塑料件注塑基本知识

塑料的分类•热固性–酚醛树脂–氨基塑料–有机硅塑料–硅酮塑料–环氧树脂•热塑性–Generalpurpose•ABS,PP,PE…..–Engineering•PC,PC+ABS,PBT,PET,Nylon….–Reinforced•Fiber,Mineral…..热固性塑料的填料•粉状填料–滑石粉,云母粉,石英粉•流动好,比容小,塑料性脆,成型压力小.–木粉•流动好,比容小,易吸湿.热固性塑料的填料•纤维填料–棉纤维,石纤维,碎布纤维…….•流动性差,比容大,易吸湿,成型压力大,强度好.•填充性不良,易熔接不良.•玻璃纤维–流动性差,方向明显.–比容大,装模不便,模具磨损大.–加压时机:过早,填料与树脂分离,溢料多.过晚易发生填充不足.热塑性塑料•成形收缩率–塑料粒子•分子量大小,结晶/非结晶.–塑件结构•嵌件布局/数量,料流方向–料流方向大，垂直小–玻纤增强：料流方向小，垂直大–浇口形式,尺寸,分布–成型条件热塑性塑料•流动性好–分子量大小:分子量小,分子量分布寛.–分子结构规整性差–熔融指数高–表现粘度小–流动比大.热塑性塑料•结晶性–结晶型•壁薄,冷却快,结晶低,收缩小,透明度高•各向异性,内应力大.•易变形,翘曲–非结晶型热塑性塑料•热敏性及水敏性–热敏性:料温高,易变色,易降解,对模具的腐蚀大.–水敏性:在有水的情况下,在高温,高压下会降解.热塑性塑料•吸湿性–吸湿,粘附水份–不易吸湿,粘附水份•水解使树脂起泡,流动性下降,外观及机电性能不良.塑件设计•脱模斜度–精度高,取小值–较高,较大的尺寸,取小值–形状复杂不易脱模取大值–收缩率大的取大值–壁厚较厚者取大值–型心面比型腔面小.–增强塑料宜取大,自润材料可取小.塑件的壁厚•壁厚均匀原则•壁厚越厚,流程越长•壁厚决定塑件的使用性能:–强度,–电气性能,–尺寸稳定性–装配•壁厚一般为1~6mm,常用2~3mm避免翘曲变形的设计•保持壁厚均匀–检查相交部分•逐渐改变壁厚加强筋•加强筋的厚度必须小于相连接的壁厚•网格式加强筋须低于四周的高度.•有可能的情况下,螺丝柱需与本体连接.支承面•小支承面的配合优于大支承面•以螺丝柱部位可得到高强度的可靠装配．圆角和孔•连接处以圆角过渡：–减小应力，改善流动，提高强度：0.5~1mm•孔间距不宜太小：用长圆孔加凸台．•螺钉孔加倒角以容屑．铰链•铰链的截面不易过长•壁厚减薄过渡处以圆弧过渡•壁厚一般为0.2~0.4mm•材料：ＰＰ•注：融体流向必须是通过铰链部分，使其线性分子延主链折弯．塑件的尺寸精度•影响因素–成型材料–成型条件–塑件形状–模具结构：Gate,Flow,Direction,Parting,Tooling–存放条件塑料机的发展•开炼机和压延机•螺杆挤出机(十九世纪后期)•柱塞式注射成型机(二十世纪初)•线式螺杆注射机(1956年)塑机的分类•混炼机械–捏合，开炼，密炼机•压铸机•挤出机•注射机•压延机：人造革，塑料薄膜等•吸塑机•吹塑机注射机的结构组成•注射装置–塑化部件：螺杆，料筒和喷嘴–料斗，计量装置，传动装置，注射和移动油缸•合模装置–前后固定模板，移动模板，连接前后固定板用拉杆，合模油缸，移动油缸，连杆机构，调模装置，顶出装置．注射成型过程合模注射保压冷却螺杆预塑开模顶出FillInjectionPackInjectionHoldScrewReturnDecompressionCoolingTimeMoldOpenEjectorForwardEjectorBackMoldCloses注射机的基本参数•公称注射量•注射压力•注射速率•塑化能力•锁模力•合模装置的基本尺寸–模板尺寸，拉杆空间，模板最大开距，动模板的行程，模具最大／小厚度注射模分类•单分型面注射模具•双分型面注射模具•带有活动镶件的注射模具•横向分型轴芯注射模具•自动卸螺纹模具•定模顶出模具•无流道模具（热流道，绝热流道）单分型面注射模具双分型面注射模具注射模典型结构•成型零部件•浇注系统•导向部分•分型抽芯机构•顶出装置•冷却，加热系统•排气系统LeaderPinClampingPlateStationaryHalfMoveableHalfEjectorPlateCavitySprueBushing•Thepathwayformaterialtofollowtogetfromtheinjectionnozzletothemoldcavity.•Comprisedof:-Sprue-Runner-GateRunnerSystem•UseBalancedRunnerSystems•Diameter(min)vs.Length(max)3/16”=6”long5/16”=12”long3/8”=15”longRunnersUnbalancedBalancedColdwell•Trapscoldslugsformedattipofinjectionnozzle•KeepsslugsfromenteringmoldColdwellRunnersFullRoundModifiedTrapezoidalTrapezoidalHalfRoundArunnerisonlyasefficientasthelargestfullroundrunnerdrawninit’scrosssectionSprueBushings•Sizing•Draft(1.5°-3.5°PerSide)•Pullers&ColdwellAspruebushingistheentryportforinjectingresinintothemoldUndercutRingBallPullerZPullerReverseTaperDesignedtopullthespruefromthespruebushingwhenthemoldisopenedSpruePuller浇口设计•流动的分布需均匀•开在最厚的部分，以便保持最大的保压•浇口应设计到熔体最后冷却的地方•注意玻纤排列方向的影响浇口的类型•针点式浇口•潜伏式浇口•边缘浇口•扇形浇口•平缝式浇口（薄片浇口）•圆环形浇口浇口的类型•轮輻式浇口•爪浇口•护耳式浇口•直浇口浇口的类型Tunnel/SubEdgePinpointHotManifoldsHotManifolds•Hotmanifoldssystems:-Providesheatedpassagetomoldcavity-Allows15%to20%fastercycles-Eliminatessprue&runnerscrap-Improvespartquality-Reducesmolded-instressExternallyHeatedManifold•AIRGAPINSULATESMANIFOLDFROMPLATES•UNIFORMTEMPERATUREALONGMELTCHANNEL•EXTERNALLYHEATED–UNRESTRICTEDFLOW–LESSPRESSUREDROP–EASIERMAINTENANCECourtesyofHotManifoldsHeaterProbeMeltChannelCoolingPlugLocatorRingHeaterManifoldPocketMeltChannelHeaterCoolingINTERNALLYHEATEDEXTERNALLYHEATEDHotManifolds•Externallyheatedhotrunnersystemsarerecommended:-Reducepressuredrop-Reduceshearandthermalhistory-Preventburnandbrownstreaks-Easechangesincolorormaterial-FacilitatepurgingValve-GatedHotManifoldsCYLINDERPISTONVALVEPINSPRUEBUSHINGMANIFOLDINSULATORINSULATINGAIRGAPNOZZLEHOUSINGNOZZLETIPNOZZLEHEATERMANIFOLDPLATECAVITYPLATEHotManifolds•Manifoldsizing•Streamlining•Tipdesign•Stand-offs/insulation•ControlsHotManifoldsBALANCEDMANIFOLDUNBALANCEDMANIFOLD分型抽芯机构•手动侧向分型抽芯•机动侧向分型抽芯–弹簧，斜导柱，弯销，斜导槽，锲块，斜滑块•液压／气动侧向分型抽芯分型抽芯机构模具模拟动画八上一个返回分型抽芯机构Cooling/Heating•Wateristypicallyusedtoheatorcoolmold•Uniformmoldtemperatureiscriticalto:-Cycletime-Warpagecontrol-Shrinkage-Dimensionalcontrol-Surfaceappearance-Stresscontrol-Crystallinity-Sinksandvoids-Weldlines-Blush-Glass/mineral-Jetting-ColdflowPlanWaterFirstWhenDesigningMoldCooling/Heating•Somecriticaldetails:-Depth/pitch/diameter-Turbulentflow-MTLsofconstruction-DesignWaterChannelsVenting•Unfilledproducts.0005”-.001”•FilledProducts.001”-.002”(over10%)D1TheroutebywhichairisallowedtoescapefromthecavityPartingLineVentD1OtherVentingTechniques•Pin“flats”•Continuousvent•Blades•Porousmetal•Vacuum•OverflowMoldSurfaceEjectorPinPinVentingEjection•Blades•Pins•Lifters•Stripperrings•SleevesDraft•Draftallowseasierpartejectionfromtooling•Conventional:1°perside•Withtexture:(1°+1.5°per.001”depth)NodraftDraftDrawDirectionToolingMetalSelectionMaterialTypeHomopolymersandUnfilledCopolymersReinforcedMaterialSteelTypeP20S7H13420ToolSteelCharacteristicsMediumAlloyMoldSteelShockresistingtoolsteelHotworktoolsteel(Crbased)StainlesssteelTypicalHardnessasFinished(RockwellC)30-36Rc54-56Rc50-52Rc50-52Rc模流分析(CAE)缺陷分析Troubleshooting•缩痕•变形•毛邊•熔合线•银丝•喷纹•烧焦缺陷分析Troubleshooting•Burnmarks:–Addvents–Reduceinjectionspeed–Movegatelocation缺陷分析Troubleshooting•Sinkmarks:–Increasepackpressureortime–Reduceinjectionspeed–Reduceribtowallthicknessratio缺陷分析Troubleshooting•Stringing:–Reducenozzletemper