《cae概念射出及流动概念》由会员分享，可在线阅读，更多相关《cae概念射出及流动概念（36页珍藏版）》请在金锄头文库上搜索。
1、CAE application-Introduction tolInjection MoldinglFlow BehaviorlDesign PrinciplesHopperScrew (Ram)BarrelHydraulic UnitToolInjection Molding MachineCooling TimeMold Open TimeFill TimeHold TimeInjection Molding CycleCycle Time:Fill Time:Hold Time:Cooling Time:Mold Open Time:22Sec.19102Injection Moldin
2、g CycleHopperBarrelScrewMoldScrew is applying a specifiedpressure to the polymer meltin order to pack more plasticinto the cavity. Also called“compensation stage”.Injection Molding ProcesslFillingMold closes, screw rapidly moves forward, frozen polymer skin forms at mold wallslPacking Time (Holding)
3、Cavity filled, packing begins, cooling occurringlCoolingPacking complete, gate freezes off, cooling continuesScrew moves back and begins plasticating resin for next shotlMold OpenCooling completes, mold opensInjection Molding ProcessThe Injection Molda.k.a. Stationary Halfa.k.a. Moving Half(a)(b)Noz
4、zleFlow BehaviorlWhat Does a Plastic Molecule Do in an Injection Mold?Phases of MoldinglFillingVolumetrically fill the cavity lPressurizationBuild up pressure in the cavitylCompensationAdd extra material to reduce shrinkageFilling PhasePressurization PhaseCompensation PhaseMeltFountain FlowlDescribe
5、s the phenomena of how plastic flows in a moldlMaterial that first enters shows up at the surface near the gatelMaterial that enters the cavity last, shows up in the center downstreamlHas direct influence on molecular and fiber orientation at the part surfaceShear rate - min maxLow orientationHigh o
6、rientationtensile forcetensile forceCross-Sectional FlowMolecular OrientationlMolecular Orientation is caused by shear flow. The high amount of shear is inside the frozen layer, therefore the highest orientationFasterInjection RateSlowerInjectionRateVS.Cold MoldHot Plastic MeltHeat Lossinto the Tool
7、Frozen LayerHeatInputHighShearRatePlasticFlowlThere should be a balance between heat input from shear and heat loss to the toolCross-Sectional Heat TransferMOLDFLOW Scan Injection Time - Flow 1Pressure MPaTime secInjection Time /Frozen layer thicknesslFaster injection times will produce a thinner fr
8、ozen layer, and a thicker flow channelPressure-Volume-Temperature (PVT)lDescribes the temperature/pressure relationship for polymers over the entire processing rangeGate along edgeFinal PartMoldShrinkagelShrinkage in the direction of flow is usually much greater than across the flow for un-filled ma
9、terialsDesign PrincipleslUse Design Principles and Moldflow technology so you dont have to do this:Moldflow Design PhilosophylNumber of gatesThe number of gates used is based on the pressure to fill the cavity. In general, one selects the minimum number of gates to fill the cavity.lPosition of gates
10、The position of the gate is determined by the flow balancing principle.lFlow patternThe mold should fill with a straight fill pattern with no changes in direction during filling.Moldflow Design PhilosophylRunner DesignThe runner system is designed to achieve the required filling pattern in the cavit
11、y.lSequence of AnalysisThe procedure of the mold design always starts with the cavity.Project Design Procedure Using MoldflowlDetermine the design criteria for the projectlUse previous experience of analystlDiscuss the project with all disciplines involved in the projectlUse Moldflow Design Principl
12、eslUse Moldflow Design Rules with the softwarelInterpret results and make changes where necessarylDiscuss changes with all disciplines involved in the projectlRepeat Moldflow analysis to ensure acceptable resultsFlow ConceptslUnidirectional and controlled flow patternlFlow balancinglConstant pressur
13、e gradientlMaximum shear stresslUniform coolinglPositioning weld and meld lineslAvoid hesitation effectslAvoid underflowlBalancing with flow leaders and flow deflectorslAcceptable runner/cavity ratioOrientation is different Directions, flow marks, high stresses, & warping.Orientation in one directio
14、n, Uniform, shrinkage, & stresses.Uni-Directions and Controlled Flow PatternlThe uni-directional flow principle says that the plastic should flow in one direction with a straight flow front throughout filling. This gives a uni-directional orientation patternFlow BalancinglThe flow balancing principl
15、e says all flow paths within a mold should be balanced, i.e. fill in equal time with equal pressurelNaturally balanced runner systemSame distance and conditions between the nozzle and all cavitiesAll cavities filling at the same time pressure and temperatureFlow BalancinglArtificially balanced runne
16、r systemSizes of the runners are different in order to deliver plastic melt to all cavities at the same pressure, so that all the cavities fill at the same timeBeforeAfterFlow BalancinglArtificially balanced runnersLimitations:Very small partsParts which contain very thin sectionsParts where sink ma
17、rks are importantWhere the ratio of runner lengths to be balanced is too greatPressure spiking at end of fill before switchover lowers pressureConstant Pressure GradientlThe constant pressure gradient principle says that the most efficient filling pattern is when the pressure gradient, i.e. pressure
18、 per unit length, is constant along the flow pathMaximum Shear StresslThe shear stress during filling should be less than the critical level. The value of this critical level depends on the material and applicationMaterial: ABSStress Limit: 0.3 MpaStress plotted is above the material limitlWhen plas
19、tic is in contact with the mold, and one side is cold and the other is hot, differential cooling takes place. This causes a bowing to the hot side, as the hot side takes longer to cool and shrinkUniform CoolingHot SideCold SideTensile StressHeat is concentrated in the corner of the coreCavityColdCor
20、eHotHot Corner(shrinks relative to frozen sections, causing warpage)Uniform CoolinglPart cross-section should cool evenly, cavity to core. If it does not in a corner, the corner will pull in to less than 90 degrees, producing the typical bowed box warpagelPosition weld and meld lines in the least se
21、nsitive areas, if they cant be eliminatedWeld Lines are formed when two flow fronts meet head on Meld Lines are formed when two flow fronts meet and flow in the same directionPositioning Weld and Meld LinesGateRib did not fillAvoid Hesitation EffectslPosition gates as far away as possible from where
22、 the flow divides into thick and thin flow paths to avoid hesitation effectsGateGATES make poor flow control devicesLow pressure drop in runnersMiddle cavity hesitating more than right cavityHESITATION EFFECTMaterial freezes off in the gate closest to the sprueTRADITIONAL APPROACHFirst gate opened 0
23、.010” in thickness and width, from 0.030” to 0.040”Now first cavity filling much faster than other cavitiesAvoid Hesitation EffectsGoodNotGood!Avoid UnderflowlA change in flow direction between the time an area fills and the end of filllThe blue velocity angle arrows should be perpendicular to the m
24、ulti-color fill contour linesFLOI4Arrows show direction plastic moving at the instant of fillFlow frontWeld Line moves inside frozen layerAvoid UnderflowUniform ThicknessBalanced ThicknessBalanced FillingUnbalanced FillingBalancing with Flow Leaders and Flow DeflectorslSubtly increase (leader) or de
25、crease (deflector) the wall thickness to influence the filling pattern to create a balanced fill within the partVolume of parts: 192.0 ccVolume of feed system: 13.4 ccFeed system: 7.0% of part volumeAcceptable Runner/Cavity RatiolDesign runner systems for high pressure drops, thus minimizing material in the runner, in order to give a low ratio of runner to cavity volumeQUESTIONS?
