me3162 summary
DESCRIPTION
THE PREVIEW HERE IS DAMAGED. DOWNLOAD THE FULL DOCX FOR THE BEST VIEW. A simple summary made by me to speed up the process of looking up for stuffs in this open book examination. There are formulas missing for the second part. Not really familiar with that part. Use it at your own discretion and further edits are permitted. STRICTLY not for sale. This upload is to help people, not steal from them. May you have the blessings from the Bell Curve God.TRANSCRIPT
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