1 Rapid Guidelines for Joining of Plastics and Efficient Use of This Handbook... 1

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1 1 Rapid Guidelines for Joining of Plastics and Efficient Use of This Handbook Efficient Use of This Handbook Rapid Guidelines for Assembly of Plastics Adhesives (Chapter 7) Liquids: Solvent-Based, Water-Based, and Anaerobic Adhesives Mastics Hot Melts Pressure-Sensitive Adhesives Fasteners and Inserts (Chapter 8) Hinges (Chapter 9) Hot Plate/Hot Die/Fusion and Hot Wire/Resistance Welding (Chapter 10) Hot Gas Welding (Chapter 11) Induction Welding (Chapter 12) Insert Molding (Chapter 13) Multipart Molding (Chapter 13) Press Fits/Force Fits/Interference Fits/Shrink Fits (Chapter 14) Solvent Joining (Chapter 7) Snap Fits (Chapter 15) Spin Welding (Chapter 16) Staking/Swaging/Peening/Cold Heading/Cold Forming (Chapter 17) Threads Molded in (Chapter 18) Threads Tapped (Chapter 18) Ultrasonic Welding (Chapter 19) Vibration Welding (Chapter 20) Welding with Lasers (Chapter 21) Assembly Methods Selection by Size Assembly Methods Selection by Joining Time Designing for Efficient Assembly Avoiding Part Distortion Inside Corner Stress Ribs and Bosses Draft Shrinkage Fitments Drawing Conventions for Plastic Assembly Importance of Tolerancing for Assembly Special Drafting Practices for Plastics Procedure for Establishing Tolerances Design Practices for Looser Tolerances in Plastics Three-Point Location... 28

2 xiv Contents Hollow Bosses Crush Ribs Flexible Ribs Inside/Outside Fitments Step Fitments More Relaxed Tolerances for Large Parts Drill in Place Oversize Hole with Washer Criss Cross Slots Separation of Functions Corner Clearance Semidovetail Joint Minimizing the Effect of Misalignment on Appearance The Plastic Product Design for Assembly Checklist Testing Cost Reduction In Assembly Introduction The Micro Approach to Part Reduction Combining Parts Through Materials Combining Parts Through Processes The Macro Approach to Part Reduction Multiple Material Processing Coextrusion Coinjection Molding Multipart or Two-Color Injection Molding Elimination of Fasteners Multiple Parts per Fastener Press and Snap Fits Integral Hinges Combining Fastener Elimination Concepts Holistic Design The Overall Design Considerations The Thread Design The Processing Considerations The Tooling Considerations Execution Toward Holistic Design Design for Disassembly and Recycling Introduction Design for Disassembly Reopenable Assemblies Permanent Assemblies Design for Recycling Simplification Assembly Method Selection... 65

3 xv Reopenable Methods Permanent Methods Material Selection Additives Contaminants Material Reduction Identification and Disassembly Instructions Assembly Method Selection by Material Thermoplastics Versus Thermosets Amorphous Versus Semicrystalline Thermoplastics Postmolding Shrinkage Coefficient of Linear Thermal Expansion Weldability Solvent Sealability Thermosets Assembly Method by Material Properties and Assembly-Related Data for Selected Materials Adhesives Using the SPI Tables Material Databases Material Suppliers Assembly Method Selection by Process Introduction Blow Molding The Process Assembly Considerations Casting, Potting, Encapsulation, and Embedment The Processes Assembly Considerations Coextrusion Co-Injection Molding Cold Press Molding The Process Assembly Considerations Compression Molding The Process BMC: Bulk Molding Compound SMC: Sheet Molding Compound Assembly Considerations Extrusion The Process Coextrusion Assembly Considerations Filament Winding The Process Assembly Considerations

4 xvi Contents 6.10 Gas-Assisted Injection Molding Gas Counter Pressure Structural Foam Molding Injection Molding The Process Assembly Considerations Lay-up and Spray-up The Processes Assembly Considerations Machining The Process Thermoplastics Thermosets Assembly Considerations Pultrusion The Process Assembly Considerations Reaction Injection Molding (RIM) The Process Assembly Considerations Resin Transfer Molding (RTM) The Process Assembly Considerations Rotational Molding The Process Assembly Considerations Structural Foam Molding, Gas Counterpressure Structural Foam Molding, and Coinjection Molding The Processes Assembly Considerations Thermoforming The Processes Thin-Gauge Thermoforming Heavy-Gauge Thermoforming Pressure Thermoforming Other Forming Processes Assembly Considerations Twin-Sheet Thermoforming The Process Assembly Considerations Transfer Molding The Process Assembly Considerations Process Selection Thermoplastic Open Shapes Thermoset Open Shapes Hollow Parts Profiles Ultra High Strength

5 xvii 7 Adhesive and Solvent Joining Advantages and Disadvantages Advantages Disadvantages Basic Theory and Terminology Methods for Measuring the Wettability of a Plastic Surface Contact Angle Test Wetting Tension Test (ASTM D , Wetting Tension of Polyethylene and Polypropylene Films) Adhesion Ratio Test (Tentative ASTM D R) Water Spreading Test Dye Stain Test Ink Retention Test Surface Treatments Solvent Cleaning Solvent Immersion Solvent Wiping Solvent Spray Vapor Degreasing Ultrasonic Vapor Degreasing Ultrasonic Cleaning with Liquid Rinse Abrasive Methods Dry Abrasion Dry Abrasive Blast Wet Abrasive Blast Wet Abrasive Scour Detergent Scrub Surface Energy Treatments and Process Selection Factors Chemical Treatment Corona Treatment Plasma Treatment Flame Treatment Process Selection Factors Shelf Life of Surface Treatments Design for Adhesion Shear Stress Tensile Stress Cleavage Peel Adhesive Joint Designs Load-Bearing or Non-Load-Bearing Joints Lap Joints Butt Joints Screw and Glue Adhesives Acrylics Anaerobics Cyanoacrylates

6 xviii Contents Epoxies Hot Melts Phenolics Polyurethanes Polysulfides Pressure-Sensitive Adhesives Silicones Solvent-Based Adhesives Water-Based Adhesives Solvents Adhesive and Solvent Assembly Techniques Fixturing Clamping Application Methods Capillary Method Dip or Soak Method Adhesive and Solvent System Selection Glossary Sources Fasteners and Inserts Advantages and Disadvantages Advantages of Using Fasteners Disadvantages of Using Fasteners Basic Design Considerations for Fasteners Creep Effects Stress Relaxation Effects Notch Sensitivity Craze Resistance Stiffness Considerations Differentials in the Coefficients of Linear Thermal Expansion Loss of Properties Due to Moisture Clamp Load Strain Method Torque Method Vibration Resistance Methods of Using Fasteners with Plastics Press-in Fasteners Self-Tapping Screws Strength of Plastic Threads Thread-Forming and Thread-Cutting Screws Special Screws for Plastics Narrow Thread Forms Alternating Thread Heights Asymmetrical Thread Forms Selection of Self-Tapping Screws Cost Criteria Fail/Drive Ratio and Differential

7 xix Strength Criteria Thread Cutting or Thread Forming Tapped or Molded-in Threads Threaded Inserts: Advantages Boss Cap Helical Coil Inserts Self-Tapping Inserts Press-in Inserts Glue-in Inserts Expansion Inserts Molded-in Inserts Ultrasonic Inserts Heat-Installed Inserts Induction Inserts Hermetic Seals Studs Insert Design Considerations U- or J-Clips Tee Nuts Machine Screws Tapping and Stud Plates Plastic Screws Screw Heads and Washers Boss Designs Design Criteria Boss Sinks Coring Location Support Material Surface Treatment Weld Lines Self-Threading Nuts Twist Nuts Press-on Nuts Spring Clips Push-in Fasteners Rivets Sources Fasteners and Inserts Threaded-Insert Thermal Insertion Equipment Induction Insertion Equipment Ultrasonic Insertion Equipment Hinges Advantages and Disadvantages Advantages

8 xx Contents Disadvantages One-Piece Integral Hinges The Living Hinge Living Hinge Design Living Hinge Molding Considerations Living Hinges by Other Processes The Mira Spring Hinge Standard Hinges Tab Hinges Two-Piece Plastic Hinges Ball-and-Socket Hinges Two-Piece Lug-and-Pin Hinges Hook-and-Eye Hinges Three-Piece Hinges Three-Piece Lug and Pin Piano Hinge Latches Snaps Rathbun Spring Number of Hinges and Location Hot Plate/Hot Die/Fusion and Hot Wire/Resistance Welding Advantages and Disadvantages Description Advantages Disadvantages Materials The Process Types of Hot Plate Welding Low Temperature Hot Plate Welding High Temperature Hot Plate Welding Noncontact Hot Plate Welding Hot Plate Welding Joint Designs Equipment Hot Wire/Resistance Welding Sources Hot Gas Welding Advantages and Disadvantages Advantages Disadvantages The Process Tack Welding Permanent Hot Gas Welding High Speed Welding Extrusion Welding Joint Designs Welding Practice

9 xxi Appearance Problems Cracking Problems Distortion Fusion Problems Penetration Porosity Scorching Testing the Weld Nondestructive Testing Visual Examination Leak Tests Destructive Tests Tensile Test Bending Test Rod Removal Test Chemical Test Spark Test Applications Sources Welding Rods Welding Equipment Welding Rod And Equipment Induction/Electromagnetic Welding Description Advantages and Disadvantages Advantages Disadvantages The Equipment The Process The Coil Single-Turn Coils Hairpin Coils Multi-Turn Coils Split Coils Other Types of Coils Coil Positioning Flux Concentrators Materials Polymers The Electromagnetic Material Molded-in Pre-Forms Hot Melt Electromagnetic Materials Liquid Electromagnetic Materials Joint Designs Encapsulation Film and Sheeting Intermittent Sealing

10 xxii Contents Continuous Sealing Inserting Metal into Plastic Sources Insert and Multipart Molding Description Insert Molding Advantages of Insert Molding Disadvantages of Insert Molding Design with Threaded Inserts Mold Considerations for Threaded Inserts Custom-Designed Inserts Outserts: Inserts Larger than the Moldment Hermetic Seals Preparation of Inserts Decorative Inserts Multi-Part Molding Description Advantages Particular to Multi-part Molding Disadvantages Particular to Multi-part Molding The Process Materials Sources Press Fits/Force Fits/ Interference Fits/Shrink Fits Advantages and Disadvantages Advantages Disadvantages Press Fit Engineering Engineering Notation Geometric Factor Changes Due to Temperature Variations Hoop Stress Metal Shaft in Plastic Boss Shaft and Boss of Same Material Shaft and Boss of Different Plastics Quick Methods Assembly and Disassembly Forces Dimensional Changes Due to Assembly Relationships Equation Limitations Safety Factor Processing Material Selection Part Design Heavy-Duty Press Fits Light-Duty or Reopenable Press Fits Other than Round

11 xxiii 14.7 Case Studies Determination of Changes in Diameter Due to Temperature Variations The Geometric Factor for Use In Press Fit Equations Determination of Design Stress and for a Metal Shaft in a Plastic Boss Maximum Allowable Interference for a Metal Shaft in a Plastic Boss Dimensional Changes Due to Assembly Metal Shaft in Plastic Boss Plastic Shaft and Metal Boss Determination of Design Stress and Maximum Allowable Interference for a Shaft and Boss of the Same Material Determination of Design Stress and Maximum Allowable Interference for a Shaft and Boss of Different Plastics Determination of Assembly and Disassembly Forces Determination of Torsional Holding Capacity Snap Fits Advantages and Disadvantages Advantages Disadvantages General Applications General Engineering Principles Allowable Dynamic Strain Corner Stress Concentrations Engineering Adjustments When Both Parts Are Elastic Finite Element Analysis Cantilever Snap Fits Cantilever Snap Fit Designs Cantilever Snap Fit Engineering Cylindrical, Ring, Perimeter, or Annular Snap Fits Cylindrical Snap Fit Designs Engineering of Cylindrical, Ring, Perimeter, or Annular Snap Fits Maximum Permissible Interference Transverse and Axial Forces Torsion Snap Fits Torsion Snap Fit Designs Engineering of Torsion Snap Fits Strippable Snap Fits The Injection Molding Process Molds for Snap Fits The Basics of Injection Mold Construction Ejection and Cooling Systems for Stripping Molds Cores for Nonstripping Molds Snap Fit Details in the Mold Cavity Conclusions Case Studies Cantilever Snap Fit Determination of Permissable Deflection Cantilever Snap Fit Determination of Radial and Mating Forces

12 xxiv Contents Annular Snap Fit Determination of Maximum Permissable Interference Annular Snap Fit Determination of Maximum Design Strain Annular Snap Fit Determination of Transverse and Axial Forces for a Snap Fitment Located Near the End of the Tube Annular Snap Fit Determination of Transverse and Axial Forces for a Snap Fitment Located Remote From the End of the Tube Self-locking Angle Spin Welding Description of Spin Welding Advantages and Disadvantages of Spin Welding Advantages Disadvantages Spin Welding Process Materials Design for Spin Welding Overall Design Considerations Joint Designs The Equipment for Spin Welding Drill-Press-Based Spin Welders Tooling for Drill-Press-Based Inertial Welding Tooling for Drill-Press-Based Pivot Tool Welding Commercial Inertia Spin Welders Commercial Direct-Drive Spin Welders Sources Staking/Swaging/Peening/ Cold Heading/Cold Forming Advantages and Disadvantages of Staking/ Cold Forming Advantages Disadvantages Staking Cold Forming of Stakes Hot Air/Cold Staking Ultrasonic Cold Forming Hot Die Forming of Stakes (Thermal Staking) Ultrasonic Hot Forming of Stakes Laser Staking Stake Design The Stud Stake Heads Swaging Sources Thermal Staking Hot Air/Cold Staking Laser Staking Ultrasonic

13 xxv 18 Threads: Tapped and Molded-in Advantages and Disadvantages of Integral Threads Advantages Common to Threads of Both Types Disadvantages Common to Threads of Both Types Drilled and Tapped Holes in Plastics Advantages Unique to Tapped Threads Disadvantages Unique to Tapped Threads Drilling Holes in Plastics Reaming Holes in Plastics Tapping Holes in Plastics Molded Threads in Plastics Advantages Unique to Molded-in Threads Disadvantages Unique to Molded-in Threads Thread Design Molds for Threads Stripping Molds for Internal Threads Collapsing Core Molds for Internal Threads Expandable Cavity Molds for External Threads Split-Cavity Molds for External Threads Unscrewing Molds for Internal Threads Unscrewing Chuck Plate Mold Molds for Parts with Less than One Turn of Thread Sources Collapsing Cores and Cavities Unscrewing Chuck Ultrasonic Welding Advantages and Disadvantages of Ultrasonic Welding Advantages Disadvantages General Applications The Principle of Ultrasonic Welding Materials for Ultrasonic Welding Additives and Contaminants Colorants Fillers, Extenders, and Fibrous Reinforcements Flame Retardants Foaming Agents Impact Modifiers Lubricants Mold Releases Painted Parts Plasticizers Regrind Part Design for Ultrasonic Welding Overall Ultrasonic Welding Considerations Strength Requirements Appearance Requirements

14 xxvi Contents Rigidity Considerations Joint Fundamentals Part Alignment Uniform Vibration Travel Distance Minimal Initial Contact Area Energy Director Joints Butt Joint Joint Layout Textured Surface Step Joint Tongue-and-Groove Joint Thin-Walled Joint Shear Joints Hermetic Seals Scan Welding Stud Welding, Staking, Swaging, and Spot Welding Staking and Swaging Stud Welding Spot Welding Fabric and Film Sealing The Ultrasonic Equipment The Basic Principles The Power Supply or Generator The Converter or Transducer The Booster The Horn The Fixture The Controls Equipment Frequency Automation of Ultrasonic Welding Sources Vibration Welding Advantages and Disadvantages Comparison with Ultrasonic Welding Advantages of Vibration Welding Disadvantages of Vibration Welding The Process of Vibration Welding Linear Vibration Welding Orbital Vibration Welding Angular Vibration Welding Materials Vibration Welding Part Design Basic Considerations Joint Designs for Linear Vibration Welding The Equipment Sources

15 xxvii 21 Welding with Lasers Advantages and Disadvantages Non-Contact, Surface, Direct, or Butt Laser Welding Laser Staking Through Transmission Infra-Red Laser Welding Advantages of Through Transmission Laser Welding Disadvantages of Through Transmission Laser Welding The Process of Laser Welding The Laser Basic Through Transmission Laser Welding Methods Spot or Contour Welding Simultaneous Through Transmission Infra-Red (STTIr) Laser Welding (Also Known as Simultaneous Line or Flash Welding) Quasi-Simultaneous Laser Welding Mask Welding (Leister Patented Process) Materials for Laser Welding Material Properties Affecting Laser Weldability Effects of Refraction Properties on Material Selection Effects of Pigments, Fillers, and Additives on Light Transmission Laser Welding Transmitting Materials Compatibility of Plastics for Laser Welding Joint Designs Equipment Applications Sources References Index

FUNDAMENTAL MANUFACTURING PROCESSES Plastics Machining & Assembly NARRATION (VO): AN ASSEMBLY METHOD. NARRATION (VO): MANUALLY..., OR AUTOMATICALLY.

Copyright 2002 Society of Manufacturing Engineers --- 1 --- FUNDAMENTAL MANUFACTURING PROCESSES Plastics Machining & Assembly SCENE 1. CG: Plastics Assembly white text centered on black SCENE 2. tape 739,