Chap 8 Ppt

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8-1

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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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

Documents

Chap 8 Ppt