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1、Part and Mold DesignBayer CorporationTHERMOPLASTICS A Design Guide Part and Mold Design Engineering Polymers THERMOPLASTICS KU-GE028Copyright 2000, Bayer CorporationPrinted in U.S.A. 570 (25M) 04/00 Printed on recycled paper Bayer Corporation 100 Bayer Road Pittsburgh, PA 15205-9741 1-800-622-6004 h
2、ttp:/ Sales Offices: California:9 Corporate Park Drive, Suite 240, Irvine, CA 92506-5113 1-949-833-2351 Fax: 1-949-752-1306 Michigan:2401 Walton Boulevard, Auburn Hills, MI 48325-1957 1-248-475-7700 Fax: 1-248-475-7701 New Jersey:1000 Route 9 North, Suite 103, Woodbridge, NJ 07095-1200 1-732-726-898
3、8 Fax: 1-732-726-1672 Illinois:9801 W. Higgins Road, Suite 420, Rosemont, IL 60018-4704 1-847-692-5560 Fax: 1-847-692-7408 Canadian Affiliate: Ontario:Bayer Inc. 77 Belfield Road, Etobicoke, Ontario M9W 1G6 1-416-248-0771 Fax: 1-416-248-6762 Quebec:Bayer Inc. 7600 Trans Canada Highway, Pointe Claire
4、, Quebec H9R 1C8 1-514-697-5550 Fax: 1-514-697-5334 Note:The information contained in this bulletin is current as of April 2000. Please contact Bayer Corporation to determine whether this publication has been revised. INTRODUCTION The manual focuses primarily on plastic part and mold design, but als
5、o includes chapters on the design process; designing for assembly; machining and finishing; and painting, plating, and decorating. For the most part, it excludes information covered in the following Bayer companion publications: Material Selection: Thermoplastics and Polyurethanes: A comprehensive l
6、ook at material testing and the issues to consider when selecting a plastic material. Joining Techniques: Includes infor- mation and guidelines on the methods for joining plastics including mechanical fasteners, welding techniques, inserts, snap fits, and solvent and adhesive bonding. Snap-Fit Joint
7、s for Plastics: Contains the engineering formulas and worked examples showing how to design snap- fit joints for Bayer thermoplastic resins. A product of the Bayer Design Engineering Services Group, this manual is primarily intended as a reference source for part designers and molding engineers work
8、ing with Bayer thermo- plastic resins. The table of contents and index were carefully constructed to guide you quickly to the information you need either by topic or by keyword. The content was also organized to allow the manual to function as an educational text for anyone just entering the field o
9、f plastic-part manufacturing. Concepts and terminology are introduced pro- gressively for logical cover-to-cover reading. Contact your Bayer sales representative for copies of these publications. This publication was written specifically to assist our customers in the design and manufacture of produ
10、cts made from the Bayer line of thermoplastic engineering resins. These resins include: MakrolonPolycarbonate ApecHigh-Heat Polycarbonate BayblendPolycarbonate/ ABS Blend MakroblendPolycarbonate Blend TriaxPolyamide/ABS Blend Lustranand NovodurABS LustranSAN CadonSMA CentrexASA, AES and ASA/AES Weat
11、herable Polymers DurethanPolyamide 6 and 66, and Amorphous Polyamide Texinand Desmopan Thermoplastic Polyurethane PocanPBT Polyester 1 Bayer CAMPUS: Software containing single and multi-point data that was generated according to uniform standards. Allows you to search grades of Bayer resins that mee
12、t a particular set of performance requirements. Bayer Web site containing product information on-line. This manual provides general information and guidelines. Because each product application is different, always conduct a thorough engineering analysis of your design, and prototype test new design
13、s under actual in-use conditions. Apply appropriate safety factors, especially in applications in which failure could cause harm or injury. Most of the design principles covered in this manual apply to all of these resins. When discussing guidelines or issues for a specific resin family, we referenc
14、e these materials either by their Bayer trade names or by their generic polymer type. The material data scattered throughout the chapters is included by way of example only and may not reflect the most current testing. In addition, much of the data is generic and may differ from the properties of sp
15、ecific resin grades. For up-to-date performance data for specific Bayer resins, contact your Bayer sales representative or refer to the following information sources: Bayer Engineering Polymers Properties Guide: Contains common single-point properties by resin family and grade. Bayer Plastics Produc
16、t Information Bulletin: Lists information and properties for a specific material grade. In addition to design manuals, Bayer Corporation provides design assistance in other forms such as seminars and technical publications. Bayer also offers a range of design engineering services to its qualified cu
17、stomers. Contact your Bayer sales representative for more information on these other services. 2 Chapter 1 PART DESIGN PROCESS: CONCEPT TO FINISHED PART 7Design Process 8Defining Plastic Part Requirements 8Mechanical Loading 8Temperature 8Chemical Exposure 8Electrical Performance 8Weather Resistance
18、 8Radiation 8Appearance 9Agency Approvals 9Life Expectancy 9Dimensional Tolerances 9Processing 9Production Quantities 9Cost Constraints 10Assembly 10Thermoplastic Processing Methods 10Injection Molding 11Extrusion 12Thermoforming 12Blow Molding 13Rotomolding 13Optimizing Product Function 14Consolida
19、tion 14Hardware 14Finish 15Markings and Logos 15Miscellaneous 15Reducing Manufacturing Costs 15Materials 16Overhead 17Labor 17Scrap and Rework 17Prototype Testing Chapter 2 GENERAL DESIGN 19Wall Thickness 22Flow Leaders and Restrictors 24Ribs 24Rib Design 24Rib Thickness 26Rib Size 27Rib Location an
20、d Numbers 27Bosses 30Gussets 30Sharp Corners 32Draft 33Holes and Cores 34Undercuts 34Slides and Cores 36Louvers and Vents 37Molded-In Threads 40Lettering 40Tolerances 42Bearings and Gears TABLE OF CONTENTS 3 4 Chapter 4 DESIGN FOR ASSEMBLY 83Part Consolidation 84Mechanical Fasteners 85Snap-Fit Joint
21、s 88Welding and Bonding 89Ultrasonic Welding 90Vibration and Hot-Plate Welding 91Spin Welding 91Solvent and Adhesive Bonding 92Retention Features 92Alignment Features 94Orientation 94Expansion Differences 94Tolerances Chapter 5 MACHINING AND FINISHING 97Drilling and Reaming 99Tapping 99Sawing 100 Pu
22、nching, Blanking, and Die Cutting 101 Milling 101 Turning and Boring 102 Laser Machining 103 Filing 103 Sanding 103 Polishing and Buffing 104 Trimming, Finishing, and Flash Removal Chapter 3 STRUCTURAL DESIGN 45Structural Considerations In Plastics 46Stiffness 46Viscoelasticity 48Stress-Strain Behav
23、ior 50Molding Factors 51Short-Term Mechanical Properties 51Tensile Properties 52Tensile Modulus 52Tensile Stress at Yield 52Tensile Stress at Break 53Ultimate Strength 53Poissons Ratio 53Compressive Properties 53Flexural Modulus 53Coefficient of Friction 54Long-Term Mechanical Properties 54Creep Pro
24、perties 56Stress Relaxation 56Fatigue Properties 58Structural Design Formulas 58Use of Moduli 59Stress and Strain Limits 60Uniaxial Tensile and Compressive Stress 61Bending and Flexural Stress 65Shear Stress 66Torsion 67Designing for Stiffness 67Part Shape 70Wall Thickness 71Ribs 73Long-Term Loading
25、 76Designing for Impact 78Fatigue Applications 80Thermal Loading Chapter 7 MOLD DESIGN 121 Mold Basics 121 Types of Molds 124 Mold Bases and Cavities 125 Molding Undercuts 128 Part Ejection 130 Mold Venting 130Parting-Line Vents 131Vent Placement 133 Sprues, Runners, and Gates 133Sprues 134Runners 1
26、37Runners for Multicavity Molds 140Gates 144Other Gate Designs 145Gate Optimization 147Gate Position 149 Hot-Runner Systems 149Hot-Runner Designs 149Hot-Runner Gates 151Valve Gates 151 Thermal Expansion and Isolation 152Flow Channel Size 153 Mold Cooling 154Mold-Cooling Considerations 155Cooling-Cha
27、nnel Placement 158Cooling-Line Configuration 159Coolant Flow Rate 160 Mold Shrinkage 162 Mold Metals 163 Surface Treatments 164 Mold Cost and Quality APPENDICES 165 Index 169 Part Design Checklist Chapter 6 PAINTING, PLATING, AND DECORATING 105 Painting 105Types of Paints 106Paint Curing 106Paint-Se
28、lection Considerations 107Spray Painting 108Other Painting Methods 108Masking 109Other Design Considerations for Painting 109 In-Mold Decorating 110 Film-Insert Molding 111 Metallic Coatings 111Electroplating 112Design Considerations for Electroplating 113Molding Considerations for Electroplating 11
29、4Vacuum Metallization 115Design Considerations for Vacuum Metallization 115EMI/RFI Shielding 115Design Considerations for EMI/RFI Shielding 116 Printing 118 Labels and Decals 119 Texture 5 6 Chapter 1 PART DESIGN PROCESS: CONCEPT TO FINISHED PART DESIGN PROCESS Like a successful play in football, su
30、ccessful plastic product design and production requires team effort and a well-developed strategy. When designing plastic parts, your team should consist of diverse players, including conceptual designers, stylists, design engineers, materials suppliers, mold makers, manufacturing personnel, process
31、ors, finishers, and decorators. Your chance of producing a product that successfully competes in the marketplace increases when your strategy takes full advantage of team strengths, accounts for members limitations, and avoids overburdening any one person. As the designer, you must consider these fa
32、ctors early in strategy development and make adjustments based upon input from the various people on the design team. Solicit simultaneous input from the var- ious “players” early in product develop- ment, before many aspects of the design have been determined and cannot be changed. Accommodate sugg
33、estions for enhancing product performance, or for simplifying and improving the various manufacturing steps such as mold construction, processing, assembly, and finishing. Too often designs pass sequentially from concept development to manufacturing steps with features that needlessly complicate pro
34、duction and add cost. Many factors affect plastic-part design. Among these factors are: functional requirements, such as mechanical loading and ultraviolet stability; aesthetic needs, such as color, level of transparency, and tactile response; and economic concerns, such as cost of materials, labor,
35、 and capital equipment. These factors, coupled with other design concerns such as agency approval, processing parameters, and part consolidation are discussed in this chapter. Early input from various design and manufacturing groups also helps to focus attention on total product cost rather than jus
36、t the costs of individual items or processes. Often adding a processing step and related cost in one area produces a greater reduction in total product cost. For example, adding snap latches and nesting features may increase part and mold costs, and at the same time, produce greater savings in assem
37、bly operations and related costs. Likewise, specifying a more-expensive resin with molded-in color and UV resistance may increase your raw- material cost, while eliminating painting costs. When designing and developing parts, focus on defining and maximizing part function and appearance, specifying
38、actual part requirements, evaluating process options, selecting an appropri- ate material, reducing manufacturing costs, and conducting prototype testing. For the reasons stated above, these efforts should proceed simultaneously. 7 Chemical Exposure Plastic parts encounter a wide variety of chemical
39、s both during manufacturing and in the end-use environment, including mold releases, cutting oils, degreasers, lubricants, cleaning sol- vents, printing dyes, paints, adhesives, cooking greases, and automotive fluids. Make sure that these chemicals are compatible with your selected material and fina
40、l part. Electrical Performance Note required electrical property values and nature of electrical loading. For reference, list materials that are known to have sufficient electrical performance in your application. Determine if your part requires EMI shielding or UL testing. Weather Resistance Temper
41、ature, moisture, and UV sun exposure affect plastic parts properties and appearance. The end-use of a product determines the type of weather resistance required. For instance, external automo- tive parts such as mirror housings must withstand continuous outdoor exposure and perform in the full range
42、 of weather conditions. Additionally, heat gain from sun on dark surfaces may raise the upper temperature requirement considerably higher than maximum expected temper- atures. Conversely, your requirements DEFINING PLASTIC PART REQUIREMENTS Thoroughly ascertain and evaluate your part and material re
43、quirements, which will influence both part design and material selection. When evaluating these requirements, consider more than just the intended, end-use conditions and loads: Plastic parts are often sub- jected to harsher conditions during manufacturing and shipping than in actual use. Look at al
44、l aspects of part and material performance including the following. Mechanical Loading Carefully evaluate all types of mechanical loading including short-term static loads, impacts, and vibrational or cyclic loads that could lead to fatigue. Ascertain long-term loads that could cause creep or stress
45、 relaxation. Clearly identify impact requirements. Temperature Many material properties in plastics impact strength, modulus, tensile strength, and creep resistance to name a few vary with temperature. Consider the full range of end-use temperatures, as well as temperatures to which the part will be
46、 exposed during manufacturing, finishing, and shipping. Remember that impact resistance generally diminishes at lower temperatures. may be less severe if your part is exposed to weather elements only occasionally. For example, outdoor Christmas decorations and other season- al products may only have
47、 to satisfy the requirements for their specific, limited exposure. Radiation A variety of artificial sources such as fluorescent lights, high-intensity dis- charge lamps, and gamma sterilization units emit radiation that can yellow and/or degrade many plastics. If your part will be exposed to a radi
48、ation source, consider painting it, or specifying a UV-stabilized resin. Appearance Aesthetic requirements can entail many material and part-design issues. For example, a need for transparency greatly reduces the number of potential plastics, especially if the part needs high clarity. Color may also
49、 play an important role. Plastics must often match the color of other materials used in parts of an assembly. Some applications require the plastic part to weather at the same rate as other materials in an assembly. 8 Chapter 1 PART DESIGN PROCESS: CONCEPT TO FINISHED PART continued contact, United States Department of Agriculture (USDA) for plastics in meat and poultry equipment, and National Sanitation Foundation Testing Laboratory, Inc. (NSF) for plastics in food-