Citation preview
DONALD V. ROSATO, PH.D.
Kluwer Academic Publishers Boston/Dordrecht/London
Distributors for North, Central and South America: Kluwer Academic
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\A Electronic Services < http://www.wkap.nl> c,r Library of
Congress Cataloging-in-Publication Data
Injection molding handbook / Dominick V. Rosato, Donald V. Rosato,
Marlene G. Rosato. - 3rd ed.
p. cm. ISBN 0-7923-8619-1 1. Injection molding of
plastics-Handbooks, manuals, etc. I. Rosato, Dominick
Rosato, Donald V. 111. Rosato, Marlene G. 7. I
TP1150.155 2000 668.4' 12-dc2 1
99-049946
Copyright 0 2000 by Kluwer Academic Publishers.
All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system or transmitted in any form or by any
means, mechanical, photo-copying, recording, or otherwise, without
the prior written permission of the publisher, Kluwer Academic
Publishers, 101 Philip Drive, Assinippi Park, Norwell,
Massachusetts 02061
Printed on acid-free paper.
Contents
Preface Chapter 1 The Complete Injection Molding Process
Introduction Machine Characteristics Molding Plastics Molding
Basics and Overview
People and Productivity 6; Plastic Materials 6; Morphology and
Performance 9; Melt Flow and Rheology 11; Plasticating 12; Screw
Designs 14; Molds 15; Processing 16; Process Controls 18; Control
Guides 20; Art of Processing 21; Fine Tuning 21
Automatic 22; Semiautomatic 22; Manual 22; Pri- mary 23; Secondary
23
Molding Operations
Training Programs Processor Certifications Plastics Machinery
Industry Summary
Captive 23; Custom 24; Proprietary 24
Chapter 2 Injection Molding Machines Introduction Reciprocating
(Single-Stage) Screw Machines Two-Stage Machines
Reciprocating vs. Two-Stage Machines Other Machine Types Machine
Operating Systems Hydraulic Operations
Injection Hydraulic Accumulator 32
Reservoirs 40; Hydraulic Controls 42: Propor- tional Valves 42;
Servovalves 43: Digital Hydraulic Control 43: Hydraulic Fluids and
Influence of
xxix 1 1 4 4 4
22
vi Contents
Heat 44; Pumps 44; Directional Valves 45; Servo and Proportional
Valves 46
Electric Motors 47; Adjustable-Speed Drive Mo- tors 47; Servo
Drives 47; Microtechnology Mold- ings 47; Injection Molding: A
Technology in Tran- sition to Electrical Power 48
Electrical Operation
Hybrid Operations Clamping Systems
Clamping Pressures 60; Hydraulic Clamps 61; Toggle Clamps 62;
Hydromechanical Clamps 62; Hydroelectric Clamps 63; Comparison of
Clamp Designs 64; Tie-bars 64; Tie-barless Systems 69; Platen
Systems 71
Barrel Borescoping 72; Barrel and Feed Unit 72; Barrel Heaters 73;
Barrel Cooling 74; Barrel Char- acteristics 75
Barrels
Screw Operations Machine Sizes and Design Variations Rebuilding and
Repairs
Stripping, Polishing, and Plating 79; Machine Downsizing and
Upsizing 79
Machine Lockout 80; Machine Safety 81; Identi- fication of Hazards
82; Safety Built into the Ma- chines 82; Current and Former
Installations 88; IMM Safety Checklist 88; Safety Rules for Mold-
ing Department 88; American National Standard 92; Safety Standards
92; Plasticator Safety 93; Barrel-Cover Safety 93; Plant Safety 93;
Safety Information 93
Designing Facilities Upgrading 93; Clean Room 94; Clean Machines
94
Noise Generation Startup and Shutdown Operations Molding Operation
Training Program
Safety
First Stage: Running an IMM 99; The Sequence in a Cycle 102; Second
Stage: Parameter Setting and Starting a Job 105
Factors to Consider 113; Operating the Ma- chine 127; Final Stage:
Optimizing Molding Pro- duction 128; Specification Information,
General 130; Specification Information, Details 131; Pro- ductivity
and People 134; Training Information 136
Shear-Rate-Sensitive and -Insensitive Materials
46
Plastics Melt Flow 154; Barrel Temperature Over- ride 157
Feed Section 157; Transition Section 161; Meter- ing Section
162
Screw Rotation 163; Soak Phenomena 164; In- jection Stroke 165;
Injection Pressure Required 166
Screw Design Basics 170; Sequence of Oper- ations 172; Advantages
of Screw Plasticizing 173; Length-to-Diameter Ratios 173; Compres-
sion Ratios 174; Rotation Speeds 175
Screw Sections
Screw Plasticizing
Mechanical Requirements 177; Torque 177; Torque vs. Speed 177
Injection Rates Back Pressures Melt Performance Melt Pumping Melt
Temperature
Temperature Sensitivity 179; Temperature Con- trols Required 179;
Barrel Heating 180; Cooling 180
Melt Performance Residence Time Melt Cushions Melt Shear Rate Melt
Displacement Rate Shot Size
Screw-Barrel Bridging Vented Barrels
Overview 182; Basic Operations 184; Barrel- Venting Safety
188
Design Basics 189; Design Performance 189; Mix- ing and Melting
Devices 189; Screw Barriers 193; Specialized Screw Designs 196;
Screw Tips 197; Influence of Screw Processing Plastics 201; Melt
Quality 202; Materials of Construction 204
Screw Designs
Screw Outputs Influence of Screw and Barrel Wear on Output
Influence of the Material on Wear 205; Screw Wear 205; Production
Variations 205; Screw Wear Inspections 207; Output Loss Due to
Screw Wear
151 151 151
181 181 181 181 181 181
182 182
Chapter 4
Purging Patents Influence Screw Designs Terminology
Molds to Products Overview
Interrelation of Plastic, Process, and Product 221; Molding Process
Windows 221; Cycle Times 223; Molding Pressure Required 224;
Products 224
Basics of Melt Flow 225; Mold Filling Hesitation 225; Melt
Cushioning 225; Mold Filling Monitor- ing 225; Sink Marks 226
Processing Plastics
Mold Types Computer Systems 235
Molds For Thermosets 238; Mold Classifications 241
Cold-Slug Well 243; Melt Orientation 244;
Fill Rates 250; Melt Temperature 250; Mold Tem- perature 250;
Packing Pressure 251; Mold Geom- etry 251; Flash Guide 251
Plastic Melt Behaviors
Cavity Melt Flow
Molding Variables vs. Performance Shot-To-Shot Variation
Cavities
Cavity Melt Flow Analyses 254; Cavity Melt Foun- tain Flow
254
Machine Size 258; Plasticizing Capacity 258; Eco- nomics 258;
Cavity Draft 259; Cavity Packing 259; Cavity Surface 259
Contact Area at Parting Line 262
Sprues 263; Runner Systems 264; Gates 277; Gate Summary 287
Correcting Mold Filling Imbalances in Geometrically Balanced Runner
Systems
Isolating Mold Variations in Multicavity Molds 291
Ejector Systems 293; Ejector Pin Strength 296; Sprue Pullers 300;
Side Actions 300; Angle Pins 301; Cam Blocks 302; Stripper-Plate
Ejection 302;
Cavity Evaluation
Clamping Forces
Sprue-Runner-Gate Systems
Mold Components
Contents ix
External-Positive-Return Systems 302; Cam Ac- tuation 303; Sprue
Bushing and Locating Ring 303; Ring and Bar Ejection 303;
Top-and-Bottom Ejection 304; Inserts 305; Side Guide Slides 307;
Ejector Blades 307
Mold Venting Molds for Thermoset Plastics
Mold Construction 313; Cold-Runner Systems 314;
Injection-Compression Moldings 314
Overview 314; Design Considerations 315; Ba- sic Principles of Heat
Flow 317; Heat Transfer by Heat Pipes 321; Heat Balance of Halves
321; Mold Connection for Fluid 321; Cooling Time 321; Cooling with
Melt Pulses 322; Flood Cooling 322; Spiral Cooling 322; Cooling
Rates 322; Cooling Temperatures 322; Cooling Flow Meters 323
Mold Cooling
Undercuts Mold Shrinkages and Tolerances
Ejection of Molded Products Mold Release Agents Mold Materials of
Construction
Shrinkage vs. Cycle Time 329
Steels 334; Heat Treating 342; Requirements to be Met by Mold Steel
342; Aluminum 343; Beryllium-Copper 343; Kirksite 343; Brass
343
Etching Cavity Surfaces Machining Safety Moldmaker Directory Mold
Material Selection Software Fabrication of Components
Hobbing 346; Cast Cavities 346; Electroforming 346;
Electric-Discharge Machining 346
Tooling Polishing
SPI Finish Numbers 348; Hand Benching 349; Direction of Benching
350; Ultrasonic Tools 351; Textured Cavities 351; Patterns of
Different Tex- tures 351; Mold Steels 352; Conditions Required for
Polishing 352
Nickel 355; Chrome 355; Nitriding and Carbur- izing 356; Other
Plating Treatments 357; Coating Treatments 357; Heat Treatments
358
Overview 359; Manual Cleaning 362; Oven Clean- ing 362; Solvent
Cleaning 362; Triethylene Gly- col Cleaning 363; Postcleaning 363;
Salt Bath Cleaning 363; Ultrasonic Solvent Cleaning 363;
Fluidized-Bed Cleaning 363; Vacuum Pyrolysis Cleaning 363
Platings, Coatings, and Heat Treatments
Cleaning Molds and Machine Parts
307 313
347 347
X Contents
Chapter 5
Strength Requirements for Molds Stress Level in Steel 364; Pillar
Supports 365; Steel and Size of Mold Base 366
Mold Filling 367; Deflection of Mold Side Walls 368
Eyebolt Holes Quick Mold Change Mold Protection
Preengineered Molds Standardized Mold Base Assemblies Specialty
Mold Components Collapsible and Expandable Core Molds
Prototyping
Deformation of Mold
Overview 387; Stereolithography 387; Rapid Tooling 388
Introduction 389; Industry Guide 389; Purchase Order 390; Mold
Design 390; Production of Molds 392
Buying Molds
Mold Storage Computer-Aided Mold and Product Design Production
Control Systems Computer Monitoring of Information Productivity and
People Value Analyses Zero Defects Terminology
Fundamentals of Designing Products Overview Molding Influences
Product Performance Design Optimization
Material Optimization Material Characteristics Behavior of
Plastics
Molding Tolerances
Thermal Stresses 437; Viscoelastic Behavior 437
Tolerances and Designs 443; Tolerance Allow- ances 443; Tolerances
and Shrinkages 444; Tole- rances and Warpages 444; Thin-Wall
Tolerances 444; Micron Tolerances 444; Tolerance Damage 444; Full
Indicator Movements (FIMs) 444; Tole- rance Selection 444;
Tolerance Stack-Ups 445; Standard Tolerances 445
Tolerance Measurement and Quenching Dimensional Properties
Dimensional Tolerances
Product Specifications 449; Using Geometric Tol- erancing 450
364
367
389
415 415 417 421
423 423 43 1
Accidental Orientation 453; Orientation and Chemical Properties
453; Orientation and Me- chanical Properties 454; Orientation and
Optical Properties 454; Orientation Processing Character- istics
454; Orientation and Cost 454
Molecular Orientation: Design of Integral Hinges Interrelation of
Material and Process with Design Design Shapes Shapes and Stiffness
Stress Relaxation Predicting Performance Choosing Materials and
Design
Design Concept 458; Engineering Considerations 458
Design Parameters 460; Types of Plastics 460
Designing with Creep Data 463; Allowable Work- ing Stress 465;
Creep Behavior Guidelines 466
Stapler 466; Snap-Fits 467; Springs 467
Design Considerations
Design Examples
Design Approach Example Design Accuracy Risks and the
Products
Acceptable Risks 472; Acceptable Goals 473; Ac- ceptable Packaging
Risks 473; Risk Assessments 473; Fire Risks 473; Risk Management
473; Risk Retention 473
Perfection Cost Modeling Innovative Designs Protect Designs
Summary
Terminology Molders’ Contributions 476
Molding Materials Overview
Definition of Plastics 484; Heat Profiles 488; Costs 489; Behavior
of Plastics 490; Checking Materials Received 491
Neat Plastics Polymer Synthesis and Compositions
Copolymers Interpenetrating Networks Graftings
455 455 455 456 457 458 458
459
461
466
477
Alloys and Blends Thermoplastic and Thermoset Plastics
Thermoplastics 511; Thermoset Plastics 511; Cross-Linking 512;
Cross-Linking Thermoplastics 512; Thermoplastic Vulcanizates (TPVs)
512; Cur- ing 512; Heat Profiles 513
Liquid Crystal Plastics (LCPs) Elastomers, Thermoplastic, and
Thermoset
Thermoplastic Elastomers 515; Thermoset Elas- tomers 515; Natural
Rubbers 515; Rubber Elas- ticity 515; Rubber Market 515
Commodity and Engineering Plastics Injection Molding Thermoplastics
and Thermosets High Performance Reinforced Moldings
Injection Moldings 518; Bulk Molding Com- pounds (BMCs) 518;
Characterizations 519; Di- rectional Properties 521
Newtonian Flow 522; Non-Newtonian Flow 523 Viscosities
Viscoelasticities Plastic Structures and Morphology
Chemical and Physical Characteristics 524; Crys- talline and
Amorphous Plastics 524; Catalysts and Metallocenes 526; Plastic
Green Strength 527
Average Molecular Weight 527; Molecular Weight Distribution 529;
Additives 529; Molecular Weight and Melt Flow 530; Molecular Weight
and Aging 530
Flow 531; Viscosity 531; Viscoelasticity 532; In- trinsic Viscosity
533; Shear Rate 533; Laminar and Nonlaminar Melt Flows 535; Melt
Flow Analyses 535; Melt Flow Analysis Programs 535; Analyzing Melt
Flow Results 536; Melt Flow Defects 536; Hindering Melt Flow with
Additives 536; Melt Fractures 536
Molecular Weight ( M W )
Rheology and Melt Flow
Weld Line Strengths and Materials Material Selections
Colorants 548; Concentrates 549; Barrier Plastics 549
Melt Shear Behaviors 537
498 498
507 510
513 514
Thermal Properties and Processability Melt Temperatures 554; Glass
Transition Tem- peratures 555; Dimensional Stabilities 555; Ther-
mal Conductivities and Thermal Insulation 556; Heat Capacities 556;
Thermal Diffusivities 556; Coefficients of Thermal Expansion 556;
Thermal Stresses 556
Shrinkages Drying Material Handling Annealing Recycling
Recycled Plastic Definitions 559; Recycled Plas- tic Identified
560; Recycled Plastic Properties 560; Recycling Size Reductions
560; Recycling Mixed Plastics 560; Integrated Recycling 560; Re-
cycling Methods and Economic Evaluations 560; Recycling and
Lifecycle Analysis 561; Recycling Commingled Plastics 561;
Recycling Automati- cally Sorting Plastics 561; Recycling and
Common Sense 561; Recycling Limitations 561
Recycling Facts and Myths Warehousing
Storage and Condensation 562; Material Storage 562; Silo Storage
562
Processing Different Plastics Polyethylenes
Molding Conditions 570
Molding Conditions 573; Purging 574; Shutdown and Start-up 574;
Thermal and Rheological Prop- erties 574; Drying 574; Mechanical
Properties 575; Chemical Resistance 575; Weatherability 575; Color
575
Formulations 576; Molding Conditions 576; Screw Design 577;
Material Handling Equipment 578; Processing Parameters 579; Problem
Solving 579; Splay 579
Molding Conditions 581; Performance Parame- ters 585; Design
Parameters 586; Molding Perfor- mance Parameters 591; Mold Release
593; Close Tolerance: Fast Cycles 595; Recycling Plastics 596
Molding Variables and Cause-and-Effect Links 597; Molding Variables
and Property Responses 599; Appearance Properties 599; Warping
600;
Polypropylenes
561 562
563 563
xiv Contents
Chapter 7
Mechanical Properties and Molding Variables 601; Izod impact 602;
Molding for Electroplating 605; Property Variation with Position
Mold Ge- ometry 605; Summary 606
Drying 606; Recycle and Virgin Proportions 607; Processing 608;
Hydrolysis 609; Rheology 609; Heat Transfer 609; Residual Stress
610; Annealing 61 1
Process 613; Hot- and Cold-Runner Molding 614; Material Stuffer
615
Polycarbonates
Process Control Process Control Basics
Developing Melt and Flow Control 630; Inspec- tion 630; Computer
Process Data Acquisition 630; Control Flow Diagrams 632; Fishbone
Diagram 632
Technology 636; Fast Response Controls 638; Control Approaches 639;
Process Control Meth- ods 640; Production Monitoring 640;
On-Machine Monitoring 641
Overview
Temperature Control of Barrel and Melt Electronic Controls Fuzzy
Logic Control Process Control Techniques Process Control
Approaches
What Are the Variables? 652; Why Have Process Control? 654; Control
of Which Parameters Can Best Eliminate Variability? 654; What
Enables Parameter Controllability? 657; Where Does the Process
Controller Go? 661; Basic Features a Pro- cess Controller Should
Have 662; Applications 664; Summary 666
Process Control Problems Cavity Melt Flow Analyses
Problem 669; Melt Viscosities versus Fill and Pack 669; Test
Methodology 670; Analyzing Results 673; Example Test 673; Using
Empirical Test Data to Optimize Fill Rates 674; Melt Vibrations
dur- ing Filling 675; Stabilizing via Screw Return Time 675
Sensor Requirements 676; Molding Parameters 676; Display of
Monitored Molding Parameters
Relating Process Control to Product Performances
606
611
667 668
Functions 680; Rotary and Linear Motion 680
Optimization via PVT 681; PMT Concept 683
Designs 684
Controllers
Transputer Controllers Temperature Controllers
Temperature Variations 688; Melt Temperature Profiles 690;
Automatic Tuning 691; Temperature Sensors 691; Fuzzy Logic Controls
692; Fuzzy-PID Controls 692
Temperature Timing and Sequencing Pressure Controls
Pressure PID Controls Screw Tips 692; Cavity Fillings 692
PID Tuning: What It Means 693; The Need for Rate Control on
High-speed Machines 694
Fuzzy-Pressure Controls Injection Molding Holding Pressures Process
Control Fill and Pack Process Control Parameter Variables
Injection Molding Boost Cutoff or Two-Stage Control Injection
Molding Controller Three-Stage Systems
Mold Cavity Pressure Variables Programmed Molding
Adaptive Ram Programmers 696
Parting Line Controls 702; Computer Micropro- cessor Controls 703;
Computer Processing Con- trol Automation 703
Molding Thin Walls Control System Reliabilities Operations
Optimized Control Tradeoffs Process Control Limitations and
Troubleshooting
Control 705; Tie-Bar Growth 706; Tie-Bar Elon- gation 706; Thermal
Mold Growth 706; Shot-to- Shot Variation 706
Intelligent Communications 709; Systematic In- telligent Processing
710
Intelligent Processing
709
Automatic Detections Terminology
Chapter 8 Design Features That Influence Product Performance
Overview
Audits 717; Computer Approaches 717; Design Feature That Influence
Performance 718
Plastic Product Failures Design Failure Theory Basic Detractors and
Constraints
Tolerance and Shrinkage 721; Residual Stress 725; Stress
Concentration 726; Sink Mark 727
Design Concept Terminology Sharp Corners Uniform Wall Thickness
Wall Thickness Tolerance Flow Pattern Parting Lines Gate Size and
Location Taper or Draft Angle Weld Lines
Vent, Trapped Air, and Ejector Undercuts Blind Holes Bosses Coring
Press Fits Internal Plastic Threads External Plastic Threads
Molded-In Inserts Screws for Mechanical Assembly Gears Ribs
Geometric Structural Reinforcement Snap Joints Integral Hinges Mold
Action
Meld Lines 740
Communication Benefits 773; Computerized Databases of Plastics 775;
CAD/CAM/CAE Methods 775; Computer-Integrated Manufactur- ing
775
710 710 710 71 1
712 713
716 716
727 730 730 732 732 733 733 733 735 738
740 740 740 747 750 751 752 752 753 754 759 760 763 764 765
766
770 770
Benefits of CAD/CAM/CAE for Mold Design Productivity 776; Quality
777; Turnaround Time 778; Resource Utilization 778
Mechanical Design 779; Computer-Aided Engi- neering 780
Product Designers 783; Mold Designers and Moldmakers 784; Injection
Molders 785
Multisections 789; Finite Element Techniques 790; Shrinkage and
Warpage 791; Benefit Appraisal 795; Moldflow Basic Technology
795
Introduction 796; Fundamentals 799; Mold Cool Analysis 801
Modeling Methods Applied to Part and Mold Design Wire Frame
Modeling 824; Surface Modeling 826; Solids Modeling 828
Group Technology 829; Finite Element Model- ing 830; Digitizing
831; Layering 832; Groups 833; Patterns 833; Large-Scale Geometry
Manipu- lation 833; Local Coordinates or Construction Planes 834;
Model and Drawing Modes and Associativity 834; Verification of
Geometric Rela- tionships 835; Automatic Dimensioning and Au-
tomatic Tolerance Analysis 836; Online Calcula- tion Capabilities
and Electronic Storage Areas 836
Illustration of Mold Design Process The Manual (Paper) Method
837
The CAD/CAM/CAE Method Online Databases
Basics in CAD/CAM/CAE Modeling
Computer Capabilities for Part and Mold Design
The Database Concept 843; Graphics Databases 844; Defining the
Library Database 845
Tolerances and Dimensional Controls Computer Controllers
CAD/CAM/CAE and CIM Numerical Control Process Programmable
Controller Safety Devices Computer Optical Data Storage Artificial
Intelligence Computers and People Computer-Based Training Myths and
Facts Capability and Training Computer Software Molding Simulation
Programs RAPRA Free Internet Search Engine Software and Database
Programs
xvii
776
778
781
786
796
823
829
836
840 843
846 846 847 849 849 850 850 850 850 850 85 1 852 854 854 854
xviii Contents
Injection Moldings and Molds 856: Materials 857; Shrinkage 858;
Materials and Designs 859; Design Products 860: Engineering 861;
Graphics 861; Management 862: General Information 862; Training
862
Plastics, Toys, and Computer Limitations Computers Not Designed for
Home Summary Terminology
Chapter 10 Auxiliary Equipment and Secondary Operations
Introduction
Energy Conservation 870; Planning Ahead, Sup- port Systems
871
Hoppers 871; Material Handling, Feeding, and Blending 872; Material
Handling Methods 872: Sensors 874
Bulk Density 875; Basic Principles of Pneumatic Conveying 876; Air
Movers 883; Pneumatic Ven- turi Conveying 886; Powder Pumps 886;
Pip- ing 888; Hoppers 889; Filters 889; Bulk Storage 891; Blenders
891; Unloading Railcars and Tank Trucks 894
Nonhygroscopic Plastics 895; Hygroscopic Plas- tics 895; Drying
Overview 895; Dryers 896
Overview 904; Heat-Transfer Calculations 905; Requirements Vary
with Materials 905; Water Re- covery 907; General considerations
908; Calcula- tion of the Cooling Load 911; Determining Water Loads
913
Overview
Energy-Saving Heat Pump Chillers Granulators
Safety 916; Basics 917; Hoppers 917; Cutting Chambers 918; Cutting
Chamber Assembly 921; Hard Face Welding 921; Screen Chambers 922;
Auger Granulators 922; Granulating and Perfor- mance 924
Dewpoints 929; Mold Surface Temperatures 929; Effect of Change in
Air Properties 930; Air Condi- tioning and Desiccant
Dehumidification 931; De- humidification System 932
Controlled Motions 933; People and PHE 935; Different Types 935;
Value in Use 937; Detriments 938: Robots Performance 938; Safety
Measures 938
Mold Dehumidification
Parts-Handling Equipment
Adhesives 941; Solvents 946; Welding Techniques 948; Welding
Process Economic Guide 953
Abrasives 953; Carbon Dioxide 953; Cryogenic Deflashing 954; Brass
954; Hot Salts 954; Solvents 954; Ultrasonics 954; Vacuum Pyrolysis
954; Coat- ings 955
Potential Preparation Problems 955; Pretreat- ments 959; Removing
Mold Release Residues 959
Robot Terms 966
Joining and Assembling
Definitions
Troubleshooting Guides Flashes Injection Structural Foams
Hot-Runners Hot-Stamp Decorating Paint-Lines Granulator Rotors
Auxiliary Equipment Screw Wear Guide
Plastic Material and Equipment Variables 970
Defects 972
Inspection Rollers 1010; Diameters 1010; Depths 1011; Concentricity
and Straightness 1011; Hard- ness 1011; Finish and Coating
Thickness 1012; Screw Manufacturing Tolerances 1012
Inside Diameters 1012; Straightness and Concen- tricity 1012;
Barrel Hardness 1012; Barrel Speci- fications 1012
Cleaning the Plasticator Screw 1014; Oil Changes and Oil Leaks
1015; Checking Band Heaters, Thermocouples, and Instruments 1015;
Align- ment, Level, and Parallelism 1015; Hydraulic,
Barrel Inspection Guide
1001 1001 1001
Pneumatic, and Cooling-Water Systems 1015; Hydraulic Hose
1016
Keep the Shop Clean Keep Spare Parts in Stock Return on Investment
Maintenance
Hydraulic Fluid Maintenance Procedures 1020; Problems and Solutions
1020; Downtime Mainte- nance 1021: Preventative Maintenance 1021;
Ser- vices 1022
Safety Maintenance Software Summary Terminology
Testing, Inspection, and Quality Control Testing Design and Quality
Basic versus Complex Tests Sampling
Acceptable Quality Level 1032; Sampling Plan 1032; Sampling Size
1033
Orientation and Weld Lines 1033; Density and Specific Gravity 1035;
Morphology: Amorphous and Crystalline Plastics 1036; Molecular
Struc- tures 1037
Mechanical Test Equipment 1042; Tensile Test 1042; Deflection
Temperature under Load 1045; Creep Data 1045
Characterizing Properties and Tests
Liquid Chromatography 1049; Gel Permeation Chromatography 1049: Gas
Chromatography 1050; Ion Chromatography 1050; Thermoanalyt- ical
Method 1051; Thermogravimetric Analysis 1051; Differential Scanning
Calorimetry 1052; Thermomechanical Analysis 1053; Dynamic Me-
chanical Analysis 1054; Infrared Spectroscopy 1054: X-Ray
Spectroscopy 1055; Nuclear Mag- netic Resonance Spectroscopy 1055;
Atomic Ab- sorption Spectroscopy 1055; Raman Spectroscopy 1055;
Transmission Electron Microscopy 1056; Optical Emission
Spectroscopy 1056; Summary of Characterizing Properties 1056
Selected ASTM Tests 1062; Viscoelastic Proper- ties 1079; Rheology,
Viscosity, and Flow 1080;
Types of Tests
1033
1041
Optical Analysis via Microtoming Thermal Properties
Useful Temperature Range 1084; Glass Transition and Melt
Temperatures 1084; Thermal Conduc- tivity 1086; Heat Capacity 1086;
Coefficient of Linear Thermal Expansion 1086; Temperature
Dependence of Mechanical Properties 1089; Dif- fusion and Transport
Properties 1091; Permeabil- ity 1091; Migration 1092
Overview of Plastic Properties Melt Tests
Melt Flow Tests 1095; Melt Index Test 1095; Melt Index Fractional
Tests 1098; Molding Index Tests 1098; Measurements 1098
Types of Scales 1099
Radiography 1099; Ultrasonics 1100; Liquid Pen- etrants 1100;
Acoustics 1100; Photoelastic Stress Analysis 1100; Infrared Systems
1101; Vision Sys- tem Inspections 1101; Computer Image Proces- sors
1102
Temperature Scales
Nondestructive Tests
Laboratory Organizations Worldwide Determining Moisture Content
1103
American Society for Testing and Materials 1105; International
Organization for Standardization 1105; Underwriters’ Laboratory
Classifications 1106
International System of Units Inspections Identification of
Plastics Estimating Plastic Lifetimes Quality Control
Quality Control Defined 1110; Quality Control Variables 1110
No More ABCs 1112; Need for Dependability 1112; Quality Auditing
1112
QC Begins When Plastics Are Received
Reliability and Quality Control Failure Analysis Quality Control
Methods
Quality Control and Quality Assurances Auditing by Variables
Analysis Acceptable Quality Levels Quality Optimization Goals
Quality System Regulation
Image Quality Indicators 1114
1111
xxii Contents
Total Quality Management Training and People Training and Quality
Emerging Trends in Training Training versus Education Economic
Significance of Quality
Terminology Cost of Quality 1119
Chapter 13 Statistical Process Control and Quality Control
Overview
Combining Online SPC and Offline SQC 1127; Improve Quality and
Increase Profits 1128; Statis- tical Material Selections:
Reliabilities 1128; Sta- tistical Material Selections:
Uncertainties That Are Nonstatistical 1129; Statistical
Probabilities and Quality Control 1129; Statistics and Commit-
ments 1129; Statistics and Injection Molding 1129 Computers and
Statistics 1131; Statistical Tools 1134
Online Monitoring of Process Variables Gathering and Analyzing Data
Process Control and Process Capability
Defect Prevention Understanding Modern Methods of Control
Control Charts 1138
Standard Deviations 1142; Frequency Distribu- tion 1143; Control
Chart 1145
Standard Deviation versus Range Basic Statistical Concepts
Mean Value, Range, and Standard Deviation 1148; Distribution 1149;
Process Control Chart 1150; Machine Capability 1150; Process
Capabil- ity 1150
Importance of Control Charts Practical Example
Machine Capability 1153; Process Capability 1153; Control Limits
for the Process Control Chart 1154
Production Controls 115.5; SPC Step One: Raw Material 1156; SPC
Step Two: Materials Han- dling 1156; SPC Step Three: Injection
Molding 11.56; SPC Implementation: Summary of Experi- ence
1156
How to Succeed with SPC Outlook Terminology
A Successful SPC System
1119
Chapter 14 Costing, Economics, and Management Overview
Machine Sales 1163; Formulas for Business Fail- ures 1164; Managing
1164
Estimating Part Cost 1167; Automation of Data Gathering 1169;
Machinery Financing 1169; En- ergy Savings 1170
Costing
Technical Cost Modeling Cost Analysis Methods
Material Times Two 1171; Material Cost plus Shop Time 1172;
Material Cost plus Loaded Shop Time 1172; Quotes 1172
Variable Cost Elements 1173; Fixed Costs 1174; Summary of Fixed and
Variable Costs 1177; Pro- cess Parameters 1178; Technical Cost
Modeling 1178; Summary of Technical Cost Analysis 1179
Technical Cost Analysis
Financial Plant Management Cost Management
Information Necessary for Product Costing and Cost Control 1182;
Reporting from the Produc- tion Floor and Management Control
Reports 1183
Gathering the Data for Profit Planning and Bud- geting 1186;
Establishing Profit, Goals, and Sales Forecasts 1186; Developing
the Detailed Plans and Budgets 1187; Flexible Budgeting 1187
Order Processing 1188; Inventory Control 1189; Production
Scheduling and Control 1189; Scheduling Approaches 1190; Purchasing
1191
Profit Planning and Budgeting
Injection Blow Moldings 1201; Stretched Blow Moldings 1204;
Stretched Blow Moldings with Handle 1206; Stretched Blow Molding
Operation Specialties 1207; Blow Molding Shrinkages 1209;
Troubleshooting 1211; Blow Molding versus In- jection Molding
1215
Coinjection Molding Injection Molding Sandwich Structures
Gas-Assist Injection Molding
Advantages and Disadvantages 1220; Basic Pro- cesses and Procedures
1220; Molding Aspects 1223; Shrinkage 1224; Summary 1224
1163 1163
Gas Counterflow Molding Melt Counterflow Molding Structural Foam
Molding
Overview 1225; Performance 1226; Plastic Mate- rials 1226;
Characteristics of Foam 1226; Design Analysis 1227; Blowing Agents
1229; Methods of Processing SF with Chemical Blowing Agents 1230;
Processing SF with Gas Blowing Agents 1232; Tooling 1234; Start-up
for Molding 1234
Injection-Compression Molding (Coining) Multiline Molding
Counterflow Molding Oscillatory Molding of Optical Compact
Disks
Continuous Injection Molding Digital Video Disk Moldings 1238
Velcro Strips 1239; Electrically Insulated Buttons for Coaxial
Cables 1242; Railtrack Molding 1243
The Mold 1248; Process Controls 1249 Reaction Injection
Molding
Liquid Injection Molding Soluble Core Molding Insert Molding
Inmolding
Two-Color Molding 1253; Decoration 1253; Paint Coating 1254; Back
Molding 1254; Two-Shot Molding 1254; Inmold Assemblies 1254;
Double- Daylight Process 1255
Overmolding Compatible Plastics with No Welding Closure
Moldings
Unscrewing Closures 1256; Conventional Un- screwing Molds 1256;
Unscrewing System Mold- ings 1256; Collapsible and Expandable Core
Molds 1257; Split-Cavity Molds 1258; Strippable Thread Molds
1258
Vacuum Molding Tandem Injection Molding Molding Melt Flow
Oscillations Ram Injection Molding Golf Ball Moldings Micro
Injection Molding Aircraft Canopies Injection Molding
Nonplastics
Introduction 1266; Metal Injection Molding 1266; Ceramic Injection
Molding 1268
Terminology
1225 1225 1225
1268
Contents xxv
Cold Forming Cold Draw Forming Dip Forming Pressure Forming Rubber
Pad Forming Compression-Stretched Moldings Solid-Phase Scrapless
Forming Solid-Phase Pressure Forming Slip Forming Castings Foam
Molding Expandable Plastics
Compression Molding
Transfer Molding
Reinforced Plastics
Molds 1291
Directional Properties 1301; Processes and Prod- ucts 1301
Stampable Reinforced Plastics Machining Plastics Processor
Competition Legal Matters
Accident Reports 1304; Acknowledgments 1304; Chapter 11 Act 1304;
Conflicts of Interest 1304; Consumer Product Safety Act 1304; Copy-
right 1305; Defendant 1305; Employee Inven- tion Assignment 1305;
Expert Witness 1305; In- surance Risk Retention Act 1305; Invention
1305; Mold Contractional Obligation 1305; Patent 1305;
Patentability 1306; Patent Information 1306; Patent Infringement
1306; Patent Pooling with Competitors 1306; Patent Search 1306;
Patent Term Extension 1306; Patent Terminology 1306; Plaintiff
1306; Processor, Contract 1307; Product Liability Law 1307;
Protection Strategies 1307; Quotations 1307; Right-To-Know 1307;
Shop- Right 1307; Software and Patents 1307; Tariff 1307; Term
1307; Tort Liability 1308; Trademark 1308; Trade Name 1308;
Warranty 1308
17 Summary The Most Important Forming Technique Processing Trends
Productivity
Machine Aging 1315; Response to Change 1316
1284 1288 1289
1291 1292 1292 1292 1292 1293 1293 1293 1293 1293 1294 1294
1295
1298
1298
Process and Material Selections Plastics and Equipment Consumption
Machinery Sales
Trends in Machinery 1318; Computers and Injec- tion Molding 1320;
Interfacing Machine Perfor- mance 1320
Molding in an Industrialized Country Compromises Must Frequently Be
Made Standard Industrial Classification Plastic Industry Size
Energy and Plastics Plastic Data: Theoretical Versus Actual Values
Markets
Packaging 1325; Velcro for Flexible Packaging 1327; Building and
Construction 1327; Lumber 1327; Pallets 1327; Automotive Parts
1329; Printed Circuit Boards and Surface Mounted Technology 1330;
U.S. Postal Service 1330; Medical Applica- tions 1330; Toilets and
Water Conservation 1330; Bearings 1330; Blow Molding Innovations
1330; Beer Bottles 1331; Collapsible Squeeze Tubes 1331; Asthma
Inhalers 1331
Automated Production 1334; Energy Savings 1335
Discipline 1337; Productivity 1338; Experience 1338; Plant Controls
1338
Example 1 1339; Example 2 1339; Example 3 1340
Myths and Facts 1341; Limited Oil Resources 1342; Limited US. Steel
Resources 1342; Plastic Advocates 1342
Statistics: Fact and Fiction 1344; Landfill 1345; Re- cycling 1345;
Incineration 1345; Degradable 1346
Economic Control of Equipment
Correcting Misperceptions about Plastics
Analyze Failures Creativity
Innovations and the Markets 1348; Industrial De- signers 1348; Da
Vinci’s Creativity 1348
Target for Zero Defects 1349 Design Successes
Excess Information: So What’s New? Fabricating Employment
History
Barrel History 1351; Hopper Magnet 1352; Blow Molding 1352;
Coca-Cola Bottle 1353; Coor’s Beer Bottle 1353; Recycling History
1353; Squeeze Tube 1353; Zipper 1353; Waste Contain- ers 1354;
Shotgun Shells 1354; Water Treatment 1354
1318 1318 1318
1331
1337
1339
1341
1342
Profits and Time 1354
Appendices 1. Abbreviations 2. Conversions 3. Symbols and Signs 4.
Web Sites on Plastics
References
1411
Preface
This third edition has been written to thoroughly update the
coverage of injection molding in the World of Plastics. There have
been changes, including extensive additions, to over 50% of the
content of the second edition. Many examples are provided of
processing different plastics and relating the results to critical
factors, which range from product design to meeting performance
requirements to reducing costs to zero-defect targets. Changes have
not been made that concern what is basic to injection molding.
However, more basic information has been added concerning present
and future developments, resulting in the book being more useful
for a long time to come. Detailed explanations and interpretation
of individual subjects (more than 1500) are provided, using a total
of 914 figures and 209 tables. Throughout the book there is
extensive information on problems and solutions as well as
extensive cross- referencing on its many different subjects.
This book represents the ENCYCLOPEDIA on IM, as is evident from its
extensive and detailed text that follows from its lengthy Table of
CONTENTS and INDEX with over 5200 entries. The worldwide industry
encompasses many hundreds of useful plastic-related computer
programs. This book lists these programs (ranging from operational
training to product design to molding to marketing) and explains
them briefly, but no program or series of programs can provide the
details obtained and the extent of information contained in this
single sourcebook.
In the manufacture of molded products there is always a challenge
to utilize advanced techniques, such as understanding the different
plastic melt flow behaviors, operational moni- toring and control
systems, testing and quality control, and statistical analysis.
However, these techniques are only helpful if the basic operations
of molding are understood and characterized, to ensure the
elimination or significant reduction of potential problems.
The book provides an understanding that is concise, practical, and
comprehensive and that goes from A to Z on the complete subject of
injection molding. It provides concise information for either the
technical or the nontechnical reader, interrelating and
understanding basic factors starting with the plastic’s melt flow
behavior during processing. It should be useful to the fabricator,
moldmaker, designer, engineer, maintenance person, accountant,
plant manager, testing and quality control worker, cost estimator,
sales and marketing person, venture capitalist, buyer, vendor,
educator/trainer, workshop leader, librarian/information provider,
lawyer, consultant, and others. People with different interests can
focus on and interrelate across subjects that they have limited or
no familiarity with in the World of Plastics. As explained
throughout this book, this type of understanding is required in
order to be successful in the design, prototyping, and manufacture
of the many different marketable molded products worldwide.
xxix
xxx Preface
The reader will have a useful reference for pertinent information
readily available in the table of contents and the index. As past
book reviewers have commented, the information contained in this
book is of value to even the most experienced designers and
engineers, and provides a firm basis for the beginner. The intent
is to provide a complete review of all aspects of the injection
molding process that goes from the practical to the theoretical,
and from the elementary to the advanced.
This book can provide people not familiar with injection molding an
understanding of how to fabricate products in order to obtain its
benefits and advantages. It also provides information on the most
common and costly pitfalls or problems that can develop, resulting
in poor product performance or failures. Accompanying the problems
are solutions. This book will enhance the intuitive skills of those
people who are already working in plastics. Its emphasis is on
providing a guide to understanding the worldwide technology and
business of injection-molded products.
From a pragmatic standpoint, every theoretical aspect that is
presented has been expressed so that it is comprehensive and
useful. The theorist, for example, will gain insight into the
limitations of plastics relative to other materials such as steel
and wood. After over a century of worldwide production of all kinds
of injection-molded products, they can be processed successfully,
yielding high quality, consistency, and profitability. As described
in this book, one can apply the correct performance factors based
on an intelligent understanding of the subject.
This book has been prepared with the awareness that its usefulness
will depend on its simplicity and its ability to provide essential
information. With the experience gained in working in the injection
molding industry worldwide and in preparing the first and second
editions as well as other books, we believe that we have succeeded
in that purpose and have provided a useful, practical reference
work.
The injection molding industry consumes about 32 wt% of all
plastics. The plastics industry as a whole is ranked as the fourth
largest industry in the United States. With plastics, to a greater
extent than other materials, opportunity for improvement will
always exist, since new and useful developments in materials and
processing continually are on the horizon. Examples of these
developments are given in this book, providing guides to future
trends in the world of plastics.
The limited data presented on the properties of plastics are
provided as comparative guides; readers can obtain the latest
information from material suppliers, industry software, and/or
sources mentioned in this book’s reference section. Our focus in
the book is to present, interpret, analyze, and interrelate the
basic elements of injection molding for processing plastic
products. As explained in this book, there are over 17,000 plastic
materials worldwide, and selecting the right one requires
specifying all product performance requirements, properly setting
up and controlling the injection molding process to be used, and
intelligently preparing a material specification purchase document
and work order to produce the product.
The many properties of different plastics are important for
different purposes. Some meet high performance requirements such as
long-time creep resistance, fatigue endurance, or toughness. On the
other hand, for some plastics, ready supply and low cost are the
main ad- vantages. As explained in this book, each of the different
materials requires specific injection molding operating
procedures.
Patents or trademarks may cover some of the information presented.
No authorization to utilize these patents or trademarks is given or
implied; they are discussed for informa- tion purposes only. The
use of general descriptive names, proprietary names, trade names,
commercial designations or the like does not in any way imply that
they may be used as common nouns. While the information presented
is believed to be true and accurate, neither the authors nor the
publisher can accept any legal responsibility for any errors,
omissions, inaccuracies, or other factors.
Preface xxxi
In preparing this book and ensuring its completeness and the
correctness of the subjects reviewed, use was made of the authors’
worldwide personal, industrial, and teaching expe- rience that
totals over a century, as well as worldwide information from
industry (personal contacts, conferences, books, articles, etc.)
and trade associations.
THE ROSATOS
Introduction
This chapter provides an introduction and overview of the injection
molding machine (IMM) process. It provides text with pictorial
reviews. Details on the important informa- tion pertaining to IMM
and reviewed in this chapter are provided in the other chapters.
Figure 1-1 provides an overview that basi- cally summarizes what
should be considered to ensure that the molded product meets per-
formance requirements and provides a good return on investment to
produce all types and shapes of products for all types of
markets.
Injection molding is a major part of the plastics industry and is a
big business world- wide, consuming approximately 32 wt% of all
plastics. It is in second place to extrusion, which consumes
approximately 36 wt% (1, 3, 7). 11: the United States alone there
are about 80,000 IMMs and about 18,000 extrud- ers operating to
process all the many differ- ent types of plastics. In the industry
an IMM is not regarded as an extruder; however, it is basically a
noncontinuous extruder and in some operations is even operated
continu- ously (Chap. 15). IMMs have a screw plas- ticator, also
called a screw extruder, that pre- pares the melt (3).
As summarized in Fig. 1-2, injection mold- ing is an important
plastic processing method. The figure shows the necessary
components for the injection molder to be successful and
profitable. Recognize that the first to market with a new product
captures 80% of mar- ket share. The young tree cannot grow if it is
in the shadow of another tree or if it does not keep up with
competition. You need to be at the top of the tree looking over the
other trees. Factors such as good engineer- ing and process control
are very important but only represent pieces of the pie. Without
proper marketinghales you are literally out of business. This
diagram is basically a philo- sophical approach to the overall
industry in that it provides examples of all aspects of the
technology and business that range from local to global
competition. The old adage about the better mousetrap is no longer
com- pletely true, since you need factors such as the support
services from the “tree” to achieve commercial success and meet
product design requirements (Chap. 5) (1,499).
There are many different types of IMMs that permit molding many
different prod- ucts, based on factors such as quantities, sizes,
shapes, product performance, or eco- nomics. These different types
of IMMs are
1
~
I Individual CONTROL for each aperatton, from sorimre to
hardware
-m SOFTWARE --- ANALYSIS approach to meet psiiormanoo
FALLO Follow ALL Opportunities
I I Y SOFTWARE
MOLDED PART
Set UP TESTINQ I QUALITY CONTROL !
Immediately afier part is in production--next step IMPORTANT STEP
-- is to produce part to meet same requirements but produced at a
lower cost
Use FALLO approach. Reevaluate all parameters used from part design
(use less plastic), use lower cost plastic with similiar process-
ing cost (or plastic with higher cost, but faster process, results
in lower total cost), check hardware performance, & other para-
meters described in the IM HANDBOOK.
A Characterize properties, mechanical, physical, chemical, thermal,
etc
I t- Set up practical i useful TROUBLESHOOTING
potential faults. C/ GUIDE based on causes & remedies of
I I I ! D.V.1
Fig. 1-1 The FALLO approach: Follow ALL Opportunities.
reviewed throughout this book, particularly in Chap. 15. Small- and
large-size IMMs both have their advantages. For example, if sev-
eral small machines are used rather than one large one, a machine
breakdown or shutdown for routine maintenance will have less effect
on production rates. However, the larger ma- chine is usually much
more profitable while it is running. Because there are fewer
cavities in molds for the small machines, they may per- mit closer
control of the molding variables in the individual cavities.
The two most popular kinds of IMM are the single-stage and the
two-stage; there are also molding units with three or more stages.
The single-stage IMM is also known as the reciprocating-screw IMM.
The two-stage IMM also has other names, such as the piggy- back
IMM. It is comparable in some ways to a continuous extruder.
The IMM has three basic components: the injection unit, the mold,
and the clamping system. The injection unit, also called the
plasticator, prepares the proper plastic melt
and via the injection unit transfers the melt into the next
component that is the mold. The clamping system closes and opens
the mold.
These machines all perform certain essen- tial functions: (1)
plasticizing: heating and melting of the plastic in the
plasticator, (2) injection: injecting from the plasticator under
pressure a controlled-volume shot of melt into a closed mold, with
solidification of the plastics beginning on the mold's cavity wall,
(3) afterjiilling: maintaining the injected material under pressure
for a specified time to prevent back flow of melt and to compen-
sate for the decrease in volume of melt during solidification, (4)
cooling: cooling the ther- moplastic (TP) molded part in the mold
until it is sufficiently rigid to be ejected, or heat- ing: heating
the thermoset (TS) molded part in the mold until it is sufficiently
rigid to be ejected, and (5) molded-part release: opening the mold,
ejecting the part, and closing the mold so it is ready to start the
next cycle with a shot of melt.
1 The Complete Injection Molding Process 3
Selecting Material Proce
Compression Reinforced Plastics
Cost Analysis
r Rheology
t LEADS
I Etc.
First to market with a new product captures 80% of market share.The
young tree cannot grow if it is in the shadow of another tree or if
it does not keep up with the competition.You need to be at the top
of the tree looking over the other trees.
DVR
Fig. 1-2 Plastic product growth compared to tree growth.
This cycle is more complex than that other processes such as
extrusion in that it involves moving the melt into the mold and
stopping it, rather than having a continuous flow of melt. The
injection molding process is, how- ever, extremely useful, since it
permits the manufacture of a great variety of shapes, from
simple ones to intricate three-dimensional (3-D) ones, and from
extremely small to large ones. When required, these products can be
molded to extremely very tight tolerances, very thin, and in
weights down to fractions of a gram. The process needs to be thor-
oughly understood in order to maximize its
4 1 The Complete Injection Molding Process
performance and mold products at the least cost, meeting
performance requirements, and with ease (see the section on Molding
Toler- ances in Chap. 5).
Machine Characteristics
IMMs are characterized by their shot ca- pacity. A shot represents
the maximum vol- ume of melt that is injected into the mold. It is
usually about 30 to 70% of the actual available volume in the
plasticator. The dif- ference basically relates to the plastic
mate- rial’s melt behavior, and provides a safety factor to meet
different mold packing con- ditions. Shot size capacity may be
given in terms of the maximum weight that can be in- jected into
one or more mold cavities, usu- ally quoted in ounces or grams of
general- purpose polystyrene (GPPS). Since plastics have different
densities, a better way to ex- press shot size is in terms of the
volume of melt that can be injected into a mold at a spe- cific
pressure. The rate of injecting the shot is related to the IMM’s
speed and also the process control capability for cycling the melt
into the mold cavity or cavities (fast-slow- fast, slow-fast,
etc.).
The injection pressure in the barrel can range from 2,000 to at
least 30,000 psi (14 to 205 MPa). The characteristics of the
plastic being processed determine what pressure is required in the
mold to obtain good products. Given a required cavity pressure, the
barrel pressure has to be high enough to meet pres- sure flow
restrictions going from the plastica- tor into the mold cavity or
cavities.
The clamping force on the mold halves re- quired in the IMM also
depends on the plastic being processed. A specified clamping force
is required to retain the pressure in the mold cavity or cavities.
It also depends on the cross- sectional area of any melt located on
the part- ing line of the mold, including any cavities and mold
runner(s) that are located on the parting line. (If a TP hot-melt
runner is lo- cated within the mold half, its cross-sectional area
is not included in the parting-line area.) By multiplying the
pressure required on the melt and the melt cross-sectional area,
the
clamping force required is determined. To provide a safety factor,
10 to 20% should be added.
Molding Plastics
Most of the literature on injection mold- ing processing refers
entirely or primarily to TPs; very little, if any at all, refers to
ther- moset TS plastics. At least 90 wt% of all injection-molded
plastics are TPs. Injection- molded parts can, however, include
combi- nations of TPs and TSs as well as rigid and flexible TPs,
reinforced plastics, TP and TS elastomers, etc. (Chap. 6). During
injection molding the TPs reach maximum tempera- ture during
plastication before entering the mold. The TS plastics reach
maximum tem- perature in the heated molds.
Molding Basics and Overview
The following information provides a com- plete overview of the
process of IM (Figs. 1-3 to 1-10). Continually required is better
under- standing and improving the relationship of
process-plastic-product and controlling the complete process.
Injection molding is a repetitive process in which melted
(plasticized) plastic is injected (forced) into a mold cavity or
cavities, where it is held under pressure until it is removed in a
solid state, basically duplicating the cavity of the mold (Fig.
1-11). The mold may con- sist of a single cavity or a number of
similar or dissimilar cavities, each connected to flow channels, or
runners, which direct the flow of the melt to the individual
cavities (Fig. 1-12). Three basic operations take place: (1) heat-
ing the plastic in the injection or plasticizing unit so that it
will flow under pressure, (2) al- lowing the plastic melt to
solidify in the mold, and (3) opening the mold to eject the molded
product.
These three steps are the operations in which the mechanical and
thermal inputs of the injection equipment must be co- ordinated
with the fundamental properties and behavior of the plastic being
processed; different plastics tend to have different
1 The Complete Injection Molding Process 5
Fig. 1-3 View of an injection molding machine.
-Clamping cylinder Injection unit
Fig. 1-4 Basic elements of injection molding.
melting characteristics, with some being ex- tremely different.
They are also the prime de- terminants of the productivity of the
process, since the manufacturing speed or cycle time (Fig. 1-13)
will depend on how fast the ma- terial can be heated, injected,
solidified, and ejected. Depending on shot size and/or wall
thicknesses, cycle times range from fractions of a second to many
minutes. Other impor- tant operations in the injection process in-
clude feeding the IMM, usually gravimetri- cally through a hopper,
and controlling the plasticator barrel’s thermal profile to ensure
high product quality (Fig. 1-14).
An example of complete injection molding operation is shown in Fig.
1-1. This block di- agram basically summarizes what should be
considered to ensure a good return on in-
Heating Injecting Molding Fig. 1-5 The basic cycle.
vestment to produce all types and shapes of molded products. The
block diagram meets the objective in bringing you up to date on
today’s technology as well as what is ahead. These important steps
must come together properly to produce products consistently
meeting performance requirements at the lowest cost. Basically, the
approach is to: (1) design a mold around the product to be molded,
(2) put the proper auxiliary equip- ment around the mold, and (3)
set up the necessary fabricating process such as qual- ity
controls, troubleshooting guides, preven- tative maintenance, and
operational safety procedures. To be effective, the evaluation of a
product should proceed according to a logical step-by-step process
(Fig. 1-15). The result is to target for zero defects.
6 1 The Complete Injection Molding Process
Fig. 1-6 Schematic of plastic material flow through hopper and
screw to the mold cavity.
People and Productivity
The recipe for productivity includes a list of ingredients such as
R&D, new technologies, updated equipment, computer automation
systems, and adequate modern facilities. But the one ingredient
that ties the recipe to- gether is people. None of the ingredients
have much use without the right people. As an example, computer
software (CAD, CAM, CIIM, etc.) have their place together with the
systems hardware. However, while the software and hardware all
provide impor- tant resources for automating the manufac- turing
line, to have the line run efficiently re- quires people to use
these resources properly. Equipment and plastic materials are not
per- fect, so that they require the human touch to ensure their
repeatability, etc. (see the sub- section on Plastic Material and
Equipment Variables in Chap. 11 .).
Achievable processing plans begin with the recognition that smooth
does not mean perfect. Perfection basically is an unrealis- tic
ideal, however one strives to approach it. The expectation of
perfection can block gen- uine communication between workers, de-
partments, management, customers and ven- dors (see the section on
Perfection in Chap. 5 ) . A smooth run program can be defined as
one that creates a product meeting fac- tors such as performance
specification and
delivery time and that falls within budget. It can be said that
perfection is never reached; there is always room for more
development and/or improvement. As has been stated throughout
history, to live is to change, and to approach perfection is to
have changed often (in the right direction).
Plastic Materials
Many thousands of different plastics (also called polymers, resins,
reinforced plastics, elastomers, etc.) are processed (Chap. 6).
Each of the plastics has different melt be- havior, product
performance (Figs. 1-16 and 1-17), and cost.
To ensure that the quality of the different plastics meets
requirements, tests are con- ducted on melts as well as molded
products. There are many different tests to provide all kinds of
information. Important tests on molded products are mechanical
tests such as those shown in Fig. 1-18, the main one being the
tensile test (Chap. 12).
There are basically two types of plastic ma- terials molded.
Thermoplastics (TPs), which are predominantly used, can go through
repeated cycles of heating/melting [usu- ally at least to 260°C
(500"F)I and cool- ing/solidification. The different TPs have dif-
ferent practical limitations on the number
1 The Complete Injection Molding Process 7
CLAMP OPEN
INJECTION MOLD INJECT ION
C L A M P HYDRAULIC C Y L l NDE R
T I M E R S ELECTRIC MOTOR
CLAMP OPEN
INJECTION MOLD INJECT ION
C L A M P HYDRAULIC C Y L l NDE R
T I M E R S ELECTRIC MOTOR
ELECTRICAL
START CYCLE
SWITCH DIRECTING O I L TO
INJECT
P U M P PRESSURIZES SYSTEM
OIL FLOWS TO CLAMP CYLINDER C L A M P CLOSES
FROM HYDRAULIC MANIFOLD
4 . INJECTION T I M E S OUT
5 . C L A M P COOLING T I M E S OUT
AND SCREW TRIPS SHOT S I Z E
L I M I T SWITCH
OIL FLOWS TO SCREW DRIVE SCREW PUMPS ITSELF
MOTOR BACK A S PARTS COOL IN
MOLD
OIL FLOWS TO CLAMP CYLINDER SCREW STOPS ROTATING
ROD AND C L A M P OPENS
6. EJECTION L I M I T SWITCH I S OIL FLOWS TO EJECTOR CYLINDER PART
I S EJECTED FROM
TRIPPED MOLD
7. RECYCLE T I M E R T I M E S OUT S T A R T CYCLE ETC.
Fig. 1-7 Molding-machine functions.
Density
Process
Fig. 1-8 Interrelation of product, resin, and process.
of heating-cooling cycles before appear- ance and/or properties are
affected. Ther- mosets (TSs), upon their final heating [usually at
least to 120°C (248"F)], be- come permanently insoluble and
infusible. During heating they undergo a chemical (cross-linking)
change. Certain plastics re- quire higher melt temperatures, some
as high as 400°C (752°F) (see section on Recycling in Chap.
6).
Extensive compounding of different amounts and combinations of
additives (colorants, flame retardants, heat and light stabilizers,
etc.), fillers (calcium carbonate, etc.), and reinforcements (glass
fibers, glass flakes, graphite fibers, whiskers, etc.) are
used
with plastics. Compounding also embraces the mixing (alloying,
blending, etc.) of two or more plastics that may be miscible or
immiscible, with or without additives.
With TPs, the mold initially is kept at as low a temperature as
possible, below the melting point of the plastic melt. This
approach causes the injected hot melt to initiate surface freez-
ing on the cavity wall, followed by formation of the solid product.
After a sufficient cool- ing time, the mold opens and the part(s)
are ejected. When processing TSs [from the in- jection unit
(plasticizer)], the hot melt enter- ing the heated mold initially
remains below the temperature that would cause premature
solidification due to its exothermic reaction.
P R O C E S S P R O D U C T
Fig. 1-9 Simplified processing steps.
1 The Complete Injection Molding Process 9
1 Performance Requirements I
I Material Selection I
.;........;l=r;’ Ideal choiceiCompromise
Fig. 1-10 Flow diagram for setting up the selec- tion
procedure.
After properly filling the cavity or cavities, the mold’s higher
temperature causes the melt to undergo its final chemical cross-
linking action resulting in solidification.
Morphology and Performance
The processability and performance of TPs, such as meeting product
tolerance re- quirements and mechanical properties, are influenced
by factors such as molecule size and weight, molecular
distribution, and shapes or structures of individual molecules. TPs
are formed by combining into long chains of molecules, or molecules
with branches (lat- eral connections) to form complex molecular
shapes. All these forms exist in either two or three dimensions,
Because of their geome- try (morphology), some of these molecules
can come closer together than others. These are identified as
crystalline (such as PE, PP, and PA); the others are amorphous
(such as PMMA, PS, SAN, and ABS). Morphology pertains to TPs but
not TSs. When TSs are processed, their individual chain
segments
scmw tJOzzle 2.25 in. dla.
16.000 wl
Mold injector -\
CUREINMOLDCAW
10 I The Complete Injection Molding Process
MATERIAL
INJECTION
TEMPERATURE PRESSURE
SHRINKAGE CCCCRS
TIME
are strongly bonded together during a chem- ical reaction that is
irreversible.
Plastics are either truly homogeneous, amorphous solids or
heterogeneous, semi- crystalline solids. There are no purely crys-
talline plastics; so-called crystalline materials also contain
different amounts of amorphous material. The term semicrystalline
is techni- cally more accurate, but seldom used. Vari- ous methods
of characterizing and evaluating
HIGH-QUALITY I MOLDED PARTS I 1 GOODMOLD 1 ADEQUATE MOLD
CLAMPING FORCE
Complete preliminary appraisal
Assign deaign prlorlty
1 The Complete Injection Molding Process 11
TOUGH
Fig. 1-16 Range of properties.
plastics are used, such as their molecu- lar weight distribution
(MWD). A narrow MWD enhances the performance of plastic products.
MWD affects melt flow behavior (Chap. 6).
Melt Flow and Rheology
Rheology is the science that deals with the deformation and flow of
matter under various conditions. An example is plastic melt
flow.
The rheology of plastics, particularly TPs, is complex but
manageable. These materials combine the properties of an ideal
viscous liquid (pure shear deformations) with those of an ideal
elastic solid (pure elastic defor- mation). Plastics are therefore
said to be vis- coelastic. The mechanical behavior of plastics is
dominated by the viscoelastic parameters such as tensile strength,
elongation at break, and rupture energy. The viscous attributes of
melt flows are very important considerations during any processing
system (see section on Molding Thin Walls in Chap. 7).
Viscosity is a material's resistance to vis- cous deformation
(flow). Quantitatively it is expressed by the modulus of elasticity
E (Chap. 12).
Plastics undergo non-Newtonian flow: the curve of pressure vs. flow
rate for the melt is not a straight line. By contrast, the flow of
water is nearly Newtonian.
Not only are there these two classes of deformation; there are also
two modes in which deformation can be produced: simple shear and
simple tension. The actual beha- vior during melting, as in a screw
plasticator (injection unit), is extremely complex,
NATURAL GAS PETROLEUM COAL AGRICULTURE v
I 1
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7 ETHYLENE STYRENE FORMALDEHYDE POLYOL ADIPATE PROPYLENE VINYL
CHLORIDE CUMENE ACRYLIC 77 v 1
T? \I 1
77 v 1
TK? \I 1
ELECTRICAL CONSUMER INDUSTRIAL 7
PRODUCTS SIDING COMMUNICATION ELECTRICAL MEDICAL AUTO TOOL - 1
I
Fig. 1-17 Raw materials to products.
12 1 The Complete Injection Molding Process
Tensile loud %+4
*--\
Fig. 1-18 Examples of mechanical tests.
displaying many types of shear-tension re- lationships. Together
with the screw design, the deformation determines the pumping ef-
ficiency of the plasticator and controls the re- lationship between
output rate and pressure drop through the melt flow to
solidification in the mold cavity(s).
Plasticating
Plasticating is the process that melts the plastics. Different
methods are used. The most common are the single-stage
(recip-
rocating screw) and the two-stage. In Fig. 1-19, (a) and (b) show
the ram (also called plunger) systems used in the original IMMs
since the 1870s, and now used mainly to pro- cess plastics with
very little melt flow, such as ultrahigh-molecular-weight
polyethylene. They use a piston, with or without a torpedo, for
plastication. Part (c) shows the single- stage reciprocating screw
plasticator, and (d) the two-stage screw plasticator.
There are different IMM operating de- signs in use: all-hydraulic,
all-electrical, and hybrid (combination of hydraulic and
electrical). Each design provides different
1 The Complete Injection Molding Process 13
- I I MOLD 4 E , i E , SINGLE-STAGE RAM INJECTION
MOLD
SCREW PLASTICATOR
Fig. 1-19 Examples of different plasticating systems.
advantages such as reducing product weight (reducing plastic
consumption), eliminat- ing or minimizing molded-in stresses, mold-
ing extremely small to very large products, and/or improving
performance. There are also IMMs that perform specialty molding
operations. An example is the gas-injection molding machine (GIMM)
systems. They ba- sically involve the injection of an inert gas,
usually nitrogen, into the melt as it enters
the mold. The gas forms a series of inter- connecting hollow
channels within the melt. The gas pressure at about 4,300 psi (30
MPa) is maintained through the cooling cycle. In effect the gas
packs the plastic against the cavity (Chap. 15).
Another design is injection-compression molding, also called
injection stamping or more often coining. It uses a compression
type mold having a male plug that fits into
I 4 1 The Complete Injection Molding Process
Fig. 1-20 Sections of a screw.
a female cavity. After a short shot enters the mold (which has been
previously opened and closed so that it is unpressurized), the
stress-free melt is compressed to mold the finished product. Other
systems include coin- jection, two-color injection molding, coun-
terflow injection molding, multi-live injec- tion molding,
oscillatory injection molding, reaction injection molding, liquid
injection molding, foam injection molding, fusible- and
soluble-core injection molding, tandem in- jection molding,
injection blow molding, in- jection molding with rotation,
continuous injection molding (Velcro strips, etc.), metal- plastic
injection molding, and vacuum injec- tion molding (Chap. 15)
Screw Designs
The primary purpose for using a screw located in the plasticator
barrel is to take advantage of its mixing action. The motion of the
screw is controlled to keep the IMM’s process controls operating at
their set points. The usual variation in melt temperature, melt
uniformity, and melt output is kept to a mini-
mum prior to entering the mold. Heat is sup- plied by heater bands
around the barrel and by the mixing action that occurs when the
plastic is moved by the screw. Both conduc- tion heating and
mechanical friction heating of the plastic occur during screw
rotation. The different controls used during injection mold- ing,
such as back pressure and screw rota- tional speed, influence the
melt characteris- tics (Chap. 3).
Most IMMs use a single constant-pitch, metering-type screw for
handling the plastics. The screw has three sections, for feed,
melt- ing (transition), and metering (Fig. 1-20). The feed section,
which is at the back end of the screw (where plastic first enters),
can occupy from very little to 75% of the screw length, usually 50
to 75%. Its length essentially de- pends upon how much heat has to
be added to the plastic that enters the hopper, where it may be
preheated.
The melting (transition) section is where the softening of the
plastic occurs; the plastic is transformed into a continuous melt.
It can occupy from 5 to 50% of the screw length. This section,
usually called the compression zone, has to be sufficiently long to
make
1 The Complete Injection Molding Process 15
sure that the plastic is melted. A straight compression-type screw
is one having no feed or metering section. For certain plastics,
par- ticularly TSs, there tends to be no compres- sion zone, since
overheating and solidifica- tion of the melt could occur between
the screw and barrel.
In the metering section, the plastic is smeared and sheared to give
the melt its fi- nal uniform composition and temperature for
delivery to the mold. As high shear action will tend to increase
the melt’s temperature, the length of the metering section is
depen- dent upon the plastic’s heat sensitivity and whether any
additional mixing is required. For certain heat-sensitive plastics
very little or no metering action can be tolerated. For other
plastics it averages about 20 to 25% of the screw length. Both the
feed and meter- ing sections usually have a constant cross sec-
tion (zero compression ratio). However, the depth of flight in the
feed section is greater than that in the metering section. The
screw’s compression ratio can be determined by di- viding the
flight depth in the feed section by that in the metering section.
Depending on the plastic processed, ratios usually range from 0 to
4.
Molds
The mold is the most important part of the IMM. It is a
controllable, complex, and ex- pensive device. If not properly
designed, op- erated, handled, and maintained, its opera- tion will
be a costly and inefficient.
Under pressure, hot melt moves rapidly through the mold. During the
injection into the mold, air in the cavity or cavities is re-
leased to prevent melt burning and the for- mation of voids in the
product. With TPs, temperature-controlled water (with ethylene
glycol if the water has to operate below its freezing point)
circulates in the mold to re- move heat; with TSs, electrical
heaters are usually used within the mold to provide the additional
heat required to solidify the plastic melt in the cavity.
The mold basically consists of a sprue, a runner, a cavity gate,
and a cavity. The sprue is the channel located in the stationary
platen that transports the melt from the plastica- tor nozzle to
the runner. In turn, melt flows through the runner and gate and
into the cav- ity. With a single-cavity mold, usually no run- ner
is used, so melt goes from the sprue to the gate.
Different runner systems are in use to meet different processing
requirements. The most popular are cold and hot runners. With a TP
cold runner, the melt flowing from the sprue to the gate solidifies
by the cooling action of the mold as the melt in the cavity or
cavities solidifies. With a TP hot runner the sprue to the gate is
insulated from the chilled cavity or cavities and remains hot, so
that the melt never cools; the next shot starts from the gate,
rather than from the nozzle as in a cold run- ner. With a TS hot
runner, the melt in the runner solidifies. The TS cold runner keeps
the plastic melted by using a cooled insulated manifold; its next
shot starts from the gate, rather than from the nozzle as in a TP
hot runner.
Molds are provided with different means, such as sliders,
unscrewing devices, undercuts (Fig. 1-21), and knockout systems, to
eject products as well as solidified runners at the proper time.
These basic operations in turn
Nominal thickness should be maintained throughout part
deeper hole intersecting side walls
Fig. 1-21 Methods of molding holes or openings in side walls
without undercutting mold movements.
16 1 The Complete Injection Molding Process
DEPTH OF DRAW !-L DIMENSION DIFFERENCE
Fig. 1-22 Example of mold-cavity draft angle re- quired to ensure
removal of molded product dur- ing its mold ejection action.
require control of various parameters such as fill time and hold
pressure (Chap. 4).
To simplify molding, whenever possible one should design the
product with fea- tures that simplify the mold-cavity melt filling
operation. Many such features can improve the product’s performance
and/or reduce cost. An example is choosing the mold-cavity draft
angle according to the plastic being processed, tolerance
requirements, etc. (Fig. 1-22). Figure 1-23 shows a situation where
it is possible to eliminate or significantly re- duce shrinkage,
sink marks, and other defects (Chap. 8).
Processing
Processing steps are summarized in Figs. 1-9, 1-10, and 1-24 to
1-27. Different ma- chine requirements and material conditions are
considered in choosing the most efficient injection molding
process. It is important to understand and properly operate the
basic IMM as well as its auxiliary equipment. In particular, in
practically all operations the screws must not be damaged or worn
and the plastic must be properly dried. Special dryers and/or
vented barrels are required for drying hygroscopic TP materials
such as PC, PMMA, PUR, and PET (Chap. 10).
Use of TP regrind may have little effect on product performance
(appearance, color, strength, etc.). However, reduction in perfor-
mance can occur with certain TPs after even one passage through the
IMM. Granulated TSs cannot be remelted but can be used as additives
or fillers in plastics.
Many TPs can be recycled indefinitely by granulating scrap,
defective products, and so on. During these cycles, however, the
plas- tic develops a “time-to-heat” history or res- idence time.
This phenomenon can signifi- cantly compromise processing
advantages
POOR DESIGN SINK MARKS
v2 t
MATCH OUTSIDE CONFIGURATION TO INSIDE CORES
POOR RECTANGULAR PART WITH ROUND HOLES
Fig. 1-23 Example of coring in molds to eliminate or reduce
shrinkage and sink marks.
1 The Complete Injection Molding Process
Fig. 1-24 Relationship between manufacturing process and properties
of products.
Bulk density
Shrinkage characteristic Water content Stickiness (adhesion)
Feeding ease I Feeding accurcy
I ~~ ~
Pre-heating
pre-heating (temperature, time) mold filling (time, pressure)
curing (temperature, time)
Dimensional stability Demoldlng behavior
Mold life Machine wear
Fig. 1-25 Processing behavior.
OPERATING RANGES MACHINE PARAMETER
Fig. 1-26 Process control model.
17
Preimpregnated
and properties, requiring compensation in the product design or
process setup, and/or material modification by incorporating addi-
tives, fillers, and/or reinforcements.
For all types of plastics, injection molding troubleshooting guides
have been written to allow fast corrective action when products do
not meet their performance requirements. Examples of errors in the
mold and product design with possible negative consequences during
processing and/or product perfor- mance are presented throughout
this book. Troubleshooting guides can be incorporated in process
control systems (Chap. 11). An ex- ample is checking dryer
performance as sum- marized in Table 1.1.
Process Controls
Proper injection of plastic melt into the mold is influenced by
several process control conditions (Chap. 7). Any one or combina-
tion of these can affect various performance parameters, such as
the rate of which the raw
material is fed into the IMM (Fig. 1-28), flow of melt, packing of
mold cavity or cavities and cycle time, which in turn affect
product performance (Chap. 8). As an example, pa- rameters that
influence product tolerances in- volve (1) product design, (2)
plastics used, (3) mold design, (4) IMM capability, and ( 5 )
molding cycle time.
Different types of machine process con- trols (PCs) can be used to
meet different re- quirements based on the molder’s needs. PC
systems range from simple monitors (alarm buzzers, flashing lights,
etc.) to very sophisti- cated program controllers [personal comput-
ers (PCs) interrelate different IMM functions and melt process
variables]. (Note that PC has two meanings; see Appendix 1,
Abbrevi- ations.)
Knowledge of the machine and plastic ca- pabilities is needed
before an intelligent PC program can be developed (Chap. 9). The
use of PC or SPC (statistical PC) software requires continual study
of the endless new computer technology as it applies to basically
melting plastic (Chap. 13).
1 The Complete Injection Molding Process
Table 1-1 Trouble shooting dehumidifier dryer performance
19
Heater failure.
Line, hopper, or filter blockage.
2. Dewpoint as measured at air inlet to the hopper is unacceptable.
line fuses.
Loss of regeneration heaters in one or both beds or
Loss of timer or clock motor ability to switch from one head to the
other, Le., continuous operation on only one desiccant bed.
Desiccant has deteriorated or been contaminated.
Loss of power to one or both desiccant beds.
3. Airflow low or nonexistent.
Fan motor burned out. Loose fan on motor shaft. Clogged filter(s).
Restricted or collapsed
Blower motor is reversed. air lines.
Check process air or afterheaters- regeneration heaters play no
part in this aspect of operation.
Locate and repair-if the hose is old and brittle, replace. Shorten
all hose to minimum lengths.
Check for collapsed or pinched lines, valves that are closed (some
makes have airflow valves located on the air inlet side of the
hopper). Filters should be changed or cleaned frequently- a good
trial period is every four weeks until experience dictates a
shorter or longer period.
These can be checked with a voltmeter at the control panel.
Check clock motor for movement by observing either function
indicators or valve-shifting mechanisms. Note that loss of
regeneration heaters may occur if the clock motor or shifting
mechanism malfunctions.
Most manufacturers suggest checking the desiccant annually and
replacing when it does not meet test criteria. Typically two to
three years is a reasonable interval, depending upon the severity
of service.
During regeneration cycle, exterior of the desiccant bed should be
hot to touch. Check contacts on relays or printed circuit board for
flaws; check line fuses if so equipped.
Replace. Tighten. Change. Correct and relieve restrictions.
Use of a pressure gauge or flowmeter is suggested. Proper rotation
is that at which the highest flow is indicated.
20 I The Complete Injection Molding Process
4 \
Control Guides
Adequate PC and its associated instrumen- tation are essential for
product quality con- trol (QC). The goal in some cases is precise
adherence to a control point. In other cases, maintaining the
temperature within compar- atively small range is all that is
necessary for effortless control (of temperature, time, pressure,
melt flow, rate, etc.) that will pro- duce the desired results
(Chaps. 7,9, and 13).
Regardless of the type of controls available, the processor setting
up a machine uses a sys- tematic approach that should be outlined
in the machine and/or control operating man- uals. Once the machine
is operating, the op- erator methodically targets one change at a
time to achieve maximum injection molding efficiency.
With injection molding, as with all types of plastics processing,
troubleshooting guides are established to take fast corrective
action
1 The Complete Injection Molding Process 21
when parts do not meet their performance re- quirements (Chap. 11).
This problem-solving approach fits into the overall PC and fabri-
cating interface.
Control systems for units with complex processes such as injection
molding are be- coming increasingly common. Such systems consist
mostly of control chains and circuitry that are often coupled in
their functions, as well as the corresponding exchange of data. In
a broad sense, the control systems serve the purpose of cost
reduction by monitoring quality and establishing high line
efficiency, in addition to the reduction of raw mate- rial
consumption and labor costs. A control system contributes in
different ways, partic- ularly in controlling the flow of plastic
melt. It can function by itself and fulfill the duties assigned to
it, often resulting in product im- provement.
Since the 1960s, a procedure to influence important properties of
the final product has been developed. The solutions, when intro-
duced into practice, served first of all to improve the product
line in different manu- facturing plants. However, initially these
sys- tems established themselves in only relatively small niches of
the commercial market. Later many more came aboard.
The use of flexibly automated injection molding controls and
systems definitely de- pends on the tasks the machine has to
perform and the production sequences re- quired. Automation is one
possibility for putting in-house aims into practice and/or meeting
market-dictated demands such as (1) production-cost reduction, (2)
short job processing time, (3) low expenditure on setup, (4)
greatest possible preparedness for meeting delivery dates, (5)
large product range, and (6) improved delivery consistency.
In order to utilize the advantages of flexi- bly automated
injection molding cells, a con- siderably larger capital investment
is nec- essary than with other choices of systems, which are less
automated and flexible. This increases the investment risk, so that
the question of the profitability of such systems becomes more
urgent. The following are examples of productivity-increasing
effects: (1) an increase in the annual utilization time,
(2) an increase in annual production vol- ume, (3) a reduction of
demolding time, and (4) a shortening of transit time if additional
activities can be carried out within the pro- grammed cycle
time.
The profitability of a flexibly automated injection molding plant
is influenced by (1) increased capital cost, (2) reduced per-
sonnel costs due to fewer personnel required, and (3) changes in
energy costs and the mold-cost structure. With automation, new
goals can be met through plant flexibility, such as (1) improved
delivery consistency, (2) greatest possible preparedness for meet-
ing delivery dates, (3) large range of products, and (4) short job
processing time. There are also quality-related effects that result
in im- proved quality assurance and a reduced num- ber of rejects.
Work environment changes oc- cur in (1) psychological and physical
stresses on staff, (2) qualification requirements from staff, (3)
social welfare of staff employed on the injection molding machine,
and (4) the ac- cident risk situation. An evaluation of the uti-
lization efficiency serves for assessing the cri- teria that cannot
be quantified in monetary terms. An established utilization
efficiency value can be taken as a decision aid, which in
conjunction with the investment calculation will allow a better
selection of alternatives under consideration.
Art of Processing
Processing of plastic is an art of detail. The more you pay
attention to details, the fewer hassles you will get from the
process. If a pro- cess has been running well, it will continue
running well unless a change occurs. Correct the problem; do not
compensate. That may not be an easy task, but understanding your
equipment, material, environment, and peo- ple can make it
possible.
Fine Tuning
A computer-integrated injection molding (CIIM) system makes it
possible to target for: (1) approaching a completely
automated
22 1 The Complete Injection Molding Process
injection molding system, (2) simultaneously achieving high quality
(zero defects), ( 3 ) increasing productivity, and (4) minimizing
cost. It does this in several ways, basically by enabling the
molder to fine-tune all the re- lationships that exist among the
many ma- chine settings and properties of the plastic melt. These
systems, when properly used, readily adapt to enhanced processing
capa- bilities.
Once processing variables (machine and plastic) are optimized
through computer sim- ulation (rather than the usual
trial-and-error method), these values are entered in com- puter
programs in the form of a rather large number of machine settings.
Establishing the initial settings during startup can be inher-
ently complex and time-consuming. Regard- less, the many benefits
of these systems are well recognized and accepted. However, it is
evident that self-regulation of injection molding can be effective
only when the de- sign of the product and the mold are opti- mized
with the correct processing conditions. Otherwise, a
self-regulating IMM is confused and can issue conflicting
instructions. The re- sults can be disastrous, including damage to
the machine and/or the mold as well as safety hazards. Therefore,
the efficient utilization of microprocessor control systems depends
on the success of utilizing correct and opti- mum programs with
knowledgeable people (Chap. 9). On the horizon is the potential for
fuzzy control to provide an important aid to optimizing process
control performance. As reviewed in Chap. 7, fuzzy logic, since its
in- ception in 1981, has striven with increasing success to mimic
the control actions of a hu- man operator.
Molding Operations
The following modes of operations typify injection molding
operations.
functions repeat. The IMM stops only in the event of a malfunction
or if it is man- ually interrupted. Machinery and mecha- nisms are
self-controlled so that manual in- put is not necessary during
operation. The continuing development of more sophisti- cated
processing equipment in turn allows the development of more
integrated process- ing equipment. This action results in many
improvements, such as (1) increased operat- ing efficiency through
reducing scrap and/or rejects, (2) improved quality through uni-
form, repeatable manufacturing procedures, (3) decision making and
record keeping by converting data to information, (4) access to
manufacturing information by supervisors and management, and ( 5 )
process control and process management.
Automation level The automation level is the degree to which a
process operates au- tomatically. The choice of level must take
into account the ability of the system to di- agnose problems in
operation, the ability of the system to recover from error or
fault, the ability of a system to start up and shut down without
human intervention, and the like.
Automated vision Vision automation provides a means to achieve
automatic equipment operation by adaptive part re- moval. It
provides the capability of detecting a variety of part problems or
defects by critical part inspection.
Semiautomatic
A semiautomatic machine will perform a complete cycle of programmed
molding func- tions automatically and then stop. It will then
require an operator to start another cycle manually.
Manual Automatic
A machine operating automatically will perform a molding cycle
where programmed
It is an operation in which each function and the timing of each
function is controlled manually by an operator.
1 The Complete Injection Molding Process 23
Primary
Identifies the main molding operation equipment to fabricate
products namely the injection molding machine (Chap. 2).
Secondary
After fabricating (primary) molded prod- ucts, secondary operations
may be required to produce the final finished product. These
operations can occur online or offline. They include any one or a
combination of opera- tions such as the following: annealing (to
re- lieve or remove residual stresses and strains), postcuring (to
improve performance); plat- ing; joining and a