AE 142 - Lecture 1 Introduction to Machine Design

8/11/2019 AE 142 - Lecture 1 Introduction to Machine Design

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AE 142

Engr. Vasma A. Hassan

Mindanao State University


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It is the art of planning or devising new

or improved machines to accomplish

specific purposes.

It consists of a combination of several

different mechanical elements properlydesigned and arranged to work

together, as a whole.


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Agriculture is the primary industry of thePhilippines.

Agricultural development can be speed upthrough mechanization.

Increase in crop production and reduction inpostharvest losses can be achieved by the use ofappropriate agricultural machines.

At present, there is a limited supply of locallyavailable designs of agricultural machines is thePhilippines.

Experienced have shown that designingagricultural machines suitable for farmers is quite

a difficult job because one should come up with amachine that is low cost but effective and efficient.

In order for the designer to meet this challenge,he or she needs to have enough skills and abilityto do the job.


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The designers need to have a full understanding of the

variable of the field conditions and other factors which

influence machinery performance including the

environmental and human-related factors. Note that

the machine should be operationally reliable and

economically acceptable to farmers.

The designers need to apply engineering principles so

that functional requirements of a certain machine aremet. This includes the laws of mechanics, strength of

materials, fluid flows, heat transfer, etc.


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The designers should have the knowledge

of the analytical design process which isessential in the design of machine

components, main frames, mounting

arrangement, balancing, etc.The designers must integrate analytical

design and results of experimental

investigation to develop machines that aresimple to fabricate, affordable, light in

weights, easy to maintain, and require

readily available and low cost materials.


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Unless the designer tries to meet the

needs of actual users, no amount of

design work will be utilized.

The success of a good design is

indicated by the extent by which the

machine is adopted by farmers.


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It includes the process of organizing the

methodology needed to proceed from concept

to final product, determining which

technological resources to use, the economicsof production and operation, and the human

and social factors that will be needed.


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To attempt to predict the stress or

deformation in the part in order that

it may safely carry the loads whichwill be imposed upon it, and that it

may last for the expected life of the

machine.


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Mathematical calculations be looked

upon as absolute and final. They are all

subject to the accuracy of the various

assumptions which must necessarily be

made in engineering work.


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To produce a machine which is

not only sufficiently rugged to

function properly for areasonable life, but is at the same

time cheap enough to be

economically feasible.


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Loading

Type of kinematic elements to be

usedCorrect utilization of the properties

of engineering materials

Economic consideration


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Cost of design

Manufacture

Sale

Installation

Cost of Servicing

Safety

Aesthetics


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A. Based on the Design Information andConsideration Needed in Coming Upwith the Product

Rational Designcarried out using mathematicalformula and other engineering principles.

Empirical Designbased upon empiricalformula derived from existing practices and past

experiences. Industrial Designinvolves consideration like

aesthetics, ergonomics, and production aspect.


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B. Based on the Process that is Taking Placein Coming Up with the Product

Original Designdoes not exist before and it isonly done by few dedicated designer who havepersonal qualities of a sufficiently high order. Thisalso requires a lots of research, experimental

activities, and creative brain. Adaptive Designthis is more concerned of the

adoption of existing designs. This does notdemand special knowledge or skills. Problemscan be solved with ordinary training.

Development Design -This begins with anexisting design but the final result may quietlydiffer from the initial product.


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Imaginative powerHighly developed intellectual powerGood memory

Ability to work thoroughly andconscientiously

Inventive talent and good judgmentAbility to concentrateSense of responsibility and self-

confidence Integrity


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Ability to work with people

Ability to do simulation, experiments,

and measurements

Environment conscious

Aesthetics and conscious on the

ergonomics of machine

Ability to make technical reportsAbility to optimize design


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Used to include uncertainties in thedesign.

The degree of use of the FS depends onthe technical competence and design

experience of the designer. Large FS are usually uneconomical.

Sufficient FS is required if failures andloss in time, and inconveniences are to be

minimized The use of excessive FS can be minimized

if the latest tools and techniques indesigning are to be used.


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Excessive strength and oversized

machine are usually wasteful in

engineering design.

Machine to be design if possible should

have 99.9% reliability.

Continuous replacement of defective

machine components may keep thedesign more reliable and economical.


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Technical reports approved and

recommended for practice by engineers.

The use of standard is voluntary and no

liability is assumed by the sponsoring

organization for their misuse.

The use of standard can minimize the

potential liability of the organization in

designing a product. It is a mechanism for interchanging

machinery parts thus resulting to a lower

product cost to consumers.


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The durability, service, and cost agriculturalmachines depends largely on the kind and quality

of materials used in manufacturing the machine.

Machine fabricated from substandard materials are

usually easy to wear off and have short life span. Heavy materials usually affects power requirement

and performance.

Engineers should have a knowledge of the physical

characteristics, selective and effective utilization ofmaterials and their processing techniques to avoid

waste and spoilage.


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Metals

Ferrous

Iron and steel, Cast Iron, Carbon

Steel, Alloy Steel, etc

Non-Ferrous

Aluminum, copper, magnesium, etc


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Non-MetalsInorganic materials

glass, ceramics, plastic, etc

Organic Materials

wood, rubber, leather, canvass,


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Metallic ore is mined beneath the earth

surface. Iron is produced from iron ore while

copper is produced from copper ore.

Aluminum is produced from an ore calledbauxite. A blast furnace is used to produce

metal by passing a hot gases to the furnace

that is mixed with iron ore, limestone, and

coke at about 3000 C. Melted metal isseparated into a ladle for cooling to form pig

iron. Pigs are then melted and poured into

mold to make iron, steel, and cast iron.


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Hard

Easy to shape

High melting temperature

Low specific heat

Good electrical conductivityGood thermal conductivities

Ability to be deformed without fracture


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Pure Metalare single element that are notcombined with any other chemical element.

They are too soft, low and strength, or low insome other desired property to be used inany commercial applications.

Alloysare mixture of two or more metal toproduce new metal. Example are stainlesssteel, bronze, etc.


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It is a pure ferrite.

Pig ironit is produced from ore of hematite

or magnetite in the blast furnace by melting

with limestone and coke.

Cast Iron with carbon content of 1.7 to

6/7%. They are low cost, good casting

property, high compressive strength, highwearing resistance, brittle and lower tensile

strength.


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It is a molten steel that is cast into an ingot andthen rolled, forged, hammered, pressed, or

machine into desired shape

Structural steel, steel bars and cylinder, and

steel plate are commonly used as machineelements and frame

Soft Centered Steeldurable to shock because

the mild steel in the center layer is deformable

and is higher wear resistance than hard steel at

the outer side. They are usually used for

moldboard and share of a plow.


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Low Carbon Steelwith carbon contentnot exceeding 0.25%.

Medium Carbon Steelcontains 0.25 to0.50% carbon. They are usually used inmaking structural and machinery steel.

High Carbon Steelcarbon content isabove 0.50%. They are usually used inthe manufacture of spring and tool steel.


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Mild Steel (MS)

contains carbon of 0.15 to0.25%. They are malleable and easy to cut

and weld.

Cold Rolled Steel (CRS)are medium carbon

steel which are used for parts andcomponents of machine requiring greater

strength and hardness such as shafting and

connecting rods.

Stainless Steel (SS)1% Ni, 11-14% Cr, 0.6%

Mn, 0.6% Si. They have high resistance to

corrosion and oxidation. They are used for

valves, nozzles, and dairy machines.


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Includes all the metals such as

copper, aluminum, magnesium,

and zinc in which iron is not

present in large amount


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Have an outstanding characteristics of good

strength, light weight, high thermal and electrical

conductivities, and good corrosion resistance.

Y alloy (4%Cu, 2% Snalloy)it is strong as a castingand is used for cylinder head and piston.

Silmin(14% Sialloy)casting metal used for

cylinder head and crankcase.

Duralumin (4% Cu, 0.5-1.5% Mg, 0.4 Mnalloy)quenched at high temperature and then aged to

gradually increase strength and hardness.


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It has high electric conductivity and thermal

conductivity, soft, high resistance tocorrosion.

Commonly use for electric wire, fuel pipe,gasket, radiator, and electric motor

Brass (10-40% zinc alloy)used for radiator,pipe, screen, and instrument parts.

Bronze (5-20% tin alloy)used for bushing,spring, pipe, fittings, sprayer and pump.

Kelmet Alloy (20-40% lead alloy) used forbearing of diesel engine.


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Sheets, Strips, and Plates Sheet-a piece of metal which has been rolled into a

sheet of 3/16 in. or less in thickness. Commonly

available sizes are 3 wide x 6 long and 4 wide and

8 long. The thickness is expressed in terms ofgauge number which is equivalent to number of

sheets in 1 in. thick pile pf metal sheet.

Stripsa long sheet of metal that is less than 12 in.

wide Platea metal with thickness over 3/16 in.

Commonly available size is 4 wide x 8 long.

Thickness are given in terms of mm or in inch.


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Metal Barsmade of different shapes and are

usually available in standard length of 20 ft or 6meters. They are purchased in terms of quantity,shape, size, and kind of metal used.

Structural Shapescommonly used in theconstruction of agricultural machines. They arespecified in terms of quantity wanted, the kind ofmaterial and shape, size, and length of eachpiece.

Tubular Productsincludes all hollow metalshapes such as pipes and tubes. They areavailable in round, square, and rectangular inshape. Specifications are given in terms of shape,schedule number, size, and length.


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Physical Propertiescharacteristics of metalswhen not acted upon by outside forces. This

includes color, density, weight, and electrical and

heat conductivity.

Mechanical Propertiescharacteristics exhibitedby metal when outside forces are applied to them.

The understanding of these property would result

in a better processing of metal into product.

Chemical Propertiescharacteristics of the

chemical composition of metal and their chemical

reaction to other metals. Example, resistance to

corrosion.


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Tensile Strengthit is the greatest stress seen by

the materials resistance to being pulled apart. Itis sometimes called as the ultimate strength.

Yield Strengthusually designated at a 0.2%

permanent elongation. Ductilityindicate how much a material is

deformed as it is stretched. The greater thedeformation the more ductile is the material.

Hardnessit is the materials resistance topenetration and permanent deformation.

Brittlenessis the tendency of a material to breakunder impact.


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Compressive strengthis a materials resistance

to being compressed.

Malleabilityis the capability of a material to beshaped and formed.

Toughnessis the ability of a material to

withstand bending and twisting. It is the

desirable property for loader frame andcrankshaft.

Grain Sizeis the microscopic measurement of

metal that shows differences in sizes that relate

directly to strength.

Machinabilitythe ease with which metals are

machined or cut by a machine tool.


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Fusibilityis the property to which metal when it is

at the liquid state easily join with other metals. Metal

with high fusibility are usually high in weldability.

Strengthis the resistance to deformation.

Tensile strengthresistance from being pulled

apart.

Compressive strengthresistance of being

squeezed together.

Shear strengthresistance to cutting or slicing

forces.

Torsional strengthresistance to twisting forces.

Elasticitythe ability of metal to return to its original

size and shape after the external force causing a

change in shape has been removed.


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Wood

Plastics

RubberCeramics

Fibers

Glass


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Heart Wood- the hard solid wood in thecenter of the trunk

Sap Wood- the layer of wood beneath the

bark of a tree and carries moisture.

Bark- the outer part of the wood

The wood is turned into lumber in a lumber

mill, after the bark has been removed,mechanical saws cut the wood into thin

planks or thicker beams, depending on what

the lumber is to be used for.


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Material obtained from rubber tree. It iscapable to withstand extreme

deformability with more or less complete

recovery upon removal of deforming

force.

Engineering applications:

shock, noise, and vibration control,

Sealing, Corrosion protection,Friction production, Electrical and

thermal insulation, Waterproofing,

Confining other materials, Load bearing


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Latex are collected by tapping rubbertree.

Adding of Acid- helps the latex to

coagulate or clot in a vat.Rollers form the coagulated latex into

sheets called crepe.

Rubber is dried in hot air or over smoke.

Rubber is dyed to desired color.

Rubber is shaped and finished into the

final product


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Large group of materials consisting of

combination of carbon and oxygen,

hydrogen, nitrogen, and other organic

and organic elements.

Non-metallic material that can be

molded into shape. They are light inweight, resistance to deterioration by

moisture, low elastic and thermal

conductivity, and good color range.


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Acrylic thermoplasticsEpoxy

Flouroplastics

NylonPhenolic Resin

Phenylene oxide

Polystyrene

Polyurethene

Polyvinyl chloride

Silicone


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Materials ranging from glass to

furnace brick

This includes ceramic oxides, glass-

ceramics, carbides and nitrides


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The oldest engineering material that

includes jute, flax, and hemp.

Usually used for engineered products

such as rope, cordage, nets, water hose,and containers.

Plant and animal fibers are used for felt,

paper, brushes, and heavy structuralcloth.

This includes metal fibers, glass fibers,

and aramid fibers


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A non-crystalline or amorphous solid

Most glass are made from silica, lime, and

sodium carbonate

Types includes soda-lime glass,

Borosilicate glass, lead-alkali glass,aluminosilicate glass, silica glass, and

fused silica.

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AE 142 - Lecture 1 Introduction to Machine Design

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