1Injection Moulding Technology Mould Design & Construction Part 3Mould Design & ConstructionREAD.
2Session aimTo gain an understanding of general mould design and construction techniques, and to become familiar with the purpose and function of the various component parts.READ.
3READ. Session objectives By the end of the session you will be able to:Detail the requirement for venting the mould.Identify the component parts of a two plate mould.List two advantages and limitations for various gatedesign alternatives.State the three elements of the feed system.Identify applications for typical runner less moulddesigns.Explain the importance of mould temperaturecontrol.READ.
4IMAGINE YOUR MOULD DESIGNERS. WHAT NEEDS TO BE CONSIDERED? lifeMouldmaterialCostrestraintsMouldDesignMouldingmachineComponentdetailQuantityComponentmaterialIMAGINE YOUR MOULD DESIGNERS.WHAT NEEDS TO BE CONSIDERED?BRAINSTORM!MouldmakingtechniquesPostmouldingoperations
5READ. Two Plate Mould Tool Support blocks and risers Core plate Split lineMoving backplateTwo Plate Mould ToolPush back pinCavity plateEjector pinFixed back plateSprue puller pinLocating ringColdSlugWellREAD.Sprue bushRunnerSprueEjector plateCooling channelAir ventDowel or Guide pinGuide bush
6Question 1 List the advantages & disadvantages of a multi-plate mould?
12ASK DELEGATES THE FOUR ZONES. The hot runnerIdeally the spruebush, hot tipsand the manifoldshould haveseparatecontrollers andthermocouples.On the examplefour zonesare required.READ.ASK DELEGATES THE FOUR ZONES.
13READ. DISADVANTAGE. ADVANTAGE. DESCRIBE. Hot runner systemsThe 2 plate toolIncreases themould height.Saved materialwaste from thesprue & runner.READ.DISADVANTAGE.ADVANTAGE.DESCRIBE.Material delivered to the cavities in the same condition as the melt leftthe barrel.
14Question 3 Please list 3 advantages and 3 limitations when using hot runner moulds?
15Limitations of a hot runner Increased set-up times.Warm up period required.Increased tooling costs.Manifold leaks.Higher maintenance costs.Degradation with certain polymers.Heat expansion problems.READ.SOFT START!CARTRIDGE HEATERS ABSORB MOISTURE AS THEY COOL.
17Advantages of a hot runner No feed system to be removed.Reduced mould open stroke.Reduced shot weight.Injection time reduced.Automatic de-gating.Easier to balance gates.Increased number of cavities possible.ASK DELEGATES.READ.
18When using hot runner moulds Avoid regrind to avoid blocked nozzles.Avoid heat sensitive polymers.Do not flick off cold slugs.Keep systems fully maintained.READ.
19Question 4 What is the primary function of a stack mould?
20Stack mould - reduced projected area Braun IrelandDESCRIBE.WHY DO WE USE.TO REDUCE PROJECTED AREA.WEVE SEEN AIR EJECTION CAN YOU NAME ANY OTHERS.
24Question 5 What are the different types of ejector pins and methods of ejection?
25Combination round/blade ejection Blade ejectorsDESCRIBE WHY WE USE.USE PROPS.Round ejectors
26USED TO PRODUCE CORE IN MOULDING. Sleeve ejectionCore pinSleeveDESCRIBE.USE PROPS.USED TO PRODUCE CORE IN MOULDING.
27PIN STAYS STILL SLEEVE COMES FORWARD. Sleeve ejectionGood even ejectionaround bosses butquite expensive.PIN STAYS STILL SLEEVE COMES FORWARD.
28Stripper plate ejection Stripper blockASK DELEGATES.DISADVANTAGE.CAN’T SHORT SHOT.ADVANTAGE.LEAVES NO WITNESS MARKS.
29USED USUALLY WITH STIPPER PLATES ON DEEP DRAWN COMPONENTS. Air ejectionDESCRIBE.USED USUALLY WITH STIPPER PLATES ON DEEP DRAWN COMPONENTS.BUCKETS, BOWLS, BINS.Air off - spring returns valve to its rear position
30Question 6 When would mechanical or hydraulic core movement be used?
32HYDRAULIC CYLINDERS CAN MOVE CORES. Core pullingHYDRAULIC CYLINDERS CAN MOVE CORES.MORE EXPENSIVE.
33Core movement by hydraulics Points to remember:Machines will need to be programmed.There are many different sequences.Must know the sequence, before opening orclosing the mould.READ.WRITE ON BOARD COMMON CORE SEQUENCES.TOOLS ARE EXPENSIVE.IF TIME.GO TO BALCONY.BREAK 3.10.If in doubt ASK!
34Question 7 When designing a mould, utilising a cold runner system, what are the primary considerations to be addressed?
35NAME PARTS. SPRUE, RUNNER, GATE. The feed systemNAME PARTS.SPRUE,RUNNER,GATE.
36COLD POINTS. MISS MATCH. MODIFIED TRAPIZOIDAL. Runner shapeWhich shape will give the best flow?10 degCOLD POINTS.MISS MATCH.MODIFIED TRAPIZOIDAL.
44SIZE SMALLER. FEED FREEZE OFF. Gate considerationsSize in relation to section thickness of the moulding.Always feed into the thickest section.Position gate to give even filling.SIZE SMALLER.FEED FREEZE OFF.
47Question 10 What are the general considerations for the correct moulding temperature?
48Mould temperature control High enough to allow filling of the mould, withoutpremature freezing of the polymer melt.As uniform as possible, to ensure the mould iscooled equally in all areas.Mould temperature has the greatest influenceon part quality.READ.
49Piping up considerations ASK DELEGATES CORRECT WAY TO PIPE UP.1in2in1out2out
50Cool core pin technology Coolant flowUsed as an alternativeto cooling channels.BERILIUM.MOULDMAX.USED WERE CHANNELS CANT BE PUT.Core
55Injection Moulding Technology Mould Design & Construction Part 3Mould Design & ConstructionREAD
56Injection Moulding Technology Part 3Plastics Materials
57AimTo provide an understanding of plastics materials technology and processing behaviour when injection moulded.
58Objectives By the end of the session you will be able to: Describe, in simple terms, the molecular structureof plastics materials.State three methods of classifying plastics,giving examples.Describe the MFI test and it’s relevance.Identify five common additives to modern plastics.
59What are plastics? Synthetic - Man made Organic - Based on carbon Polymers -Describes the MOLECULES of polymersMany unitsTo show that polymers are based on oil by-products hence when PP degrades or is over heated it returns to an oil like substance
60Polymerisation example HHcHcHcHcHHExampleETHYLENEMonomer
61Polymerisation example Catalyst -heat, pressure and timecHHccHeat and pressure in side reaction vesselInitiator starts reactionMonomer units start to link togetherReaction continues in a random manner but must be controlledTerminator added to stop reaction giviong polymer chains of similar length – Molecular weight distributionETHYLENEmonomerPOLYETHYLENEpolymer
62Polymer examples Propylene monomer Polypropylene polymer Styrene PolystyrenepolymerVinyl ChloridemonomerPolyvinylchloridepolymerSequence first monomer to polymer for PP and PSNext two start with Polymer to monomer – get delegates to think what monomer you start with.Polycarbonate – this is to demo that not all polymers follow the same route.In the case of polycarbonate:Produced by polycondesnation from Bisphenol A – this is manufactured by mixing phenol, acetone and phosgenePhosgeneBis-Phenol AcetonemonomerPolycarbonatepolymer
63Summary Polymer chains have a coiled spring like structure. Picture shows the chain in reality – not just a line drawing it’s a 3D structureDemo spring like structure of polymer in real termsDiscuss length of chains, size of atoms, behaviour in mould – spring stretches during injection relaxes, recoils as it cools hence shrinkageAbout 5,000 times longer than their diameter.Chains are upwards of 1,000,000 repeat units long.Processing of polymers reduces the chain length andhence the loss of properties when using regrind.
64Curing/solidification Cross-linking reaction Classifying plasticsThermosetsExample - BakeliteFlows due to pressureHeatMeltCuring/solidificationHeat & PressureCross-linking reactionThermoset materialsWarm barrel 100 to 150, hot tool 150 to 200Soften polymer so it will flow, force into mould, under pressure and heat chemical reaction occursCross-links – chicken wire effect – can not be reversedSome thermosets such as expoy resin require a catalyste to start reaction e.g Araldite two part epoxy resin, mix the two elements reaction occurs cross links are formed
65Classifying plastics Thermosetting Bakelite Rubber Epoxy Melamine Polyester(Chemical change - Boiled egg)PET (Polyester) in both lists since it is possible eto have both a Thermoset PET – car body repair kits and a thermoplastic PET for bottles.
66Example - Polyethylene Classifying plasticsThermoplasticsExample - PolyethyleneMeltFlows underpressureHeatCool/remove heatSolidificationPET (Polyester) in both lists since it is possible eto have both a Thermoset PET – car body repair kits and a thermoplastic PET for bottles.Thermmoplastics – hot barrel / cooler toolSome interaction or bonds between chains such as Van der Waals forces, entanglement, structure but can be reversed when heat applied
67Classifying plastics Thermoplastics Polyethylene Polystyrene PolycarbonateNylonPolyester(Physical change - Ice to water)PET (Polyester) in both lists since it is possible to have both a thermoset PET – car body repair kits and a thermoplastic PET for bottles.Discuss Thermopastic Elastomers – rubber type properties but can be processed on a thermoplastic machine, structural difference gives rise to hard and soft domains – Two shot machine
69Prices are only approximate Classifying plasticsCommodityPrice/tonnePlasticPolypropyleneHDPELDPEPolystyreneSANAcrylicABS£600 - £950£500 - £900£600 - £900£600 - £1200£900 - £1500£ £2500Commodity plasticsHigh volume partsDisposable goods / packaging industryService properties lowLow strength / heat resistance / chemical resistance etc.High volume production of polymer hence low costPrices are only approximate
70Classifying plastics Engineering Plastic Price/tonne PETAcetal (POM)Nylon (PA)PBTPCPAIPEEK£ £1200£ £1900£ £2400£ £2700£ £3500£ £40000£ £69000Engineering materials will have much better mechcanical properties such as tensile strength, a high strength to weight ratio, good chemical resistance and much more expensivePEEK - £4,500 per tonneManifold PA66 GF35Prices are only approximate.
71Amorphous versus Semi-crystalline! What are the differences? Classifying plasticsAmorphous versus Semi-crystalline!What are the differences?Engineering materials will have much better mechcanical properties such as tensile strength, a high strength to weight ratio, good chemical resistance and much more expensivePEEK - £4,500 per tonne
72Structural changes of polymers Molten stateFlowCOOLAmorphousRandom structureSemi-CrystallineOrdered structure
73Classifying plastics Thermoplastics Amorphous Semi-crystalline PolycarbonateA.B.S.PolystyreneS.A.N.AcrylicPolyethylenePolypropyleneNylonAcetalPolyesterIntroduce concept of amorphous and semi-crystalline sub-divisions of thermoplastics
74Why is crystallinity important? Property differencesWhy is crystallinity important?AmorphousSemi-crystallineGenerally clearGenerally opaqueHigh mould Shrinkage1.5%-2.5%Low mould shrinkage0.5%Wide melting rangeNarrow melting range
75+ Flow behaviour Semi-crystalline Ease Amorphous of flow Temperature Amorphous plasticsMelt and solidify over aWIDE temperature range.(PA)+EaseofflowTemperatureAmorphousSemi-crystalline plasticsMelt and solidify over aNARROW temperaturerange. (i.e they have a crystalline melting point)(PMMA)
76Examples: HDPE, PA, POM, PVC, PS, PP. Homo-polymersThe homo-polymer chains comprise of the same repeat unit for their entire length.Examples: HDPE, PA, POM, PVC, PS, PP.
77Co-polymersCo-polymer chains comprise of two or more different repeat units, which are linked together.Examples: ABS, SAN, POM, PP, HIPS.(ABS – Acrylonitrile-Butadiene-Styrene)Mention Co-polymers can be symmetrical, random or branched use white baord to illustartaeRatio of component polymers changed to give different properties I.e ABS increase Butadiene to give greater impact strength, increase Acrylonitrile for chemical resistance this leads to a range of grades of ABS being available fro the supplier.
78High Impact Polystyrene Blends & AlloysBlendsTwo or more different polymers in the same matrix but not linked.NorylPPO/PSHIPSHigh Impact PolystyreneAlloysTwo or more different polymers in the same matrix plus a chemically adhesive additive.XenoyBayblendPC/PBTPC/ABS
79Additives in polymers Why use additives? Modify service performance.Modify processing performance.
80Types of additives Assist processing Heat stabilisers Lubricants Essential additivesModify bulk mechanical propertiesPlasticisersReinforcing fillersToughening agents= Flexible PVCReduce costs???Powdered fillers e.g. talc or chalk
83Melt Flow Index apparatus WeightThermometer insidean oil filled wellBarrelInsulationPolymer MeltAvg. weight of extruded plastic in 10 mins.Die
84Effects of processing Chain length First pass Lower viscosity Higher MFILower strength materialChain lengths can be shortened by processing or regrinding.
85Melt Flow Index Summary The bigger the value - the easier the flow. Values can reflect relative chain lengths.Low shear (not representative of injection moulding)Spiral flow test better.Used as a quality control for incoming material.Specific test conditions must be used.
87Pre-treatment of plastics Moisture absorption - HygroscopicPOM, PE, PP, PS, PVCNot affected - drying not usually required.PMMA, ABS, SAN, PP + talcWater absorbed - may need drying.Do not forget to mention that certain additives may require drying I.e. Talc fillersUse coaster from dupont one moulded dry condition and one moulded without dryingDry part – tough / strongWet part – visual no diffenerce, will break very easilySAFE – MUST WEAR GLOVES TO DO DEMO POTENTIAL FOR INJURYLast class all polymers in this list are oxidised or attacked by moisture if processed in damp condition this damages the chain and therefore the mechcanical properties PC is the samePC, PET, PA, PBT, PURDamaged by water - needs drying.
88Pre-treatment of plastics Methods for removing moisture:Vacuum ovenDehumidifying dryerDo not forget to mention that certain additives may require drying I.e. Talc fillers
89Pre-treatment of plastics Key drying considerations:Type of material – ABS, PC, PA plus virgin or regrind.Temperature and time required.Volume held in dryer to give correct throughput.Maintenance of dryer.Do not forget to mention that certain additives may require drying I.e. Talc fillers
90Injection Moulding Technology Part 3Plastics Materials
91Injection Moulding Technology Processing & Troubleshooting Part 3Processing & Troubleshooting
96Example of skin formation Previous colourNew colourSkinReal example of skin forming and demos that the material flows threw the centre then out to the sidesParts produced when production changed from yellow to black colored partsYellow material enters cavity first and is pushed out to the surface and forms the skin, the black material follows in behind and forms the core.Principle applied in some two shot process’s where internal layer is a regrind or second polymer.
98Molecular orientation Fast Injection SpeedMould cavityHigh orientation/Easy flowThinner frozen layers
99Slower filling or colder moulds Residual stressSlower filling or colder mouldsThick frozen layersMould cavityHigh residual stress !
100Faster filling or hotter moulds Residual stressFaster filling or hotter mouldsThin frozen layersMould cavityLow residual stress !
101Effect of residual stress Fast fill rate - Lower internal stressSlow fill rate - Higher internal stressTwo moulding with different internal stress’s due to the rate of fill of the cavityBoth parts made from same machine in the same material with all conditions the same accept for the injection speedOne injected at 99% speed the other at 10% speedBoth then placed in an oven at 100C for 24 hours – stress is then allowed to relax as the material heats up hence the distortionWhich has the highest stress levels ?Why ?
102Injection phase Summary Aim to fill the mould as quickly as possible. Uniform melt front speed as part fills.Mould cavities fill evenly.Ensure mould is 99% full.
103Aims during the holding phase Start Mould SafetyApply Locking TonnageMouldClosesOpenPeriodInjection Speed& PressureInjectionPhaseMouldOpensMould99% FullHoldPressure& TimeHoldingPhaseCoolingPhaseGateFreeze-off
104Polymer compression Pressure is applied to the melt. Melt density increases.Material shrinkage reduces.
106Holding phase Summary Ensure adequate compression of the melt. Reduce sinks and voids by compensating for the shrinkage of the polymer chainsObtain consistent component quality by establishing gate freeze-off time.Obtain correct component weight/dimensions by the application of a suitable pressure.Rule of thumb:Amorphous plastics require a low holding pressure.Semi-crystalline plastics require a high holdingpressure.
107Aims of the cooling phase Start Mould SafetyApply Locking TonnageOpenPeriodMouldClosesInjection Speed& PressureMouldOpensInjectionPhaseMould99% FullScrew BackCompletedHoldingPhaseHoldPressure& TimeCoolingPhaseGateFreeze-offStart Screw Rotation
108Factors to consider Polymer type – Semi-crystalline or Amorphous. HDT – Heat Distortion Temperature.Capacity of temperature control unit.Cooling time versus refill time (open nozzle).
109Cooling rate, shrinkage & distortion Mould Tool?HOT SIDECOLD SIDEWhich way will the part bend ?
110Cooling rate, shrinkage & distortion Residual orientation effect (stress)Normal shrinkage effectHot sideCold sideHot sideCold sideMoreshrinkageLow orientationHigh orientationAimated to show the two effectsDistortion at the moulding machineWarpage as part relaxes in service or storage
111Cooling phaseSummaryTo remove heat at an appropriate rate to promote maximum service properties.To remove the heat from all cavities evenly.To allow the part to be ejected without distortion.To provide sufficient time to plasticise a homogeneous mass of molten polymer.
113Troubleshooting Is the fault acceptable – check the first off. ASSESSMENTIs the fault acceptable – check the first off.CORRECTIONIf not, then check the basics first:The mould (damage, vents).The material (grade, batch, moisture).The machine (wear, malfunction).
114Slower filling or colder moulds Residual stressSlower filling or colder mouldsThick frozen layersMould cavityHigh residual stress !
115Faster filling or hotter moulds Residual stressFaster filling or hotter mouldsThin frozen layersMould cavityLow residual stress !
116Relationship between faults & cycle steps OUT OF CYCLECOOLINGHOLDINGINJECTIONFlashShortGas trapJettingFlow linesWeld linesDieselingWeightSinkingFlashVoidsDimensionsDistortionContaminationMica marksIllustartion to show where faults occur within cycleGet delegates to say where examples such as flash,weld lines etc. occur then show listsNote: Some faults can be related to more than one specific part of the injection moulding cycle.
117Examine the mouldings and determine the: TroubleshootingExamine the mouldings and determine the:FaultCauseRemedyIssue samples – get delegates to consider fault – Cause - Remedy
118Example of Fault - Cause - Remedy Burn mark (Dieseling)TrappedgasClean vents.Reduce Locking tonnage.Reduce injectionspeeds or profile.Example to showFault – definintion of problem ( Flash – excess material arouond edge of part )Cause – why flash occursRemedy – how to cure, note multiple remedies, need to determine appropiate stepsReduce melt temperatures.
119Processing variables Short term Long term Locking tonnage Holding pressure timeCooling timeInjection speedHolding pressureChange over positionShot weightDecompressionEjector speedMelt temperatureMould temperature(Oil temperature)Determine actualtemperatures usinga pyrometer forboth mould and melt.Short term vs long termBack pressureScrew speed
120Systematic approach Eliminate faults in order of priority: Those that potentially damage the mould- Flash- Gas burns/trapsOptimise the filling phase% fullOrder in which problems addressedFilling phase faults- Jetting- Flow lines- Weld lines
121Systematic approach Holding phase related - Voids - Sinks - Undersized Optimise the holding phase- Holding pressure- Gate freeze-off time- Cushion SizeOrder in which problems addressedOptimise the cycle time- Cooling time
122Troubleshooting Summary Adopt a logical and systematic approachChange one condition at a timeConsider the interaction of conditionsKeep samplesKeep notesBe patientDon’t be a knobTwiddler!!
123Injection Moulding Technology Processing & Troubleshooting Part 3Processing & Troubleshooting