COLD WORKINGstrength (directional)surface hardness + wear resistancesurface finish & toleranceNo oxide layerSome too brittle to be cold-workedSubsequent operations difficultLarge parts need ↑energy↓corrosion resistance↑electrical resistanceNeeds annealing to relieve stress

TENSILE DRAWINGFor very small diameterTo reduce cross section of bars and tubesSeamless tubes of very high strengthStronger than cold rollingBest straightnessMust be done COLD

- Directional properties

WELDINGLow carbon steels excellent for weldingHigher carbon steel and iron need special techniquesNon-ferrous need special techniquesQuick, convenientCheapOnly affect the weld area microstructural propertiesDependent on human factorsDefects are common (porosity, inclusions)

LASER BEAM WELDINGFor inaccessible parts cause tinyEnergy easily controlled(Advantages same as Electron Beam except EBW need vacuum)

SAND CASTINGNo size limitCheapNo directional propertiesCan make complicated shapesGood for m.p. metalsRough surfaceSlowPoor dimensional tolerancesHOT WORKING

metal crackingGrain refinement possibleNo annealing neededpowerRepairs casting defectsductilityFasterOxide layerSome metals cannotExpensive

FORGINGStrongest of all manufacturing processesDurable, reliableVery strength toughness fatigue strength surface hardness wear resistanceSuitable for mass productionAny metal can useCreates fibrous structure which cannot be removedExpensive Hammer Forging Drop Forging

Superior mechanical propertiesComparatively high production rateHigh density

Press ForgingBetter homogeneityBetter dimensionBetter than hammer forgingFor finishing, secondary and larger sectionsMore expensive

Upset Forging Done along its length

Roll Forging

GAS WELDINGFor thin sheetsCheap, portableNo electricity neededMetal with high heat conductivity conducts heat away

DIE CASTINGIdeal for m.p. materials production rate surface finish and tolerancesCan be used for non-ferrous metals alloyingOne directionalParting line (MOST CASTING)

ARC WELDINGThicker sectionsWill burn thin sectionsFaster and greater depth of penetrationMust have heat conductivitySlowFlux corrode aluminium

ROLLINGTo thicknessOnly ductile metals can be cold rolledZn & Mg cannotCold rolling – Shining surface + small thicknessBetter homogeneity – toughCheaper than extrusionFor thin materials Cold Hot

CENTRIFUGAL CASTINGFiner grain size – tougherCleanerDense structure, free of defects production ratesBest mechanical properties for castingAccurate

RESISTANCE WELDINGIdeal for steels – high resistanceImpossible for low resistance metalsBoth metal must about same thicknessLocalized heatFastNo filler metalEasily automatedHigh costDifficult to join different thickness

CONTINUOUS CASTINGFor recyclingDon’t need to cast ingotsFully automatedCheapQuick

EXTRUSIONFor soft material and uniform cross sectionCreate tube with no seam

No point of weaknessSteel hard to extrude unless want seamless

- Prefer rollingCan produce hollow sectionsGood dimensional accuracy (straight)Surface defects when metal leaves chamber

SUBMERGED ARC WELDINGAutomatic feedMolten flux forms protective coating welding speedLots of space and $Automation necessary

INVESTMENT CASTINGVery surface finishComplicated shapes tolerancesCan use high m.p. metalsGood for Tungsten and Cobalt (hard to machine)

SHEET METAL WORKINGUsually mild steelStart with blank or sheet metal to form thin metal productsUsually done cold unless sheet too

FRICTION WELDINGCan join dissimilar metalsFastOnly for ROUND sections

Direct Indirect Impact Hot

Long pieces of uniform cross section

Cold Hydrostatic

Less likely to crackVery thin tube + brittle materialsHigh reduction in cross-sectional area

thickRUBBER PAD FORMINGNo need dieSHEARINGTrim out smaller sheetFastBlanking (save round part)Piercing (throw round part)

ExpensiveLimited sizeSlow

METAL INERT GAS WELDINGNo need to remove fluxIdeal for sheet metal & positional workDon’t need to replace electrode (TIG)More flexibility (TIG)More expensive

ALL CASTING SHRINKS – POOR TOLERANCECasting defects– porosity, cracking (fast cooling)

All casting not very strong

POWDER METALLURGYStrength determined by density m.p. materials can fabricate below m.p.Close to final shapeNon-metallic constituents can be added tolerancesNo waste speed costDie must be simple & one directionSize limited by diesBrittle tensile strength ductility, fatigueDifficult for low m.p. – meltCannot be cold-worked or bent

PLASTICSColour choices Thermal insulation Electrical insulation Corrosion resistanceLightEasy to processCheapRigid, transparent or translucent plastics can be madeCannot repairAbsorbs odoursNot for temperatureCreep under loadWeak mechanical propertiesDeteriorate under Sun

CALENDARINGThermoplastics onlySimilar to rollingThinner than Extrusion

TIPSPipe and tubeMaterial Aluminium, copper, brass:

EXTRUSION|Softer, lower m.p. Cheaper

Steel, stainless steel: COLD ROLLING

|When welding might have air trapped For low strength application only|Steel is expensive for extrusion

For high strength use,EXTRUSION or MENNESSMANN create seamless tubes

For raw material must always HOT ROLLNormally the raw material comes in big blocks Hot roll faster in reducing size

Cold rolling always the BEST and CHEAPEST for bar with uniform cross section quick mass production

Die casting more expensive than sand casting

THERMOFORMINGThermoplastics onlySimilar to sheet metal forming

CASTINGFor prototypingThermoplastics and thermosetsCheap

PLASTISOL MOLDINGCoating

INDUCTION WELDING OF COLD ROLLED STRIPLow costWill have seamLow strengthWelded by Electrical Resistance weldingNot good for good conductors(REFER BOOK. SHORT CHAPTER)

INJECTION MOLDINGThermoplastics onlySimilar to die castingLarge scale productionWill have parting line

LAMINATINGCoatingPlane flat sheets onlyREINFORCED MOLDINGMaking compositesNot limited to plane flat sheetsFOAM MOLDINGCreate sponge-like material

ELECTRICAL DISCHARGE MACHININGUsed to make moldsHarden before machineAll automatedCan machine hard material

COMPRESSION MOLDINGThermoset onlySimilar to press forgingLarge scale but slower than Injection

TRANSFER MOLDING

BRASSCorrosion resistantStrongDurableGoldExpensive

Forging even more expensive

If diameter >10mm, cannot extrude directly

toleranceNo mechanical strainsWorkpiece must be electrically conductiveVery slowElectrode wear – poor toleranceWIRE CUT EDMHigh precision machiningComplicated profiles

Same as CompressionNo flashCan mold small intricate parts

REACTION INJECTION MOLDINGHybrid of Compression and Injection

STAINLESS STEELSilverDurableCorrosion freeExpensive

MILD STEELCheapStrongCorrodes

MEDIUM CARBON STEELStrongExpensive

ALUMINIUMCorrosion resistantStrongNot as shiny

EXTRUSIONThermoplastics onlyVery large scaleNo need high temperatureBLOW MOLDINGThermoplastic onlyLarge scale

ROTATIONAL MOLDINGThermoplastics onlyCheapSlowSmall scale

THERMOPLASTICSAcetal (Polyacetyl)Very strength but not boiling waterUsed for load-bearing components

AcrylicMost transparentBecame opaque from UV

CellulosicsExtremely cheapComes in many formsTransparent unless altered

FluorocarbonsCan stand temperature and corrosive environments coefficient of friction surface energy (non-stick)ExpensiveHeaviest of all common plastics

PolyamidesNylonExcellent toughness & wear resistance coefficient of frictionCheapUsed for load bearing if dimensions not critical

PolypropyleneStrongerCan stand boiling waterSoftFloats in waterMore expensive

Refer book for LDPE (extremely cheap), HDPE, UHMWPE and PP

PolyurethaneReplacement for rubberUsed in non-foam (solid) form

StyrenesCheapTransparent for low and sub-zero temperatureNon-toxicWill get dentedBrittle

ABSOpaqueImpact resistantCannot stand boiling water

SAN

EpoxyHigh strengthVery chemically inertVery corrosion resistantDimensionally very stableExcellent adhesiveTends to be brittleExpensive

PhenolicExcellent chemical, electrical and heat resistanceExtremely hard and brittle

Polyesters weathering characteristicsCorrosion resistance

PolyurethaneFlexibleLast much longer than StyrofoamMore expensive

SiliconeSoft and rubberyOften used to replaced rubber when temperature is encounteredConvenient for making large objects and for joining/sealing purposes

Poor dimensional stability

AramidsVery strength and stiffnessBulletproof

PolyestersPolycarbonate impact stressCan stand boiling waterTransparent

PETHigh boiling point but changes shape

PolyolefinsCorrosion resistantNon-toxicWaxy surface

PolyethyleneVery lightCan stand very corrosive materialsCannot stand boiling water

TransparentCan stand boiling waterMore brittle

Vinyls (PVC)CheapestTransparentRigid and hardCannot stand boiling water

THERMOSETTING RESINSGenerally can be used at higher temperatures but brittle

Amino Plastics (Formaldehyde)Hard surfaceWear resistantStrongStain resistant

CaseinsHigh flexural strengthToughObsolete and seldom used

MACHINING AND MACHINE TOOLS

CuttingRotational motion of the workpiece at V relative to the tool

Chip cross-section area Ac

Ac=f apwhere f is the feed per revolution

f=V fnw

Material removal rateZw=AcV av=f a pV av

¿ πf apnw (dm+ap)

For small ae / dt

Material removal rate

ae−depth of cut∨ap−width of workpieceMachining time

tm=lw+d tV f

if facemilling

DrillingUndeformed chip thickness

kr is the major cutting edge angle

Machining time

Shear plane model

The apparent shear strength of the material s on the shear plane

TOOL WEAR AND TOOL LIFE

Power requiredPm=psZw ps – specific cutting energyElectrical power consumed

Pe=Pm❑m

Vertical milling

Maximum undeformed chip thickness

¿a f=fN

=V fN nt

if facemilling

lw is the length of the drilled holent is the rotational frequency of the tool

Material removal rate

MECHANICS OF METAL CUTTINGSpecific cutting energy

Specific cutting energy ps :

Economics of metal cutting operationAverage cost per workpiece

Number of tools required

Average cost per workpiece

Where

Minimum CostCutting speed

Tool life

Depreciation time

Tool costa) Regrindable tools

(b) Disposable inserts

Tool changing time

Machine Tool Maximum Power Restriction

t = tool life

Machining time

where

Tooling cost and tool changing cost per workpiece

Number of tools per workpiece

Minimum Production TimeCutting speed

Tool life

Estimation of cost FactorsTotal Machine and Operator Rates

c, and are constants

Maximum Force Restriction

Surface Finish

R is tool nose radius

Total production time= no. of pieces x (loading time + tool return time + rough cut time + finish cut time)

tmr=V olumeof removedmaterial

Zw