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DEFECTS IN INJECTION

MOULDINGGROUP MEMBERS:

SITI HAJAR BINTI PAIMAN 2012763798NURATIQAH BINTI MOHD SALLEH 2012850174

NUR FATIN AFIQAH BINTI ISMAIL @ AHMAD 2012815616

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing Faulty

Sink mark A sink is a dip ordepression in thepart which does notfollow the molds

surface. In clearparts, bubbles can

be seen in thickareas. Thesebubbles can be theprecursors of shrink

Sink mark occurs duringthe cooling process:-The thermalcontraction (shrinkage)of the plastic cannot becompensated in that

area.-The outside walls ofthe molded part are notstable enough, due toinsufficient strength,the outer layer is drawninside by coolingstresses.-Low injection andpacking pressure.-Short hold time or

cooling time.

-Cross-sectionarea of gate is toosmall.-Inconsistent wallthickness. i.e.Thick areas

adjacent to thinareas.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Short shot The incompletefilling of a moldcavity whichresults in theproduction of anincomplete part.

-Flow restrictions.-Back pressure dueto unvented airtraps can cause ashort shot.-Low melt and/ormold temperaturesInsufficientmaterial enteringthe cavity.-Under packing,

low injectionpressure.

-Due tochannelsfreezing orinadequaterunner design.-An undersizedmachine, lowshot volume, orinadequate ramspeed.-Last part of the

mold to fill.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing Faulty

Flash Excess plasticsqueezing outperpendicular to thepart at parting line.Found at locationswhere the moldseparates, notablythe parting surface,movable core,vents, or ventingejector pins.

-Improper moldingconditions, such as ahigh melttemperature (whichmakes a thinner melt)or high injectionpressure.-If the clamp force ofthe injection machineis too weak to holdthe mold plates

together during themolding process.-The parting surfacedoes not contactcompletely, due to adeformed mold

structure.

-An improperlydesigned ventingsystem, a verypoor ventingsystem, or aventing systemthat is too deep.-Along any partingline.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Discoloration Deviation fromthe originalintended color ofthe material ascompared to themanufacturers

color chip.

-Contaminatedresin.-Overheated resin.-Incorrect regrindratio.-Incorrect color

mixing or blending.

-Entire part

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Warpage The failure tomaintain flatnessof a plastic partthat was intended

to be flat. Adistortion of theshape of the finalinjectionmolded item.

Caused bydifferentialshrinkage,that is, the

pattern, shape,and thickness ofribs on the part ifone area ordirection of thearticle undergoes

a different degreeof shrinkage thananotherarea or direction,the part will warp.

-Molded instresses-Differentialmold

temperatures.-Distribution ofwall thickness,areas with non-uniformdistribution are

included.-Detected onlarge flat parts.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Excessiveshrinkage

A characterizedby mouldedparts whichappear smallerthan theintended

dimensions orshow warpage.

-Cure time tooshort-Pack pressure toolow-Mould or stocktemperature too

high-Insufficientinjection pressure

-Runners orgates too small.-Poor partdesign, varyingwall thickness.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Blister Hollow Created OnOr In The MoldedPart

-Air Traps OccursWhen ConvergingFlow Fronts SurroundAnd Trap A Bubble OfAir.

-- Air Bubbles WillSolidified WhileFlowing Around

-The Surface OfThe Molded Part

-- Voids In ThickWalled MoldedPart

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

Faulty

Weld line -Witness marks oftwo or more meltflow fronts at theirjoining zone.

- Weld lines arecreated when twoor more melt flowfronts meetpossibly causing a

cosmetically visibleline.

-Low melttemperature-injection pressurelow

-excessive mouldlubricant on themould-improper ventingin the mould-low mould

temperature-poor material flowproperties-injection speedvery slow

- Area in thefinished moldedpart especiallywith filled

resins.

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

FaultyDiesel effect/burn marks

Show up on thefinish molded partsas charred or darkplastic causeb bytrapped gas and

usuallyaccompanied by adistinctive burntsmell.

-Due to entrapped airat the end of flowpath and poorventilation near rib.

-The trapped gas iscompressed and getsheated to a highdegree causing theburn on the plastic.

- at blind holes-Fillets-Narrows ribs-Near placeswhere several

flow fronts meet-End of flowpaths

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

FaultySilver streak Gaseous

components in theplastic appear at themolding surface andcollapse.

-Insufficient drying-Inclusion of air-Degradation-Incompatible ofmaster batch

-Molding surfaceof product

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

FaultyColor streak The phenomenon of

color streaking ischaracterized bylocalized changes inthe color of a

molded componentor by streaking.

Variation from theoriginal color

-Poor thermalstability of coloringagent-Low die temperature-High speed of flow

-Poor distribution ofcoloring agent

-Welds-Ribs-Surface ofmolded part-Part which likely

to induce shearflow

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Defects Definition Physical cause

Possible Part or

Mold Design

Processing

FaultyFlow mark A flow mark or halo

is a surface defect inwhich circularripples or waveletsappear near the

gate.

-Low melttemperature-Low moldtemperature-Low injection speed

-Low injectionpressure-Small runner stemand gate

-Around thegates when theplastic hasflowed throughthe die