注塑模具培训injection moulding proces1

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1、INJECTIONMOULDINGPROCESSThemouldingprocessreferstoshapingofplasticmeltinsidethemould.Thisinvolves·Fillingphase,·Switchoverpoint,peakpressureoccurafterslightdelay.·Pressurephase,·Coolingphase.Sequenceintheprocess·Itisdesirabletohavehighestpossiblefillingspeed(Injec

2、tionRate)duringfillingphase.·Fillingspeedisnormallylimitedbylimitationofshearinginengineeringpolymers.Highlythermallystablematerial-commoditypolymers-canbefilledathighfillingratewithoutanyfearofdegradationofpolymersmelt.·Fillingphasecovers85to98%oftotalinjectionst

3、roke.·HighspeedfillingisterminatedatSwitch-overpointandlowspeedPressurephasecommences.·Duetorelaxationofcompression(10-15%)ofmeltduringinjectionstroke,meltexpandsandfillsupremainingemptyspaceinthemould.Itoverfillstoraisethecavitypressureasrelaxationcompletes.·Ifwe

4、don'tleaveanyspaceforrelaxationofmeltthen,tremendousamountofpressuregenerated.Thiscandamagethemould.·Sincemouldsurfaceismaintainedatlowertemperature(thanthatofmelt),meltcoolsandhencetriestoloweritsvolumeasperthepvTcharacteristics.·Atthispointthecompensationforshri

5、nkageissuppliedatlowerspeed.Sincelessthan10%ofspaceistobefilled,itdoesnotrequirehighspeedfilling.Thecavitypressureisjusttobemaintainedinsuchamannertocompensateforvoidcreatedbytheshrinkingmeltonaccountoffallingmelttemperature.Thepressurephasehastobemaintainedtillth

6、emelttransferstops.·Thereafterthemelthastobecooledfurther,belowheatdefectiontemperatureofmaterial.Thiswouldpreventdeformationofmouldingduringejection.ImportantnoteDuringfillingphase,pressurevalueshouldbeset15-25barabovetheactualpressureencounteredinthecavity.Thisi

7、sbecauseifthereliefvalveisactuatedduringthefillingphase,oilwoulddrainandyoulosscontroloverthespeed.Incaseofdoubt,itisoktosetvalueatabout80%ofmaximumpressureforthemachinethroughoutthefillingphase.Thevalueofmaximumhydraulicsystempressureisrecommendedinthemanual.Toma

8、intaintheconstantmeltfrontvelocity,itisrequiredtoadjusttheinjectionspeedinstrokedependentmultiplesteps.Duringpressurephase,thefillingspeedislowandconsta