注塑件成型与设计.pptx

Injection Molding and Design 注塑注塑成型与设计成型与设计Injection Molding Process OverviewPart and Tool Design Terminology Common Molding Defects Molded Part Design Best Practices Injection Molding Process OverviewInjection Molding Process OverviewInjection molding is used to produce most of our complex plastic parts.Injection molding is a process which involves forcing molten plastic into a machined mold cavity under high pressure.Injection Molding PressThe injection molding press operation includes a means to:nOpen and close and clamp the injection mold.nMeasure,melt,and inject the plastic resin.nCool the molten plastic in the mold.nEject the finished part from the mold.nComputer control system.Injection MoldThe injection mold forms both the show(A)side and the back(B)side of the part.The show side of the part is generally the cavity side of the tool,and the back side is the core side.The interface between the cavity and core is the parting line.The number of cavities is the number of parts produced per cycle.Injection Mold ComponentsCavityCoreClamp PlatesEjector Plate&PinsLiftersSlidesWater LinesGates and SpruesHot Runner System,etcHot Runner Manifold&Multiple Valve Gates The manifold in a large mold heats and delivers the hot plastic from the molding machine to the gate locations on the part.Lifters-Form Die-Locked FeaturesLifters are mechanisms which move approximately in the direction of the mold opening(die angle).They are usually activated by lifter rods operated by the ejector plate.Lifters often move on an angle to the part during mold opening and ejection to unlock a die-locked feature.Mold OpenMold ClosedDie Direction(mold opening angle)LifterCore Slides-Form Die-Locked FeaturesA core slide is a mechanism on the core which moves normal(90)to die angle direction to form die-lock features or undercuts in the part design.The slide is actuated by pins,cams,or hydraulic or pneumatic cylinders during and after the mold cavity opens.Simple Core Slide and EjectionPlastic PartEjection PinCoreWith SlideCavityWith Horn Pin*Actually,the cavity is stationary,and the core side moves to open the tool when mounted in the molding machine.AcceleratingEjection PinInjection SprueEjection with LifterCavity and Core with Lifter and PinPlastic PartEjection PinCorewith lifterCavityTravelingAngled LifterForms rib with flangeInjection SprueCam Operated Core PinForms hole in flange*Actually,the cavity is stationary,and the core side moves to open the tool when mounted in the molding machine.CamDesign TerminologyPart and Tool Design TerminologyPart and Tool Design Terminology-Die Angles&Draft Angles,拔模角-A Surface,B Surface,etc.A 面,B 面-Parting Lines,Lifter Lines,分模线-Doghouses,Ribs,Flanges 安装支座,加强筋,翻边-True Holes,Molded Holes,注塑孔-Tooling Considerations,注塑模考虑.Die Angle&Parting LineDie Angle(Die Vector)Mold opening directionParting Line where the core,cavity,and part meet together.Part(2 cavity)CoreCavityDraft AnglesParts must have open draft angles in the part geometry design.Part draft angle is measured relative to the die opening angle.If there is no draft angle,the part will cool and shrink onto the tool and will be difficult or impossible to remove without damage.We generally use minimum 3 degrees draft per side.More draft is needed for grained surfaces.Cavity A surface vs.Core B surfaceOriginal Part,tooled wrong,core/cavity.Ejection pins on show surface(A surface).Revised Part,eliminate pins on A surfaceDo you know the difference?Does your supplier and tool shop?Did you indicate it clearly in your math data file?Oops!Molding Issues and Common DefectsMolding Issues and Common DefectsMold Expansion/Part ShrinkageThermoplastics shrink as they cool and solidify during the molding process and after part ejection.The mold cavity is machined larger than the final desired part size in order to compensate for part shrinkage as the part cools.Mold shrinkage data for the specific plastic material can be used to calculate the amount of mold expansion needed.Mold shrinkage units are expressed as length-per unit-length,or as a percentage,and is calculated using the following formula:(mold dimension part size)/mold dimension =Shrink FactorMolding Issues and Common DefectsDimensional Size Errors(too long,too short,too thin,too thick,etc.)Dimensional Warpage,Distortion,&StressSink&Shrink MarksLifter Line Read-ThroughFlow Lines,Weld(Knit)LinesMetallic Flake OrientationPorosityNon-isotropic Behavior(different behavior in different directions)Flow Lines,Metal Flake OrientationThis section of metallic molded-in-color rocker molding show appearance defects caused by flow lines and metal flake alignments formed around the attaching hole pins.GateFlow ObstructionFlow Line&Metal Flake OrientationWeld Lines(Knit Lines)Weld(knit)lines are appearance and structural defects which are formed when the molten plastic must divide to go around an obstruction and then rejoin itself.We often find this problem on doghouses and also at attaching holes near a part edge.Sink MarksSink Marks form around the center of the larger mass of material and shrink towards the center of the mass.Sink marks are appearance defects caused by poor part design.Sinks marks are difficult to improve by tooling or processing.Ribs and GussetsRibs and gussets should have angled corners to avoid trapping air during filling.Square corners are more difficult to fill compared to angled or radiused corners.Chrome Plating ConsiderationsChrome plating is an electrochemical process,and the deposition of the metal to the part is attracted to sharp outside radii and is rejected by sharp inside radii.Non-uniform chrome deposit causes surface profile appearance problems.Use radii and fillets to eliminate sharp features and make the chrome deposition more uniform.Chrome Plating ConsiderationsStiffen edges if possible to reduce damage.Avoid flat surfaces due to risk of non-uniform chrome deposition and also plastic shrinkage sink marks.Use crowned(large radius,not flat)surfaces to maintain uniform chrome thickness and avoid shrink marks.Runner,Gating,Filling Molding AnalysisDo analysis before you design and build the tool!Part Design Best PracticesPart Design Best PracticesDesign For Success Follow a PlanAfter you gather and understand the part requirements:Select the proper part construction,materials selection,and process.(material type,stiffness,weatherable,paintable,moldable,etc.)Study and understand the material behavior and design requirements(minimum wall stock thickness,rib sensitivity,hole sensitivity,shrinkage,etc.Seek assistance from Materials Engineers,suppliers,Lead Engineers,colleagues,etc for design review and advice.Conduct Peer Reviews of your design with molders and tool shops as it develops.Injection Material FamiliesThermoplastic:Category of plastics which deforms and re-melts when reheated.recyclable“Common Fillers:Glass Fiber:Short,Long,Continuous,MatMineral:MicaTalcThermoplastic MaterialsThermoplastics common in automotive:TPO,PPABS,ABS+PC,ASA,ASA+PC PC,PC+PBT,PMMAPA6,PA66,Nylon,+mineral or glass fiberThermoplastic materials are usually high pressure injection molded but some grades can also be blow-molded or extruded or thermoformed.Part Materials Usage MatrixUniform Wall Stock(thickness)Poor DesignGood DesignDesigning parts for uniform wall stock(thickness)is probably the single most important thing you can do to make a design which is robust for molding and painting.Uniform wall stock parts mold with better filling and reduced internal stresses.Uniform wall stock parts cool and shrink more uniformly,reducing dimensional distortion and warpage.Corner RadiiMaintain constant part thickness in corner radii.Avoid Thick-thin-thick or Thin-thick-thin section transitions.Non-uniform thickness creates flow,stress,shrinkage,and warpage conditions in the part as the plastic cools and shrinks at different rates due to different thicknesses.Good!Thickness TransitionsAvoid sudden or sharp changes in section shape.Sudden changes affect flow and fill characteristics,and also create high stress concentrations in the part.Use smooth transitions between sections.Avoid Solid MassesPoor DesignGood DesignThick masses of solid plastic.Cools slowly.Some areas are thinner.Shrinks unevenly.Uniform constant thicknessOffset RibsOffset ribs can help hide sink marks and make them less visible.Sink marks and shrinkage are easier to hide when they occur on small radius surfaces.Sink marks are difficult to hide on large radius(flat)surfaces.It is generally good practice to place any ribs behind part surface feature lines,rather than behind flat surfaces.Rib Design PracticesAvoid thick rib features which can cause part warpage and surface sink marks.Avoid tall thin rib features which can buckle or bend under load.Rib Design GuidelinesRib design is largely affected by material selection.Consult with Resin suppliers and molders for assistance.Generally,we design a minimum of 3 degrees draft per side for ribs and surfaces for robust molding and ejection.Smaller draft can sometimes be used if you have agreement from your molder and tool shop.However,large ribs increase the chance of surface sink marks.0.3-0.4 TRib WarpageIt is always better to gain structure through surface shape change,rather than added ribs and gussets on the back side.Ribs add structure but can cause warpage due to cooling of non-uniform geometry.Fillers have a varied effect on cooling and warpage.It is difficult to predict,analyze,or control warpage from plastic rib structure.Glass Filled resinUn-Filled resinMultiple RibsSometimes a single large rib can be replaced by multiple smaller ribs to avoid sink marks,etc.Boss DesignsThis shows a typical boss design for a screw or stud for referenceDetails vary depending on materials and fastener design.Consult fastener and materials assistance.The important idea shown is to reduce the wall thickness of the molding at the bottom of the boss to reduce the sink mark on the surface due to the excess mass of material.Boss DesignsOpen boss design maintains uniform thickness in the part wall,and avoids a thin tool steel condition.Boss Core DepthWill form sink markWill form sink markGood,pin could be a little longer.Pin may be too long.Part may be too thin.Basic Part Design PracticesSome oils and coatings on fasteners attack PC and ABS+PC.Use Hi-Lo type threaded screws for direct engagement into TPO,ASA,and Nylon plastic bosses.Use metal threaded studs and inserts for high load attachments.Basic Part Design PracticesAvoid designing variable cross section areas because it allows material to flow faster in some areas than in others.Ejector pins sometimes interfere with cooling water circuits,and pins apply force only in small areas.Some parts eject better by controlling cooling rather than exerting mechanical force.Basic Part Design PracticesDraft angle of 3 degrees is normally used for painted exterior parts.More is added for grained parts.3+1.5/0.001 grain deepthAvoid sharp corners and stress concentrations.Taper the cross section of beam elements to distribute deflection energy and create constant-strain designs.Basic Part Design PracticesAvoid sharp radii on inside corners when possible,however adding radii can sometimes lead to non-uniform wall thickness and surface sink marks.Maintain constant wall thickness around corners on part flanges and throughout the part section.This is necessary to maintain constant cooling and shrinkage and to avoid warpage.Crown Height versus StiffnessSurface shape is an important method for gaining both stiffness and structure.It is almost always better to add stiffness using surface shape,rather than by adding ribs and gussets.Adding StiffnessParts can be made stiffer and also more dimensionally stable by the careful placement of flanges and section shape.Avoid adding ribs to increase stiffness.Increase stiffness by changing surface shape and profile.Core-Cavity ShutoffTooling action and cost can often be avoided by designing features to use only the core and cavity shutoff for forming the feature.Core-Cavity ShutoffMore examples of forming features without slides or lifters.This can often be used to form non-critical holes and slots in plastic parts without moveable pins.thanks