1、Plastic injection molding part checklistCao Hui2019-3-15优尔孚电子有限公司yoof1.Radii,FilletsSharp corners should be avoided.Sharp corners act as stress risers or concentrators,reducing part strength and causing premature failures.Sharp corners may also effect plastic flow,producing parts with objectionable
2、surface flow patterns Design rules:3.2 mm minimum radius requirement in the homologation.(Interior)2.5 mm minimum radius at the 100 mm ball contacting area.(Exterior)1 mm minimum radius at the seat belt passing through opening.Inside corner radii 50%of wall thickness Outside corner radii 150%of wall
3、 thickness Radii at base of ribs or bosses 0.25 mmRisks/potential issues:Excessive residual stress at the sharp corner.Poor mechanical properties.The plastic material is hard to flowyoofRadius and Stress-concentration factoryoofMaintain the uniform thickness at the corner.R2=R1+thickness.yoofRadius
4、helps the material flow.yoofWhy you supplier does not round at the base of the ribs?Sink mark concern.Hard to manufacture.Most of the ribs are manufactured by EDM.ToolElectrodeyoofWhich condition you did not need to add the radius.Parting Line.Undercut.Do not add radius at the inner edge of the unde
5、rcut.SliderNo radius at the parting lineyoof2.Wall ThicknessThe wall must be uniform and thick enough to flow,but thin enough to cool and stay fluid,the suitable thickness is a balance of strength and economy.Design rules:Maintain uniform part thickness in Class A surface sections.Minimum wall thick
6、nessthermoplastics:PC 2.5 mm,Nylon 1.6 mm,PP 2 mm,ABS 2.3 mmthermosets:3.2 mmthe thinnest ribs are not less than 0.8mm.Avoid sharp part edge.If non-uniform walls required:change in thickness should be 15%of the nominal wall and transition gradually.Local thickening of the part can be done based on t
7、he rule of 1%extra thickness using a transition of 5mm.Risks/potential issues:Thickness change too fast:flow line;Wall too thick:Sink marks,voids;Wall too thin:hard to fill full;Residual stress;Differential shrinkage/warpage caused by uneven cooling.yoofyoofIf you do need to change the part thicknes
8、syoof3.RibsRibs are usually used to increase the stiffness/strength of the plastic parts.Design rules:-40%max of wall thickness for appearance parts,non-grained or shallow(0.04 mm depth)A surface,if the resin shrinkage rate is bigger than 0.8%.-50%max of wall thickness for appearance parts,heavy gra
9、ined A surface -80%max of wall thickness for structural parts if sink marks ok Better to increase the number of ribs instead of increasing rib height For thick ribs core out the rib from the back to creates a hollow space and maintain uniform wall thickness For ribs height more than 15mm.use the ins
10、ert to help venting.The draft of the ribs height less than 15mm should be bigger than 0.5.Risks/potential issues:Read through.Sink marks.Short shot.yoofSink mark:Can be defined as a depression,resembling a dimple or groove.caused by excessive localized shrinking of the material after the part has co
11、oled.The plastic heat conduction rate is low,the plastic in the circle will keep cooling and shrinking when other plastic surround it already cool down,then pull the surface depress.yoofyoofyoofSink mark saverAll B-Side features which are on a tooling lifter and directly behind the Class A nominal w
12、all must have a sink saver feature designed into them.yoof4.BossesBosses are commonly used as locator,heat stake and screw receiver.Design rules:Avoid thick wall sections.Avoid sharp corners which cause stress concentrators and affect plastic flow.To avoid the sink mark,the thickness rule is the sam
13、e as ribs.Height of the boss 2 1/2 times the diameter of the hole in the boss.Outer diameter of boss 2.5 times the screw diameter for self-tapping screw applications.Thick-walled bosses with bases greater than 50%of the wall could form visible sink marks.Instead,design thinner walled boss of 2.0 tim
14、es screw diameter or less with multiple ribs.Avoid stand-alone bosses.Attach bosses to walls or ribs for structural stabilityRisks/potential issues:Sink mark.Boss is broken after screw.Boss deformedyoofIP Design RulesyoofIP Design RulesyoofIP Design RulesyoofHow to ensure the thickness is bigger eno
15、ugh for the screw,but would not have sink mark issue.yoofIf you need to design a boss at the corner.yoof5.Draft AnglesThe draft is in the offset angle in a direction parallel to die draw.Since plastics shrink when cooled,it is common for parts to shrink(or grip tightly)to cores.Design rules:The draf
16、t is more bigger,the force is smaller.The part is more easily be removed from the mold.1.0-2.0 draft angle on part walls.Ask the grain supplier for recommended draft if the parts need be grained.1.0-3.0 draft angle on ribs for themoplastics;and 5 draft angle for thermosets.Be careful,to the ribs,the
17、 base thickness should not be bigger than 40%the wall thickness.If minimum draft can not be avoided,polish the ribs and feature depth=20 mm.Risks/potential issues:Part sticking into tool,hence ejector pin marks on the part A surface.Scratch on the appearance surface.Common on the grain parts.yoofGra
18、in are undercuts on the cavity,the bigger the draft,the smaller the risk of scuffing the part.Heavy grain needs bigger draft.Ask the grain supplier to recommend the draft angle.yoofParts will leave core after certain distance ejection if there is draft.yoof6.Parting Lines.A mark on a molded piece wh
19、ere the sections of a multi-piece mold have met in closing.Usually,choose the outline of the part when project the part along the ejection direction.Design rules:Ask the supplier to mark the parting line on the part 3D model,and submit to PD to review.Avoid the parting line,ejector pins at below are
20、a:Visible Touchable.Functional MAX 0.06 mm Parting Line due to mold mis-match high touchable and visible area.Max 0.1 mm parting line in the invisible area.With close tolerances,the mold mating steel parts should take in an allowance for possible mismatches.The allowance should be in the 0.005 to 0.
21、010 range relative to the finished dimension.To some holes need be concentric,it should be formed in the same mold half.Risks/potential issues:Objectionable touch and appearance,flash,thin steel,sharp corner.yoofParting linesyoofMark the parting line on the part CADyoofHow to have 0 mismatch parting
22、 line.yoofConcentric holesNO OKOKyoofyoofLighting system design rulesFor lamp surfaces that form compression/interference sealing function,the seal surfaces must be free of any tooling irregularities.I.e.,surface must be free of:insert lines,parting lines or knockout pins when DVA of the sealing sur
23、face is included.yoofLighting system design rulesFor headlamps with second surface parting lines,there must be 1mm additional clearance between parting line surface and adjacent surfaces above and beyond minimum normal surface to surface clearance.yoof7.UndercutA feature prevent the part from direct
24、ly removing from the core or cavity.They are categorized into internal and external undercuts,where external undercuts are on the exterior of the part and interior undercuts are on the inside of the part.Design rules:Enough space for a lifter or slider near by the undercut.Be careful to add the radi
25、us at the edge.Use the tool shut-off to avoid undercut.Draft angle in the lifer/slider movement direction.Risks/potential issues:Parting line on the A surface.Thin lifter or slider.yoof8.Shut off angleDesign rules:When an opening is desired(such as to accommodate a snap-fit),and is to be formed with
26、out core pulls,a 5 angle mating of the core and cavity is required.Risks/potential issues:The core and cavity wear quickly,hence flash appears.yoofShut off to avoid to use lifter or sliders in the tool.yoofShut off to avoid to use lifter or sliders in the tool.yoofShut off surfaceCore insertCavity i
27、nsertyoof9.Analytical Mold FlowDesign rules:Use the CAE software to help decide the gate position.Predict weld line and vent locations (weld lines are not located in high stress areas.Weld lines and vents are not located on surface with stringent cosmetic quality requirement)Predict temperature dist
28、ribution-temperature difference does not exceed 10C or per benchmark analysis.Risks/potential issues:Appearance,functional,structural issues not found until 1st shot parts are made.yoof10.ShrinkageDesign rules:Material/resin:Crystalline and semi-crystalline materials exhibit higher shrinkage than am
29、orphous materials.Unreinforced plastics have higher shrinkage than reinforced grades.Select grade of material before the mold is constructed and specify proper mold shrinkage.Obtain basic shrinkage data from ASTM tests or ISO tests.Thick walls will have higher shrinkage rates than thin,variation in
30、section thickness can cause differential shrinkage and warpage;flow direction will effect shrinkage,particularly with glass fiber-reinforced grades(more when perpendicular to flow and less when parallel to flow.Process:As cavity pressure increases,shrinkage will decrease.The mold and melt temperatur
31、e influence shrinkage.Cooler molds will reduce shrinkage while hotter melt temperatures will increase shrinkage especially with semi-crystalline materials.Risks/potential issues:Stress and sink marks due to uneven shrinkage.Hard to meet the dimension requirements.Especially for those narrow and long
32、 parts.yoof11.GatingThe material go through the gate into the cavity and shaped as the desired part.Most of the injection imperfects are due to the wrong gate design or location.Design rules:Avoid gate are put at visible,touchable,functional area.Gates should be located to make sure the part was fil
33、led at the same time.the flow path is the shortest.Gates should be located at the thickest position.Gates should be located to make sure the gas could be vented at the flow period ending.Avoid the gate flow directly to the thin steel,small insert.Gates should be located away from high stress or impa
34、ct areas.Gate configuration and location should minimally affect part appearance.Gate design and location should eliminate secondary degating operations if possible.The gate should be located to best fill the part;position flow for advantageous glass fiber orientation if present and locate knit line
35、s in low-stress areas.Risks/potential issues:Knit lines,flow lines,sink marks at last fill areas,excessive shrinkage.blush.hard to fill,flash near by the gate,gate vestige.yoofGate type:Direct gateEdge gateFan gatePin gateTunnel gateCurved tunnel gate/Banana gateyoofDirect gateyoofTunnel gateyoofTun
36、nel gateyoofD shape tunnel gate(Flowerpot gate)yoofFan gateyoofGate recessionyoof12.EjectionDesign rules:Avoid ejection are put at visible,touchable,functional area.Ejection should be even.Ejector pin should be put near by the place warp tightly.Ejector pin should be big if possible.Ejector pin top
37、should be flat with core insert whenever possible.Risks/potential issues:warp age after ejection.ejector pin mark,scratch.yoofEjector pin affect the lighting sealingyoofEjection pad and ejector pinUse the ejector pad for deep ribsEjector pin,Most common ejector wayEjection typeyoofEjection padyoofSl
38、eeve is used for the height more than 15mm bossesSleeveSleeve ejectorEjector pinyoof13.Critical CharacteristicDesign Rules:If such feature is a control factor to your operation effort,interface with the other component.Make it easy to tune.i.e.inserts.Risks/potential issues:Infeasible to tune the to
39、ol.High tooling tuning costyoof14.CoolingDesign rules:waterline should be no less than 15 mm from part and parting line.Add the waterline at anywhere possible,lifter,slider.Cool the place near the sprue if possible.the temperature difference between the In and out“can not be bigger than 5 degree.the
40、 temperature difference between the cavity and core be bigger than 5 degree.Do not cool the predict weld line position.Use the Be-Cu for where hard to dissipate heat.Core and cavity water lines are to be perpendicular to each other wherever possibleRisks/potential issues:warpage,long cycle time.Blis
41、ter,crack.Excessive stress.yoofyoofyoof15.VentsClearance in the tool to allow the air to escape from the cavity.Venting is usually put on the parting line.Design rules:Vent the runner system.A cavity is adequately vented when plastic can be injected at high rates without showing signs of burn marks.The clearance between the two inserts.The clearance between the ejector pins and core.Vent inserts.The venting channel on the parting line.Risks/potential issues:Excessive injection pressure,short shots,burn marks,blushyoofyoofThanksyoof
