Seminar onGas Assisted Injection MoldingBy

INTRODUCTIONA method of pressurizing an injection molded part with gas via a network of flow channels or directly into a part to provide the necessary packing force to produce a quality molded product

One involving the bonding of two halves produced by injection molding.

Blow molding.

Draw Backs

Difficult to produce if they were not mirror images

They require fixtures to ensure components are held in proper position

Gas Assisted Processcontrolled short shot volume Material is injected

Nitrogen gas is injected to complete the filling of cavity

Gas penetration completes fill of mould cavity with plasticAfter the part has cooled sufficiently, the gas is vented to atmosphere allowing the part to be demoulded

Two Basic Types Of GAIMConstant volume process

Constant pressure process

Constant volume system gas pressure profile

TIME

Constant pressure system gas pressure profile

Different Methods of Gas InjectionThe gas is injected Directly into nozzleDirectly into mold cavity, runner or into part

Fig :Gas injection into the runner

Gas injection directly into the cavity

Gas Injection Directly Into Mould

Figure : Injection sequence for gas Injection into mold

HELGA (Hettinga Liquid Gas Assist) is quite different from previous methods that usenitrogen gas to create the channel.

HELGA (Hettinga Liquid Gas Assist)Figure HELGA liquid gas-assist process: Liquid gas is injected into the mold using a special nozzle and then expands to form hollow cores

Gas PinIn nozzle method of gas assist a resign shut off valve prevents the GAS from entering the barrel.

Benefits Of Gas Assisted Molding

Reduction in injection pressureReduction in clamp tonnageIncrease in strength and rigidity of partReduction in sink markImproved aestheticsReduces material weightReduced cycle timeReduced tooling costs as a result of replacing hot runner systems with gas channels

DisadvantagesCost of machineLimited gas entry pointsUse of sprue break to vent the gasIt produces noiseCost of gas nozzle

MaterialsAcrylonitrile butadiene styrene (ABS)Polycarbonate (ABS/PC)AcetalHi-Impact Polystyrene (HIPS)Polyamide (nylon)Poly butylene terephthalate (PBT)

PolycarbonatePolyetherimidePolyethylene (HDPE)Polyethylene terephthalate (PET), glass-reinforcedPolypropylene (glass and mineral grades)PolystyrenePolyvinyl chloride (PVC

Defects In GaimFingeringGas bubblesBurning of resinCold slugGas blow outInsufficient venting of gas

FingeringFigure : Gas Migrating Into Undesired Areas

Gas Bubbles

Figure:Gas bubble

Cold SlugsIncorporating good slug well into the sprue and runner design will catch any unmelted resign before it enter the part

Burning of resin Causes(part surface)Insufficient venting of moldResin injection speed too fastGas pressure too highResin temperature too highCauses (inside the part)Gas pressure too high Low gas purity

Insufficient venting of gas CausesPoor gas pin designGas pin clearance should allow for sufficient venting of gas back through gas lineIncorrect gas pressure profile Experiment with different gas pressure profiles to correct the problem

Application

Automotive Bumper

Television CabinetsElimination of secondary operations to add plastic or metal bracketNo sink marksMaterial savingShorter cycle time due to reduction in material

Plastic Lawn ChairSinks marks were eliminatedSingle gate with flow runnerSink free surface on seat portion of chair

Wash TubResin saving up to 14%.Improved quality.Eliminate part stress.

Conclusion

Thank you

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