How to Make Injection Molds

by Menges, Georg; Michaeli, Walter; Mohren, Paul

• ISBN13: 9781569902820
• ISBN10: 1569902828
• Edition: 3rd
• Format: Hardcover
• Copyright: 2001-06-01
• Publisher: Hanser Pub Inc

Summary

Economic success in the plastics processing industry depends on the quality, precision, and reliability of its most common tool: the injection mold. Consequently, misjudgments in design and mistakes in the manufacturing of molds can result in grave consequences.

Table of Contents

Materials for Injection Molds	1	(30)
Steels	2	(10)
Summary	2	(4)
Case-Hardening Steels	6	(1)
Nitriding Steels	7	(1)
Through-Hardening Steels	7	(2)
Heat-Treated Steels	9	(1)
Martensitic Steels	10	(1)
Hard Mold Alloys	10	(1)
Corrosion-Resistant Steels	10	(1)
Refined Steels	11	(1)
Cast Steel	12	(1)
Nonferrous Metallics	12	(7)
Copper Alloys	12	(1)
Beryllium-Copper Alloys	13	(1)
Zinc and its Alloys	14	(2)
Aluminum Alloys	16	(2)
Bismuth-Tin Alloys	18	(1)
Materials for Electrolytic Deposition	19	(1)
Surface Treatment of Steels for Injection Molds	20	(6)
General Information	20	(1)
Heat Treatment of Steels	21	(1)
Thermochemical Treatment Methods	21	(1)
Carburizing	21	(1)
Nitriding	22	(1)
Boriding	22	(1)
Electrochemical Treatments	23	(1)
Chrome Plating	23	(1)
Nickel Plating	23	(1)
NYE-CARD Process	24	(1)
Hard Alloy Coating	24	(1)
Coating at Reduced Pressure	24	(1)
CVD Process	24	(1)
PVD Process	25	(1)
Laser Surface Treatment	26	(2)
Laser Hardening and Re-Melting	27	(1)
Laser Alloying, Dispersing, and Coating	27	(1)
Electron Beam Hardening	28	(1)
Lamcoat Coating	28	(3)
References	28	(3)
Mold Making Techniques	31	(54)
Production of Metallic Injection Molds and Mold Inserts by Casting	32	(3)
Casting Methods and Cast Alloys	32	(1)
Sand Casting	33	(2)
Precision Casting Techniques	35	(1)
Rapid Tooling for Injection Molds	35	(15)
State of the Art	37	(2)
Direct Rapid Tooling	39	(1)
Direct Fabrication of Metallic Molds	39	(1)
Generative Methods	39	(3)
Direct Fabrication of Nonmetallic Molds	42	(1)
Indirect Rapid Tooling (Multistage Process Chains)	43	(1)
Process Chains Involving a Positive Pattern	44	(2)
Process Chains Involving a Negative Pattern	46	(4)
Outlook	50	(1)
Hobbing	50	(4)
Machining and Other Material Removing Operations	54	(5)
Machining Production Methods	54	(1)
Surface Treatment (Finishing)	55	(1)
Grinding and Polishing (Manual or Assisted)	55	(1)
Vibratory Grinding	56	(1)
Sand Blasting (Jet Lapping)	56	(1)
Pressure Lapping	57	(1)
Electrochemical Polishing	57	(1)
Electric-Discharge Polishing	57	(2)
Electric-Discharge Forming Processes	59	(4)
Electric-Discharge Machining (EDM)	59	(3)
Cutting by Spark Erosion with Traveling-Wire Electrodes	62	(1)
Electrochemical Machining (ECM)	63	(1)
Electrochemical Material Removal-Etching	63	(2)
Surfaces Processed by Spark Erosion or Chemical Dissolution (Etching)	65	(2)
Laser Carving	67	(1)
Rapid Tooling with LASERCAV	68	(1)
Molds for the Fusible-Core Technique	68	(17)
Molds for Sheathing the Fusible Cores	71	(3)
Gating the Molding	74	(1)
Thermal Considerations Concerning Mold Design	74	(1)
Core Shifting	75	(1)
Venting	75	(2)
Molds for Making the Fusible Cores	77	(1)
Core Material	78	(1)
Construction of a Casting Mold	78	(1)
Gating Systems	78	(2)
Thermal Considerations Concerning the Core-Casting Mold	80	(1)
Demolding Cast Fusible Cores	81	(1)
References	81	(4)
Procedure for Estimating Mold Costs	85	(20)
General Outline	85	(1)
Procedures for Estimating Mold Costs	85	(3)
Cost Group I: Cavity	88	(7)
Computation of Working Hours for Cavities	89	(1)
Time Factor for Machining Procedure	90	(1)
Machine Time for Cavity Depth	90	(1)
Time Consumption for Cavity Surface	91	(1)
Time Factor for Parting Line	92	(1)
Time Factor for Surface Quality	92	(1)
Machining Time for Fixed Cores	92	(1)
Time Factor for Tolerances	93	(1)
Time Factor for Degree of Difficulty and Multifariousness	93	(1)
Time Factor for Number of Cavities	94	(1)
Computation of Working Hours for EDM Electrodes	94	(1)
Cost Group II: Basic Molds	95	(1)
Cost Group III: Basic Functional Components	96	(3)
Sprue and Runner System	96	(2)
Runner System	98	(1)
Hot-Runner Systems	98	(1)
Heat-Exchange System	98	(1)
Ejector System	99	(1)
Cost Group IV: Special Functions	99	(1)
Other Cost Calculation Methods	100	(5)
Costs Based on Similarity Considerations	100	(3)
The Principle behind Hierarchical Similarity Searching	103	(1)
References	103	(2)
The Injection Molding Process	105	(38)
Cycle Sequence in Injection Molding	105	(4)
Injection Molding of Thermoplastics	107	(1)
Injection Molding of Crosslinkable Plastics	107	(1)
Injection Molding of Elastomers	108	(1)
Injection Molding of Thermosets	108	(1)
Terms Used in Connection with Injection Molds	109	(1)
Classification of Molds	109	(1)
Functions of the Injection Mold	110	(28)
Criteria for Classification of Molds	111	(4)
Basic Procedure for Mold Design	115	(1)
Determination of Mold Size	115	(1)
Maximum Number of Cavities	115	(6)
Clamping Force	121	(1)
Maximum Clamping Area	121	(1)
Required Opening Stroke	121	(1)
The Flow Length/Wall Thickness Ratio	122	(1)
Computation of Number of Cavities	123	(4)
Algorithm for the Determination of the Technically and Economically Optimum Number of Cavities	127	(9)
Costs for Sampling, Setup, and Maintenance	136	(2)
Cavity Layouts	138	(5)
General Requirements	138	(1)
Presentation of Possible Solutions	139	(1)
Equilibrium of Forces in a Mold During Injection	139	(1)
Number of Parting Lines	140	(1)
References	141	(2)
Design of Runner Systems	143	(62)
Characterization of the Complete Runner System	143	(1)
Concept and Definition of Various Types of Runners	144	(1)
Standard Runner Systems	144	(1)
Hot-Runner Systems	144	(1)
Cold-Runner Systems	144	(1)
Demands on the Runner System	145	(1)
Classification of Runner Systems	146	(1)
The Sprue	146	(5)
Design of Runners	151	(1)
Design of Gates	152	(9)
Position of the Gate at the Part	156	(5)
Runners and Gates for Reactive Materials	161	(3)
Elastomers	161	(1)
Thermosets	162	(1)
Effect of Gate Position for Elastomers	162	(1)
Runners for Highly-Filled Melts	163	(1)
Qualitative (Flow Pattern) and Quantitative Computation of the Filling Process of a Mold (Simulation Models)	164	(28)
Introduction	164	(1)
The Flow Pattern and its Significance	165	(1)
Using the Flow Pattern for Preparing a Simulation of the Filling Process	166	(2)
Theoretical Basis for Producing a Flow Pattern	168	(1)
Practical Procedure for Graphically Producing a Flow Pattern	169	(1)
Drawing the Flow Fronts	169	(1)
Radius Vectors for the Presentation of Shadow Regions	169	(3)
Areas with Differences in Thickness	172	(3)
Flow Patterns of Ribs	175	(1)
Flow Patterns of Box-Shaped Moldings	176	(1)
Analysis of Critical Areas	176	(3)
Final Comments	179	(1)
Quantitative Analysis of Filling	179	(1)
Analytical Design of Runners and Gates	180	(1)
Rheological Principles	180	(6)
Determining Viscous Flow Behavior under Shear with the Aid of a Capillary Viscometer	186	(3)
Elongational Viscosity	189	(1)
Simple Equations for Calculating Loss of Pressure in Gates and Runners	189	(3)
Special Phenomena Associated with Multiple Gating	192	(2)
Design of Gates and Runners for Crosslinking Compounds	194	(11)
Elastomers	194	(1)
Calculation of Filling Process	194	(1)
Effect of Processing Characteristics on the Basis of Processing Windows	195	(1)
Criticism and Examples Concerning the Processing-Window Model	196	(2)
Thermosets	198	(1)
Flow-Curing Behavior of Thermosets	198	(2)
References	200	(5)
Design of Gates	205	(54)
The Sprue Gate	205	(1)
The Edge or Fan Gate	206	(2)
The Disk Gate	208	(1)
The Ring Gate	208	(2)
The Tunnel Gate (Submarine Gate)	210	(2)
The Pinpoint Gate in Three-Platen Molds	212	(2)
Reversed Sprue with Pinpoint Gate	214	(1)
Runner less Molding	215	(2)
Molds with Insulated Runners	217	(3)
Temperature-Controlled Runner Systems - Hot Runners	220	(29)
Hot-Runner Systems	221	(1)
Economic Advantages and Disadvantages of Hot-Runner Systems	221	(1)
Hot Runners for Various Applications and New Possibilities	222	(1)
Design of a Hot-Runner System and its Components	223	(4)
Sprue Bushing	227	(1)
Melt Filters	228	(1)
Manifold Blocks	228	(1)
Single Cavity Molds	228	(1)
Manifold Beams	229	(1)
Multi-Cavity Molds	229	(2)
Nozzles for Hot-Runner Molds	231	(3)
Data Concerning the Design of Hot Runner Manifolds	234	(1)
Manifold Beams	234	(3)
Nozzle Design	237	(1)
Notes on Operating Hot Runners	238	(1)
Heating of Hot Runner Systems	238	(1)
Heating of Nozzles	238	(1)
Heating of Manifolds	239	(1)
Computing of Power Output	240	(1)
Temperature Control in Hot Manifolds	241	(1)
Placement of Thermocouples	241	(1)
Cold Runners	242	(1)
Cold-Runner Systems for Elastomer Injection Molds	242	(6)
Cold-Runner Molds for Thermosets	248	(1)
Special Mold Concepts	249	(10)
Stack Molds	249	(3)
Molds for Multicomponent Injection Molding	252	(1)
Combination Molds	253	(3)
Two-Component Sandwich Injection Molds	256	(1)
Bi-Injection Molds	256	(1)
References	256	(3)
Venting of Molds	259	(12)
Passive Venting	260	(5)
Active Venting	265	(1)
Venting of Gas Counter-Pressure Injection Molds	266	(5)
References	268	(3)
The Heat Exchange System	271	(64)
Cooling Time	272	(3)
Thermal Diffusivity of Several Important Materials	275	(2)
Thermal Diffusivity of Elastomers	276	(1)
Thermal Diffusivity of Thermosets	276	(1)
Computation of Cooling Time of Thermoplastics	277	(6)
Estimation	277	(1)
Computation of Cooling Time with Nomograms	277	(2)
Cooling Time with Asymmetrical Wall Temperatures	279	(1)
Cooling Time for Other Geometries	280	(3)
Heat Flux and Heat-Exchange Capacity	283	(10)
Heat Flux	283	(1)
Thermoplastics	283	(4)
Reactive Materials	287	(1)
Thermosets	287	(6)
Analytical, Thermal Calculation of the Heat-Exchange System Based on the Specific Heat Flux (Overall Design)	293	(15)
Analytical Thermal Calculation	294	(2)
Calculating the Cooling Time	296	(1)
Heat Flux Balance	296	(2)
Coolant Throughput	298	(2)
Temperature of the Cooling Channel	300	(2)
Position of the Cooling Channels	302	(5)
Design of Cooling Circuit	307	(1)
Flow Rate of Coolant	307	(1)
Pressure Drop	308	(1)
Numerical Computation for Thermal Design of Molded Parts	308	(4)
Two-Dimensional Computation	309	(1)
Three-Dimensional Computation	309	(1)
Simple Estimation of the Heat Flow at Critical Points	310	(1)
Empirical Correction for Cooling a Corner	311	(1)
Practical Design of Cooling Systems	312	(13)
Heat-Exchange Systems for Cores and Parts with Circular Cross-Section	312	(4)
Cooling Systems for Flat Parts	316	(2)
Sealing of Cooling Systems	318	(2)
Dynamic Mold Cooling	320	(2)
Empirical Compensation of Corner Distortion in Thermoplastic Parts from Heat-Flux Differences	322	(1)
Cold Core and Warm Cavity	323	(1)
Modification of Corner Configuration	323	(1)
Local Adjustment of Heat Fluxes	324	(1)
Calculation for Heated Molds for Reactive Materials	325	(1)
Heat Exchange in Molds for Reactive Materials	325	(4)
Heat Balance	325	(3)
Temperature Distribution	328	(1)
Practical Design of the Electric Heating for Thermoset Molds	329	(6)
References	331	(4)
Shrinkage	335	(16)
Introduction	335	(1)
Definition of Shrinkage	335	(2)
Tolerances	337	(5)
Causes of Shrinkage	342	(1)
Causes of Anisotropic Shrinkage	343	(2)
Causes of Distortion	345	(1)
Effect of Processing on Shrinkage	346	(2)
Supplementary Means for Predicting Shrinkage	348	(3)
References	349	(2)
Mechanical Design of Injection Molds	351	(36)
Mold Deformation	351	(1)
Analysis and Evaluation of Loads and Deformations	351	(2)
Evaluation of the Acting Forces	352	(1)
Basis for Describing the Deformation	353	(2)
Simple Calculation for Estimating Gap Formation	353	(1)
More Accurate Calculation for Estimating Gap Formation and Preventing Flash	354	(1)
The Superimposition Procedure	355	(3)
Coupled Springs as Equivalent Elements	356	(1)
Parallel Coupling of Elements	357	(1)
Elements Coupled in Series	358	(1)
Computation of the Wall Thickness of Cavities and Their Deformation	358	(6)
Presentation of Individual Cases of Loading and the Resulting Deformations	359	(1)
Computing the Dimensions of Cylindrical Cavities	360	(2)
Computing the Dimensions of Non-Circular Cavity Contours	362	(1)
Computing the Dimensions of Mold Plates	363	(1)
Procedure for Computing Dimensions of Cavity Walls under Internal Pressure	364	(1)
Deformation of Splits and Slides under Cavity Pressure	364	(6)
Split Molds	364	(6)
Preparing for the Deformation Calculations	370	(6)
Geometrical Simplifications	372	(2)
Tips on Choosing Boundary Conditions	374	(2)
Sample Calculations	376	(9)
Other Loads	385	(2)
Estimating Additional Loading	385	(1)
References	386	(1)
Shifting of Cores	387	(14)
Estimating the Maximum Shifting of a Core	387	(1)
Shifting of Circular Cores with Lateral Pinpoint Gate at the Base (Rigid Mount)	388	(2)
Shifting of Circular Cores with Disk Gates (Rigid Mount)	390	(4)
Basic Examination of the Problem	391	(1)
Results of the Calculations	392	(2)
Shifting of Cores with Various Types of Gating (Rigid Mount)	394	(1)
Shifting of Inserts	395	(4)
Analytical Calculation of Deformation of Metal Inserts Using a Cylindrical Roll Shell as an Example	395	(1)
Evaluation of the Deflection Line for Different Part Geometries	396	(3)
Design Examples for Core Mounting and Alignment of Deep Cavities	399	(2)
References	400	(1)
Ejection	401	(74)
Summary of Ejection Systems	401	(4)
Design of the Ejection System - Ejection and Opening Forces	405	(21)
General Discussion	405	(2)
Methods for Computing the Release Forces	407	(1)
Coefficients of Static Friction for Determining Demolding and Opening Forces	407	(3)
The Estimation Method for Cylindrical Sleeves	410	(3)
Rectangular Sleeves	413	(1)
Tapered Sleeves	413	(1)
Summary of Some Basic Cases	413	(1)
The Release Forces for Complex Parts Exemplified with a Fan	414	(6)
Numerical Computation of Demolding Processes (for Elastomer Parts)	420	(4)
Estimating the Opening Forces	424	(1)
Changes of State in a p-v-T Diagram for Molds with Different Rigidities	425	(1)
Indirect Opening Forces	426	(1)
Total Opening Force	426	(1)
Types of Ejectors	426	(8)
Design and Dimensions of Ejector Pins	426	(3)
Points of Action of Ejector Pins and Other Elements of Demolding	429	(4)
Ejector Assembly	433	(1)
Actuation of the Ejector Assembly	434	(3)
Means of Actuation and Selection of Places of Action	434	(1)
Means of Actuation	434	(3)
Special Release Systems	437	(6)
Double-Stage Ejection	437	(1)
Combined Ejection	437	(3)
Three-Plate Molds	440	(1)
Ejector Movement by Stripper Bolt	440	(1)
Ejector Movement by Latch	440	(1)
Reversed Ejection from the Stationary Side	441	(2)
Ejector Return	443	(3)
Ejection of Parts with Undercuts	446	(3)
Demolding of Parts with Undercuts by Pushing Them off	446	(1)
Permissible Depth of Undercuts for Snap Fits	447	(2)
Demolding of Threads	449	(12)
Demolding of Parts with Internal Threads	449	(1)
Stripper Molds	449	(1)
Collapsible Cores	449	(1)
Molds with Interchangeable Cores	450	(1)
Molds with Unscrewing Equipment	451	(1)
Semiautomatic Molds	452	(1)
Fully Automatic Molds	453	(7)
Demolding of Parts with External Threads	460	(1)
Undercuts in Noncylindrical Parts	461	(14)
Internal Undercuts	461	(1)
External Undercuts	461	(1)
Slide Molds	462	(5)
Split-Cavity Molds	467	(4)
Molds with Core-Pulling Devices	471	(1)
References	472	(3)
Alignment and Changing of Molds	475	(18)
Function of Alignment	475	(1)
Alignment with the Axis of the Plasticating Unit	475	(1)
Internal Alignment and Interlocking	476	(4)
Alignment of Large Molds	480	(2)
Changing Molds	482	(11)
Systems for a Quick Change of Molds for Thermoplastics	482	(7)
Mold Exchanger for Elastomer Molds	489	(1)
References	490	(3)
Computer-Aided Mold Design and the Use of CAD in Mold Construction	493	(34)
Introduction	493	(5)
The Flow Pattern Method Pointed the Way Forward	493	(1)
Geometry Processing Marks the Key to Success	494	(1)
Complex Algorithms Mastered	495	(1)
Simulation Techniques Still Used Too Infrequently	495	(1)
Simpler and Less Expensive	495	(1)
The Next Steps already Carved out	496	(2)
CAD Use in Mold Design	498	(29)
Introduction	498	(1)
Principles of CAD	498	(1)
2D/3D Model Representation	498	(3)
Enhancing the Performance of CAD Models by Associativity, Parametrics, and Features	501	(1)
Interfaces and Use of Integrated CAD	502	(4)
Data Administration and Flow of Information	506	(1)
CAD Application in Mold-Making	507	(1)
Modeling	507	(4)
Integrated Functions for Mold-Making	511	(3)
Application-Specific Function Extension	514	(1)
Possibilities Afforded to Concurrent Engineering through the Use of CAD	515	(2)
Selection and Introduction of CAD Systems	517	(1)
Phases in System Selection	518	(2)
Formulating the CAD Concept	520	(1)
Benchmarking	521	(1)
CAD Introduction	522	(1)
References	523	(4)
Maintenance of Injection Molds	527	(16)
Advantages of Maintenance Schedules	529	(1)
Scheduling Mold Maintenance	530	(4)
Data Acquisition	530	(2)
Data Evaluation and Weak-Point Analysis	532	(2)
Computer-Based Support	534	(1)
Storage and Care of Injection Molds	534	(4)
Repairs and Alterations of Injection Molds	538	(5)
References	541	(2)
Measuring in Injection Molds	543	(10)
Sensors in Molds	543	(1)
Temperature Measurement	543	(1)
Measuring Melt Temperatures in Molds Using IR Sensors	543	(1)
Pressure Measurement	544	(3)
Purpose of Pressure Measurement	544	(1)
Sensors for Measuring Melt Pressures in Molds	544	(1)
Direct Pressure Measurement	545	(1)
Indirect Pressure Measurement	546	(1)
Use of Sensor-Transducer Probes	547	(1)
Process Optimization	547	(1)
Monitoring Quality	548	(5)
References	550	(3)
Mold Standards	553	(7)
References	559	(1)
Temperature Controllers for Injection and Compression Molds	560	(13)
Function, Method, Classification	560	(3)
Control	563	(6)
Control Methods	563	(2)
Preconditions for Good Control Results	565	(1)
Controllers	565	(1)
Heating, Cooling, and Pump Capacity	565	(1)
Temperature Sensors	566	(1)
Installation of Temperature Sensors in the Mold	566	(1)
Heat-Exchange System in the Mold	567	(1)
Keeping the Temperature as Stable as Possible	568	(1)
Selection of Equipment	569	(1)
Connection of Mold and Equipment - Safety Measures	569	(1)
Heat Carrier	570	(1)
Maintenance and Cleaning	571	(2)
References	571	(2)
Steps for the Correction of Molding Defects During Injection Molding	573	(4)
References	576	(1)
Special Processes - Special Molds	577	(24)
Injection Molding of Microstructures	577	(10)
Molding Technology and Process Control	577	(2)
Production Processes for Microcavities	579	(2)
Silicon Technology	581	(2)
The LiGA Technique	583	(1)
Laser LiGA	584	(1)
Laser Removal	584	(1)
Electric-Discharge Removal	585	(2)
Micromachining	587	(1)
In-Mold Decoration	587	(4)
Processing of Liquid Silicone	591	(2)
Evacuation	591	(1)
Gate	592	(1)
Demolding	592	(1)
Temperature Control	592	(1)
Cold-Runner Technique	593	(1)
Injection-Compression Molding	593	(8)
References	596	(5)
Index	601