An Prod Hand Out Final 1

8/9/2019 An Prod Hand Out Final 1

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Manufacturing Process

IntroductionWhether from nature or industry materials cannot be used in their raw forms forany useful purpose. So they need to be processed.

• The basic characteristic of any Manufacturing process is some form of energy and/or mass transfer to alter the physical form and properties of an object.

• Manufacturing converts the raw materials to finished products to be used forsome purpose .

• The materials are then shaped and formed into different usefulcomponents through different manufacturing processes to fulfill the needsof day-to-day work.

The manufacturing system is therefore the design or arrangement of themanufacturing processes.

Production system:• A production system includes people, money, equipment, materials andsupplies, markets, management and the manufacturing system.

Manufacturing processes can be grouped as:Casting, foundry or molding processes.Forming or metal working processes.Machining (metal removal) processes.

Joining and assemblySurface treatments (finishing).Heat treating

These groups are not mutually exclusive. For example, some finishing processesinvolve a small amount of metal removal or metal forming.

Cutting - separating materials is done by physically breaking bonds, ormore recently by melting .Cutting techniques have found particular favorwith sheets of material, such as metal plates, metal sheets, fabrics, etc.Metallurgical/Finishing - a variety of processes that do not significantly

alter the geometry of the object, but are required for product performanceor marketing. Consider heat treating processes that will heat a metal andchange the properties. Or painting that makes a part more attractive andhelps protect the metal surface.Molding/Casting - Molding and casting technologies have been used formillennia, but they have recently begun to find interesting new techniques,and materials that expand the applications, and techniques. In general this



method uses material in a liquid form that solidifies into the shape of amold.Particulates - small particles of material have been used to manufacturelow cost parts of complex geometry at high production rates. In effect apowder is put in a mold, pressed until solid, and then heated to make it

stronger. Materials include many metals, ceramics, glass, etc.Forming - The idea of reshaping objects has been done for long periods of time (e.g. blacksmiths). Our knowledge of materials has allowed us to takeadvantage of subtle properties. Certain materials can be worked past thepoint that they would normally fracture. Materials can be bonded at anatomic level, and entire parts can be made out of a single crystal.

Joining/Cutting - By joining two or more parts we can create morecomplex geometries and assemblies. Consider parts that are glued orwelded together. Parts may also be made by cutting larger parts intosmaller pieces.

There are various manufacturing processes by which a product can be made.• Each process however has its own limitation and restriction and due to thisreason a particular process is adopted to certain specific applications.• Thus while a product can be manufactured by two or more processes, thereal problem is to select the most economical out of them.• A detailed understanding of various manufacturing processes is thus veryessential for every engineer. This helps in designing the proper productrequired for him.• He would be able to assess the feasibility of manufacturing from his designs.• He may find that there are more than one process is available formanufacturing a particular product and he can make a proper choice of theprocess which would require lowest manufacturing cost.

Why new manufacturing processes are being developed?New materials that is not suitable by traditional machining methods.New approaches to design and manufacturing

To accompany more complicated designs Tighter tolerances.



Machining Process

Machine tools are where the material removal or forming of the work piecetakes place.Material removal is essentially done on machine tools, which may be Lathe,Milling, Drilling, Shaping, Planing, Broaching and Grinding machines.

The functions of machine tools are:holding the work pieceholding the toolmoving the tool or the work piece or both relative to each other,

Supply energy required to cause metal cutting.Every machine tool has a primary cutting tool for metal removal.

Cutting Speed: Cutting speed is the distance traveled by the work surface inunit time with reference to the cutting edge of the tool, usually expressed inm/min.Feed: The feed is the distance advanced by the tool into or along the workpiece each time the tool point passes a certain position in its travel over thesurface.In case of turning, feed is the distance that the tool advances in one revolutionof the work piece.



Feed f is usually expressed in mm/rev. Sometimes it is also expressedin mm/min and is called feed rate.

Depth of cut: It is the distance through which the cutting tool is plunged into thework piece surface. Thus it is the distance measured perpendicularly between

the machined surface and the unmachined (uncut) surface or the previouslymachined surface of the work piece. Depth of cut d is expressed in mm.

Orthogonal Cutting: The cutting edge of the tool remains normal to the direction of tool feed or workfeed.

The direction of the chip flow velocity is normal to the cutting edge of the tool.Here only two components of forces are acting: Cutting Force and Thrust Force.So the metal cutting may be considered as a two dimensional cutting

Oblique Cutting:

The tool remains inclined at an acute angle to the direction of tool feed or workfeed.• The direction of the chip flow velocity is at an angle with the normal to thecutting edge of the tool. The angle is known as chip flow angle.• Here three components of forces are acting: Cutting Force, Radial force and

Thrust Force or feed force. So the metal cutting may be considered as a threedimensional cutting.

The cutting edge being oblique, the shear force acts on a larger area and thustool life is increased. THE MECHANISM OF CUTTING• Assuming that the cutting action is continuous we can develop a continuous

model of cutting conditions.• Orthogonal Cutting - assumes that the cutting edge of the tool is set in aposition that is perpendicular to the direction of relative work or tool motion. Thisallows us to deal with forces that act only in one plane.• First, consider the physical geometry of cutting, work piece has relative motiontowards tool chip tool friction shear



Cutting Tool geometry for orthogonal cutting







Cutting tool angles and their significance The rake angle has the following function:• It allows the chip to flow in convenient direction.• It reduces the cutting force required to shear the metal and consequently helpsto increase the tool life and reduce the power consumption. It provides keennessto the cutting edge.

• It improves the surface finish.

Back rake angle:•The back rake angle is the angle between the face of the tool and a line parallelto the base of the shank in a plane parallel to the side cutting edge.•The back rake angle affects the ability of the tool to shear the work material andform chip.Side Rake Angles:•It is the angle by which the face of the tool is inclined side ways.The Rake Angle:

The rake angle is always at the topside of the tool.

The side rake angle and the back rake angle combine to form the effective rakeangle. This is also called true rake angle or resultant rake angle of the tool. Thebasic tool geometry is determined by the rake angle of the tool. Rake angle hastwo major effects during the metal cutting process.One major effect of rake angle is its influence on tool strength. A tool withNegative rake will withstand far more loading than a tool with positive rake.



The other major effect of rake angle is its influence on cutting pressure. A toolwith a positive rake angle reduces cutting forces by allowing the chips to flowmore freely across the rake surface.

Positive Rake:

• Positive rake or increased rake angle reduces compression, the forces, and thefriction, yielding a thinner, less deformed and cooler chip.• But increased rake angle reduces the strength of the tool section, and heatconduction capacity.• Some areas of cutting where positive rake may prove more effective are, whencutting tough, alloyed materials that tend to work-harden, such as certainstainless steels, when cutting soft or gummy metals, or when low rigidity of workpiece, tooling, machine tool, or fixture allows chatter to occur.Negative Rake:•To provide greater strength at the cutting edge and better heat Conductivity,zero or negative rake angles are employed on carbide, Ceramic, polycrystalline

diamond, and polycrystalline cubic boron nitride cutting tools.•These materials tend to be brittle, but their ability to hold their superiorhardness at high temperature results in their selection for high speed andcontinuous machining operation.•Negative rakes increases tool forces but this is necessary to provide addedsupport to the cutting edge. This is particularly important in making intermittentcuts and in absorbing the impact during the initial engagement of the tool andwork.•Negative rakes are recommended on tool which does not possess goodtoughness (low transverse rupture strength).•Thus negative rake (or small rake) causes high compression, tool force, and

friction, resulting in highly deformed, hot chip.



Relief angles are provided to minimize physical interference or rubbing contactwith machined surface and the work piece.• Relief angles are for the purpose of helping to eliminate tool breakage and toincrease tool life.• If the relief angle is too large, the cutting tool may chip or break. If the angle istoo small, the tool will rub against the work piece and generate excessive heatand this will in turn, cause premature dulling of the cutting tool.

• Small relief angles are essential when machining hard and strong materials andthey should be increased for the weaker and softer materials.• A smaller angle should be used for interrupted cuts or heavy feeds, and a largerangle for semi-finish and finish cuts.Side relief angle : The Side relief angle prevents the side flank of the tool fromrubbing against the work when longitudinal feed is given. Larger feed will requiregreater side relief angle.



End relief angle : The End relief angle prevents the side flank of the tool fromrubbing against the work. A minimum relief angle is given to provide maximumsupport to the tool cutting edge by increasing the lip angle.

The front clearance angle should be increased for large diameter works.Side cutting edge angle :

The following are the advantages of increasing this angle:• It increases tool life as, for the same depth of cut; the cutting force isdistributed on a wider surface.• It diminishes the chip thickness for the same amount of feed and permitsgreater cutting speed.• It dissipates heat quickly for having wider cutting edge.•The side cutting edge angle of the tool has practically no effect on theValue of the cutting force or power consumed for a given depth of cut and feed.•Large side cutting edge angles are lightly to cause the tool to chatter.End cutting edge angle:

The function of end cutting edge angle is to prevent the trailing front cutting

edge of the tool from rubbing against the work. A large end cutting edge angleunnecessarily weakens the tool.Nose radius:

The nose of a tool is slightly rounded in all turning tools. The function of nose radius is as follows:• Greater nose radius clears up the feed marks caused by the previous shearingaction and provides better surface finish.• All finish turning tool have greater nose radius than rough turning tools.• It increases the strength of the cutting edge, tends to minimize the wear takingplace in a sharp pointed tool with consequent increase

Cutting Tool materials and their propertyCutting tool materials and their proper selection for a particular application arethe most important factors in manufacturing operations. A cutting tool materialmust have certain characteristics in order to produce parts economically and withgoodquality.Essential properties for cutting tool materials

The cutting tools need to be capable to meet the growing demands for higherproductivity and economy as well as to machine the exotic materials which arecoming up with the rapid progress in science and technology.

The cutting tool material of the day and future essentially require the followingproperties to resist or retard the phenomena leading to random or early toolfailure:i) high mechanical strength; compressive, tensile, and TRAii) fracture toughness – high or at least adequateiii) high hardness for abrasion resistanceiv) high hot hardness to resist plastic deformation and reduce wear rate atelevated temperature



v) chemical stability or inertness against work material, atmospheric gases andcutting fluidsvi) resistance to adhesion and diffusionvii) thermal conductivity – low at the surface to resist incoming of heat and highat the core to quickly dissipate the heat entered

viii) high heat resistance and stiffnessix) Manufacturability, availability and low cost.

Cutting Tool Materials Type of material being cut: A harder material like cast iron may be machined bysmaller rake angle than that required by soft material like mid steel or aluminum.• Type of tool material : Tool material like cemented carbide permits turning atvery high speed. At high speeds rake angle has little influence on cuttingpressure. Under such condition the rake angle can minimum or even negativerake angle is provided to increase the tool strength.• Depth of cut : In rough turning, high depth of cut is given to remove maximum

amount of material. This means that the tool has to withstand severe cuttingpressure. So the rake angle should be decreased to increase the lip angle thatprovides the strength to the cutting edge.• Rigidity of the tool holder and machine : An improperly supported tool onold or worn out machine cannot take up high cutting pressure. So whilemachining under the above condition, the tool used should have larger rakeangle.TYPES OF CUTTING TOOL MATERIAL: -

The following materials are commonly used for manufacturing the cutting tools.1. High carbon steels. 6. Stellite2. Alloy steels 7. Diamond

3. High speed steels 8. Abrasives4. Cemented carbides 9. Cubic Boron Nitride5. Ceramics 10. Coated carbides.

1 .High Carbon Steels (Plain carbon steel):- These are steels having carbon content ranging from 0.8 to 1.5% . These are

used for general applications like in turning, boring, shaping, etc. for machiningof ductile and soft materials like mild steel. Aluminum, copper etc.Advantages –Fabrication is easy and easy to harden.Disadvantages-Suitable only for machining of ductile material at low cutting speeds.

They are not able to withstand at high temperatures.



High Speed Steel (1900) : The major difference between high speed tool steeland plain high carbon steel is the addition of alloying elements (manganese,Chromium, tungsten, vanadium, molybdenum, cobalt, and niobium) to hardenand strengthen the steel and make it more resistant to heat (hot hardness).

They are of two types: Tungsten HSS (denoted by T), Molybdenum HSS (denoted

by M).

2. Alloy steels:- These steels have carbon content unto 1% and alloying elements used aretungsten, vanadium molybdenum, and chromium. These elements impact certainproperties like high hot hardness, toughness and resistance to wear anddistortion.Adv –1. These tools work for medium cutting speeds.2. Used for harder materials.Disadv-

1. They can retain hardness up to 300c only2. Due to inclusion of alloying elements the cost increases.3. High Speed steels -

The widely use material are high speed steels(HSS).These tools can operate athigh cutting speed ,where temperature as high as 900c and can operate 2 to 3times more speed than plain carbon steels.

There are 3 types HSS :-1. High tungsten steel :- It imparts higher hot hardness.2. High molybdenum Steel :- It retains sharp cutting edge.3 . High cobalt steels:- It provides high wear resistance.High tungsten steel contains 18% tungsten , 4% chromium, 1% vanadium .

These are efficient high speed steel.Molybdenum HSS (6-4-2) :-It contains 6% Mo , 4% Cr, 2% V .They posses high toughness and cuttingstrength.

Cobalt HSS :- These are known as super high speed steels due to high hot hardness and wearresistance at higher cutting speeds . It contains 15% cobalt, 10-20% tungsten, 2-4% Cr,2-4%V.Adv:- high machining performance with longer tool life.

Dis adv:- Very costly and difficult to fabricate.• Cast cobalt alloys or Stellites (1915 ): It is a non-ferrous alloy consistingmainly of cobalt, tungsten and chromium (38% to 53% Cobalt, 30% to 33%Chromium, and 4% to 20% Tungsten). Other elements added in varyingproportions are molybdenum, manganese, silicon and carbon. It has good shockand wear resistance properties and retains its harness up to 9000C. Stellite toolscan operate at speed about 25% higher than that of HSS tools.



4. Cemented carbides:- • Cemented Carbides or Sintered Carbides(1926-30): These tools are produced by powder metallurgy. Carbide tools arebasically of three types: tungsten carbide (WC), tantalum carbide (TaC), andtitanium carbide (TiC).

The carbides or combined carbides are mixed with a binder of cobalt. They are

able to retain hardness to a temperature of about 10000C. So they can be usedat high speeds. Carbide tool are available as brazed tip tools (carbide tip isbrazed to steel tool) and inserts (inserts are of various shapes- triangular, squarediamond and round).Coated cemented carbide (1960): Tool life to about 200 to 300 % or more. Athin, chemically stable, hard refractory coating of TiC, TiN or Al2O3 is used. Thebulk of the tool is tough, shock resistant carbide that can withstand hightemperatures. Because of its wear resistance, coated tool can be used at stillhigher speeds.Carbides are formed by the mixture of tungsten, titanium with carbon.The carbides in powder form mixed with cobalt which acts as a binder .Then

powder metallurgy process is applied for pressing and mixture is sintered at 550C.This mixture is pressed is applied for pressing and mixture is pressed at pressurefrom 1000kg/cm2 to 4200kg/cm2 into suitable blocks and then heated inhydrogen. The amount of cobalt used will regulate the toughness of the tool.Carbides tool have 82% tungsten carbide, 10% titanium and 8% cobalt.Adv:-1. Used for high cutting speeds.2. Very high hardness and wear resistance.Dis –adv-1. They are costly.Low toughness because of brittleness.

5. Ceramics:-Ceramics tools are made by compacting aluminum oxide powder in a mould atabout 280 kg/cm2 .The part is then sintered at 2200C and this method is knownas cold pressing .This part is in the form of tool and is ready for use as a cuttingtool material. These tool tips are fastened to the shanks.Adv-1. high compressive strength.2. high hardness3. high wear resistance and longer tool life.4. withstand stand upto 1200C temp.Dis adv-

1. very brittle and not suitable for cutting under impact load.2. low thermal conductivity.• Cemented oxides or Ceramic Cutting Tools (1950s ): Non-metallicmaterials made of pure Aluminum oxide by powder metallurgy. The applicationceramic cutting tools are limited because of their extreme brittleness. Thetransverse rupture strength (TRS) is very low. This means that they will fracturemore easily when making heavy interrupted cuts. However, the strength of



ceramics under compression is much higher than HSS and carbide tools. It hashigh hot hardness (up to 1200 degree C), so capable of running at high speeds.Cermets: Cermets are ceramic material in metal binders. TiC, nickel, TiN, andother carbides are used as binders. Cermets have higher hot hardness andoxidation resistance than cemented carbides but less toughness. They are used

for finishing operation. The main problem with cermets is that due to thermalshock the inserts crack.6. Diamond-

The diamond is the hardest known material and can be run at cuttingspeeds about 50 times greater than HSS and at temperatures upto 1650C. This isused when good surface finish and dimensional accuracy are desired.Adv-1. It is very hard and has very low co-efficient of friction.2. Low thermal expansion and high heat conductivity.Dis adv-1. It is very costly

2. Because of its harness, it is very difficult to produce the requiredshape(fabricate).Applications:-Diamonds are used for cutting very hard materials such as glass, ceramics,abrasives and steels .It is also used for dressing the grinding wheel.

• Diamond : They are of two types - industrial grade natural diamonds, andsynthetic polycrystalline diamonds. Because diamonds are pure carbon, theyhave an affinity for the carbon of ferrous metals. Therefore, they can only beused on non-ferrous metals. Feeds should be very light and high speeds Rigidityin the machine tool and the setup is very critical because of the extreme

hardness and brittleness of diamond.

7. Abrasive:- These abrasives are mainly used for grinding harder material and where asuperior finish is desired in hardened material. In general two kinds of abrasiveare used aluminum oxide and silicon carbide.

The aluminum oxide abrasive are used for grinding all high tensilematerials,where as silicon carbide abrasives are more suitable for low tensilematerials and non-ferrous metals.8. Stellites:-Stellites is the trade name of a non-ferrous cast alloy composed of cobalt

,chromium and tugsten.The rabge of elements in these alloys is 40-48%cobalt,30-35% chromium,12-19% tungsten,1.8 to 2.5 % carbon.They cannot be forged toshape ,but may be deposited directly on the tool shank in an oxy-acetyleneflame.Adv-1.they have wear resistance.2.retain its hardness upto 1000C



3.It can be used at high cutting speeds.Dis adv- It is brittle and cannot be used under impact machining conditions.9. Cubic Boron Nitride(CBN) :-Next to diamond, CBN is the hardest material currently available. Itconsists of atoms of nitrogen and boron, produced by high pressure and high

temperature processing. As cutting tool materials CBN is used in thepolycrystalline form. It has much higher tensile strength as compared todiamond.CBN being chemically inert is used as a substitute for diamond formachining steel.Adv-1. CBN has high hardness and high thermal conductivity.2. The life of a CBN tool is 4 to 5 times higher than that of a diamond tool.Application-As a grinding wheel on HSS tools for machining high temperature alloys,titanium, nimonic stainless steel, stellites and chilled CI.• Cubic Boron Nitride (1962 ): Cubic boron nitride (CBN) is similar to diamond

in its polycrystalline structure and is also bonded to a carbide base. With theexception of titanium, or titanium-alloyed materials, CBN will work effectively asa cutting tool on most common work materials. However, the use of CBN shouldbe reserved for very hard and difficult-to machine materials.10. Coated Carbides-Coated carbides have a thin coating of TiC on all faces of the tip. The coatingthickness is of the order of a few micros(0.0025 to 0.005).These tools resist thediffusion wear on the crater and give a tough shock resistance tool.Oxide coating-

The diffusion of atoms btw the tool and chip material can be retorted by coatingthe tool surface of the carbide tools with oxides of aluminium and zirconium.This

considerably increases the tool life.Coated carbides are used formachining super alloys.Cutting fluids;-Cutting fluids ,sometimes referred to as lubricants coolants are liquids and gasesapplied to the tool and w/p tot assist on the cutting operations.Purpose of cutting fluid (Functions)1. To cool the tool:-Cooling the tool is necessary to prevent metallurgical damage and to assist indecreasing friction at the tool-chip interface and at the tool workpieceinterface.2. To Cool the w/p:-

The role of the cutting fluid in cooling the w/p is to prevent its excessivethermal distortion.3. To wash the chip away from the tool.4. To improve surface finish and tool life.5. Reduces force and energy consumptions.6. To cause chips break up into small part.7. To protect the finished surface from corrosion.



Properties of cutting fluids:-A cutting fluid should have the following properties1. Good lubricating qualities to produce low-co-efficient of friction.2. High flash point so as to eliminate the hazard of fire.3. High heat absorption for readily absorbing the heat developed.

4. Harmless to the skin of the operators.5. Non-corrosive to the work or the m/c.6. Low priced to minimize production cost.7. Low viscosity to permit free flow of the liquid.8. Harmless to the bearings.9. Should be chemically natural inert.10. Transparency so that the cutting action of the tool may be observed.

Types of cutting fluids:- The types of cutting fluid to be used depends upon the work material andthe characteristic of the machining process.

1. Water:-It is principally a coolant and not a lubricant water with alkali, salt or watersoluble additive and little soap are sometimes used as a coolant. But wateralone is objectionable for its corrosiveness.2. Soluble Oils:-

These are emulsions composed of around 80% or more of water, soap andmineral oil. The soap acts as an emulsifying agent which break the oil intominute particles to disperse them throughout water. The water increases thecooling effect, and the oil provides the best lubricating properties and ensuresfreedom from rust.3. Straight Oils:-

These sare straight mineral oils (petroleum), Kerosine, low viscositypetroleum factions. Straightr fixed or fatty oils consisting of animal,vegitable, lard oil etc. They have both cooling and lubricating properties andare used in light machining operations.4. Mixed oils:-

This is a combination of straight mineral ands straight fatty oil. This makes anexcellent lubricant and coolant for automatic screw m/c work and whereaccuracy and good surface finish are of prime importance .(a) Chemical additive oil:-Straight oil or mixed oil when mixed with sulphur or chlorineIs known as chemical additive oil.Sulphur and chlorine areused to increase both the lubricating and cooling qualities of the various oilswith which they are combined.(b) Chemical compounds:- These consist mainly of sodium nitrate mixedwith a high percentage of water. These compounds act as coolantsparticularly in grinding.(c) Solid lubricants:-















Practice questions1. What roles do rake and relief angles play in cutting tools?ans. the rake angle will change the basic cutting parameters. A positive rake (sharp tool) will givelower cutting forces, but less edge strength. A negative or neutral rake will give higher cutting forces,

but more strength. The relief angle provides a gap behind the cutting edge so that the tool does not rubthe work.









Tool failure:-During the operation, cutting tool may fail due to one more of the followingreasons.1. Thermal cracking and softening.

2. Mechanical chipping.3. Gradual wear.1. Thermal cracking and softening .Due to heat generated in the metal cutting process, the tool tip and the areacloser to the cutting edge becomes very hot and if this heat crosses the hightemp, at which the tool losses its hardness the tool material starts deformingplastically. This is said to have failed due to softening.

The factors responsible for this are cutting speed, high feed rate, and excessivedepth of cut, smaller nose radius and the choice of a wrong tool material.2. Mechanical chipping :-The mechanical chipping of the nose and the cuttingedge of the tool are commonly observed causes of tool failure.

The factors responsible for this are too high cutting pressure. Mechanical impact,excessive wear, too high vibrations and chatter, weak tip and cutting edge etc3. Gradual wear:-The following two types of wears are generally found to occur incutting tools.(b) Crater wear : - This type of wear takes place in a cutting its face, at a smalldistance from its cutting edge.

This type of wear takes place while machining ductile material like steel alloys, inwhich continuous chip is produced. The resultant feature of this type of wear isthe formation of a crater or a depression at the tool-chip interface. Higher feedsand lack of cutting fluids increases the rate of crater wear.(c) Flank wear : - This type of wear occurs in the flank below the cutting edge. It

Occurs due to abrasion btw the tool flank and the w/p excessive heat generatedAs a result of the same.

The magnitude of this wear mainly depends upon the relative harnesses of thew/p tool material at the time of cutting and also the extent of strain hardness of the chip.MECHANISMS OF WEAR:-1. Abrasive wear :-Hard particles on the underside of the sliding chip,which areharder than the tool material plough into the relatively, softer material of the toolface and remove metal particles by mechanical action. The material of the toolface is softened due to the high temperature. The hard particles present on theunderside of the chip

may be,a) Fragments of hard tool material.b) Broken pieces of built up edge, which are strain hardened.c) Extremely hard constituents, like carbides, oxides, scales, etc.present in the work material.2. Attrition wear:-At relatively low cutting speeds, the flow of the material past the cutting edge isirregular and fewer streams lined. Sometimes bue may be formed and contact



with the tool may not be continous.Under these conditions, Fragments of the toolare torn intermittently from the tool surface. This phenomenon is called attrition.

This type of wear progresses slowly in the case of continuous cutting, but withinterrupted cutting or where vibrations are severe due to lack of rigidity of themachine tool or uneven work surfaces, it leads to rapid destruction of the cutting

edge. As the cutting speed is increased, the flow of metal becomes uniform andattrition disappears.3. Diffusion wear: -This occurs because of the diffusion of metal and carbonatoms from the tool surface into the work material and the chips. Wear bydiffusion is due to the high temperature and pr developed at the contact surfacesin metal cutting and rapid flow of the chip and the work surfaces past thetool.The rate of diffusion wear depends upon the metallurgical relationship btwthe tool and the work material. It is one of the major causes of wear and is of special significance in case of carbide tools.4. Plastic deformation:-When high compressive stresses act on the tool rake face, the tool may be

deformed downwards and this deformation takes place primarily in the nose areaof the insert and reduces the relief angle. This is a deformation rather than awear process, but it accelerates other wear processes which reduce the life of thetool.Deformation leads to the sudden failure of the tool by fracture or localizedheating.i) high mechanical strength ; compressive, tensile, bending to accommodatethe force created during the cutting action.ii) fracture toughness – high or at least adequate : Inspite of the tool beingtough, it should have enough toughness to withstand the impact loads that comein the start of the cut to force fluctuations due to imperfections in the work

material. Toughness of cutting tools is needed so that tools don’t chip or fracture,especially during interrupted cutting operations like milling.Wear Resistance:iii) High hardness for abrasion : The tool material must be harder than thework piece material. Higher the hardness, easier it is for the tool topenetrate the work material. . Co – efficient of friction- The coefficient of friction‘μ’ for tool material must be low, so that the tool wear will be minimum and resultin a good surface finish.iv) high hot hardness to resist plastic deformation and reduce wear rate atelevated temperature ; Hot Hardness is the ability of the cutting tool must tomaintain its Hardness and strength at elevated temperatures. This property is

more important when the tool is used at higher cutting speeds, for increasedproductivityv) Chemical stability or inertness against work material, atmospheric gases andcutting fluids. The tool should not chemically react with the work materialvi ) resistance to adhesion and diffusion vii) thermal conductivity – low at the surface to resist incoming of heat and highat the core to quickly dissipate the heat enteredviii) high heat resistance and stiffness













Factors affecting the cutting tool life1. Cutting speed2. Feed rate3. Depth of cut4. Cutting tool material5. W/p material6. Velocity of cutting fluid7. Expected tool life.8. Cost of the cutting fluid.9. Life of cutting fluid and loss of cutting fluid during operation.Machinability:-

The case with which a given material may be worked with a cutting tool ismachinability. Machinability depends on:1. Chemical composition of w/p material.2. Micro structure3. Mechanical properties.4. Physical properties.5. Cutting conditions.Factors affecting machinability:-Common machine variables affecting ease of cutting are.1. Cutting speed



2. Dimensitions of the cut.3. Tool material4. Tool form (angles, radii, etc.,)5. Cutting fluid6. Nature of engagement of tool with the work.

Common work material variables affecting ease to cutting:-1. Hardness2. Tensile properties3. Chemical composition4. Microstructure5. Degree of cold work6. Strain hare ability7. Shape and dimensions of work.8. Rigidity of work piece.

Shaper Machine



Grinding The grinding process consists of removing material from the workpiece by theuse of a rotating wheel that has a surface composed of abrasive grains. Grindingis considered to be the most accurate of the existing machining processes.Grinding processes are used when high accuracies, close dimensional tolerances,and a fine surface finishes are required. Grinding processes also allow for highproduction rates. This allows for a lowered cost of production. Hard materials canalso be machined with this type of process.Grinding may be classified as non-precision or precision, according to purposeand procedure.

Non-precision grinding: The common forms are called, snagging and offhandgrinding. Both are done primarily to remove stock that can not be taken off asconveniently by other methods. The work is pressed hard against the wheel orvice versa. The accuracy and surface finish are of secondary importance.

Precision grinding: Precision grinding is concerned with producing good surface finishes and accurate dimensions. Three types of precision grinding existsExternal cylindrical grindingInternal cylindrical grindingSurface grinding

Grinding Operations



Surface grinding is most common of the grinding operations. A rotating wheel isused in the grinding of flat surfaces. Types of surface grinding are vertical spindleand rotary tables.





Forming ProcessForging process

IntroductionForging is defined as the process in which metal is plastically deformed with applicationof temperature and pressure. It is used to change not only the shape but also the

properties of the metal because it refines the grain size and therefore improves itsstructure. Forging is a cost-effective way to produce net-shape or near-net-shapecomponents. Forged parts are used in high performance, high strength and high reliabilityapplications where tension, stress, load and the human safety are critical considerations.They are also employed in a wide range of demanding environments, including highlycorrosive and extreme temperatures and pressures.Various parameters such as complexity of the part, friction between dies and workpiece,type of press, die and workpiece temperature, material of workpiece govern the forging

process. Forging process is said to be successful if die cavity is completely filled andstress in the workpiece is less than ultimate stress corresponding to the workpiecematerial, with minimum force.\

Bending of Metals

An approximate formula for the bend allowance is



Bending deformation terminology



Residual stressBending causes residual stresses in the work piece.The smaller the bending radius relative to the sheet metal thickness, the greater these

stresses are.When a subsequent heat treatment is used to reduce residual stresses in the workpiece, it is



important to remember that heat treatment alters the work piece radii and the angles. So bending isdone considering the geometrical change (radius of bend) that will be produced by heat treatment.Welding Process

As we all know that whatever the product that is impossible to manufacture as a singlepiece.

Welding is a process which is used to join the two parts to get a desired product.Welding is a joining process. The types of welding processes are:-

Fusion welding is defined as the melting together and coalescing of materials by means of heat(usually provided by chemical or electrical means); filler metals may or may not be used. This processconstitutes a major category of welding; it comprises consumable or non consumable electrode arcwelding and high energy beam welding processes .The welded joint undergoes important metallurgicaland physical changes which in turn have a major effect on the properties and performance of thewelded component or structure.In solid-state welding joining takes place without fusion ; consequently there is no liquid (molten)

phase in the joint. The basic categories are diffusion bonding, ultrasonic, cold, friction, resistance, and

explosive welding. Diffusion bonding, combined with super plastic forming, has become an importantmanufacturing process for complex shapes. Brazing and soldering use filler metals and involve lower temperatures than welding; the heat required is supplied externally.Another classification of welding processes is given below:1. Heating the metal joint to a temperature below the solidus temperature and applying pressure.• Forge welding2. Melting of the metal at the joint (fusion welding).• Gas welding• Arc welding• Thermit welding• Flow welding

3. Melting the metal at the joint and applying pressure.• Pressure-gas welding• Stud welding• Flash welding• Resistance welding• Induction welding4. Applying pressure only to the metal joint (done at room temperature).• Cold welding

ARC WELDING• Basically, an electric arc is used to heat base metals and a consumable filler rod.

• This is the most common form of welding and is used in about half of all applications.• A power supply is used to create a high potential between an electrode (guided by the welder)and a metal work piece. When moved close enough electrodes break down the air and start toflow. The local current of the flow is so high that it heats metals up to 30000C or 54000F.• Material is added during this welding process.This material can come from a consumable electrode,or from a rod of material that is fed separately.• The electrodes/rods are often coated. This coating serves a number of functions,- it protects the welder from contact



- it deoxidizes and provides a gas shield• Problems that arise in this form of welding is contamination of the metal with elements in theatmosphere (O, H, N, etc.). There can also be problems with surfaces that are not clean. Solutions tothis include,Gas shields - an inert gas is blown into the weld zone to drive away other atmospheric gases.

metal welding table power welding stick work piece supply electric arc current flows in a loop throughthe metalFlux - a material that is added to clean the surface, this may also give off a gas to drive awayunwanted gases.

filler metal or materialmaterial added to fill-up the space in between two welding pieces during the welding process

Two types of filler metals commonly used• welding rods• welding electrodes.

welding rod refers to a form of filler metal that does not conduct an electric current duringwelding process

• The purpose of a welding rod is to supply filler metal to the joint.• used for gas welding.

Electrode• component that conducts the current from the electrode holder to the metal being

welded.• Electrode types:• consumable and non-consumable .

Consumable electrodes provide a path for the current and also supply filler metal to the joint.

• Eg.electrode used in shielded metal-arc welding.

Non-consumable electrodes• used as a conductor for the electrical current-GTAW• filler metal for GTAW, hand fed consumable welding rod.

FluxesBase metal has always impurities, called oxides

result from oxygen combining with metal & other contaminants in the base metal.if these oxides are not removed a faulty weld may result

FluxesCleaning agents that dissolve oxides and release trapped gasescombines with impurities in the base metal, floating them away in the form of a heavy slag

which shields the weld from the atmosphere.allow the filler metal and the base metal to be fusedformulated for a specific base metal on the expected welding temperatureAvailable in the form of a paste, powder, or liquid

• Common types of processes include,SMAW (Shielded Metal Arc Welding)/Stick Welding - A consumable electrode with acoating that will act as a flux to clean the metal, and to create a gas shield.



performed by striking an arc between a coated-metal electrode and the base metal.molten metal from the tip of the electrode flows together with the molten metal from the edgesof the base metal to form a sound joint, process known as fusion The coating from the electrode forms a covering over weld deposit, shielding it fromcontamination

common types of weldingOxy-fuel gas welding (OFW)arc weldingresistance weldinghigh-quality welds are made rapidly at a low costWeld surfaces have valleys and ripplesMakes interpretation difficultDiscontinuities have random orientation in the weld with other welding processesContains entire spectrum of weld discontinuities

MIG (Metal Inert Gas) - A consumable electrode in a gas shield. In addition to simplematerials, this can handle aluminum, magnesium, titanium, stainless steel, copper,etc. This torch is normally water or air cooled.TIG (Tungsten Inert Gas) - A non consumable tungsten electrode is used with a filler rodsand a gas shield. This can handle aluminum, titanium, stainless steel, copper, etc.This torch is normally water or air cooled.SAW (Submerged Arc Welding) - A normal wire is used as a consumable electrode, andthe flux is applied generously around the weld. The weld occurs within the flux,and is protected from the air.• Process variables include,- electrode current 50-300A is common- voltage- polarity- arc length- speed- materials- flux- workpiece thickness

common to all arc-welding processesa heat source, filler metal, and shielding

source of heat by arcing of an electrical current between two contacts.

concentration of heat less heat spread reduces buckling and warpingincreases depth of penetration andspeeds up welding operation

A distinct advantage of arc welding over gas weldingmore practical and economical than gas weldingIn gas welding flame spreads over a large area, causing heat distortion



GAS WELDING• Basically, filler and base materials are heated to the point of melting by a burning a gas.• Two common types are, - oxygen-acetylene

- mapp gas• These are suited to a few applications, but they produce by-products that can contaminate the final

weld.• Typically the flame is adjusted to give a clean burn, and this is applied to the point of the weld.• A welding rod will be fed in separately to melt and join the weld line.• Flux can be used to clean the welds.• Process variables include,- gas and oxygen flow rates- Distance from surface- Speed- Material types- Surface preparation of materials

GAS Metal Arc WELDING

source of heatoxy-fuel gas, such as acetylene, mixed with oxygenused in maintenance and repair works

Primary gases usedhelium, argon, carbon dioxide or a mixture of these gases

Difference between SMAW & GMAWtype of shielding

Gas metal arc welding No flux usedSuitable for thin wall sections < 10 mmHas Low base metal penetration

GTAW both the arc and the molten puddle covered by a shield of inert gas.The shield of inert gas prevents atmospheric contamination-producing a better weld.

Gas Tungsten arc weldingHigh quality welds with good base metal penetration with operator skillDiscontinuities common to GTAW

Incomplete fusion

Cold lapPorosity -if loss of shielding occursTungsten inclusions

TITANIUM WELDING• Titanium as a metal- above 885°C the material undergoes beta phase transition to body centered cubic



arrangements- melts at 1800°C- resistance to corrosion- high affinity for carbon- soft and ductile when annealed

• Above 260°C titanium absorbs oxygen, nitrogen, and hydrogen. This causes when welding, because in excess they make titanium brittle.• Titanium welding requires,- a very clean environment with no contaminants or other materials.- no drafts- the correct welding equipment• To eliminate unwanted gases and moisture from being absorbed, a gas shield is used on bothsides of the weld.• The weld must be shielded until the temperature drops below 427°C.

page 222• Gas tungsten arc welding,- gas is used to cover the tip of the torch, electrode and workpiece.• The torch is,- a split copper collect holding a tungsten electrode. A nut tightens the collet and holds theelectrode. The collet also serves to conduct current to the electrode.- tubes delivers gas to the torch, and it is channeled to the electrode in such a way as toensure uniform coverage.• Gas cups are,- Ceramic, metals or high temperature glass is used to direct the gas about the electrode.The size typically effects the gas consumption.• An optional trailing shield focuses gas on the now welded joint, to allow proper cooling time.• The electrode stickout (or electrode extension) is the distance that the electrode protrudes out the endof the collet. A larger stickout is proportional to the energy delivered, and the size of the gas cap, andit allows better visibility of the work.• A gas lens can be used to focus/balance the flow of gases, it can be used without a gas cup, or with one to improve gas coverage.• Gas backups are placed on the back of the weld seam, purging is used when the back of the weld isenclosed (eg tubes).• Typical welding parameters,TorchElectrodePrimary ArcTrailingGas ShieldCasting ProcessSAND CASTING• Sand casting is one of the older techniques. In this form a mold is made from sand, and the part iscast into it. When the metal has hardened and cooled the part is removed, and the sandremoved.

• Typical stages of operation include,



1. Patterns are made. These will be the shape used to form the cavity in the sand.2. Cores may also be made at this time. These cores are made of bonded sand that will be broken outof the cast part after it is complete.3. Sand is mulled (mixed) thoroughly with additives such as bentonite (clay) to increase bonding andoverall strength.

4. Sand is formed about the patterns, and gates, runners, risers, vents and pouring cups are added asneeded. A compaction stage is typically used to ensure good coverage and solid molds. Cores mayalso be added to make concave, or internal features for Pattern pushed into sand to make cavities. Arunner gate and the patterns are matched, and system will also be formed at this time. The same willhappen with the pouring cup facing up. Metal is heated and prepared metallurgical. It is put intocrucible / tundish/ etc for pouring. Molten metal is poured into the die finally.The part is allowed to sit and cool (large parts may take days),nextThe part is removed from the sand with the runner/gate/etc after the casting process it will continue tofurther finishing process.The part is finished and the surface is cleaned.Alignment pins may also be used for mating the molds later. Chills

may be added to cools large masses faster.5. The patterns are removed, and the molds may be put through a baking stage to increase strength(which finishing by Heat Treatment).6. Mold halves are mated and prepared for pouring metal.7. Metal is preheated in a furnace or crucible until it is above the liquidus temperature in a suitablerange (we don’t want the metal solidifying before the pour is complete).The exact temperature may beclosely controlled depending upon the application.Degassing, and other treatment processes may be done at this time, such as removal of impurities (i.e.slag). Some portion of this metal may be remelted. Scrap from previously cast parts - 10% isreasonable.8. The metal is poured slowly, but continuously into the mold until the mold is full.9. As the molten metal cools (minutes to days) the metal will shrink. As the molten metal cools thevolume will decrease. During this time molten metal may backflow from the molten risers to feed the

part, and maintain the same shape.10. Once the part starts to solidify small dendrites of solid material form in the part. During this timemetal properties are being determined, and internal stresses are being generated. If a part is allowed tocool slowly enough at a constant rate then the final part will be relatively homogenous and stress free.11. Once the part has completely solidified below the eutectic point it may be removed with noconcern for final metal properties. At this point the sand is simply broken up, and the part removed. Atthis point the surface will have a quantity of sand adhering to the surface, and solid cores inside.12. A bulk of the remaining sand and cores can be removed mechanically by striking the part. Other options are to use a vibrating table, sand/shot blaster, hand labor, etc.13. The final part is cut off the runner gate system, and is near final shape using cutters, torches, etc..Grinding operations are used to remove any remaining bulk.14. The part is taken down to final shape using machining operations. And cleaning operations may beused to remove oxides, etc.

Molds• The basic components found in many molds are shown below,



• The terms for the parts of a mold are,Pouring cup - the molten metal is poured in here. It has a funnel shape to ease pouring accuracy

problems.Runner/sprue - a sprue carries metal from the pouring cup to the runners. The runners distribute metalto the part.Gate - a transition from the runner to the cavity of the partRiser - a thermal mass where excess metal will remain in a liquid state while the part cools. As thecooling part shrinks, the molten metal in the riser will feed or fill in the shrinkage. Risers can also beused to collect impurities that rise in molten metal.Mold cavity - this is the final shape of the part.Vent - a narrow escape passage for gases that would otherwise be trapped in the mold.Parting line - a line of separation that allows the mold (made in two pieces) to be put together to makea full cavity. Note that this line does not have to be a straight line, and is often staggered to make themold making easier.

cope - the upper part of a casting molddrag - the lower part of a casting mold

• There are a number of interesting points about patterns,- molds are made by compacting sand around the shape of the pattern.- patterns are made of wood, metal and plastics - the material must be stronger if a large number of molds are to be made.- a parting agent can be used on a pattern to allow easy removal after the mold is made.



- pattern types includeOne piece patterns (loose or solid patterns) - low quantity simple shapesSplit patterns - for complex shapes made in two patterns for each half of the part.Match plate - the split patterns are mounted in a single plate. This allows gating on the drag side tomatch up with the runners on the cope.

Design of the patternsshould include consideration of shrinkage- a slight taper should be added to the sides all patterns this will make them easy to remove from thecompleted mold. i.e. a cone is easier to remove than a cylinder.• Cores are typically used for more complex shapes. Some point of interest,- Cores allow features that could not be easily formed into a sand core.- Cores are made with techniques similar to those for making sand molds.- The cores may need structural support in the mold - these metal supports are called chaplets.- The cores are added when the cavities are made, and they act as part of the mold during casting, butthey are rigid enough to allow internal features on parts.

- Cores can be made easily in automated settings.• A mold might undergo a hardening process,Green sand - no hardening, just moistCold-box - binders are mixed with the sand to increase dimensional accuracy

No-bake - liquid resin binders harden the sand at room temperatureSkin-dried - the sand is hardened by drying in an oven or air. Higher strength, but distortion and lower collapsibility.Baking - the molds are baked before casting to harden the entire mass• When the pattern and cores have been inserted into the sand it is compacted. There are a number of techniques for doing this,Squeeze Molding Machines - automatically insert and compact sand. The processes used are designedto produce a uniform compaction. Jolting is sometimes used to help settle the sand. These molds aremade in flasks.- conventional flat head- profile head- equalizing pistons- flexible diaphragmVertical Flask less Molding - the molds halves are made by blowing sand against a verticalMold. High production rates are possible.

Sand slingers - A high speed stream of sand into the flask tends to pack the sand effectively.Impact molding - an explosive impulse is used to compact the sand. The mold quality with thistechnique is quite good.Vacuum molding - an envelope of plastic is created about the sand using plastic sheeting.Air is drawnfrom the sand, and the vacuum leads to compaction.

Shell Mold Casting• The basic process for these molds is,



1. Create two mating patterns of desired shape.2. Coat the molds with a shell (sand and binders, such as a resin) until desired thickness and other

properties are obtained.3. Cure the molds and remove the patterns.4. The mold halves are mated and held firm while metal is poured.

5. The final part(s) is removed.• This technique can be very economical.• Special care must be taken to assure venting for gasses, as the mold media is less porous.• This method can easily use cores and chills to make complex molds.• Graphite molds can be used for materials that would normally react with other materials used for themolds.Lost Foam Casting (Expandable Pattern)

• This process has a number of basic steps,1. Make a mold for producing Styrofoam patterns.Start

Investment Casting• The basic steps are,1. An expendable mold of a part is made in wax, plastic, etc.2. The part has a gate and runner attached to it, and all are dipped in a ceramic slurry.3. The slurry is hardened, and the core is melted and/or burned out.4. The core is burned out and the mold is preheated to the temperature of the molten metal- 644°C for aluminum



- 1040°C for ferrous alloys- etc.5. Molds are filled by pressure, vacuum or centrifugal force.6. After cooling, the mold is broken off, the sprues are cut off, and stubs are ground off.



• Many parts can be made at the same time by attaching them to a common gating system.• Parts can be glued together to make shapes that would normally be too complex to mold.



• Typical methods used are,- cast iron- steel- aluminum alloys- brass

- bronze- magnesium- zinc• The die used to make the mold cores can be used for thousands of parts.• Typical large applications are,- large propellers- large frames- nozzles- cams- valve parts• Typical small applications are,

- dental- jewelry- orthopedic surgical implants- camera components• Advantages,- fine details can be made- thin sections are possible- high accuracy- weights from <1 ounce to > 100 lb.- any castable metal can be used- no parting lines- good surface finish (60-220 in .)- can be automated- many parts can be made at once providing lower per piece cost- high melting point metals can be used• Disadvantages,- less strength than die cast parts- process is slow- changes to the die are costly- more steps are involved in production

Die Casting• The basic process is,1. two permanent mold halves of a die (mounted in a press) are brought together.2. the molten metal is injected through a runner and gate with pressures up to 100 ksi -2000-5000 psiis common.3. air escapes into overflow wells, and out vents, and metal fills the molds4. the mold is chilled, and the injected metal freezes5. the mold is separated, and knockout pins eject the part



6. the parts are cut off the runners and sprues• Used for low melting point (non-ferrous) metals such as,- zinc- aluminum- magnesium- copper-lead- and tin• Can produce complex shapes at mass production rates.• Metal dies,

- must withstand high pressures- die life is shortened by extreme temperature fluctuations- dies often made with carbon or special alloys- multiple cavities can be used in the die• Applications,- automotive parts- appliances- office machines- bathroom fixtures- outboard motors- toys- clocks- tools• Die casting machines can use,- hot chambers with a plunger - a reservoir of molten metal is used to directly feed the machine.- a cold chamber - metal is ladled into the machine for each shot.• Hot chamber machines are,- good for low temperature zinc alloys (approx. 400°C)

- faster than cold chamber machines- cycle times must be short to minimize metal contamination- metal starts in a heated cylinder - a piston forces metal into the die- the piston retracts, and draws metal in• Cold chamber machines,- casts high melting point metals (>600°C)- high pressures used- metal is heated in a separate crucible- metal is ladled into a cold chamber - the metal is rapidly forced into the mold before it cools• All die casting processes require a large press to hold mold halves together during a cycle.• Advantages,- intricate parts possible- short cycles- inserts feasible- cycles less than 1 minute- minimum finishing operations- thin sections, high tolerances, good surface finish• Disadvantages,- metal die is costly- porous parts- not suited to large parts- long setup times- $5000-200,000 for machine- metal melting point temperature must be lower than die45.3.3 Centrifugal Casting• The basic process is,1. a mold is set up and rotated along a vertical (rpm is reasonable), or horizontal (200-1000 rpm isreasonable) axis.



2. The mold is coated with a refractory coating.3. While rotating molten metal is poured in.4. The metal that is poured in will then distribute itself over the rotating wall.5. During cooling lower density impurities will tend to rise towards the center of rotation.6. After the part has solidified, it is removed and finished.

• There are three variants on this process,true centrifugal casting - long molds are rotated about a horizontal axis. This can be used to make longaxial parts such as seamless pipes.semi centrifugal casting - parts with a wide radial parts. parts such as wheels with spokes can be madewith this technique.centrifuging - the molds are placed a distance from the center of rotation. Thus when the poured metalreaches the molds there is a high pressure available to completely fill the cavities. The distance fromthe axis of rotation can be increased to change the properties• Centrifugal and semicentrifugal casting used for axisymmetric parts (internally).• Parts from 6” to 5’ in diameter can be made, but typical diameters are 10’ to 30’.• Long tubes can be made that could not normally be rolled.

• Typical metals cast are,- steel- nickel alloys- copper- aluminum• Typical applications are,- train wheels- jewelry- seamless pressure tubes/pipes• Advantages,- good uniform metal properties- no sprues/gates to remove- the outside of the casting is at the required dimensions- lower material usage- no parting lines- low scrap rates• Disadvantages,- Extra equipment needed to spin mold- the inner metal of the part contains impurities

Furnaces• Some of the types include,

- coreless induction - magnetic fields induce eddy currents throughout the entire furnace, resulting inmelting

- core induction - magnetic fields induce eddy currents in a small section of the furnace, resulting inmelting- gas fired crucible - uses ignited gas and air to heat crucible in enclosed oven- electric arc - arcs are used to heat metals- cupolas - layers of metal and ore are placed in this refractory lined vessel, and ignited to producelarge volumes of metal.Inspection of Casting

• General problems with castings are,- Cavities- Projections



- Discontinuities- Defective surfaces- Incomplete casting- Incorrect dimensions- Inclusions

• Typical inspection methods are,- Polishers & microscopes to look at microscopic structures- Metal analyzer to determine chemical composition- X-rays are used to examine hidden cracks and blowholes

Design of Castings• When designing casting the most important consideration is the effects of shrinkage during cooling.Other important factors include metal flow, and porosity.• Some general rules of thumb are,- Avoid sharp corners - they can lead to hot tearing during cooling.- Use fillets cautiously - they lead to stresses as they shrink a radius of 1/8” to 1” are acceptable.

- Avoid large masses - they will cool more slowly, and can lead to pores and cavities in the final part.Cores can be used to hollow out these large volumes. Metal padding‘chills’ can also be placed inside the mold near large masses to help increase cooling rates.- Use uniform cross sections -this will keep the cooling rate relatively uniform and avoid stresses.- Avoid large flats - large flat areas tend to warp.- Allow some give as the part cools - by allowing the shrinkage of one part to deform another slightly,the internal stresses will be reduced. Figures of 1-2% shrinkage are common.- Put parting lines near corners - this will hide the flash.- Straight Parting Lines - where possible a straight parting line will allow easier mold making.- Use a Draft angle - A small angle of 0.5-2° on the vertical walls will make the pattern easier toremove.- Machining Allowances - allow excess material for later machining of critical dimensions- Wide Tolerances - because shrinkage occurs as the part cools it will be very hard to keep tighttolerances.- Avoid thin sections - These will be very hard to fill, and will tend to harden quickly.- Avoid internal features - These will require extra steps in mold making, and may createMetal flow problems.

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