chap 8 ppt
TRANSCRIPT
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Chapter 8 OverviewChapter 8 Overview The quality of a die casting is more thanThe quality of a die casting is more than
skin deepskin deep
A quality casting is free of defectsA quality casting is free of defects
In order to determine the quality of a casting,In order to determine the quality of a casting,
you must be able to identify the defectsyou must be able to identify the defects
There are three common types of defectsThere are three common types of defects
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Chapter 8 ObjectivesChapter 8 Objectives Correctly identify the common surfaceCorrectly identify the common surface
defectsdefects
Correctly identify the common internalCorrectly identify the common internal
defectsdefects
Correctly identify the common types ofCorrectly identify the common types of
dimensional defectsdimensional defects
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New Terms
New Terms
InclusionsInclusions
Materials that have been included in the alloyMaterials that have been included in the alloy
that should not be there, such as aluminumthat should not be there, such as aluminum
oxide, silicon carbide, fluxes and sludgeoxide, silicon carbide, fluxes and sludge
PolymorphicPolymorphic
The ability of, in certain environments, theThe ability of, in certain environments, theproperties of the alumina crystals to changeproperties of the alumina crystals to change
drasticallydrastically
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New Terms
New Terms cont.cont.
PorosityPorosity
A void in the casting, caused by trapped gas orA void in the casting, caused by trapped gas or
shrinkageshrinkage
ViscousViscous
The state of being semiThe state of being semi--fluid; not flowing freelyfluid; not flowing freely
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Surface Defects
Surface Defects
Cold flowCold flow
Cold shutCold shut
Flow marksFlow marks
ColdCold
ChillChill
Severe chillSevere chill
NonNon--fillfill
PoorPoor--fillfill
LapsLaps
Flow linesFlow lines
SwirlsSwirls
Knit linesKnit lines
MisMis--runrun
SolderingSolderingOther DefectsOther Defects
BlistersBlisters
CracksCracks
Flow DefectsFlow Defects
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Flow Defects
Flow Defects
Result from how metalResult from how metal
flows to and within the dieflows to and within the die
Adjusting processAdjusting process
variables can sometimesvariables can sometimes
impact their occurrenceimpact their occurrence
The alloy begins to freezeThe alloy begins to freeze
before the casting isbefore the casting is
completely filled outcompletely filled out
Several alloy flows convergeSeveral alloy flows converge
but do not weld or fuse completely togetherbut do not weld or fuse completely together
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Flow Defects
Flow Defects cont.cont.
Fill timeFill time Wall thicknessWall thickness
Die temperatureDie temperature
Alloy temperatureAlloy temperature
Flow distanceFlow distance Gate velocityGate velocity
Alloy typeAlloy type
VentingVenting
8Factors Affecting Flow Defects8Factors Affecting Flow Defects
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8F
actors:F
ill
Time8F
actors:F
ill
Time The maximum allowable time to fill the dieThe maximum allowable time to fill the die
cavity that results in an acceptable castingcavity that results in an acceptable casting
If exceeded, the casting will have some defectIf exceeded, the casting will have some defect
Fill time calculation based on several factorsFill time calculation based on several factors
Die temperatureDie temperature
Alloy temperatureAlloy temperature
Casting geometryCasting geometry
Alloy being castAlloy being cast
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8F
actors: Wall
Thickness8F
actors: Wall
Thickness Part of the castings geometryPart of the castings geometry
Heavy wall sections equate to a lot of heat andHeavy wall sections equate to a lot of heat and
high cooling requirementshigh cooling requirements
Thin walls equate to very little heat and minimalThin walls equate to very little heat and minimal
cooling requirementscooling requirements
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Flow Defects: Die Temperat
ure
Flow Defects: Die Temperat
ure
TimeTime--averaged temperature of the die duringaveraged temperature of the die during
sustained productionsustained production
Cannot be measured any time at any place inCannot be measured any time at any place in
the diethe die
Ideally, it will:Ideally, it will:
Be as high as possibleBe as high as possible
Still permit making the castingStill permit making the casting
Vary as little as possible over the entire cycleVary as little as possible over the entire cycle
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Flow Defects: A
lloy Temperat
ure
Flow Defects: A
lloy Temperat
ure
Temperature of the alloy as it begins to fillTemperature of the alloy as it begins to fill
the die cavity, as it passes through the gatethe die cavity, as it passes through the gate
Hard to measure in real time as the casting isHard to measure in real time as the casting is
being madebeing made
Estimated to determine fill time calculationsEstimated to determine fill time calculations
Avoiding delays in alloy transfer canAvoiding delays in alloy transfer can
minimize temperature lossesminimize temperature losses
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8F
actors:Fl
ow Distance8F
actors:Fl
ow Distance The distance that the metal must flow once itThe distance that the metal must flow once it
passes through the gatepasses through the gate
Alloy should flow to its terminal locationAlloy should flow to its terminal location
without freezingwithout freezing
If the flow distance is too long and if the alloyIf the flow distance is too long and if the alloy
speed is too slow, its difficult for the metal tospeed is too slow, its difficult for the metal to
fill the cavity without beginning to freezefill the cavity without beginning to freeze
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8F
actors: Gate Velocity8
Factors: Gate Ve
locity
The speed the alloy travels as it passesThe speed the alloy travels as it passes
through the gatethrough the gate
If not controlled, can be detrimental to theIf not controlled, can be detrimental to the
tooling causing washout and erosiontooling causing washout and erosion
If too low, the alloy may not atomize and notIf too low, the alloy may not atomize and not
have enough energy to reach the ends of thehave enough energy to reach the ends of the
casting or to properly weld togethercasting or to properly weld together
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8F
actors: All
oy Type8F
actors: All
oy Type Can make difference in the surface finishCan make difference in the surface finish
Zinc, Zamak7
was designed to have the bestZinc, Zamak7
was designed to have the bestfluidity and surface finishfluidity and surface finish
Silicon content in aluminum aids fluiditySilicon content in aluminum aids fluidity
Alloys closer to the eutectic will be more fluidAlloys closer to the eutectic will be more fluid Eutectic alloys are regarded as harder to castEutectic alloys are regarded as harder to cast
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8 Factors:8 Factors:
Venting and Vacuu
mVenting and Vacuu
m Trapped air causes blisters and gas porosityTrapped air causes blisters and gas porosity
and backpressure in the cavityand backpressure in the cavity
Back pressure can change the flow enoughBack pressure can change the flow enough
to cause surface defectsto cause surface defects
Most noticeable in blind featuresMost noticeable in blind features
May be necessary to add vacuum to removeMay be necessary to add vacuum to remove
gassesgasses
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Other Defects: BlistersOther Defects: Blisters
BubbleBubble--like bumpslike bumps
on the castingon the casting
Gases trapped in theGases trapped in the
casting near the castingcasting near the casting
surface cause themsurface cause them
When casting is ejectedWhen casting is ejectedand the casting surfaceand the casting surface
is not strong enough to withstand the gas pressure,is not strong enough to withstand the gas pressure,
the surface yields and the blister formsthe surface yields and the blister forms
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Other Defects: CracksOther Defects: Cracks Two major causes for cracks are:Two major causes for cracks are:
HeatHeat
InsufficientInsufficient
ExcessiveExcessive
Externally applied stressesExternally applied stresses
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Other Defects:S
olderingOther Defects:
Soldering
The fusion of aluminum in theThe fusion of aluminum in the
alloy with iron from the steelalloy with iron from the steel
surface of the die cavitysurface of the die cavity When soldering occurs, theWhen soldering occurs, the
casting sticks to the cavity;casting sticks to the cavity;
casting must be torn awaycasting must be torn away
Aggravated by higher than usualAggravated by higher than usualdie temperatures, high gate velocitiesdie temperatures, high gate velocities
and high metal pressuresand high metal pressures
Enhanced if the iron content in alloy is lowEnhanced if the iron content in alloy is low
Can be caused by insufficient draft anglesCan be caused by insufficient draft angles
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Impact of
Interna
lDefects
Impact of
Interna
lDefects
Mechanical properties include:Mechanical properties include:
Tensile strength, elongation, hardness, impactTensile strength, elongation, hardness, impact
strength and othersstrength and others
Measured on samples; results are publishedMeasured on samples; results are published
to help designers pick best suited materialto help designers pick best suited material
Internal defects reduce mechanicalInternal defects reduce mechanicalpropertiesproperties
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Impact of
Interna
lDefects
Impact of
Interna
lDefects
Pressure tightnessPressure tightness
An important property for some applicationsAn important property for some applications
The process has to be controlled while makingThe process has to be controlled while making
solid, low porosity castingssolid, low porosity castings
Internal defects can cause loss of pressureInternal defects can cause loss of pressure
tightness/leakstightness/leaks MachineabilityMachineability
Affected by porosity and inclusion defects, theAffected by porosity and inclusion defects, the
two types of internal defectstwo types of internal defects
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Internal Defects:Internal Defects:
Inc
lusions
Inc
lusions
Most inclusions areMost inclusions are
nonnon--metallic aluminummetallic aluminum
oxide (corundum)oxide (corundum) Oxides get into the bathOxides get into the bath
Most is removed, butMost is removed, but
some remains and endssome remains and endsup in castingsup in castings
Size and shape of the individual corundum particlesSize and shape of the individual corundum particles
varies widelyvaries widely
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Internal Defects:Internal Defects:
Inc
lusions
Inc
lusions--Oxide
Films and DrossOxide
Films and Dross
Inclusions of oxide filmsInclusions of oxide films
and dross are majorand dross are major
cause for leakers andcause for leakers andexcessive tool wearexcessive tool wear
This is generally gammaThis is generally gamma
aluminum oxidealuminum oxide
Oxide films prevent divergentOxide films prevent divergent
alloy steams knitting togetheralloy steams knitting together
properly as the cavity fillsproperly as the cavity fills
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Internal Defects:Internal Defects:
Inc
lusions
Inc
lusions--
SiCS
iC Silicon carbideSilicon carbide
refractories get intorefractories get into
castings if furnacecastings if furnace--cleaning practicescleaning practices
not maintainednot maintained
As damagingAs damaging
as corundumas corundum
Encountered infrequently compared to corundumEncountered infrequently compared to corundum
Distinguished by its very black, glassDistinguished by its very black, glass--like coloringlike coloring
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Internal Defects:Internal Defects:
Inc
lusions
Inc
lusions--
Flux
Flux
Not usually recognized during a cursoryNot usually recognized during a cursory
visual inspectionvisual inspection
Casting must be submerged in city waterCasting must be submerged in city water
overnightovernight
If flux inclusions are present, they will growIf flux inclusions are present, they will grow
crystals on the casting surfacecrystals on the casting surface
Appears as light mottling on all surfacesAppears as light mottling on all surfaces
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Internal Defects:Internal Defects:
Inc
lusions
Inc
lusions--
Sludge
Sludge
Composed of complexComposed of complex
interinter--metallic compoundsmetallic compounds
of Alof Al--SiSi--FeFe--MnMn--CrCr Is quite hard and willIs quite hard and will
damage cutter toolingdamage cutter tooling
Under high magnificationUnder high magnification
sludge is easily recognized by the extremely finesludge is easily recognized by the extremely fine
primary crystals and their pentagonal shapeprimary crystals and their pentagonal shape
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Internal Defects:Internal Defects:
PorosityPorosity A void in the castingA void in the casting
Has two root causes:Has two root causes: Trapped gasTrapped gas
ShrinkageShrinkage
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Internal Defects:Internal Defects:
PorosityPorosity--Trapped GasTrapped GasTo solve a gas porosity problem, look at allTo solve a gas porosity problem, look at all
sources of gas generationsources of gas generation
Trapped airTrapped air
Always present because of the turbulent methodAlways present because of the turbulent method
used to fill the die cavityused to fill the die cavity
Air in cold chamberAir in cold chamber
minimized by filling the cold chamber with alloyminimized by filling the cold chamber with alloy
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Internal Defects:Internal Defects:
PorosityPorosity--Trapped GasTrapped Gas
Turbulence: when alloy is subjected toTurbulence: when alloy is subjected to
turbulence in the presence of airturbulence in the presence of air
Minimize when picking up and transporting alloyMinimize when picking up and transporting alloy
to the cold chamber through ladling practicesto the cold chamber through ladling practices
Slow portion of the shot cycle must be controlledSlow portion of the shot cycle must be controlled
Optimize timing of plungerOptimize timing of plunger Accelerate plunger tip when past pour holeAccelerate plunger tip when past pour hole
When sleeve is filled, follow with a smoothWhen sleeve is filled, follow with a smooth
acceleration to the fast shot speedacceleration to the fast shot speed
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Internal Defects:Internal Defects:
PorosityPorosity--Trapped GasTrapped Gas
Improper venting: another cause for trappedImproper venting: another cause for trapped
airair
Vents must be open to allow air trapped aboveVents must be open to allow air trapped above
the alloy in cold chamber to escapethe alloy in cold chamber to escape
If vent is working, a puff of air coming out can beIf vent is working, a puff of air coming out can be
seenseen
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Internal Defects:Internal Defects:
PorosityPorosity--Trapped GasTrapped Gas
Excessive lubricants: can result in gas fromExcessive lubricants: can result in gas from
two sourcestwo sources
Release of combustion products when some ofRelease of combustion products when some of
the die lube burns when the alloy hitsthe die lube burns when the alloy hits
Most releases are diluted with waterMost releases are diluted with water
Water in lube will turn to steam and produce aWater in lube will turn to steam and produce agreat volume of gasgreat volume of gas
Gas forms when alloy runs over puddled plungerGas forms when alloy runs over puddled plunger
tip lubetip lube
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Internal Defects:Internal Defects:
PorosityPorosity--Trapped GasTrapped Gas
Other sources of trapped gasOther sources of trapped gas
If die cavity cracked, it might allow fluid from theIf die cavity cracked, it might allow fluid from the
cooling line to leak into die cavitycooling line to leak into die cavity
Water or oil in the cavity, when hit by the alloy,Water or oil in the cavity, when hit by the alloy,
will form gaswill form gas
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Internal Defects:Internal Defects:
PorosityPorosity--ShrinkageShrinkage
Shrinkage: porosity that occurs if the alloyShrinkage: porosity that occurs if the alloy
solidifies without pressure on itsolidifies without pressure on it
All alloys shrink a certain percentageAll alloys shrink a certain percentage
High pressure die castingHigh pressure die casting
Uses intensifiers/other methods to increase alloyUses intensifiers/other methods to increase alloy
pressure once cavity has been filled with alloypressure once cavity has been filled with alloy
Alloy pressure must be transmitted from theAlloy pressure must be transmitted from the
biscuit through the runner to the gatebiscuit through the runner to the gate
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Internal Defects:Internal Defects:
PorosityPorosity--ShrinkageShrinkage
Shrink defects:Shrink defects:
occur at the last placeoccur at the last place
in the casting to freezein the casting to freeze characterized by a roughcharacterized by a rough
and jagged appearanceand jagged appearance
tends to be continuoustends to be continuous
by natureby nature
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Dimensional DefectsDimensional Defects
Dimensional variations covered:Dimensional variations covered:
Linear variation, across parting line variation,Linear variation, across parting line variation,
shift and mismatch, warpageshift and mismatch, warpage
Most dimensional defects related to:Most dimensional defects related to:
Die temperaturesDie temperatures
Condition of the dieCondition of the die
Force of injectionForce of injection
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Dimensional Defects:Dimensional Defects:
Die TemperatureDie Temperature
Thermal expansion/contraction: objectsThermal expansion/contraction: objects
lengthen when heated, get smaller whenlengthen when heated, get smaller when
cooledcooled
Castings get smaller when cooledCastings get smaller when cooled
Dimensional problem can occur when one half ofDimensional problem can occur when one half of
die is much hotter than other halfdie is much hotter than other half Can be a problem for the die and the castingCan be a problem for the die and the casting
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Dimensional Defects:Dimensional Defects:
Die ConditionDie Condition
Flash Buildup at parting lineFlash Buildup at parting line
Prevents the die from closing properlyPrevents the die from closing properly
May cause an oversize dimensionMay cause an oversize dimension
Prevents wedgelock from holding slide in placePrevents wedgelock from holding slide in place
Flash buildup at front of slideFlash buildup at front of slide
Prevents slide from going to ready to castPrevents slide from going to ready to cast
positionposition
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Dimensional Defects:Dimensional Defects:
Die ConditionDie Condition
SolderingSoldering
Small core pins can be very susceptible; solderSmall core pins can be very susceptible; solder
buildup can cause an oversize outbuildup can cause an oversize out--ofof--tolerancetolerance
conditioncondition
May occur in walls; could cause an undersize orMay occur in walls; could cause an undersize or
thin wallthin wall
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Dimensional Defects:Dimensional Defects:
Force of InjectionForce of Injection
Force of injectionForce of injection
Overcomes locking capability, causing tie barsOvercomes locking capability, causing tie bars
stretch and allowing die to flashstretch and allowing die to flash
Flashing adds to size, cause slides to backoutFlashing adds to size, cause slides to backout
Normal injection force, impact, and intensificationNormal injection force, impact, and intensification
Can:Can: Reduce the mass and speedReduce the mass and speed
Minimize impactMinimize impact
Apply intensification before gates freezeApply intensification before gates freeze
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Dimensional DefectsDimensional Defects
Statistical dimensional controlStatistical dimensional control
Product gets larger or smaller over timeProduct gets larger or smaller over time
Process variables that contribute to theProcess variables that contribute to the
dimensional variation need to be identifieddimensional variation need to be identified
A control technique, such as the average andA control technique, such as the average and
range chart, needs to be appliedrange chart, needs to be applied
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SummarySummary
3 categories of defects: surface, internal, and3 categories of defects: surface, internal, and
dimensional, and many defects in eachdimensional, and many defects in each
The operator may or may not have controlThe operator may or may not have control
over themover them
2subcategories of surface defects:2subcategories of surface defects:
flow and otherflow and other
There are many types of flow defectsThere are many types of flow defects
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SummarySummary cont.cont.
2subcategories of internal defects:2subcategories of internal defects:
inclusions and porosityinclusions and porosity
Dimensional defects are related to dieDimensional defects are related to die
temperatures, die condition, and the injectiontemperatures, die condition, and the injection
forceforce