1 part and mold DesignBayer CorporationTHERMOPLASTICSA Design GuidePart and mold DesignEngineering PolymersTHERMOPLASTICSKU-GE028 Copyright 2000, Bayer CorporationPrinted in (25M) 04/00 Printed on recycled paperBayer Corporation 100 Bayer Road Pittsburgh, PA 15205-9741 1-800-622-6004 Offices:California:9 Corporate Park Drive, Suite 240, Irvine, CA 92506-51131-949-833-2351 Fax: 1-949-752-1306 Michigan:2401 Walton Boulevard, Auburn Hills, MI 48325-19571-248-475-7700 Fax: 1-248-475-7701 New Jersey:1000 Route 9 North, Suite 103, Woodbridge, NJ 07095-12001-732-726-8988 Fax: 1-732-726-1672 Illinois:9801 W. Higgins Road, Suite 420, Rosemont, IL 60018-47041-847-692-5560 Fax: 1-847-692-7408 Canadian Affiliate:Ontario:Bayer Belfield Road, Etobicoke, Ontario M9W 1G61-416-248-0771 Fax: 1-416-248-6762 Quebec:Bayer Trans Canada Highway, Pointe Claire, Quebec H9R 1C81-514-697-5550 Fax: 1-514-697-5334 Note:The information contained in this bulletin is current as of April 2000.
2 Please contact Bayer Corporation to determine whether this publication has been manual focuses primarily on plastic part and mold Design , but alsoincludes chapters on the Design process;designing for assembly; machining andfinishing; and painting, plating, and decorating. For the most part , it excludesinformation covered in the followingBayer companion publications:Material Selection: Thermoplastics andPolyurethanes: A comprehensive look atmaterial testing and the issues to considerwhen selecting a plastic Techniques: Includes infor-mation and guidelines on the methodsfor joining plastics including mechanicalfasteners, welding techniques, inserts,snap fits, and solvent and adhesivebonding. Snap-Fit Joints for Plastics: Containsthe engineering formulas and workedexamples showing how to Design snap-fit joints for Bayer thermoplastic resins. A product of the Bayer DesignEngineering Services Group, this manualis primarily intended as a referencesource for part designers and moldingengineers working with Bayer thermo-plastic resins.
3 The table of contents andindex were carefully constructed toguide you quickly to the informationyou need either by topic or by content was also organized to allowthe manual to function as an educationaltext for anyone just entering the field ofplastic- part manufacturing. Conceptsand terminology are introduced pro-gressively for logical your Bayer sales representativefor copies of these publication was written specificallyto assist our customers in the Design andmanufacture of products made from theBayer line of thermoplastic engineeringresins. These resins include: Makrolon Polycarbonate Apec High-Heat Polycarbonate Bayblend Polycarbonate/ABS Blend Makroblend Polycarbonate Blend Triax Polyamide/ABS Blend Lustran and Novodur ABS Lustran SAN Cadon SMA Centrex ASA, AES and ASA/AES Weatherable Polymers Durethan Polyamide 6 and 66, and Amorphous Polyamide Texin and Desmopan Thermoplastic Polyurethane Pocan PBT Polyester1 Bayer CAMPUS: Software containingsingle and multi-point data that wasgenerated according to uniform you to search grades of Bayerresins that meet a particular set of performance requirements.
4 :BayerWeb site containing product informationon-line. This manual provides general informationand guidelines. Because each productapplication is different, always conducta thorough engineering analysis of yourdesign, and prototype test new designsunder actual in-use conditions. Applyappropriate safety factors, especially in applications in which failure couldcause harm or injury. Most of the Design principles covered inthis manual apply to all of these discussing guidelines or issuesfor a specific resin family, we referencethese materials either by their Bayertrade names or by their generic polymer type. The material data scattered throughoutthe chapters is included by way ofexample only and may not reflect themost current testing. In addition, muchof the data is generic and may differfrom the properties of specific resingrades. For up-to-date performance datafor specific Bayer resins, contact yourBayer sales representative or refer to thefollowing information sources:Bayer Engineering Polymers PropertiesGuide: Contains common single-pointproperties by resin family and Plastics Product InformationBulletin: Lists information and propertiesfor a specific material grade.
5 In addition to Design manuals, BayerCorporation provides Design assistancein other forms such as seminars andtechnical publications. Bayer also offersa range of Design engineering servicesto its qualified customers. Contact yourBayer sales representative for moreinformation on these other 1 part Design PROCESS: CONCEPT TO FINISHED PART7 Design Process8 Defining Plastic part Requirements8 Mechanical Loading8 Temperature8 Chemical Exposure8 Electrical Performance8 Weather Resistance8 Radiation8 Appearance9 Agency Approvals9 Life Expectancy9 Dimensional Tolerances9 Processing9 Production Quantities9 Cost Constraints10 Assembly10 Thermoplastic processing Methods10 Injection Molding11 Extrusion12 Thermoforming12 Blow Molding13 Rotomolding13 Optimizing Product Function14 Consolidation14 Hardware14 Finish15 Markings and Logos15 Miscellaneous15 Reducing Manufacturing Costs15 Materials 16 Overhead17 Labor17 Scrap and Rework17 Prototype TestingChapter 2 GENERAL DESIGN19 Wall Thickness22 Flow Leaders and Restrictors24 Ribs24 Rib Design24 Rib Thickness26 Rib Size27 Rib Location and Numbers27 Bosses30 Gussets30 Sharp Corners32 Draft33 Holes and Cores34
6 Undercuts34 Slides and Cores36 Louvers and Vents37 Molded-In Threads40 Lettering40 Tolerances42 Bearings and GearsTABLE OF CONTENTS34 Chapter 4 Design FOR ASSEMBLY83 part Consolidation84 Mechanical Fasteners85 Snap-Fit Joints88 Welding and Bonding89 Ultrasonic Welding90 Vibration and Hot-Plate Welding91 Spin Welding91 Solvent and Adhesive Bonding92 Retention Features92 Alignment Features94 Orientation94 Expansion Differences94 TolerancesChapter 5 MACHINING AND FINISHING97 Drilling and Reaming99 Tapping99 Sawing100 Punching, Blanking, and Die Cutting101 Milling101 Turning and Boring102 Laser Machining103 Filing103 Sanding103 Polishing and Buffing104 Trimming, Finishing, and Flash RemovalChapter 3 STRUCTURAL DESIGN45 Structural Considerations In Plastics46 Stiffness46 Viscoelasticity48 Stress-Strain Behavior50 Molding Factors51 Short-Term Mechanical Properties51 Tensile Properties52 Tensile Modulus52 Tensile Stress at Yield52 Tensile Stress at Break53 Ultimate Strength53 Poisson's Ratio53 Compressive Properties53 Flexural Modulus53 Coefficient of Friction54 Long-Term Mechanical Properties54 Creep Properties56 Stress Relaxation56 Fatigue Properties58 Structural Design Formulas58 Use of Moduli59 Stress and Strain Limits60 Uniaxial Tensile and Compressive Stress61 Bending and Flexural Stress65 Shear Stress66 Torsion67 Designing for Stiffness67 part Shape70 Wall Thickness71 Ribs73 Long-Term Loading76 Designing for Impact78 Fatigue Applications80 Thermal LoadingChapter 7 mold DESIGN121 mold Basics121 Types of
7 Molds124 mold Bases and Cavities125 Molding Undercuts128 part Ejection130 mold Venting130 Parting-Line Vents131 Vent Placement133 Sprues, Runners, and Gates133 Sprues134 Runners137 Runners for Multicavity Molds140 Gates144 Other Gate Designs145 Gate Optimization147 Gate Position149 Hot-Runner Systems149 Hot-Runner Designs149 Hot-Runner Gates151 Valve Gates151 Thermal Expansion and Isolation152 Flow Channel Size153 mold Cooling154 mold -Cooling Considerations155 Cooling-Channel Placement158 Cooling-Line Configuration159 Coolant Flow Rate160 mold Shrinkage162 mold Metals163 Surface Treatments164 mold Cost and QualityAPPENDICES165 Index169 part Design ChecklistChapter 6 PAINTING, PLATING, AND DECORATING105 Painting105 Types of Paints106 Paint Curing106 Paint-Selection Considerations107 Spray Painting108 Other Painting Methods108 Masking109 Other Design Considerations for Painting109 In- mold Decorating110 Film-Insert Molding111 Metallic Coatings111 Electroplating112 Design Considerations for Electroplating113 Molding Considerations for Electroplating114 Vacuum Metallization115 Design Considerations for Vacuum Metallization115 EMI/RFI Shielding115 Design Considerations for EMI/RFI Shielding116 Printing118 Labels and Decals119 Texture56 Chapter 1 part Design PROCESS:CONCEPT TO FINISHED PARTDESIGN PROCESSLike a successful play in football, successful plastic product Design andproduction requires team effort and awell-developed strategy.
8 When designingplastic parts, your team should consistof diverse players, including conceptualdesigners, stylists, Design engineers,materials suppliers, mold makers, manufacturing personnel, processors,finishers, and decorators. Your chanceof producing a product that successfullycompetes in the marketplace increaseswhen your strategy takes full advantageof team strengths, accounts for members limitations, and avoids overburdeningany one person. As the designer, youmust consider these factors early instrategy development and make adjustments based upon input from thevarious people on the Design team. Solicit simultaneous input from the var-ious players early in product develop-ment, before many aspects of the designhave been determined and cannot bechanged. Accommodate suggestions forenhancing product performance, or forsimplifying and improving the variousmanufacturing steps such as mold construction, processing , assembly, and finishing.
9 Too often designs passsequentially from concept developmentto manufacturing steps with featuresthat needlessly complicate productionand add factors affect plastic- part these factors are: functionalrequirements, such as mechanical loading and ultraviolet stability; aesthetic needs, such as color, level oftransparency, and tactile response; andeconomic concerns, such as cost ofmaterials, labor, and capital factors, coupled with otherdesign concerns such as agencyapproval, processing parameters, and part consolidation are discussed in this input from various Design andmanufacturing groups also helps tofocus attention on total product costrather than just the costs of individualitems or processes. Often adding a processing step and related cost in onearea produces a greater reduction intotal product cost. For example, addingsnap latches and nesting features mayincrease part and mold costs, and at thesame time, produce greater savings inassembly operations and related , specifying a more-expensiveresin with molded-in color and UVresistance may increase your raw-material cost, while eliminating painting costs.
10 When designing and developing parts,focus on defining and maximizing partfunction and appearance, specifyingactual part requirements, evaluatingprocess options, selecting an appropri-ate material, reducing manufacturingcosts, and conducting prototype the reasons stated above, theseefforts should proceed Exposure Plastic parts encounter a wide variety ofchemicals both during manufacturingand in the end-use environment, including mold releases, cutting oils,degreasers, lubricants, cleaning sol-vents, printing dyes, paints, adhesives,cooking greases, and automotive sure that these chemicals arecompatible with your selected materialand final Performance Note required electrical property valuesand nature of electrical loading. For reference, list materials that are knownto have sufficient electrical performancein your application. Determine if your part requires EMI shielding or UL testing.