Molding Sec 7 - Plasticwright 3D Printing

1 Molding GE Plastics GE Engineering ThermoplasticsDESIGN GUIDED esign Wall Thickness Parting Lines Ejection Appearance Parts Ribs/Gussets Bosses Holes Depressions Radii, Fillets and CornersInjectionMolding Sec 6/16/99 10:13 AM Page 1 Guidelines for Injection Molded Design7-2 Guidelines for Injection Molded DesignA successful application of an engineering thermoplasticrequires more than identifying a specific product or areas design , product, process are all interrelatedand the appropriate rules in each area must be followed toensure a successful application.

2 In most cases, the processmust be determined before a specific resin grade can beselected. During this review, designers also need to considerwhether the process is capable of meeting the designrequirements such as size, shape, detail and Sec 6/16/99 10:13 AM Page 2 ContentsGuidelines for Injection Molded design 7-3 Wall Thickness ..7-4 Wall Thickness Considerations ..7-5 Parting Line and Ejection ..7-5 Appearance Parts ..7-7 Ribs ..7-9 Gussets ..7-10 Bosses ..7-11 Boss design for Fasteners.

3 7-13 Holes and Depressions ..7-14 Radii, Fillets and Corners ..7-15 Molding Sec 6/16/99 10:13 AM Page 3 Guidelines for Injection Molded Design7-4 Guidelines for Injection Molded DesignWall ThicknessThe typical plastic part may be considered to have a shell typeconfiguration with a basic surface and features which are attachedto it to meet functional requirements. From a moldability stand-point, the following are commonly regarded ProjectionsCored ProjectionsCore Out CornerSink AreaPoorGoodBestGuidelineThe basic wall of the partshould be kept provides for even flow of the melt during cooling and shrinkagethat controls part warpageand reduces molded in should be employedwhere possible to eliminatematerial masses in the results in more effi-cient designs and faster moreproductive cycle times.

4 It alsoprovides more uniform shrinkand avoids sink wall thickness transi-tions cannot be avoided, the transition should be made gradually, on the order of 3 to gradual transition avoidsstress concentrations andabrupt cooling part and the gatingshould be designed so themelt flows from the thicker section to the thinner avoids a restricted flowand reduces molded in also allows for more uniform Sec 6/16/99 10:13 AM Page 4 Wall Thickness/Parting Line and EjectionGuidelines for Injection Molded design 7-5 Wall Thickness ConsiderationsThe actual determination of the wall thickness is based on anumber of considerations.

5 These include: Application Requirements. Structural requirements including strength, impact, fatigue or deflection will beinfluenced by the wall thickness selected. Electrical loads may also impact on the wall thickness. Moldability. The size of the part and the ability of the material to fill the furthest point can determine the minimum wall. The maximum flow length is also a function of tool design with gate location and number of gates used. Agency requirements. For some agency properties, the rating is based on a minimum wall thickness which the part design must meet or exceed to satisfy an agencyrequirement.

6 This would be the case for UL flammability or Line and EjectionThe designer needs to consider how the mold will part and designin appropriate draft and shutoff. Often design changes to a featurecan eliminate the need for action in the mold, saving tooling costand maintenance costs later on. Guidelines relating to draft,shutoff and parting lines are offered ThicknessThe wall thickness specified typicallyshould meet all the considerationsnoted. From a cost standpoint, the thinnest wall utilizes the leastmaterial and results in the fastestmolding surfaces in the draw of thedie, a minimum of 1/2 shouldbe specified.

7 Typical draft is 1 .More draft aids ejection butmay generate a material masson sections contained in oneside of the is required for 2 0 POORBETTERG uidelineKeep features in the partingplane to simplify the a stepped parting line is required, allow 7 forshut off. Minimum shut offangle is 5 .BasisDrag at the shut off will wearover time and develop to restore moldto flash free parts will bemore PARTINGLINEDETAIL INPARTINGLINE7 Type5 OffAngleMolding Sec 6/16/99 10:13 AM Page 5 Guidelines for Injection Molded Design7-6 Guidelines for Injection Molded DesignP/LP/LPossible MismatchP/LMismatchP/LP/LAP/LP/LRequires side actionCan be molded in draw of dieP/LAAS ection A-A2 7 -5 DirectionMold Opening7 to5 H>3tBalde KnockoutKnockout atIntersectiontCoredOutMin Radius to ReduceIntersection ThicknessGuidelineSpecify mismatch on the parting establishes what isacceptable to the engineer forthe holes in the sidewalls so that the feature canbe obtained with

8 Shut off,thus reducing the need forside action in the advantage of designflexibility can simplify themold, reducing initial costsand minimizing maintenancethroughout deep ribs and protrusions,allow for knockouts on the topsof the ribs or at for ejection needto be incorporated into designas they are frequently greaterthan the section and must befree to travel during the ejec-tion Line and EjectionMolding Sec 6/16/99 10:13 AM Page 6 Appearance PartsGuidelines for Injection Molded design 7-7 Appearance PartsGuidelineTo maintain a Class A surfaceon a Molding , the side behindthe appearance surface mustbe free of projections anddepressions.

9 If a projectioncan not be avoided, then themaximum thickness at theintersection is half the nomi-nal wall subtle changes in the wallsection may read through ona high gloss, high quality sur-face. Even tooling lines madefrom sloppy fitting lifters mayread through noticeably onthe appearance relief may be availableto locate a structural ribopposite a Class A surface if a styling line runs directlyopposite the read through is maskedby the styling the use of textureon the appearance surface tomask read through of anydetail on the opposite texture breaks up a glossy surface and minor read through is not 1 additional draft for each in ( mm)

10 Depth in in draft angle isneeded to avoid scuffing and obtain proper SurfaceDraftMinimum DraftAngleWhere D = Texture Depth (in.)10 +D001"0 Molding Sec 6/16/99 10:13 AM Page 7 Guidelines for Injection Molded Design7-8 Guidelines for Injection Molded DesignP/LTextured In. In. surfaces stop a preferred in ( mm)or a minimum of in( mm) from any part-ing the textureimproves the durability of the parting or recessed letters on appearance surfaces have a minimum radius of in( mm).