introductiontomanufacturingprocess-131218044420-phpapp02

8/21/2019 introductiontomanufacturingprocess-131218044420-phpapp02

1/88

9/18/2014 1Hareesha N G, DSCE, Bengaluru


2/88

Unit-1: Introduction to manufacturing process

Casting Process: Introduction : Concept of Manufacturing process, its

importance.

Classification of Manufacturing processes. Introduction to Casting

process & steps involved.

Varieties of components produced by casting process. Advantages &

Limitations of casting process.

Patterns: Definition, functions, Materials used for pattern, various

pattern allowances and their importance. Classification of patterns.

Binder: Definition, Types of binder used in moulding sand.

Additives: Need, Types of additives used.

9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 2


3/88

Classification of manufacturing process



4/88

Classification of manufacturing process



5/88

Types of production systems

Mass production / continuous flow process

Batch production

Job shop production



6/88

Sand casting

9/

18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 6


7/88

Sand casting



8/88

Sand casting



9/88

Rolling

Hot-rolling

Cold-rolling

http://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=6xnKmt_gsLs


10/88

hydraulic

piston

chamber

chamber

stock

die

extruded shape

hydraulic

piston

chamber

chamber

stock

die

extruded shape

hydraulic

piston

chamber

chamber

stock

die

extruded shape

Extrusion: Schematic, Dies

Exercise: how can we get hollow parts?



11/88

Shearing

A large scissors action, cutting the sheet along a straight line

Main use: to cut large sheet into smaller sizes for making parts.



12/88

Punching

Cutting tool is a round/rectangular punch,that goes through a hole, or die of same shape

F t X edge-length of punch X shear strength

Punch

die

sheet

crack

(failure in shear)

clearance

die

piece cut away, or slug

t

F t X edge-length of punch X shear strength

Punch

die

sheet

crack

(failure in shear)

clearance

die

piece cut away, or slug

t



13/88

Lathe



14/88

Lathe operation ( Turning)



15/88

Drilling operation ( Drilling)



16/88

Milling operation ( Drilling)



17/88

Grinding operation



18/88

Water jet machining



19/88

Electric discharge machining



20/88

Electro chemical machining



21/88

Plasma arc machining



22/88

Welding operation



23/88

Riveting operation



24/88

Soldering operation



25/88

Factors to be considered for selecting a

production process

a) Shape and size to be produced - For products with simple

shape, machining is best suited. But for complex and intricateshapes, casting is preferred. The size of the product is also animportant factor. For example, 'long' products such as rails or'thin' products such as car-body panels can be best made byforming process compared to others.

(b) Quantity to be produced - Both machining and casting canbe used for producing large quantity products, but are notsuitable for small quantity products, as they are noteconomical.

(c) Type of material - Materials possess various properties like

ductility, hardness, toughness, brittleness etc. Hard materialscannot be machined easily. Brittle materials cannot bemechanically worked (Forming process). In such cases,casting is preferred.


b d d f l


26/88

Factors to be considered for selecting a

production process

(d) Surface finish and dimensional accuracy - Casting with expendable

moulds does not yield good surface finish. However," if casting

process is selected, it should be followed by machining process to

obtain the desired surface finish and dimensional tolerance.

(e) Quality and property requirements - A defect-free product withspecific properties serve its purpose for long life. Properties of cast

material are generally less when compared to that of mechanically

worked materials. Also, casting gives a lot of defects. Hence, a process

that gives better properties and quality should be selected.

(f) Cost of the product - Customers often demand for products with more

features and performance at reduced prices. Hence, a low cost

production process should be selected, but at the same time, see that

no compromise is made in terms of quality.



27/88

CASTING PROCESS



28/88

Terms involved in casting



29/88

Terms involved in casting process

Mould box (flask): It is usually a metallic

frame used for making and holding a sandmould. The mould box has two parts: the

upper part called 'cope', and the lower

part called 'drag'.

Parting line/parting surface: It is the zoneof separation between cope and drag

portions of the mould in sand casting.

Sprue:It is vertical passage through which the molten metal

will enter the gate.

Pouring basin: The enlarged portion of the sprue at its top

into which the molten metal is poured.



30/88

Terms involved in casting process Gate/ingate: It is a short passage way which

carries the molten metal from the runner/

sprue into the mould cavity.

Riser: A riser or feed-head is a vertical

passage that stores the molten metal and

supplies (feed) the same to the casting as it

solidifies.

Gate/ingate: It is a short passage way which carries the molten metal from the

runner/ sprue into the mould cavity.

Riser: A riser or feed-head is a vertical passage that stores the molten metal

and supplies (feed) the same to the casting as it solidifies.

Mould cavity: The space in a mould that is filled with molten metalto form the

casting upon solidification.

Core: A core is a pre-formed (shaped) mass of sand placed in the mould cavity

to form hollow cavities in castings.

Core print: It is a projection attached to the pattern to help for support and

correct location of core in the mould cavity.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 30


31/88

STEPS INVOLVED IN MAKING A CASTING

The basic steps in making a casting are:

(a) Pattern making

(b) Mould preparation (including gating and risering)

(c) Core making

(d) Melting and Pouring

(e) Cleaning and Inspection



32/88

a) Pattern making

A pattern is a replica of the object to be cast.

It is used to prepare a cavity into which the molten

metal is poured.

A skilled pattern maker prepares the pattern using

wood, metal, plastic or other materials with the helpof machines and special tools.

Many factors viz., durability, allowance for shrinkage

and machining etc., are considered while making apattern.



33/88

b) Mould preparation

Mould preparation involves forming a cavity by packing

sand around a pattern enclosed in a supporting metallicframe called 'flask' (mould box).

When the pattern is removed from the mould, an exact

shaped cavity remains into which the molten metal is

poured.

Gating and riseringare provided at suitable locations in

the mould.

Gating - Passage through which molten metal flows and enter the mouldcavity.

Risering- A reservoir of molten metal connected to the mould cavity to

supply additional metal so as to compensate for losses due to shrinkage, as

the metal solidifies.



34/88

c) Core making

In some cases, a hole or cavity is required in the

casting.

This is obtained by placing a core in the mould

cavity.

The shape of the core corresponds to the shape

of the hole required.



35/88

d) Melting and Pouring

Metals or alloys of the required composition are

melted in a furnace and poured into the mould

cavity.

Many factors viz., temperature of molten metal,

pouring time, turbulence etc., should be consideredwhile melting and pouring.



36/88

e) Cleaning and Inspection

After the molten metal has solidified and cooled, the

rough casting is removed from the mould, cleaned

and dressed.

This involves removing cores, adhered sand particles,

gating and risering systems, fins, blisters etc., fromthe casting surface.

then sent for inspection to check for dimensions or

any defects like blow holes, cracks etc.



37/88

Procedure for making the casting



38/88



39/88



40/88


Components Produced by


41/88

Components Produced by

Casting Process

Casting is the first step and the primary process forshaping any material.

All materials have to be cast before it is put to use.

The ingotsproduced by casting process are used as

raw material for secondary processeslike machining,

forging, rolling etc.

More than 90 %of all manufactured goods and capital

equipment use castings for their manufacture. To list the components produced by casting is an

endless process. A few major components produced by

casting are given below.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 41

Components Produced by Casting Process


42/88

Components Produced by Casting Process

Automotive sector - Nearly 90 % of the parts in automobiles are-

manufactured by castings. A few parts include brake drum,

cylinder, cylinder linings, pistons, engine blocks, universal joints,rocker arm, brackets etc.,

Aircraft- Turbine blades, casing etc.

Marine propeller blades.

Machining- Cutting tools, machine beds, wheels and pulleys,blocks and table for supports etc.

Agriculture and rail road equipments.

Pumps and compressors frame, bushings, rings, pinion etc.

Valves, pipes and fittings for construction work.

Camera frames, parts in washing machine, refrigeratorsand air-

conditioners.

Steel utensils and a wide variety of products.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 42


43/88

Advantages of casting process

Large hollow and intricate shapes can be easily cast.

Quick process, and hence suitable for mass production.

No limit to size and shape. Parts ranging from few millimeters to

meters and few grams to tons can be cast efficiently and

economically.

Better dimensional tolerances and surface finish can be obtained

by good casting practice.

Castings exhibit uniform properties in all the directions -

longitudinal, lateral and diagonal. The casting process is usually the cheapest process.

Unrelieved internal stresses are absent in cast components.

Certain metals and alloys can be manufactured by means of

casting only, e.g., Phosphor-Bronze.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 43

f


44/88

Limitations of casting process

Presence of defects in cast parts is a major disadvantage.

Casting process is not economical for small number of parts.

Properties of cast materials are generally inferior when

compared to those made by machining or forging process.

Casting process mostly deals with elevated temperatures.

There are limitations regarding thin sections.

Casting process is not suitable for very small number of

components.



45/88

INTRODUCTION TO PATTERN MAKING

A pattern is a mold forming tool in the hands of foundry men.

A pattern is a model or the replica of the object to be cast.

Except for the various allowances a pattern exactly

resembles the casting to be made. A pattern is required even if one object has to be cast.

A patternmay be defined as a model or form around which

sand is packed to give rise to a cavity known as mold cavity

in which when, molten metal is poured, the result is the CASTOBJECT.



46/88

Difference between pattern and casting

The main difference between a pattern and the casting is their dimensions.

A pattern is slightly larger in size as compared to the casting, becauseapattern,

carries Shrinkage allowance, it may be of the order of 1 to 2 mm/ 100

mm.

is given a Machining allowance to clean and finish the required surfaces.

carries a Draft allowance of the order of 1 and 3 degrees for externaland internal surfaces respectively

carries core prints.

A pattern may not have all holes and slots which a casting will have. Such

holes and slots unnecessarily complicate a pattern and therefore can bedrilled in the casting after it has been made.

A pattern may be in two or three pieces whereas a casting is in one piece.

A pattern and the casting also differ as regards the material out of which

they are made.


Functions of a patterns


47/88

Functions of a patterns A pattern prepares a mold cavity for the purpose of making a casting.

A pattern may contain projections known as core prints if the casting

requires a core and need to be made hollow.

Runner, gates and risers (used for introducing and feeding molten

metal to the mold cavity) may form a part of the pattern.

A pattern may help in establishing locating points on the mold and

therefore on the casting with a purpose to check the castingdimensions.

Patterns establish the parting line and parting surfaces in the mold.

A pattern may help position a core (in case a part of mold cavity is

made with cores), before the molding sand is rammed. Patterns that are properly made and having finished and smooth

surfaces, reduce casting defects.

Properly constructed patterns minimize overall cost of the castings.


P i l


48/88

Pattern materials

The following factors assist in selecting proper pattern material:

The number of castings to be produced. Metal patterns are

preferred when the production quantity is large.

The desired dimensional accuracy and surface finish requiredfor the castings.

Nature of molding process i.e., sand casting, permanent mold

casting, shell molding, investment casting etc.

Method of molding i.e., hand or machine molding.

Shape, complexity and sizeof the casting.

Type of molding materials i.e., sand etc.

The high probability of changing the casting and hence the

pattern in near future.

Selection of pattern materials


M t i l f ki tt


49/88

Materials for making patterns

Patterns may be constructed out of the following

materials.

(a) Wood (b) Metal

(d) Plastic (d) Plaster (POP)

(e) Wax


WOOD


50/88

WOOD The most common materials for making patterns for sand casting is the wood.

Advantages

Inexpensive. Easily available in large quantities.

Easy to machine and to shape to different configurations and forms

Easy to join to acquire complex and large pattern shapes

Light in weight

Easy to obtain good surface finish

Wooden patterns can be preserved for quite long times with the help of

suitable wood preservatives.

Limitations

Wooden patterns are susceptible to shrinkage and swelling.

They possess poor wear resistance.

They are abradedeasily by sand action.

They absorb moisture, consequently get deformed and change shape and size.

They cannot withstand rough handling.

They are weakas compared to metal patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 50

M t l


51/88

Metal

Metal patterns are employed where large number of

castingshave to be produced from the same patterns. Metal patterns are cast from wooden patterns.

The different metals and alloys used for making

patterns are,

Aluminium and Aluminium alloys

Steel

Cast Iron

Brass White Metal


Advantages of Metal Patterns


52/88

Advantages of Metal Patterns Unlike wooden patterns, they do not absorb moisture. They retain their

shape.

They are more stronger and accurate as compared to wooden patterns.

They possess life much longer than wooden patterns.

They can withstand rough handling.

They do not distort

They possess greater resistance to abrasion. They have accurate

dimensional tolerances. They are far stable under different environments. It is easy to obtain smooth surface finish.

They possess excellent wear resistance and strength to weight ratio.

Limitations of Metal Patterns

Expensiveas compared to wood patterns. Are not easily repaired e.g. (Aluminium patterns).

Ferrous patterns get rusted.

They (ferrous patterns) are heavierthan wooden patterns,

They cannot be machined so easily as wooden ones.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 52

Plastic


53/88

Plastic

Advantages

Durable Provides a smooth surface.

Moisture resistant.

A plastic pattern does not involve any appreciable change in its size or

shape.

Lightweight.

Wear and corrosion resistant.

Provides good surface finish.

It possesses low solid shrinkage.

Limitations Plastic patterns are fragileand thus light sections may need metal

reinforcements.

Plastic patterns may not work well when subject to conditions of severe

shock as in machine moulding.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 53

PLASTER


54/88

PLASTER

Advantages

can be easily worked by using wood working tools. Intricate shapes can be cast without any difficulty.

It has high compressive strength (up to 285 kg/cm2)

Disadvantages

Can be used for small castings only

Plaster Patterns Material: Plaster patterns may be

made out of Plaster of Paris or Gypsum cement.

Applications: Plaster is used for making (i) Small

and intricate patterns, and (ii) Core boxes.


WAX


55/88

WAX

Advantages

Wax patterns provide very good surface finish

They impart high accuracy to the castings.

After being molded, the wax pattern is not taken out of

the mold like other patterns; rather the mold is

inverted and heated; the molten wax comes out and/oris evaporated. Thus there is no chance of the mold

cavity getting damaged while removing the pattern.

Applications

Wax patterns find applications in Investment

casting process.


PATTERN ALLOWANCES


56/88

PATTERN ALLOWANCES

A pattern is always larger in size as compared to

the final casting, because it carries certainallowances.

The various pattern allowances are below

(a) Shrinkage or contraction allowance.

(b) Machining or Finish allowance.

(c) Draft or Taper allowance.

(d) Distortion or camber allowance.(e) Shake or rapping allowance.


Sh i k All


57/88

Shrinkage Allowance Almost all cast metals shrink or contract volumetrically after solidification and

therefore to obtain a particular sized casting, the pattern is made oversize by

an amount equal to that of shrinkage or contraction.

Different metals shrink at different rates because shrinkage is the property of

the cast metal or alloy.

The metal shrinkage depends upon

The cast metal or alloy.

Pouring temperature of the metal or alloy.

Casting dimensions(size).

Casting design aspects.

Molding conditions (i.e., mold materials and molding methods

employed).

Cast iron poured at higher temperatures will shrink more than that poured at

lower temperature.

Wood patterns used to make metallic patterns are given double allowance; one

for the shrinkage of the metal of the pattern and the other for that of metal to

be cast.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 57

Machining Allowance


58/88

Machining Allowance A casting is given an allowance for machining, because

Castings get oxidized in the mold and during heat treatment; scales etc., thus formed

need to be removed.

It is intended to remove surface roughness and other imperfectionsfrom the castings.

It is required to achieve exact casting dimensions.

How much extra metal or how much Machining allowance should be provided,

depends upon:

Nature of metal i.e., ferrous or non-ferrous. Ferrous metals get scaled whereas non-ferrous ones do not.

Size and shape of the casting. Longer castings tend to warp and need more material (i.e., allowance) tobe added to ensure that after machining the casting will be alright.

The type of machining operation (i.e., grinding, turning, milling, boring etc.) to be employed forcleaning the' castings. Grinding removes much lesser metal as compared to turning.

Casting conditions i.e., whether casting conditions result in a rough casting or a semi-finished one. Castingconditions include the characteristics of mold-materials etc.

Molding process employed. Die casting produces parts which need little machining (allowance) whereassand-casting, require more machining allowance.

Number of cuts to be taken. Machining allowance is directly proportional to the number of cuts required for finishingthe casting.

The degree of surface finish desired on the cast part.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 58

f ll


59/88

Draft or Taper Allowance It is given to all surfacesperpendicular to the parting

line.

Draft allowance is given so that the pattern can be easily

removedfrom the molding material tightly packed

around it without damaging the mold cavity.

The amount of Taper depends upon Shape and size (length) of the pattern in the depth direction in contact with

the mold cavity.

Molding method.

Mold materials.

Draft allowance is imparted on internal as well asexternal surfaces; of course it is more on internal

surfaces.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 59

Fig. shows two patterns one with taper allowance and the


60/88

g p p

other without it. It can be visualized that it is easy to draw the

pattern having taper allowance, out of the mold without

damaging mold walls or edges.

Taper on external surfaces = 10 to 25 mm/metre.

Taper on internal surfaces = 40 to 65 mm/metre,9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 60

Distortion Allowance


61/88

Distortion Allowance A Casting will distort or warp if:

it is of irregular shape,

all its parts do not shrink uniformly i.e., some parts shrink while others arerestricted from doing so,

it is U or V-shaped,

it has long, rangy arms as those of the propeller strut for the ship,

it is a long flat casting,

the arms possess unequal thickness,

one portion of the casting cools at a faster rate as compared to the other,

etc.

Distortion can be practically eliminated by providing an allowance

and constructing the pattern initially distorted i.e., outsize in theopposite direction so that the casting after cooling neutralizes the

initial distortion given on the pattern and acquires the correct shape.

The amount of distortion allowance may vary from 2 to 20 mm

depending upon the size, shape and material of the casting.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 61

Sh k All


62/88

Shake Allowance A pattern is shaken by striking the same with a wooden

piece from side to side. This is done so that the pattern isloosened a little in the mold cavity and can be easily

removed.

In turn, therefore, shaking enlarges the mold cavity

which results in a bigger sized casting.

Shake allowance is normally provided only to large

castingsbecause it is negligible in case of small castings

and is thus ignored. The magnitude of shake allowance can be reduced by

increasing the taper.



63/88

TYPES OF PATTERNS


F l i i l ki d f f ki i


64/88

For selecting a particular kind of pattern for making a casting,

one may consider the following points:

Quantityof castings to be produced.

The size and the complexity of the shape of the casting to be

produced.

Type of molding method to be used (i.e., hand or machine

molding).

Problems associated with the molding operation such as

withdrawing the pattern from the mold etc.

Other difficulties resulting from poor casting design or pattern

design.


The different types of patterns commonly used


65/88

The different types of patterns commonly used

are:

One piece(Solid) pattern

Split pattern

Loose piece pattern

Match plate pattern

Cope and Drag pattern

Sweep pattern

Gated pattern

Skeleton pattern

Follow board pattern.


O Pi ( lid) P tt


66/88

One Piece (solid) Pattern


One Piece (solid) Pattern


67/88

One Piece (solid) Pattern It is the simplest type of pattern.

As the name suggests the pattern ismade from one piece and does not

contain loose pieces or joints.

It is inexpensive. It is used for making a few large size simple castings

One piece pattern is usually made up of wood or

metaldepending upon the quantity of castings to be

produced.

For making the mold, one piece pattern is

accommodated either in the cope or in the drag.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 67

Split Pattern


68/88

Split Pattern


Split Pattern


69/88

Split Pattern Patterns of intricate (shaped) castingscannot be made in one piece

because of the inherent difficulties associated with the molding

operations (e.g. withdrawing the pattern from the mold etc.) , suchpatterns are, then, made as split or two piece patterns.

The upper and the lower parts of the split pattern are

accommodated in the cope and drag portionsof the mold

respectively. Dowel pins are used for keeping the alignment between the two

parts of the pattern.

The parting (surface or)line of the pattern forms the parting

(surface or) line of the mold. Patterns for still more intricate castings are made in more than two

pieces for facilitating their molding and withdrawing.

A pattern having three pieces will require a three piece flask for the

molding purposes9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 69

Loose Piece Pattern


70/88

Loose Piece Pattern


Loose Piece Pattern


71/88

Certain patterns cannot be withdrawn once they are

embedded in the molding sand. Such patterns are

usually made with one or more loose pieces

Piecesfor facilitating their removal from the molding

box and are known as loose piece patterns.

Loose parts or pieces remain attached with the mainbody of the pattern, with the help of dowel pins.

The main body of the pattern is drawn firstfrom the

molding box and thereafter the loose parts are

removed, the result is the mold cavity.

Loose piece patterns involve more labour and consume

more timein the molding operation.


Match Plate Pattern


72/88

Match Plate Pattern


Match Plate Pattern


73/88

Match Plate Pattern A match plate pattern consists of a match plate, on

either side of which each half of (a number of) splitpatterns is fastened.

A number of different sized and shaped patterns may be

mountedon one match plate.

The match plate with the help of locator holes can be

clamped with the drag.

The match plate has runner and gates also attached with

it. After the cope and drag have been rammed with the

molding sand, the match plate pattern is removed from

in between the two (i.e., cope and drag.)9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 73

Match Plate Pattern


74/88

Match Plate Pattern Cope and drag are then assembled and this completes

the mold. Patterns, match plate, runner and gatesall may be

made up of aluminium, because it is light and

relatively inexpensive.

Match plate patterns are normally used in machine

molding.

Match plate patterns are preferred for producing small

castings on mass scale. They produce accurate castings and at faster rates.

Piston rings of I.C. engines are produced with the help

of match plate patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 74

Sweep Pattern


75/88

Sweep Pattern


Sweep Pattern


76/88

Sweep Pattern A sweep pattern is just a form made on a wooden board

which sweeps the shapeof the casting into the sand all

around the circumference. The sweep pattern rotates aboutthe post.

Once the mold is ready, sweep pattern and the post can be removed

Sweep pattern avoids the necessity of making a full, large

circular and costly three dimensional pattern.

Making sweep pattern saves a lot of time and labour as

compared to making a full pattern.

A sweep preferred for producing large castings of circularsections and symmetrical shapes.

The manufacture of large kettles of cast iron requires a sweep

pattern.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 76

Gated Pattern


77/88

Gated Pattern

castings

Gating system


Gated Pattern


78/88

Gated patterns are usually made of metal which

increases their strength and reduces the tendency to

warp.

The sections connecting different patterns serve as

runner and gates. This facilitates filling of the mold

with molten metal in a better manner at the sametime eliminates the time and labour otherwise

consumed in cutting runners and gates.

A gated pattern can manufacture many castings at

one timeand thus it is used in mass productionsystems.

Gated patterns are employed for producing small

castings.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 78

Skeleton Patten


79/88


Skeleton Patten


80/88

A skeleton pattern is the skeleton of a desired shape. The skeleton

frame is mounted on a metal base.

The skeleton is made from wooden strips and is thus a woodenframework.

The skeleton pattern isfilled with sand and is rammed.

A strickle(board) assists in giving the desired shape to the sand

and removes extra sand. If the object is symmetricallike a pipe, the two halves(of the pipe)

can be molded by using the same pattern and then the two molds

can be assembled before pouring the molten metal.

Skeleton patterns are employed for producing a few large castings. A skeleton pattern is very economical as compared to a solid

pattern, because it involves less material costs.

Castings for turbine castings, water pipes, channels, etc., are

made with the help of skeleton patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 80

Follow Board Pattern


81/88





82/88

Follow Board Pattern A follow board is a wooden board and is used for

supporting a pattern which is very thin and fragile andwhich may collapse under the pressure when the sand

above the pattern is being rammed.

With the follow board support under the weak pattern,

the drag is rammed, and then the follow board iswithdrawn.

The rammed drag is inverted, cope is mounted on it and

rammed. During this operation pattern remains over the

inverted drag and gets support from the rammed sand of

the drag under it.

Ultimately, the pattern is removed and the cope and

drag are assembled.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 82

MOLDING SAND BINDERS


83/88

Binders produce cohesion between the molding sand grains in the

green or dry state (or condition).

Binders give strength to the molding sand so that it can retain its

shape as mold cavity.

Binders (to the molding sands) should be added as optimal

minimum.

Increasingbinder content reduces permeability of molding sand.

Increasing binder content, increases green compression strength

up to a limit; after which green compression strength remains

practically unchanged with further increase in binder content.

Clay binders are most commonly used for bonding molding sands.

The best clay is one which imparts the optimum combination of

bonding properties, moisture, life and cost of producing the

required casting.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 83



84/88

Clay binders are most commonly used for bonding molding sands.

Clay binders can be classified as:

Fire clay

Bentonite

Sodium montmorillonite

Calcium montmorillonite

Illite Kaolinite

Bentonite: The most commonly used clay binders are Bentonites as they produce

strongest bonds in foundry molding sands.

Bentonite deposits are available in India in Rajasthan and Bihar

Bentonites are the weathered product of volcanic ash and are soft creamy

white powders.




85/88

Fire Clay:

Fire clay is a refractory clay usually found in the coal measures.

Fire clay particles are about 400 times as largeas compared to those of Bentonite ;hence the same percentages of fire clay produce lower strengths.

Illite

Illite is the decomposition product of micaceous materials due to weathering.

Illite is found in natural molding sands.

Illite has softening point of about 2500F.

Illite does not swell in the same way as bentonite but gives reasonable strength.

Illite particles have thickness and width of 20 and 100-250 milli-microns respectively.

Kaolinite

Kaolinite is the residue of weathered granite and basalt. Kaolinite binder has its composition 60% kaolinite, 30% illite and 10% quartz,

Kaolinite gets Very low swelling due to water and is non-gel forming.

Kaolinite particles possess thickness and width of 20 and 100-250 milli-microns

respectively.


WATER


86/88

The amount of water may vary from 1.5 to 8%.

water is responsible for the bonding action of clays.

Water activates the clay in the sand and the clay-sand mixture developsstrength and plasticity.

Water added to the sand mixture, partly gets adsorbed by clay and partly

remains free and is known as Free Water.

The absorbed water is responsible for developing proper bond and the green

strength.

The free water acts as a lubricant,

It increases plasticity

It improves moldability, but It reduces strength of the sand mixture.

For a given type of clay and its amount, there is an optimum required watercontent.

Too little water will not develop proper strength and plasticity.

Too much water will result in excessive plasticity and dry strength.

The amount of water required to develop the optimum properties can be

found out experimentally.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 86

ADDITIVES


87/88

The basic constituents of molding sand mixture are;

Sand

binder and

water

Materials other than the basic ingredients are also added to

molding sand mixtures, of course in small quantities, in order to

enhancethe existing properties. To develop certain other properties.

to give special qualities like resistance to sand expansion, defects etc.

Some of the additive materials along are given below.


Facing materials:

F i t i l t d t bt i th d l f f ti


88/88

Facing materials tend to obtain smoother and cleaner surfaces of castings

and help easy peeling of sand from the casting surface during shake out.

A few facing materials are

Sea coal Graphite

Coke

Silica floor

Cushion materials:

Cushion materials burn when the molten metal is poured and thus give rise

to space for accommodating the expansion of silica sand at the surfaces of

mold cavity.

In the absence of cushion materials, large flat surfaces of castings may

buckle due to thermal expansion of silica sand grains.

A few cushion materials are:

Wood floor

Cellulose

Date post:	07-Aug-2018
Category:	Documents
Upload:	amrik-singh
View:	212 times
Download:	0 times

introductiontomanufacturingprocess-131218044420-phpapp02

Documents