate tend to shrink less than areas farther away. Shrinkage increases with

wall thickness and decreases with higher molding pressures. Fiber filled polymers

shrink less in the direction of flow because the fibers line up in this direction; the

shrinkage in the cross-flow direction is 2–3 times more than in the flow direction.

High service temperatures can cause shrinking in some semi-crystalline materials.

Fillers, or additives, are used to tailor certain properties of the composite such as

density, colour, flame/smoke retardance, moisture resistance and dimensional

stability. Most thermoplastics can be recycled.

3.1.17 Thermosets

If you are a do-it-yourself type, you have Araldite in your toolbox – two tubes,

one a sticky resin, the other an even stickier hardener. Mix and warm them so they

react to give a stiff, strong, durable polymer, stuck to whatever it was put on. Araldite

typifies thermosets – resins that polymerize when catalyzed and heated; when

reheated they do not melt – they degrade. The common thermosets are listed in the

table here. The first commercial thermoset was Bakelite, a trade-name for a phenolic

resin. Polyurethane thermosets are produced in the highest volume; polyesters come

second; phenolics, epoxies and silicones follow, and – not surprisingly – the cost rises

in the same order. Epoxies are two-part system that – when mixed – undergo a mildly

exothermic reaction that produces cross-linking. Phenolics are cross-linked by the

application of heat or heat and pressure. Vulcanization of rubber, catalyzed by the

addition of sulfur, can change the soft rubber of a latex glove to the rigid solid of

ebonite, depending on the level of cross-linking. Once shaped, thermosets cannot be

reshaped.

Thermosets have greater dimensional stability than thermoplastics; they are

used where there is a requirement for high temperature resistance and little or no

creep. Most are hard and rigid, but they can be soft and flexible (like natural and

synthetic rubber, as described above). Phenolics are most used where close-tolerance

30

applications are necessary, polyesters (often combined with glass fibers) where high

strength with low shrinkage is wanted.

Thermosets are shaped by compression molding, resin transfer molding,

injection molding, pultrusion and casting. They duplicate the mold finish and are

relatively free from flow lines and sink marks, depending on the mold design – high

gloss, satin or sand-blasted finishes are possible, and raised lettering can be molded in.

Molding can be adapted to low volume production by using low cost molds; but

higher production volumes, up to a million or greater, are economical only with

expensive molds that allow fast heating, cooling and extraction. Phenolics can only be

molded in black or brown; urea, melamine, alkyd and polyester compounds are

available in a wider range of colors. The fluidity of some thermosets before molding

allows them to take up fine detail, and to penetrate between fibers to create

composites. Most high-performance polymer composites have thermosetting matrix

materials. Dough and sheet molding compounds (dmc and smc) use polyesters;

filament-wound carbon or glass use epoxies as the matrix to give the highest

performance of all. Thermosets cannot be recycled.

3.1.18 Elastomers

Elastomers were originally called “rubbers” because they could rub out pencil

marks – but that is the least of their many remarkable and useful properties. Unlike

any other class of solid, elastomers remember their shape when they are stretched –

some, to five or more times their original length – and return to it when released. This

allows conformability – hence their use for seals and gaskets. High damping

elastomers recover slowly; those with low damping snap back, returning the energy it

took to stretch them – hence their use for springs, catapults, and bouncy things.

Conformability gives elastomers high friction on rough surfaces, part of the reason

(along with comfort) that they are used for pneumatic tires and footwear. Elastomers

are easy to foam, giving them the comfort of cushions, and increasing even further

their ability to conform to whatever shape is pressed against them.

31

Almost all engineering solids have elastic moduli (measuring their stiffness)

between 1 and 1000 Gpa. Elastomers are much less stiff – between 0.0001 and 1 Gpa.

This low stiffness, their ability to stretch and to remember their original shape all

derive from their structure. The molecules in an elastomer are long chains of linked

carbon (or, in silicones, silicon-oxygen chains), with hydrogen, nitrogen, chlorine or

fluorine attached to the sides. The carbon atoms that link to form the chain are

strongly bonded to each other, but the side-branches of one molecule are only weakly

attracted to those of another – indeed, at room temperature these molecule-to-

molecule bonds in an elastomer have melted. In this state the elastomer is a very

viscous liquid, its molecules tangled like a plate of cooked spaghetti, and it can be

molded. It is then cured; the curing creates occasional strong links between molecules,

freezing the tangle in its molded shape. Most of the length of any one molecule can

still slither over its neighbors, allowing stretch, but when released, the widely spaced

attachment points pull the tangle back to its original shape. In the case of natural

rubber, curing is achieved by heating with sulphur (“vulcanization”); in synthetic

rubbers the curing process is more complex but the effect is the same. This means that

elastomers are thermosets – once cured, you can’t remold them, or reshape or recycle

them, a major problem with car tires. Tires are the single biggest use of elastomers;

the second is footwear, followed by industrial rollers, belts, cushions, clothes and

sports-equipment. Elastomers are processed by casting, calendaring, extrusion, and

foaming.

3.1.19 A.B.S.

Acrylonitrile, butadiene, and styrene combine to form this common plastic often used to

make housings or other mechanical parts.

3.1.20 ACETATE

Acetates have good electrical insulating properties and is the material used to make movie

and microfilm.

32

3.1.21 ACRYLIC

Lucite and Plexiglass are trade names for acrylic which has widespread use where toughness

and transparency are required. Solvent cement is quite effective for welding pieces together.

3.1.22 BERYLLIUM OXIDE

A hard white ceramic-like material used as an electrical insulator where high thermal

conductivity is required. Beryllium oxide is highly toxic in powder form and should never be

filed or sanded and consequently has fallen out of common use. Power semiconductor heat

sinks can still be found with beryllium oxide spacers for electrical insulation.

3.1.23 CERAMIC

Ceramics are used to fabricate insulators, components, and circuit boards. The good

electrical insulating properties are complemented by the high thermal conductivity.

3.1.24 DELRIN

This Dupont acetal resin is made from polymerized formaldehyde and finds uses similar to

nylon. The material is rigid and has excellent mechanical and electrical properties making its

use common in appliances and electronics.

3.1.25 EPOXY/FIBERGLASS

This laminate is quite common due to its superior strength and excellent electrical properties

even in humid environment. Most modern circuit boards are made from a grade of

epoxy/fiberglass. (Grades include G10/FR4 and G11/FR5 extended temperature grade.)

3.1.26 GLASS

Glass insulation comes in a wide variety of forms including solid glass, fiber tapes, fiberglass

sheets and mats, woven tubing and cloth, and various composites. High temperature

operation is a key feature.

33

3.1.27 KAPTON

Polyimide film has exceptionally good heat resistance and superb mechanical and electrical

properties. Kapton tapes are fairly expensive but often indispensable.

3.1.28 KYNAR

As is Teflon, Kynar is a floropolymer with excellent chemical and abrasion resistance. It is

readily machined and welded.

3.1.29 LEXAN and MERLON

These polycarbonates have excellent electrical insulating properties. Optical grades are

available and the material is so tough that it meets U.L. requirements for burglary-resistance.

Non-transparent grades are machined to make strong insulators, rollers, and other mechanical

parts.

3.1.30 MELAMINE

Melamine laminated with woven glass makes a very hard laminate with good dimensional

stability and arc resistance. (Grades G5 is the mechanical grade and G9 is the electrical

grade.)

3.1.31 MICA

Mica sheets or "stove mica" is used for electrical insulation where high temperatures are

encountered. Thermal conductivity is high so mica insulators are useful for heat sinking

transistors or other components with electrically conductive cases. Puncture resistance is

good but the edges of the mica should be flush against a flat surface to prevent flaking. Mica

finds uses in composite tapes and sheets which are useful to 600 degrees centigrade with

excellent corona resistance. Sheets and rods of mica bonded with glass can tolerate extreme

temperatures, radiation, high voltage, and moisture. This rather expensive laminate may be

machined and it will not burn or outgas.

34

3.1.32 NEOPRENE

Neoprene rubber is the material used for most wet suits. This black rubber is commonly used

for gaskets, shock absorbers, grommets, and foams.

3.1.33 NOMEX

Nomex is a Dupont aromatic polyamide with an operating temperature range over 220

degrees centigrade and with superb high voltage breakdown. It is an excellent choice for

standardization since it outperforms many other materials.

3.1.34 NYLON

Nylon has good resistance to abrasion, chemicals, and high voltages and is often used to

fashion electro-mechanical components. Nylon is extruded and cast and is filled with a

variety of other materials to improve weathering, impact resistance, coefficient of friction,

and stiffness.

3.1.35 P.E.T.

Polyethylene terephthalate is a highly dimensionally stable thermoplastic with good

immunity to moisture. This excellent insulator has a low coefficient of friction and is

excellent for guides and other moving parts.

3.1.36 P.E.T.G.

A clear, tough copolyester commonly used for durable "bubble-packs" or food containers.

3.1.37 PHENOLICS

Phenolic laminated sheets are usually brown or black and have excellent mechanical

properties. Phenolics are commonly used in the manufacture of switches and similar

components because it is easily machined and provides excellent insulation. Phenolic

laminates are widely used for terminal boards, connectors, boxes, and components. (Grades

x, xx, xxx are paper/phenolic and grades c, ce, l, le are cotton/phenolic which is not the best

35

choice for insulation. Grade N-1 is nylon/phenolic and has good electrical properties even in

high humidity but exhibits some cold flow.)

3.1.38 POLYESTER (MYLAR)

A strong material often used in film sheets and tapes for graphic arts and electronics. Those

shiny balloons and "space blankets" are usually made from metalized Mylar. Mylar is also

used as a dielectric in capacitors.

3.1.39 POLYOLEFINS

Polyethylene is the white Teflon-like material used for food cutting board. Different densities

are available with the ultra-high molecular weight grade at the top offering toughness

outlasting steel in some applications. Polypropylene is another widely used polyolefin.

3.1.40 POLYSTYRENE

A clear insulator with superb dielectric properties. Polystyrene capacitors exhibit little

dielectric adsorption and virtually no leakage. Liquid polystyrene or Q-dope is a low-loss coil

dope used to secure windings and other components in RF circuits.

3.1.41 POLYURETHANE

Polyurethane is another common polymer which features abrasion and tear resistance along

with a host of desirable characteristics. Degrading little over time or temperature,

polyurethane is popular in both commercial and consumer applications.

3.1.42 PVC

Poly vinyl Cloride or PVC is perhaps the most common insulating material. Most wiring is

insulated with PVC including house wiring. Irradiated PVC has superior strength and

resistance to heat. PVC tapes and tubing are also quite common. Electrical and electronic

housings are commonly molded from PVC.

36

3.1.43 SILICONE/FIBERGLASS

Glass cloth impregnated with a silicone resin binder makes an excellent laminate with good

dielectric loss when dry. (Grades include G7.)

3.1.44 SILICONE RUBBER

A variety of silicone foam rubbers are available for insulating and cushioning electronic

assemblies. Silicone rubbers exhibit a wish list of characteristics including superb chemical

resistance, high temperature performance, good thermal and electrical resistance, long-term

resiliency, and easy fabrication. Liquid silicone rubbers are available in electrical grades for

conformal coating, potting, and gluing. Silicone rubbers found in the hardware store should

be avoided in electronic assemblies because they produce acetic acid. Silicone rubbers filled

with aluminum oxide are available for applications requiring thermal conductivity.

3.1.45 TFE (TEFLON)

Teflon is an excellent high temperature insulation with superb electrical properties. Teflon

tubing and wire insulation comes in a variety of colors and typically feels slippery. The

insulation is impervious to the heat and chemicals normally encountered in electronics

manufacturing but the material will "cold flow" so Teflon insulation is avoided where sharp

corners or points are encountered. Laminated TFE circuit boards take advantage of Teflon's

excellent microwave characteristics. Teflon emits a dangerous gas when exposed to extreme

heat. White Teflon terminals are commonly used where extremely good insulation is

required. The slick surface repels water so the insulation properties are fantastic even in high

humidity. High quality I.C. sockets are made from Teflon to reduce leakage currents. Teflon

and Teflon composite tapes with adhesive are available. FEP is a lower temperature Teflon.

37

3.2 Material Selection

Front plate

Function: Main role of front plate is Holding

the heater board and moving system. The

other role is to guide the moving system and

cover the inner side of toaster.

Material Properties:High Ductility, High

Melting point, Low Cost, Mettalic.

Material Selected: According to the material properties, Carbon steel, Alloy steel and

Stainless steel can be chosen from table 2.2 (in the appendix)

38

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting

2 Investment Casting

3 Die Casting

4 Injection Moulding

5 Structural Form Moulding

6 Blow Molding (Ext.)

7 Blow Molding (Inj.)

8 Rotational Molding

9 Impact Extrusion

10 Cold Heading

11 Closed Die Forging

12 Powder Metal Parts

13 Hot Extrusion

14 Rotary Swaging

15 Machining (From Stock)

16 ECM

17 EDM

18 Wire EDM

19 Sheet Metal (Stamp/bend)

20 Thermoforming

21 Metal Spinning

Not applicable Less applicable Normal applicable

39

Moving system

Function: Holding the handling plate,

Magnet, Bread’s Holder. Also sliding

movement to move the breads down and

return it up after toasting Operation.

Material Properties: High Ductility, High

Melting point, Low Cost, metallic

Material Selected: According to the material properties, Carbon steel, Alloy steel and

Stainless steel can be chosen from table 2.2 (in the appendix)

40

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

Not applicable Less applicable Normal applicable

41


Function: Fastening the wire of plug to the

switch.

Material Properties: High Ductility, High

conductivity, metallic

Material Selected: According to the material properties, Copper and alloys can be chosen

from table 2.2 (in the appendix)

42

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

43

Bottom cover

Function: To cover and maintain all

assembled parts and the main cover

Material Properties: Heat resistance, good

insulator, approximately high melting point.

Low cost, non-metalic

Material Selected: According to the material properties, Thermoplastic and Thermosets can

be chosen from table 2.2 (in the appendix)

44

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

45

Top Cover

Function: Covering all Sub assembly parts.

Material Properties: Heat resistance, good

insulator, approximately high melting point.

Low cost, non-metallic

Material Selected: According to the material properties, Thermoplastic and Thermosets can

be chosen from table 2.2 (in the appendix)

46

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

47

4 Suitable process for each part

4.1 Shape attributes

4.1.1 Depressions (Depress)

The ability to form recesses or grooves in the surfaces of the part. The first column

entry refers to the possibility of forming depressions in a single direction, while the second

entry refers to the possibility of forming depressions in more than one direction. These two

entries refer to depressions in the direction of tooling motion and those in other directions.

The following are some examples of tooling motion directions. Processes with split moulds—

the direction of mold opening. Processes that generate continuous profiles-normal to the

direction of extrusion or normal to the axis of the cutting medium. Forging (impact)

processes—the direction of impact of the tooling onto the part.

Uniform wall (UniWall ):

Uniform wall thickness. Any no uniformity arising from the natural tendency of the

process, such as material stretching or build-up behind projections in centrifugal processes is

ignored, and the wall is still considered uniform.

Uniform cross section (UniSect):

Parts where any cross sections normal to a part axis are identical, excluding draft.

Axis of rotation (AxisRot):

Parts whose shape can be generated by rotation about a single axis: a solid of

revolution.

48

Regular cross section (RegXSec):

Cross sections normal to the part's axis contain a regular pattern (e.g., a hexagonal or

splined shaft). Changes in shape that maintain a regular pattern are permissible (e.g., splined

shaft with a hexagonal head).

Captured cavities (CaptCav):

The ability is needed to form cavities with reentrant surfaces (e.g., a bottle).

Enclosed (Enclosed):

Parts are hollow and completely enclosed.

Draft-free surfaces (NoDraft):

The capability of producing constant cross sections in the direction of tooling motion.

Many processes can approach this capability when less than ideal draft allowances are

specified, but this designation is reserved for processes where this capability is a basic

characteristic and no draft can be obtained without cost penalty.

49

The sample of shape attributes

1 Depression YES/NO

2 Uniform wall YES/NO

3 Uniform cross section YES/NO

4 Axis Rotation YES/NO

5 Regular Cross section YES/NO

6 Capture Cavity YES/NO

7 Enclosed Cavity YES/NO

8 No Draft YES/NO

From this figure we find the attribute of each part’s shape and it can help us to choose

primary process of materials. So with next table that illustrate the primary process selection.

In primary process selection if YES or NO from attribute table under attributes. After that

from the vertical columns, all the processes that which have, N below YES in table and M

below NO are eliminating. The sample of table for primary process selection is shown in

table 2.2 in the appendix, at first some information about process can be useful.

50

Front plate

1 Depression YES

2 Uniform wall YES

3 Uniform cross section NO

4 Axis Rotation NO

5 Regular Cross section NO

6 Capture Cavity NO

7 Enclosed Cavity NO

8 No Draft NO

According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.

51

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

52

Moving System

1 Depression YES

2 Uniform wall YES

3 Uniform cross

section NO

4 Axis Rotation NO

5 Regular Cross

section NO

6 Capture Cavity NO


8 No Draft NO


53

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

54

1 Depression YES

2 Uniform wall YES

3 Uniform cross

section NO

4 Axis Rotation NO

5 Regular Cross

section NO

6 Capture Cavity NO


8 No Draft NO


55

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

56

1 Depression YES

2 Uniform wall NO

3 Uniform cross

section NO

4 Axis Rotation NO

5 Regular Cross

section NO

6 Capture Cavity NO


8 No Draft NO

According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2.

In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.

57

NO Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

58

1 Depression YES

2 Uniform wall YES

3 Uniform cross

section NO

4 Axis Rotation NO

5 Regular Cross

section NO

6 Capture Cavity NO


8 No Draft NO

According to shape attributes and referring to table 2.2, the items with Yes will eliminate

process that are not capable producing these features which are shown in the table with N and

those futures with No answer will eliminate process which are only capable of producing

parts with present features which are shown with M in table 2.2.

In the following table the result for 8 shape attributes have been summarized. The Black color

is shown the process which eliminated.

59

N

O Process

Ca

st Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

60

4.2 Appropriate Manufacturing Processes

4.2.1 Sand Casting:

The traditional method of casting metals is in sand molds and has been used for millennia.

Sand casting is still the most prevalent form of casting. Typical applications of sand casting

include machine bases, large turbine impellers, propellers, plumbing fixtures, and a wide

variety of other products and components (Figure 8.).

Basically, sand casting consists of (a) placing a pattern (having the shape of the desired

casting) in sand to make an imprint, (b) incorporating a gating system, (c) removing the

pattern and filling the mold cavity with molten metal, (d) allowing the metal to cool until it

solidifies, (e) breaking away the sand mold, and (f) removing the casting.

Figure 8. Schematic illustration of a sand casting, showing various features.

61

Process Part Size

Tolerances Surface Finish

Shape Produced Competitively

Process Limitation

Materials

Sand Casting

Weight : 0.2 lb -450 ton Min Wall: 0.125 in

General : +-0.02 ( 1 in ) +- 0.1 ( 24 in ) For dimensions across parting line add +-0.03 ( 50 Sq in ) +- 0.04 ( 200 Sq in )

500-1000 micro inches

Large parts with walls and internal passages of complex geometry requiring good vibration damping characteristics

Secondary machining usually required production rates often lower than that for other casting processes Tolerances, Surface finish Coarser than other casting processes

1.Cast Iron, 2.Carbon Steel 3.Alloy Steel 4.Stailnless steel 5.Alluminium 6.Copper 7.Zinc 8.Magnesium 12.Nickel

4.2.2 Investment Casting:

The investment casting process, also called the lost wax process, was first used during the

period from 4000 to 3000 B.C. Typical parts made are components for office equipment, as

well as mechanical components such as gears, cams, valves, and ratchets. Parts up to 1.5 m in

diameter and weighting as much as 1140 Kg have been cast successfully by this process. The

pattern is made of wax, or of a plastic such as polystyrene, by molding or rapid-prototype

techniques. The pattern is then dipped into a slurry of refractory material such as very fine

silica and binders, including water, ethyl silicate, and acids. After this initial coating has

dried, the pattern is coated repeatedly to increase its thickness for better surface finish in the

casting; subsequent layers use larger particles and are intended to build coating thickness

quickly (Figure 9.)The term investment derives from the fact that the pattern is invested

(surrounded) with the refractory materials. Wax patterns require careful handling because

they are not strong enough to withstand the forces encountered during mold making;

however, unlike plastic pattern, wax can be recovered and reused.

62

Process Part Size Tolerances Surface Finish

Shape Produced

Competitively

Process Limitation

Materials

Investment Casting

Weight : 1 Oz-110 lb ,

Major Dimension: to 50 lb ,

Min Wall : 0.025 (

Ferrous ) , 0.060

Nonferrous)

General : +- 0.002 (

1 in ) +- 0.004

(6in)

63-25 Micro inches

Small intricate parts

requiring good surface finish, good dimensional control, and high strength

Most investment casting are less than 12

in, Long and

less than 10 lbs,

L/D ratio of though or blind holes less than

4:1 and 1:1 respectively

Tooling cost and lead time generally

greater than for

othercasting processes except die

casting

2.Carbon Steel

3.Alloy Steel 4.Stailnless

steel 5.Alluminium

6.Copper 12.Nickel

Figure 9. Schematic illustration of the investment casting (lost wax) process.

4.2.3 Die Casting:

In pressure die casting, the metal is injected into the mold at high

primarily used for high-volume production of zinc, aluminum, and magnesium alloys,

although ferrous and copper-base alloys may also be cast. The process is capable of high

production rates. Production rates are related to the siz

complex as automotive engine blocks and transmission housings are routinely made by die

casting.

Die Casting Processes. There are two major types of die casting machines: hot

chamber and cold chamber. In the hot cham

gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into

the mold. This method avoids one metal transfer operation, and it is used primarily for zinc

and magnesium. In the cold chamber process (

poured or metered into the shot sleeve. The piston is then activated to force the metal into the

mold. Cold chamber machines are used for aluminum, because the process minimizes the

amount of time that the molten alloy is in contact with the die casting machine.

Fig. 19 Schematic showing the principal components of a hot chamber die casting machine

In pressure die casting, the metal is injected into the mold at high pressures. The process is

volume production of zinc, aluminum, and magnesium alloys,

base alloys may also be cast. The process is capable of high

production rates. Production rates are related to the size and complexity of the part. Parts as



chamber and cold chamber. In the hot chamber machine (Fig 19) ,the injection chamber is a



the cold chamber process (Fig20) the metal is melted separately and



of time that the molten alloy is in contact with the die casting machine.


63

pressures. The process is

volume production of zinc, aluminum, and magnesium alloys,

base alloys may also be cast. The process is capable of high

e and complexity of the part. Parts as



the injection chamber is a



the metal is melted separately and




Fig. 20 Schematic showing the principal components of a cold chamber die casting

Dies. The die consists of at least two parts, the cover half and the ejector half (

dies are made of heat-resistant tool steels. The metal enters the die through the nozzle or shot

sleeve, which is located in the cover half. The cover

pins, which are activated when the ejector half retracts after the casting is solid, are located in

the ejector half of the die. The gating is also generally placed in the ejector half of the die.

Undercuts in the casting may be formed by metal slides or retractable cores in the die, which

can enter the die space from each side as well as the top and bottom. Ceramic cores may be

placed in the die to make configurations that cannot be made any other way; the cores

removed chemically after the casting is solid.

Fig. 21 Components of a single-cavity die casting die for use in a hot chamber machine

The die also contains vents and overflow areas where excess metal flows during

injection. In addition, most dies

permanent molding, proper placement of the water lines is critical to obtaining good quality

castings, especially for multiple-cavity dies.

Processing sequence: The sequence of the die casting proc

open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution.

This spray coats the die with a thin layer of mold release, and the water evaporates, cooling

the die surface. The die is closed, and m

ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first

stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal

Fig. 20 Schematic showing the principal components of a cold chamber die casting

Dies. The die consists of at least two parts, the cover half and the ejector half (

resistant tool steels. The metal enters the die through the nozzle or shot

sleeve, which is located in the cover half. The cover half is stationary during casting. Ejector



e casting may be formed by metal slides or retractable cores in the die, which


placed in the die to make configurations that cannot be made any other way; the cores

removed chemically after the casting is solid.

cavity die casting die for use in a hot chamber machine


injection. In addition, most dies contain water cooling lines to control die heating. As in


cavity dies.

The sequence of the die casting process begins when the die is



the die surface. The die is closed, and metal is either injected into the die (hot chamber) or



64

Fig. 20 Schematic showing the principal components of a cold chamber die casting machine

Dies. The die consists of at least two parts, the cover half and the ejector half (Fig 21 ). The

resistant tool steels. The metal enters the die through the nozzle or shot

half is stationary during casting. Ejector



e casting may be formed by metal slides or retractable cores in the die, which


placed in the die to make configurations that cannot be made any other way; the cores are

cavity die casting die for use in a hot chamber machine


contain water cooling lines to control die heating. As in


ess begins when the die is



etal is either injected into the die (hot chamber) or



65

before injection begins. In the second stage, the piston moves very quickly, forcing the metal

into the mold cavity. The dies are filled in less than 0.15 s. Pressure builds up on the metal

during this phase. In the third stage, pressure is intensified to minimize the formation of

porosity. The high pressures (up to 70 MPa, or 5 tsi) require elaborate locking mechanisms to

keep the dies closed during the cycle; locking forces of up to 45,000 kN (5000 tonf) are used

in the largest machines.

After the casting is solid, the dies open, and the casting and its runner system are removed

from the die. Slides and cores are usually retracted first, and then the dies open. The gates are

trimmed off on a separate trim press. High production die casting operations are highly

automated, with the cycle controlled by computer and robots handling the metering of metal

into the shot sleeve and removing the casting and gating from the die. After the casting is

removed, the die is sprayed again, and the cycle is repeated.Risers are rarely used in die

casting because the metal freezes so quickly that feeding does not have time to occur. The

gating system is designed to fill the mold as quickly and efficiently as possible. The area

where the shot plunger comes to rest in the gating system is called the "biscuit."Molten metal

may be transferred to the shot sleeve by means of hand ladling, automated ladling, or by

being pumped from the melting furnace to the shot sleeve, using pumps made of ceramics, or

using electromagnetic force.Die casting machines are complex. They must be capable of

rapid, repetitive motion. The dies must maintain alignment during operation to avoid being

damaged, and the cycle of the machine must be controlled accurately. Die failure is usually

by thermal shock (heat checking). Iron is often added to aluminum alloys used in die casting

to prevent soldering of the alloy to the die. The amount of iron must be controlled, as excess

iron (above 0.8%) forms a sludge in the alloy, which, if carried over into the casting as

inclusions, will lower casting properties and casting machinability.

Air Entrapment: The rapid injection of metal into the die cavity inevitably traps air in

the casting. This air expands during heat treatment, forming blisters on the surface of the

casting. For this reason, most conventional die castings are not heat treated. However, there

are a number of methods that may be used to minimize the entrapment of air in the die cavity.

In one, the air in the cavity is evacuated prior to making the shot. In another method used for

aluminum alloys, the die cavity is filled with oxygen before the shot. During the shot, the

oxygen reacts with the aluminum alloy, forming tiny particles of aluminum oxide, which are

dispersed in the casting. Because all of the gas in the c

no gas to form gas bubbles in the casting.Because of the limitations of conventional die

casting, a variation on the process has been developed to substantially reduce air entrapment.

In this method, called "vertical squeezecasting," the shot sleeve is located beneath the die

cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The

metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are

larger than those used in conventional die casting to assure that mold filling is even and free

of turbulence, which causes air entrapment. Production rates are slightly lower using vertical

squeeze casting, but casting quality is improved. Vertical squeez

confused with another process known as squeeze casting, in which liquid is ladled into the

bottom half of a metal die, and the die is closed, similar to a forging press. This process

eliminates porosity.

dispersed in the casting. Because all of the gas in the cavity is used in this reaction, there is



l squeezecasting," the shot sleeve is located beneath the die





squeeze casting, but casting quality is improved. Vertical squeeze casting is not to be



66

avity is used in this reaction, there is



l squeezecasting," the shot sleeve is located beneath the die





e casting is not to be



67

Process Part Size


Shape Prodeuced Competitively

Process Limitation

Materials

Die Casting

Min Wall ( in ) : 0.025 Min Hole dia: 0.04-0.08 in Max Weight : 35 (Zn) , 20 (Al) , 10 (Mg)

General : +-0.0002 ( 1in ), Zinc +-0.003 (1 in) .( Allum & Mg) Add +- 0.004 across parting line or moving core

32-85 Micro inches

Small to minimum sized parts with intricate detail and good surface finish

Triming operations required for flash and overflow removal porosity can be present , Die life limited to approximately 200 K shots in Al or Mg or 1 million Zn.

5.Alluminium 6.Copper 7.Zinc 8.Magnesium

4.2.4 Injection molding:

The largest quantity of plastic parts is made by injection molding. Plastic compound is

fed in powdered or granular form from a hopper through metering and melting stages and

then injected into a mold. After a brief cooling period, the mold is opened and the solidified

part is ejected is a manufacturing process for both thermoplastic and thermosetting

plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity

where it cools and hardens to the configuration of the mold cavity. After a product is

designed, usually by an industrial designer or an engineer molds are made by

a MoldMaker (or toolmaker) from metal, usually either steel or aluminum, and precision-

machined to form the features of the desired part. Injection molding is widely used for

manufacturing a variety of parts, from the smallest component to entire body panelsof cars.

68

Effects on the material properties:

The mechanical properties of a part are usually little affected. Some parts can have

internal stresses in them. This is one of the reasons why it's good to have uniform wall

thickness when molding. One of the physical property changes is shrinkage. A permanent

chemical property change is the material thermoset, which can't be remelted to be injected

again.

Tool materials:

Tool steel or beryllium-copper are often used. Mild steel, aluminum, nickel or epoxy

are suitable only for prototype or very short production runs. Modern hard aluminum (7075

and 2024 alloys) with proper mold design, can easily make molds capable of 100,000 or more

part life.[Citation needed]

Geometrical Possibilities:

The most commonly used plastic molding process, injection molding, is used to create

a large variety of products with different shapes and sizes. Most importantly, they can create

products with complex geometry that many other processes cannot. There are a few

precautions when designing something that will be made using this process to reduce the risk

of weak spots. First, streamline your product or keep the thickness relatively uniform.

Second, try and keep your product between 2 to 20 inches.

69

The size of a part will depend on a number of factors (material, wall thickness, shape,process

etc.). The initial raw material required may be measured in the form of granules, pellets or

powders. Here are some ranges of the sizes.

Method Raw materials Maximum

size Minimum size

Injection molding (thermo-

plastic)

Granules, pellets,

powders 700 oz.

Less than 1

oz.

Injection molding (thermo-

setting)

Granules, pellets,

powders 200 oz.

Less than 1

oz.

Machining of Mold:

Molds are built through two main methods: standard machining and EDM.

Standard Machining, in its conventional form, has historically been the method of building

injection molds. With technological development, CNC machining became the predominant

means of making more complex molds with more accurate mold details in less time than

traditional methods.

The electrical discharge machining (EDM) or spark erosion process has become

widely used in mold making. As well as allowing the formation of shapes that are difficult to

machine, the process allows pre-hardened molds to be shaped so that no heat treatment is

required. Changes to a hardened mold by conventional drilling and milling normally require

annealing to soften the mold, followed by heat treatment to harden it again. EDM is a simple

process in which a shaped electrode, usually made of copper or graphite, is very slowly

lowered onto the mold surface (over a period of many hours), which is immersed in paraffin

oil. A voltage applied between tool and mold causes spark erosion of the mold surface in the

inverse shape of the electrode.

70

The Cost:

The cost of manufacturing molds depends on a very large set of factors ranging from

number of cavities, size of the parts (and therefore the mold), complexity of the pieces,

expected tool longevity, surface finishes and many others. The initial cost is great, however

the piece part cost is low, so with greater quantities the overall price decreases.

Injection molding cycle:

The sequence of events during the injection mold of a plastic part is called the injection

molding cycle. The cycle begins when the mold closes, followed by the injection of the

polymer into the mold cavity. Once the cavity is filled, a holding pressure is maintained to

compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to

the front screw. This causes the screw to retract as the next shot is prepared. Once the part is

sufficiently cool, the mold opens and the part is ejected.

The time it takes to make a product using injection molding can be calculated by adding:

Twice the Mold Open/Close Time (2M)+Injection Time (T)+Cooling Time (C)+Ejection

Time(E), Where T is found by dividing:Mold Size (S) / Flow Rate (F)

Total time = 2M + T + C + E ; T = V/R ; [V = Mold cavity size (in3), R = Material flow, rate

(in3/min)]

4.2.5 Blow Molding (Ext.):

In extrusion blow molding, a tube or perform (usually oriented so that it is vertical) is

first extruded. It is then clamped into a mold with a cavity much larger than the tube diameter

and blown outward to fill the mold cavity. (Figure 3.) Depending on the material, the blow

ratio may be as high as 7:1. Blowing usually is done with a hot air blast at a pressure ranging

from 350 to 700 kPa. Drums with a volume as large as 2000 liters can be made by this

process. Typical die material are steel, aluminum, and beryllium copper.

71

In some operations, the extrusion is continuous and the molds move with the tubing. The

molds close around the tubing, sealing off one end, breaking the long tube into individual

sections, and moving away as air is injected into the tubular piece. The part is then cooled

and ejected from the mold. Corrugated-plastic pipe and tubing are made by continuous blow

molding in which the pipe or tubing is extruded horizontally and blown into moving molds.

4.2.6 Blow Molding (Inj.):

In injection blow molding, a short tubular piece (parison) is injection molded (Figure

4.) into cool dies. (Parisons may be made and stored for later use.) The dies then open, and

the parison is transferred to a blow molding die by an indexing mechanism. Hot air is injected

into the parison, expanding it do the walls of the mold cavity. Typical products made are

plastic beverage bottles (typically made of polyethylene or polyetheretherketone, PEEK) and

small, hollow containers.

72

4.2.7 Impact Extrusion:

Impact extrusion is similar to indirect extrusion, and the process often is included in

the cold extrusion category. The punch descends rapidly on the blank (slug), which is

extruded backwards (Figure 5.). Because of volume constancy, the thickness of the tubular

extruded section is a function of the clearance between the punch and the die cavity. Some

products made by impact extrusion are collapsible tubes (similar to those used for

toothpaste), light fixture, automotive parts, and small pressure vessels. Most nonferrous

metals can be impact extruded in vertical presses and at production rates as high as two parts

per second.

The maximum diameter of the parts made is about 150 mm. The impact extrusion process can

produce thin-walled tubular sections having thickness to diameter ratios as small as 0.005.

Consequently, the symmetry of the part and the concentricity of the punch and the blank are

important.

73

4.2.8 Cold Heading:

In cold heading or upsetting, force applied by one or more blows of a tool displaces metal in

a portion or all of a slug, wire, or rod blank. This plastic flow produces a section or part of

different contour, larger in cross section than the original material. Force is generally applied

by a moving punch to form that portion of the blank protruding from a stationary die. As seen

in

Fig. 3.7.1, some parts are upset in the punch, some in the die, some in both punch and die,

and others between the punch and the die.

Related Processes: Upsetting is often combined with forward or backward extrusion,

particularly in cold-forming large-headed, small-shanked parts. Warm heading is applied for

processing difficult-to-head metals such as medium-to high-carbon steels, austenitic stainless

steels, and other materials that work-harden rapidly. In this compromise between cold and hot

heading, the metal is preheated to between 150 and 540°C (300 and 1000°F) or more

(depending on the particular metal, but below its recrystallization temperature) to increase its

plasticity and reduce the force required for heading.

74

Rotary forging is a related process in which deformation is induced progressively rather than

by a single direct squeeze. The workpiece is subjected to a combined rolling and squeezing

action to produce progressive upsetting. This method is particularly suitable for thin, intricate

flange sections.

Secondary Operations Many secondary operations are performed on cold-upset parts,

depending on th design and application of the part. These include grooving, shaving,

pointing, flattening, bending, piercing, drilling, tapping, threading (often done with a thread-

rolling machine made an integral part of the header), heat treating, and plating.

Cold-Heading Machines:

Most cold-heading machines used in high production are fed coil stock. A machinemay

include a straightener, draw die, feed rolls, and shear. Sheared slugs are automatically

transferred to a stationary die, and the projecting end of each slug is struck axially by the

upsetting tool (punch). In some cases, as in nail making, the stock can be upset first and then

sheared to length. Multistation and progressive headers, as well as bolt-making machines, are

equipped with automatic-transfer mechanisms to move parts to successive stations and may

have trimming, pointing, and thread-rolling stations.

Headers and forming machines are available in a wide variety of sizes and types. They are

frequently rated by maximum-diameter-cutoff capacity and feed lengths (generally up to 14

times rated diameter, but this capacity can vary).

Suitable Materials:

Any material that is malleable when cold can be cold-formed. Materials having the lowest

yield strength and the greatest range between yield and ultimate strengths are the most

malleable. Since strain or work hardening during cold working decreases formability, the rate

of strain hardening of the material is an important consideration. Hardness of the material is

also critical, since too hard a material is impracticable to cold-work.

Prior operations, sometimes required to prepare material for upsetting, can include

heat treating, drawing, descaling, and lubricating. The upsetting properties of most steels are

improved by annealing or spheroidizing.

Whenever possible, the designer should avoid specifying exact material analyses, since this

limits the upsetter’s flexibility and may increase production costs. Several different analyses

75

of a basic material often can satisfy service requirements, but they may vary in upsettability,

availability, and cost.

• Steels: Low-carbon steels , Medium high-carbon steels , High-carbon steels , Alloy

steels , Rimmed steels ,

• Stainless Steels

• Nickel Alloys

• Aluminum Alloys

• Copper and Copper Alloys

• Other Materials: Titanium, beryllium, and refractory metals are less formable at

room temperatures, and they are likely to crack when cold-headed. As a result, they

are often processed warm.

Dimensions: As wide a tolerance as possible should be allowed on lugs, fins, tapers and

projections because metal-flow behavior is sometimes unpredictable in forming these shapes.

Radii generally can be formed to tolerances of 0.13 mm (0.005 in).

Geometry: Concentricity variations of 0.025 to 0.08 mm (0.001 to 0.003 in) TIR are not

uncommon in blank sizes up to 6 mm in) in diameter if the difference between the two

referenced diameters is not too great. Greater concentricity tolerance is generally needed for

larger-size parts and larger differences in diameters. If closer tolerances are needed,

secondary operations such as machining, shaving, or grinding are generally required.

Straightness of cold-upset parts can generally be held to about 0.4 percent of length.

Surface Finishes: A finish of 0.4 to 0.8m (16 to 32 in) usually can be obtained

economically.

Upsetting of heads, however, sometimes can decrease the quality of surface finish unless high

pressures are exerted on the sidewalls of the containing die. High-quality finishes generally

also require the use of high-quality clean wire.

Surface finish also can vary among different parts or different areas of the same part,

depending on the surface of the wire or bar being headed, the amount of cold working

performed in various areas, the lubricant used, and the condition of the tools. The best finish

on any part is usually achieved when direct contact has been made with the tools.

76

4.2.9 Powder Metal Parts

Powder metallurgy is used for manufacturing products or articles from powdered metals by

placing these powders in molds and are compacting the same using heavy compressive force.

Typical examples of such article or products are grinding wheels, filament wire, magnets,

welding rods, tungsten carbide cutting tools, self-lubricating bearings electrical contacts and

turbines blades having high temperature strength. The manufacture of parts by powder

metallurgy process involves the manufacture of powders, blending, compacting, profiteering,

sintering and a number of secondary operations such as sizing, coining, machining,

impregnation, infiltration, plating, and heat treatment. The compressed articles are then

heated to temperatures much below their melting points to bind the particles together and

improve their strength and other properties. Few non-metallic materials can also be added to

the metallic powders to provide adequate bond or impart some the needed properties. The

products made through this process are very costly on account of the high cost of metal

powders as well as of the dies used. The powders of almost all metals and a large quantity of

alloys, and nonmetals may be used. The application of powder metallurgy process is

economically feasible only for high mass production. Parts made by powder metallurgy

process exhibit properties, which cannot be produced by conventional methods. Simple

shaped parts can be made to size with high precision without waste, and completely or almost

ready for installation.

Powder Metallurgy Process:

The powder metallurgy process consists of the following basic steps: 1. Formation of

metallic powders. 2. Mixing or blending of the metallic powders in required proportions. 3.

Compressing and compacting the powders into desired shapes and sizes in form of

articles. 4. Sintering the compacted articles in a controlled furnace atmosphere. 5. Subjecting

the sintered articles to secondary processing if needed so.

77

Particle shape:

There are various shapes of metal powders namely spherical, sub-rounded, rounded,angular,

sub-angular, flakes etc. Particles shape influences the packing and flow characteristics of the

powders.

Chemical Composition:

Chemical composition of metallic powder implies the type and percentage of

alloyingelements and impurities. It usually determines the particle hardness and

compressibility. The chemical composition of a powder can be determined by chemical

analysis methods.

Particle microstructure:

Particle microstructure reveals various phases, inclusions and internal porosity.

Apparent density:

Apparent density is defined as the weight, of a loosely heated quantity of powder necessaryto

fill a given die cavity completely.

Flow characteristics:

Flow-ability of metal powders is most important in cases where moulds have to be filled

quickly. Metal powders with good flow characteristics fill a mould cavity uniformly.

78

Secondary Operations:

Some powder metal parts may be used in the sintered condition while in some other cases

additional secondary operations have to be performed to get the desired surface finish, close

tolerance etc. The secondary operations may be of following types:

1. Annealing.

2. Repressing for greater density or closer dimensional control.

3. Machining.

4. Polishing.

5. Rolling, forging or drawing.

6. Surface treatments to protect against corrosion.

7. In some cases infiltration is needed to provide increased strength, hardness,

densityobtainable by straight sintering.

8. The procedures for plating powdered metal parts are quite different from those usedfor

wrought or cast metal parts. In powdered metal parts, porosity must be eliminated before the

part is plated. After the porosity has been eliminated regular plating procedures can be used.

79

Advantages of Powder Metallurgy:

1.The processes of powder metallurgy are quite and clean.

2. Articles of any intricate or complicated shape can be manufactured.

3. The dimensional accuracy and surface finish obtainable are much better for many

applications and hence machining can be eliminated.

4. Unlike casting, press forming machining, no material is being wasted as scrap and the

process makes utilizes full raw material

5. Hard to process materials such as diamond can be converted into usable components and

tools through this process.

6. High production rates can be easily achieved.

7. The phase diagram constraints, which do not allow an alloy formation between mutually

insoluble constituents in liquid state, such as in case of copper and lead are removed in this

process and mixtures of such metal powders can be easily processed and shaped through this

process.

80

8. This process facilitates production of many such parts, which cannot be produced through

other methods, such as sintered carbides and self-lubricating bearings.

9. The process enables an effective control over several properties such as purity, density,

porosity, particle size, etc., in the parts produced through this process.

10. The components produced by this process are highly pure and bears longer life.

11. It enables production of parts from such alloys, which possess poor cast ability.

12. It is possible to ensure uniformity of composition, since exact proportions of constituent

metal powders can be used.

13. The preparation and processing of powdered iron and nonferrous parts made in this way

exhibit good properties, which cannot be produced in any other way.

14. Simple shaped parts can be made to size with 100 micron accuracy without waste

15. Porous parts can be produced that could not be made in any other way.

16. Parts with wide variations in compositions and materials can be produced.

17. Structure and properties can be controlled more closely than in other fabricating

processes.

18. Highly qualified or skilled labor is not required. in powder metallurgy process

19. Super-hard cutting tool bits, which are impossible to produce by other manufacturing

processes, can be easily manufactured using this process.

20. Components shapes obtained possess excellent reproducibility.

21. Control of grain size, relatively much uniform structure and defect such voids and blow

holes in structure can be eliminated.

Limitations of Powder Metallurgy:

1. Powder metallurgy process is not economical for small-scale production.

2. The cost of tool and die of powder metallurgical set-up is relatively high

3. The size of products as compared to casting is limited because of the requirement of large

presses and expensive tools which would be required for compacting.

4. Metal powders are expensive and in some cases difficult to store without some

deterioration.

5. Intricate or complex shapes produced by casting cannot be made by powder metallurgy

because metallic powders lack the ability to flow to the extent of molten metals.

81

6. Articles made by powder metallurgy in most cases do not have as good physical properties

as wrought or cast parts.

7. It may be difficult sometimes to obtain particular alloy powders

8. Parts pressed from the top tend to be less dense at the bottom.

9. A completely deep structure cannot be produced through this process.

10. The process is not found economical for small-scale production.

11. It is not easy to convert brass, bronze and a numbers of steels into powdered form.

Applications of Powder Metallurgy:

The powder metallurgy process has provided a practical solution to the problem of producing

refractory metals, which have now become the basis of making heat-resistant materials and

cutting tools of extreme hardness. Another very important and useful item of the products

made from powdered metals is porous self-lubricating bearing. In short, modern technology

is inconceivable without powder metallurgy products, the various fields of application of

which expand every year. Some of the powder metal products are given as under:

1. Porous products such as bearings and filters.

2. Tungsten carbide, gauges, wire drawing dies, wire-guides, stamping and blankingtools,

stones, hammers, rock drilling bits, etc.

3. Various machine parts are produced from tungsten powder. Highly heat and wearresistant

cutting tools from tungsten carbide powders with titanium carbide, powders are used for and

die manufacturing.

4. Refractory parts such as components made out of tungsten, tantalum and molybdenum are

used in electric bulbs, radio valves, oscillator valves, X-ray tubes in the form of filament,

cathode, anode, control grids, electric contact points etc.

5. Products of complex shapes that require considerable machining when made by other

processes namely toothed components such as gears.

6. Components used in automotive part assembly such as electrical contacts, crankshaft drive

or camshaft sprocket, piston rings and rocker shaft brackets, door, mechanisms, connecting

rods and brake linings, clutch facings, welding rods, etc.

7. Products where the combined properties of two metals or metals and non-metals are

desired such as non-porous bearings, electric motor brushes, etc.

8. Porous metal bearings made which are later impregnated with lubricants. Copper and

graphite powders are used for manufacturing automobile parts and brushes.

82

9. The combinations of metals and ceramics, which are bonded by similar process as metal

powders, are called cermets. They combine in them useful properties of high refractoriness of

ceramics and toughness of metals. They are produced in two forms namely oxides based and

carbide based.

4.2.10 Hot Extrusion: In the extrusion process (Fig. 6), metal is compressively forced to flow through a suitably

shaped die to form a product with reduced cross section. Although it may be performed either

hot or cold, hot extrusion is employed for many metals to reduce the forces required, to

eliminate cold-working effects, and to reduce directional properties. The stress state within

the material is triaxial compression.

Lead, copper, aluminum, and magnesium, and alloys of these metals, are commonly

extruded, taking advantage of the relatively low yield strengths and extrusion temperatures.

Steel is more difficult to extrude. Yield strengths are high and the metal has a tendency to

weld to the walls of the die and confining chamber under the conditions of high temperature

and pressures. With the development and use of phosphate-based and molten glass lubricants,

substantial quantities of hot steel extrusions are now produced.

These lubricants adhere to the billet and prevent metal-to-metal contact throughout the

process.

Almost any cross-section shape can be extruded from the nonferrous metals. Hollow shapes

can be extruded by several methods. For tubular products, the stationary or moving mandrel

process is often employed. For more complex internal cavities, a spider mandrel or torpedo

die is used. Obviously, the cost for hollow extrusions is considerably greater than for solid

ones, but a wide variety of shapes can be produced that cannot be made by any other process.

The extrusion force F can be estimated from the formula:

F=A0K ln (A0/A); where ‘k’ extrusion constant depends on material and temperature (see

Fig. 7); A0 = billet area A; F: finished extruded area

83

4.2.11 Rotary Swaging:

The diameters of wires and tubes may be reduced by rotary swaging. Shaped dies arerotated

around the wire or tube and hammer the work piece as they rotate. This causes aswirled

microstructure. In a wire drawing plant, swaging is used to reduce the ends of wires so they

can be fed through drawing dies in the initial setup. Figure 6.8 is a schematic of the tooling

used in swaging.

Process Part Size Tolerances Surface Finish


Process Limitaion

Materials

Hot Extrusion

Cross Sectional area: 0.1-225 Sq in,( Alum ) ,0.5-40 Sq in ,( LC Steel ) ,Min Wall : 1.5 % of Circumscribed dia.

General +- 0.01 in , +- 0.03 ( 6 in ) , +- 0.005 if drawn after extrusion, Twist: 1 deg per foot for width less than 2 in ,flatness: 0.004 in./in

63 Micro in

Straight part with Constant cross section which is fairly complex ,but balanced without extereme changes in wall thickness.

Dimensional Accuracy and part to part consistency generally not as high as competing proceses,Warp and Twist can be troublesome.

2.Carbon Steel 3.Alloy Steel 4.Stailnless steel 5.Alluminium 6.Copper 7.Zinc 8.Magnesium 9.Titanium

84

Rotary swaging process is usually a cold working process, used to reduce the diameter,

produce a taper, or add point to a round workpiece. It can also impart internal shapes in

hollow workpiece through the use of a mandrel (the shape must have a constant cross-

section).Swaging a bearing into a housing means flaring its groove's lips onto the chamfer of

the housing.

A swaging machine works by using two or four split dies which separate and close up to

2000 times a minute. This action is achieved by mounting the dies into the machine's spindle

which is rotated by a motor. The spindle is mounted inside a cage containing rollers (looks

like a roller bearing). The rollers are larger than the cage so as the spindle spins the dies are

pushed out to ride on the cage by centrifugal force, as the dies cross over the rollers they push

the dies together because of their larger size. On a four-die machine, the number of rollers

cause all dies to close at a time; if the number of rollers do not cause all pairs of dies to close

at the same time then the machine is called a rotary forging machine, even though it is still a

swaging process.

A variation of the rotary swage is the creeping spindle swaging machine where both the

spindle and cage revolve in opposite directions, this prevents the production of fins between

the dies where the material being swaged grows up the gap between the dies.

85

There are two basic types of rotary swaging machine, the standard (also known as a tagging

machine), and the butt swaging machine. A butt swaging machine works by having sets of

wedges that close the dies onto the workpiece by inserting them between the annular rollers

and the dies, normally by the use of a foot pedal. A butt swaging machine can allow a

workpiece to be inserted without the dies closing on it, for example a three foot workpiece

can be inserted 12 inches and then the dies closed, drawn through until 12 inches remain and

the dies are then released, the finished workpiece would then, for example, be four feet long

but still of its initial diameter for a foot at each end. The most common use of swaging is to

attach fittings to pipes or cables (also called wire ropes); the parts loosely fit together, and a

mechanical or hydraulic tool compresses and deforms the fitting, creating a permanent joint.

Pipe flaring machines are another example. Flared pieces of pipe are sometimes known as

"swage nipples," "pipe swages," "swedge nipples," or "reducing nipples."

86

4.2.12 Machining:

As large number of components require further processing after the primary

processes. These components are subjected to one or more number of machining operations

in machine shops, to obtain the desired shape and dimensional accuracy on flat and

cylindrical jobs. Thus, the jobs undergoing these operations are the roughly finished products

received through primary shaping processes. The process of removing the undesired or

unwanted material from the workpiece or job or component to produce a required shape using

a cutting tool is known as machining. This can be done by a manual process or by using a

machine called machine tool (traditional machines namely lathe, milling machine, drilling,

shaper, planner, slotter). In many cases these operations are performed on rods, bars and flat

surfaces in machine shops. These secondary processes are mainly required for achieving

dimensional accuracy and a very high degree of surface finish. The secondary processes

require the use of one or more machine tools, various single or multi-point cutting tools

(cutters), job holding devices, marking and measuring instruments, testing devices and

gauges etc. for getting desired dimensional control and required degree of surface finish on

the workpieces. The example of parts produced by machining processes includes hand tools

machine tools instruments, automobile parts, nuts, bolts and gears etc. Lot of material is

wasted as scrap in the secondary or machining process. Some of the common secondary or

machining processes are:

(1)Turning, (2) Threading, (3) Knurling, (4) Milling, (5) Drilling, (6) Boring, (7) Planning,

(8) Shaping, (9) Slotting, (10) Sawing, (11) Broaching, (12) Hobbing, (13) Grinding, (14)

Process Part Size


Shape Produced Competitively

Process Limitation Materials

Rotary Swaging

Dia: 0.01-5.0 in (bar) 14 in Tubing

Dia: (+ - ) 0.003 (1in)

20% of Original Stock finish (5 –Fold improvement)

Tapered cylindrical Rod Tubing

Taper Should be 6 Deg,or Less included angle for manual feeding and up to 14 degrees for power feed,shoulders perpendicular to part axis not possible

Carbon Steel,Alloy Steel,Stainless Steel, Aluminum and Alloys,Copper& Alloys,Nickel & alloys,Limited: Zinc & Magnesium

87

Gear cutting, (15) Thread cutting and (16) Unconventional machining processes namely

machining with Numerical Control (NC) machines tools or Computer Numerical Control

(CNC) machines tools using ECM, LBM, AJM, USM setups etc.

Turning specific operations include:

Turning:

This operation is one of the most basic machining processes. That is, the part is rotated while

a single point cutting tool is moved parallel to the axis of rotation. Turning can be done on

the external surface of the part as well as internally (boring). The starting material is

generally a workpiece generated by other processes such as casting, forging, extrusion,

or drawing.

Tapered turning:

a) From the compound slide

b) from taper turning attachment

c) using a hydraulic copy attachment.

d) using a C.N.C. lathe

e) using a form tool

f) by the offsetting of the tailstock - this method more suited for shallow tapers

Spherical generation:

The proper expression for making or turning a shape is to generate as in to generate a form

around a fixed axis of revolution. a) using hydraulic copy attachment b) C.N.C.

(computerised numerically controlled) lathe c) using a form tool (a rough and ready method

d) using bed jig (need drawing to explain)

Hard turning:

88

Hard turning is a turning done on materials with a Rockwell C hardness greater than 45. It is

typically performed after the workpiece is heat treated.

The process is intended to replace or limit traditional grinding operations. Hard turning, when

applied for purely stock removal purposes, competes favorably with rough grinding.

However, when it is applied for finishing where form and dimension are critical, grinding is

superior. Grinding produces higher dimensional accuracy of roundness and cylindricity. In

addition, polished surface finishes of Rz=0.3-0.8z cannot be achieved with hard turning

alone. Hard turning is appropriate for parts requiring roundness accuracy of 0.5-12 microns,

and/or surface roughness of Rz 0.8–7.0 microns. It is used for gears, injection pump

components, hydraulic components, among other applications.

Facing:

Facing is part of the turning process. It involves moving the cutting tool at right angles to the

axis of rotation of the rotating workpiece This can be performed by the operation of the cross-

slide, if one is fitted, as distinct from the longitudinal feed (turning). It is frequently the first

operation performed in the production of the workpiece, and often the last- hence the phrase

"ending up".

Parting:

This process is used to create deep grooves which will remove a completed or part-complete

component from its parent stock.

Grooving:

Grooving is like parting, except that grooves are cut to a specific depth by a form tool instead

of severing a completed/part-complete component from the stock. Grooving can be

89

performed on internal and external surfaces, as well as on the face of the part (face grooving

or trepanning).

90

This table shows the Production Rate of machining Operations:

This table indicates Surface Roughness of all machining operations: The range of surface

roughness obtained in various machining processes. Note the wide range within each group,

especially in turning and boring.

91

4.2.13 ECM (Electrochemical Machining):

Electrochemical Machining is basically the reverse of electroplating. An electrolyte

acts as current carrier (Figure 6.), and the high rate of electrolyte movement in the tool

workpiece gap (typically 0.1- 0.6 mm) washes metal ions away from the workpiece (anode)

before they have a chance to plate onto the tool (cathode). Note that the cavity produced is

the female mating image of the tool shape. The shaped tool, either a solid or tubular form, is

generally made of brass, copper, bronze, or stainless steel. The electrolyte is a highly

conductive inorganic fluid, such as an aqueous solution of sodium nitrate. It is pumped

through the passage in the tool at rates of 10 to 16 m/s. A DC power supply in the range from

10 to 25 V maintains current densities, which, for most applications, are 20 to 200 A/cm^2 of

active machined surface. The material removal rate (MRR) in electrochemical machining for

a current efficiency of 100% may be estimated from the equation: MRR= CL,

Where MRR is in (mm^3/min), I is the current in amperes, and C depends on the valence:

The higher the valence, the lower is its value of C.

Process Part Size Tolerances Surface Finish Shape Prodeuced Competitively

Process Limitaion

Materials

Machining

Limited by Machine Capability

Turning: +- 0.001 ,Boring: +- 0.0005 ,Milling :+-0.002 ,Drilling: +-0.008-0.002 ,Broaching: +-0.005 ,Grinding: +-0.002 (dia), General: +- 0.001

Turning: 63-125, Boring: 32-125 , Milling: 63-125 , Drilling: 63-125 , Grinding: 8-32 , Reaming: 63

Rotational:axisymetrical part with L/D 3 or less and major dia, of 2 or less, Nonrotational:Rectangular part with all feature parallel and open in the same direction, Highly Accurate Complx: or finaly hardened materials or those susceptible to damage due to heat buld-up.

Limits opportunity for part consolidation most parts produced by sequence of severaloperations and machines,need for multiple operations can impact part quality tool wear is significant.

Cast Iron,Carbon Steel,Alloy Steel,Stailnless steel,Alluminium,Copper,Zinc ,Magnesium,Titanium,Thermoplastics,Thermosets,Nickel

92

Figure 6. Schematic illustration of the Electrochemical Machining process.

4.2.14 EDM (Electrical-discharge Machining):

The principle of electrical-discharge machining (also called electrodis charge or

spark-erosion machining) is based on the erosion of metals by spark discharges. We know

that when two current conducting wires are allowed to touch each other, an arc is produces. If

we look closely at the point of contact between the two wires, we note that a small portion of

the metal has been eroded away, leaving a small crater (Figure 7.).

The basic EDM system consists of a shaped tool (electrode) and the workpiece, connected to

a DC power supply and placed in a dielectric (electrically non-conducting) fluid.

Process Part Size Tolerances Surface Finish Shape Produced Competitively

Process Limitation

Materials

Electro Chemical Machining ( ECM )

Min Hole Dia : 0.01 in Max Hole Depth : 50x dia

General : +- 0.001

8-63 Micro Inches

Highly Accurate complex or finely detailed shapes in hardened materials or those susceptible to damage due to heat build-up Production of high aspect or burr free holes and processing of filmsy materials

Some taper of walls Minimum Radius of 0.002 all around, Material must be electronically conductive

1.Cast Iron, 3.Alloy Steel 6.Copper 9.Titanium 12.Nickel

93

Although this phenomenon has been known since the discovery of electricity. The EDM

process has become one of the most important and widely used production technologies in

manufacturing.

4.2.15 Wire EDM:

In this process, which is similar to contour cutting with a bans saw, a slowly moving

wire travels along a prescribed path, cutting the workpiece. This process is used to cut plates

as thick as 300 mm and to make punches, tools, and dies from hard metals. It also can cut

intricate components for the electronics industry.

The wire is usually made of brass, copper, tungsten, or molybdenum; zinc or based coated

and multicoated wires also are used. The wire diameter is typically about 0.30 mm for

roughing cuts and 0.20 mm for finishing cuts. The wire should have high electrical

conductivity and tensile strength, as the tension on it is typically 60% of its tensile strength.

The wire is usually used only once, as it is relatively inexpensive compared with the type of

operation it performs. It travels at a constant velocity in the range from 0.15 to 9 m/min, and

a constant gap (kerf) is maintained during the cut. The trend in the use of dielectric fluids is

toward clear, low-viscosity fluids.

Sheet Metal (Stamp/bend):

Sheet metal Stamping includes a variety of operations, such as punching, blanking,

embossing, bending, flanging, and coining; simple or complex shapes formed at high

production rates; tooling and equipment costs can be high, but labor cost is low.

94

Bending is one of the most common industrial forming operations. We merely have to look at

an automobile body, appliance, paper clip, or file cabinet to appreciate how many parts are

shaped by bending. Furthermore, bending also imparts stiffness to the part by increasing its

moment of inertia. The terminology used in the bending of a sheet or plate is shown in

(Figure 13). Note that the outer fibers of the material are in tension, while the inner fibers are

in compression. Because of the Poisson effect, the width of the part (bend length, L) has

become smaller in the outer region and larger in the inner region than the original width. This

phenomenon may be observed easily by bending a rectangular rubber eraser and observing

the changes in its shape.

\

4.2.16 Thermoforming:

Thermoforming is a process for forming thermoplastics sheets or films over a mold

through the application of heat and pressure. In this process, a sheet is (a) clamped and heated

to the sag point (above the glass transition temperature), usually by radiant heating, and (b)

forced against the mold surfaces through the application of a vacuum or air pressure. The

sheets used in thermoforming are available filled with various materials for making parts with

specific applications.

The mold is generally at room temperature; thus, the shape produced becomes set

upon contact with the mold. Because of the low strength of the materials formed, the pressure

difference caused by a vacuum usually is sufficient for forming. However, thicker and more

complex parts require air pressure, which may range from about 100 to 2000 kPa, depending

on the type of material and thickness of the sheet. Mechanical means, such as the use of

plugs, also may be employed to help from the parts.

95

4.2.17 Metal Spinning:

Spinning is a process that involves the forming of axisymmetric parts over a mandrel

by the use of various tools and rollers; a process is similar to that of forming clay on a

potter’s wheel. The spinning process is fairly simple. A mandrel, also known as a form, is

mounted in the drive section of a lathe. A pre-sized metal disk is then clamped against the

mandrel by a pressure pad, which is attached to the tailstock The mandrel and workpiece are

then rotated together at high speeds. A localized force is then applied to the workpiece to

cause it to flow over the mandrel. The force is usually applied via various levered tools.

Simple workpieces are just removed from the mandrel, but more complex shapes may require

a multi-piece mandrel. Extremely complex shapes can be spun over ice forms, which then

melt away after spinning. Because the final diameter of the workpiece is always less than the

starting diameter the workpiece must thicken, elongated radially, or buckle circumferentially.

Process Part Size Tolerances

Surface Finish


Process Limitaion Materials

Thermoforming

Area: 1 Sq in ,-300Sq ft

General : +-0.05 % of dimension Wall : +-20% of nominal

60-120 Micro inches

Large ,Shalow, Thin wall Parts with generous radi

Low degree of part complexity Low dimensional accuracy Minimal opportunity for integral fasteners or attachment points

10.Thermoplastics

96

A more involved process, known as reducing or necking, allows a spun workpiece to

include reentrant geometries. If surface finish and form are not critical, then the workpiece is

"spun on air"; no mandrel is used. If the finish or form are critical then an eccentrically

mounted mandrel is used.

"Hot Spinning". This process involves spinning a piece of metal on a lathe and with

high heat from a torch the metal is heated. Once heated, the metal is then shaped as the tool

on the lathe presses against the heated surface forcing it to distort as it spins. Parts can then

be shaped or necked down to a smaller diameter with little force exerted, providing a

seamless shoulder.

Several operations can be performed in one set-up. Work pieces may have re-entrant profiles

and the profile in relation to the center line virtually unrestricted.

Forming parameters and part geometry can be altered quickly, at less cost than other

metal forming techniques. Tooling and production costs are also comparatively low. Spin

97

forming, often done by hand, is easily automated and an effective production method

for prototypes as well as high quantity production runs.

Other methods of forming round metal parts include hydroforming, stamping

and forging or casting. Hydroforming and stamping generally have a higher fixed cost, but a

lower variable cost than metal spinning. Forging or casting have a higher fixed cost due to the

large equipment needed, but generally a lower variable cost. As machinery for commercial

applications has improved, parts are being spun with thicker materials in excess of 1" thick

steel. Conventional spinning also wastes a considerably smaller amount of material than other

methods.

Objects can be built using one piece of material to produce parts without seams.

Without seams, a part can withstand higher internal or external pressure exerted on it. For

example: scuba tanks, CO2 cartridges, and oxyacetylene tanks.

One disadvantage of metal spinning is that if a crack forms or the object is dented, it

must be scrapped. Repairing the object is not cost-effective.

Spinning is a sheet-forming process that is suitable for axially symmetric parts. A tool

forces the sheet metal disc to conform to a mandrel as shown in Figure 17.3. The tool usually

consists of a small wheel. The process should be controlled so that all of the deformation is

pure shear under the tool. If the tool causes more thinning than would be produced by shear,

the unsupported flange will wrinkle. Even though spinning is slow, it is suitable for low

production items because the tooling costs are low.

The reduction r is

98

Any additional thinning would cause the flange to wrinkle. The shear strain γ is

γ = cot (a/2).

Spinning may also be used to reduce the wall thickness of tubes and cups.

99

5 Reasons for the materials and manufacturing processes selections

5.1 Front plate For this parts, the most suitable material is Carbon steel, Alloy Steel and Stainless steel.where this material meet the requirement of High Ductility, High Melting point, Low Cost.

N

O Process

Cas

t Iro

n

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Co

ppe

r an

d A

lloys

Zin

c a

nd

Allo

ys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

fra

ctio

n M

eta

ls

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

100

According to the table 2.2 (in the appendix) the best Process for producing front plate

is Sheet metal and the suitable material for this part is carbon steel due to support this

component’s requirements and characteristics. It would produced a good shape and good

dimensional accuracy.

Some process are eliminated for following reason

• Sand casting is eliminated because of minimum wall is 0.125 in for sand casting while the thickness of wall is 1mm for this part.

• Invest casting is not suitable for 15000 production part.

• Closed die forging is not suitable due to the size of component.

• Machining (From Stock) is eliminated due to the size of part and because of

deformation in machining process.

• The ECM machine is so expensive

• EDM is eliminated because of low material removal rate.

• Sheet metal process is suitable for this part because of low cost to manufacture the

15000 number of parts in compare with other methods.

101

5.2 Moving System For this parts, the most suitable material is Carbon steel, Alloy Steel and Stainless steel.where this material meet the requirement of High Ductility, High Melting point, Low Cost.

N

O Process

Ca

st I

ron

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

and

Allo

ys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

102

According to the table 2.2 (in the appendix) the best Process for producing Moving

Systemis Sheet metal and the suitable material for this part is carbon steel due to support

this component’s requirements and characteristics. It would produced a good shape and

good dimensional accuracy.


• Sand casting is eliminated because of minimum wall is 0.125 in for sand casting while

the thickness of wall is 1mm for this part.





• The ECM machine is so expensive



15000 number of parts in compare with other methods.

103

5.3 Electrical connection snap-fit For this parts, the most suitable material is Copper and alloy where this material meet the

requirement of High Ductility, High conductivity, metallic.

NO Process

Ca

st I

ron

Ca

rbon

Ste

el

Allo

y S

teel

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Cop

per

an

d A

lloys

Zin

c a

nd A

lloys

Ma

gne

sium

and

Allo

ys

Tita

nium

an

d A

lloys

Nic

kel a

nd A

lloys

Re

fra

ctio

n M

eta

ls

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

104

According to the table 2.2 (in the appendix) the best Process for producing Electrical

connection snap-fit

is Sheet metal and the suitable material for this part is Copper alloys due to support this

component’s requirements and characteristics. It would produced a good shape and good

dimensional accuracy.


• Sand casting is eliminated because of minimum wall is 0.125 in for sand casting while

the thickness of wall is 1mm for this part.


• .Die Casting is less applicable.




• The ECM machine is less applicable.



15000 number of parts in compare with other methods

105

5.4 Bottom cover For this parts, the most suitable materials are thermoplastic and thermoset where this material

meet the requirement of Heat resistance, good insulator, approximately high melting point,

Low cost.

Process

Cas

t Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Co

ppe

r an

d A

lloys

Zin

c a

nd

Allo

ys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

106

According to the table 2.2 (in the appendix) the best Process for producing Bottom

coveris Injection molding process and the suitable material for this part is thermoplastics due

to support this component’s requirements and characteristics. It would produced a good shape

and good dimensional accuracy. Thermosets material is less applicable so it is not suitable

for our production.


• Machining is eliminated because of less applicable

• Structural foaming is not suitable for small size because it’s usage is for large size

components.

• Suitable process for this part is injection molding.

107

5.5 Top Cover For this parts, the most suitable materials are thermoplastic and thermoset where this

material meet the requirement of Heat resistance, good insulator, approximately high melting

point, Low cost.

Process

Cas

t Ir

on

Ca

rbon

Ste

el

Allo

y S

tee

l

Sta

inle

ss S

tee

l

Alu

min

um a

nd A

lloys

Co

ppe

r an

d A

lloys

Zin

c a

nd

Allo

ys

Ma

gne

sium

and

Allo

ys

Tita

nium

and

Allo

ys

Nic

kel a

nd A

lloys

Re

frac

tion

Me

tals

The

rmop

last

ics

The

rmos

ets

1 Sand Casting


3 Die Casting






9 Impact Extrusion

10 Cold Heading



13 Hot Extrusion

14 Rotary Swaging


16 ECM

17 EDM

18 Wire EDM


20 Thermoforming

21 Metal Spinning

108

According to the table 2.2 (in the appendix) the best Process for producing Bottom coveris

Injection molding process and the suitable material for this part is thermoplastics due to

support this component’s requirements and characteristics. It would produced a good shape

and good dimensional accuracy. Thermosets material is less applicable so it is not suitable

for our production.


• Machining is eliminated because of less applicable

• Structural foaming is not suitable for small size because its usage is for large size

components.

• Suitable process for this part is injection molding.

109

6 Discussion

Discussion about the process and material selected from boothroyd DFM table (Compatibility

between processes and materials).

Front plate

Discussions

Material suggestion from table :

Carbon steel, Alloy Steel and Stainless steel

Material selection according to our

requirements. High Ductility, High Melting

point, Low Cost is carbon steel.

Process Suggestion from table:

Sand casting, Invest casting, Machining

(From Stock), Closed die forging, ECM,

EDM, Sheet metal.

Process Selected according to reasons from

previous chapter:

Sheet metal.

In summery

To manufacture Front plate the selected material is Carbon steel and the process selected can be sheet metal.

110

Moving system

Discussions


Carbon steel, Alloy Steel and Stainless

steel


requirements. High Ductility, High

Melting point, Low Cost is carbon steel.


Sand casting, Invest casting, Machining

(From Stock), Closed die forging, ECM,

EDM, Sheet metal.

Process Selected according to reasons

from previous chapter:

Sheet metal.

In summery

To manufacture Moving system the selected material is Carbon steel and the process selected can be sheet metal.

111


Discussions


Copper and alloy


requirements. High Ductility, High

conductivity.


Sand casting, Invest casting, Die Casting,

Machining (From Stock), Closed die

forging, ECM, EDM, Sheet metal.


previous chapter:

Sheet metal.

In summery

To manufacture Electrical connection snap-fit the selected material is Copper and alloys and the process selected can be sheet metal.

112

Bottom Cover

Discussions


Thermoplastics and thermosets


requirements. Heat resistance, good insulator,

approximately high melting point, Low cost.


Machining, Structural foaming and injection

molding.


previous chapter:

Injection Molding

In summery

To manufacture Bottom cover, the selected material is Thermoplastic and the process selected can be Injection molding.

113

Top Cover

Discussions


Thermoplastics and thermosets


requirements. Heat resistance, good insulator,

approximately high melting point, Low cost.


Machining, Structural foaming and injection

molding.


previous chapter:

Injection Molding

In summery

To manufacture Bottom cover, the selected material is Thermoplastic and the process selected can be Injection molding.

In the end the flowchart of the DMF method to reduction the time and cost of Manufacturing has been determined bellow.

In the end the flowchart of the DMF method to reduction the time and cost of Manufacturing

114

In the end the flowchart of the DMF method to reduction the time and cost of Manufacturing

115

7 Conclusion

In this project we tried to choose the best materials and processes according to principle

and design rules for DFM.This can aid designers in specifying components and products that

can be manufactured at minimum cost. There are several factors that identified in choosing

the material and process for manufacturing. Such as quantity, cost, surface finish,

appearance, product shape, service life, recycling and properties of materials. Choosing the

wrong materials can bring tremendous failure to the product and can endangered the user of

the product. Finally we reduced manufacturing costs while simultaneously improving product

quality.

Design for manufacturing (DFM) is aimed at reducing manufacturing costs while

simultaneously improving product quality , development time and development cost but how

well a product meet design specification and quality standards, it must also meet economic

criteria in order to be competitive in the domestic and global marketplace.

DFM begins with the concept development phase and system level design phase; in

these phases important decision must be made with the manufacturing cost implication in

mind. DFM decision can affect product development lead time, product development cost,

and product quality. Trade off will frequently is necessary between manufacturing cost and

these equally important broader issues.

116

8 Reference & Appendices

Peter Dewhurst and Winston Knight, Product Design For Manufacture and

Assembly,University of Toledo , Ohio, 2rd Edition, 2002.

Serope Kalpakjian & Steve R. Schmid, Manufacturing Engineering Technology, 5th Edition,

Pearson Prentice Hall, 2006.

Dr Ariffin. Lecture Note, 2012

Zainal Abidin Ahmad, Proses Pembuatan Jilid 2, Universiti Teknologi Malaysia,

Karl T. Ulrich and Steven D. Eppinger, Product Design and Development, McGrawHill

International Edition, 4th Edition, America, New York, 2008.

Handbook Of Materials Selection,Jon Wily and Sons 2002,Myer Kutz

Mikell P. Groover, Fundamental of Modern Manufacturing ( Material, Process and system),

John Wiley & sons (Asia) Pte Ltd, 3rd Edition, 2007.

117

118

119

120

121

Date post:	15-Feb-2017
Category:	Engineering
Upload:	ali-karandish
View:	120 times
Download:	6 times