MoldFlow Book

Shoemaker Jay Shoemaker (Ed.)

Contents: • Polymer Flow Behavior in Injection Molds • Molding Conditions and Injection Pressure • Filling Pattern • Moldflow Design Principles • Meshes Used In Moldflow Analyses • Product Design • Gate Design • Runner System Design • Cooling System Design • Shrinkage and Warpage • Moldflow Design Procedure • Part Defects

ISBN-10: 1-56990-403-0 ISBN-13: 978-1-56990-403-9 Hanser Gardner Publications www.hansergardner.com ISBN-10: 3-446-40640-9 ISBN-13: 978-3-446-40640-7 Carl Hanser Verlag www.hanser.de

9 781569 904039

Moldflow Design Guide

The book provides an overview of the polymer flow behavior and the injection molding process, design principles to facilitate integrated part and mold design, and examples of how Moldflow design analysis technology can be used both to solve problems and to optimize the design of part, mold, and the molding process itself.

Shoemaker

The Moldflow Design Guide is intended to help practicing engineers solve problems they encounter frequently in the design of parts and molds and during production. Today, the global imperative to drive down the cost of manufacturing has led to the use of molding simulation as a cost optimization tool rather than just as a design and problem avoidance tool. It is critical for engineers in the plastics field to have access to flow analyses and their interpretations, including the simulation of cooling and warp effects, to aid in the successful design and manufacture of parts and molds.

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Moldflow Design Guide

Moldflow Design Guide A Resource for Plastics Engineers

Moldflow Design Guide downloaded from www.hanser-elibrary.com by 190.235.14.195 on August 30, 2012 For personal use only.

Jay Shoemaker (Editor) Moldflow Design Guide

Moldflow Design Guide downloaded from www.hanser-elibrary.com by 190.235.14.195 on August 30, 2012 For personal use only.

Moldflow Design Guide downloaded from www.hanser-elibrary.com by 190.235.14.195 on August 30, 2012 For personal use only.

Jay Shoemaker (Editor)

Moldflow Design Guide A Resource for Plastics Engineers

Hanser Publishers, Munich • Hanser Gardner Publications, Cincinnati

The Editor: Jay Shoemaker, Moldflow Corporation, Framingham, Massachusetts, USA

Moldflow Design Guide downloaded from www.hanser-elibrary.com by 190.235.14.195 on August 30, 2012 For personal use only.

Distributed in the USA and in Canada by Hanser Gardner Publications, Inc. 6915 Valley Avenue, Cincinnati, Ohio 45244-3029, USA Fax: (513) 527-8801 Phone: (513) 527-8977 or 1-800-950-8977 www.hansergardner.com Distributed in all other countries by Carl Hanser Verlag Postfach 86 04 20, 81631 München, Germany Fax: +49 (89) 98 48 09 www.hanser.de The use of general descriptive names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

Library of Congress Cataloging-in-Publication Data Shoemaker, Jay. Moldflow design guide : a resource for plastic engineers / Jay Shoemaker. p. cm. ISBN-13: 978-1-56990-403-9 (hardcover) ISBN-10: 1-56990-403-0 (hardcover) 1. Injection molding of plastics. I. Title. TP1120.S486 2006 668.4‘12--dc22 2006012438

Bibliografische Information Der Deutschen Bibliothek Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über abrufbar. ISBN-10: 3-446-40640-9 ISBN-13: 978-3-446-40640-7 All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or by any information storage and retrieval system, without permission in writing from the publisher. © Moldflow Corporation, USA 2006 Production Management: Oswald Immel Typeset by Marcia Swan, USA Coverconcept: Marc Müller-Bremer, Rebranding, München, Germany Coverdesign: MCP • Susanne Kraus GbR, Holzkirchen, Germany Printed and bound by Kösel, Krugzell, Germany

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Foreword The drive toward fast, cost-effective, and reliable plastics manufacturing has been Moldflow’s sole guiding goal since the company was founded over 25 years ago. This focused determination led us to introduce many new and exciting tools into the market, each contributing to achieving our goal in some way, whether by driving cost out of production with reduced material usage or shortened cycle times, reducing mold delivery time by minimizing re-work, or increasing the reliability of supply by enabling higher quality products to be manufactured with greater surety in scheduling. The artificially balanced, multi-cavity and family molds that are now commonplace were made practical through the advent of our early simulation and runner balancing capabilities, which were introduced in the late 1970s and early 1980s. As these tools evolved, we were able to visualize, and therefore control, flow patterns and weld lines. This evolution continued until we arrived in the 2000s with an array of sophisticated technology to control warpage, account for heat transfer, predict core shift, adapt to new molding processes, and much more. From traditional midplane technology to fully three-dimensional simulations, all our solutions are well integrated into a solid-modeling design environment. As the technology has evolved, so has its usage. When Moldflow simulation technology was introduced, its primary purpose was to search for remedies to pre-existing molding problems. It soon became evident that the insight the software provided to solve molding problems would be better applied ahead of actual molding, during the design process. This methodology, which we call “problem avoidance,” was the primary use for Moldflow technology for the first 20 years of its existence. For Moldflow, this created a unique challenge: to open the world of manufacturing to the designers of parts and molds. What constitutes an ineffective design for molding may be apparent to a seasoned processing engineer looking retrospectively at a poorly performing tool, but how can design engineers use the CAE tools to visualize, diagnose and solve these same issues ahead of time—without 20 years of molding experience? How can manufacturers go further and use information that cannot be seen in the real molding process but is revealed via simulation? The key that unlocked this puzzle began its life as the Moldflow Design Philosophy. This is widely viewed as the most important publication Moldflow has ever produced and has spawned follow-on works on related subjects. Rather than provide insight into the operation of the simulation tools, Moldflow Design Philosophy set forth simple principles that transcend any specific software application and, as a result, are as valid with today's advanced simulation products as they were over two decades ago. In more recent years, another transition has occurred. The global imperative to drive down the cost of manufacturing has led to the use of molding simulation as a cost optimization tool rather than for problem avoidance. This change has increased the number of Moldflow users by an order of magnitude across a far broader cross-section of the plastics industry. Greater design-centricity leads to even more dependence on the plastics design principles, which can be used to drive optimization.

VI

Foreword

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Despite a quarter of a century of technological advances, the golden years of CAE are ahead of us as our industry takes a broader and more integrated view of what it takes to manage a product’s life cycle. Moldflow is proud of its contributions to date and will continue to focus on developing innovative technology coupled with practical design principles to deliver more profitable manufacturing. Roland Thomas President & CEO, Moldflow Corporation

Preface

VII

Preface

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About this Book The origins of this book include not only Moldflow Design Principles, but also Warpage Design Principles published by Moldflow, and the C-MOLD Design Guide. Collectively, these documents are based on years of experience in the research, theory, and practice of injection molding. These documents are now combined into this book: the Moldflow Design Guide. The Moldflow Design Guide is intended to help practicing engineers solve problems they frequently encounter in the design of parts and molds, as well as during production. This book can also be used as a reference for training purposes at industrial and educational institutions.

How to Use this Book This book has several chapters and appendices that deal with different stages of the design process and provides background on the injection-molding process and plastic materials.

• The first three chapters introduce injection molding how polymers flow inside injection molds and how molding conditions and injection pressure influence the process.

• Chapter 4 discusses Moldflow design principles and how they relate to making quality parts.

• Chapter 5 introduces the finite element mesh technology used by Moldflow and how these meshes influence the quality of the analysis.

• Chapters 6 to 9 introduce design concepts for the product, gates, runners, and cooling systems.

• Chapter 10 introduces concepts relating to shrinkage and warpage and how Moldflow is used to determine the amount of shrinkage and warpage a molded part will have and what causes the warpage.

• Chapter 11 discusses the design procedure for analyzing injection-molded parts. • Chapter 12 discusses major part defects found on injection-molded parts. • Finally the four appendices discuss basic injection-molding machine operation, process control, variants of the standard injection-molding process, and plastic materials.

Benefits of Using CAE The injection-molding industry has recognized that computer-aided engineering (CAE) enhances an engineer's ability to handle all aspects of the polymer injection-molding process, benefiting productivity, product quality, timeliness, and cost. This is illustrated by a wealth of

VIII

Preface

literature and the ever-growing number of CAE software users in the injection-molding industry.

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CAE Predicts Process Behavior Ideally, CAE analysis provides insight that is useful in designing parts, molds, and molding processes. Without it, we rely on previous experience, intuition, prototyping, or molding trials to obtain information such as polymer melt filling patterns, weld-line and air-trap locations, required injection pressure and clamp tonnage, fiber orientation, cycle time, final part shape and deformation, and mechanical properties of molded parts, just to name a few. Without CAE analysis, other equally important design data, such as spatial distributions of pressure, temperature, shear rate, shear stress, and velocity, are more difficult to obtain, even with a well-instrumented mold. The process behavior predicted by CAE can help novice engineers overcome the lack of previous experience and assist experienced engineers in pinpointing factors that may otherwise be overlooked. By using CAE analysis to iterate and evaluate alternative designs and competing materials, engineering know-how in the form of design guidelines can be established relatively faster and more cost-effectively. User Proficiency Determines the Benefits of CAE While CAE technology helps save time, money, and raw material, as well as cuts scrap, reduces the rejection rate, improves product quality, and gets new products to market faster, it is by no means a panacea for solving all molding problems. Rather, it should be recognized that CAE analysis is essentially a tool, designed to assist engineers instead of taking over their responsibilities or replacing them. Like many other tools, the usefulness of CAE technology depends on the proficiency of the user. The benefits mentioned above will not be realized unless the CAE tool is used properly. To be more specific, the accuracy of CAE analysis depends greatly on the input data provided by the user. In addition, the results generated by CAE analysis need to be correctly and intelligently interpreted by the user before sound judgments and rational decisions are made. Otherwise, users will simply be swamped by the vast amount of data without getting any useful information.

Acknowledgements

IX

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Acknowledgements The Moldflow Design Guide would not have been accomplished were it not for the vision of Ken Welch. Ken and I have discussed the value of assembling the best of the Moldflow Design Principles, Warpage Design Principles, and the C-MOLD Design Guide into a single book for several years. With Ken's leadership, he gave the project to Steve Thompson's training group, of which I am a part. Steve helped me coordinate the resources necessary to get this project done. I could not have done this project without Steve's help and guidance. A review of the content was part of the development of the Moldflow Design Guide. Moldflow developers including Peter Kennedy, Rong Zheng, Zhongshuang Yuan, and Xiaoshi Jin have reviewed sections of the book. Moldflow's application engineers and other technical staff with Moldflow have also reviewed sections. These reviewers include Chad Fuhrman, Matt Jaworski, Christine Roedlich, Eric Henry, Olivier Anninos, Paul Larter, and Ana Maria Marin. A special thanks goes to Mike Rogers, who reviewed the entire book for me and provided critical feedback on the content and organization of the book. I would also like to thank Kurt Hayden of Western Michigan University for reviewing the appendix on process control. His many years of experience of process setup and optimization was invaluable. Finally, I would like to thank members of Moldflow's Technology Transfer group for supporting me in the writing of this book. These members include Marcia Swan, Caroline Dorin, Robert Ashley, Melissa Haslam, Darren Seamons, and Gregory Brown. On a personal note, I would like to acknowledge and thank Paul Engelmann, Professor and Department Chair, Western Michigan University, Department of Industrial and Manufacturing Engineering, for being my friend and mentor during my career. With Paul, I have been able to teach and participate in research he has done on injection molding tooling and processing at Western Michigan University. I have found working with Paul has made me a better Moldflow user and engineer by providing another perspective on how Moldflow can be used to solve injection molding problems.Jay Shoemaker, Editor

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Contents 1

Polymer Flow Behavior in Injection Molds . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.2 1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 1.2.6 1.2.7 1.2.8 1.2.9 1.2.10 1.2.11 1.2.12

Phases of Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 How Plastic Fills a Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The Filling Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The Pressurization Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 The Compensation Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 How Do Plastics Flow? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Material Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Viscoelastic Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Melt Shear Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Newtonian Fluid vs. Non-Newtonian Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Shear-thinning Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Shear Rate Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pressure-driven Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pressure Gradient and Injection Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Melt Flow Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Injection Pressure vs. Fill Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Flow Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2

Molding Conditions and Injection Pressure . . . . . . . . . . . . . . . . . . . . . . 17

2.1 2.1.1 2.2 2.3 2.3.1 2.3.2 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.4.5 2.4.6 2.4.7 2.4.8 2.5 2.5.1 2.5.2 2.5.3 2.5.4

Injection-pressure Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure Drives the Flow Front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors Influencing Injection-pressure Requirements . . . . . . . . . . . . . . . . . . . . Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circular Channel Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strip Channel Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Molding Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Melt Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mold Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fill Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shear Stress Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packing Pressure and Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow to Determine Optimum Molding Conditions . . . . . . . . . . . . . Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molding Window Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Front Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17 18 18 20 20 20 21 21 22 22 23 23 24 25 26 26 27 27 28 29

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XII

Contents

2.5.5 2.5.6

Cooling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3

Filling Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.1 3.1.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 3.2.9 3.2.10 3.2.11 3.3 3.3.1 3.3.2 3.3.3 3.4 3.4.1 3.4.2 3.5 3.5.1

Filling Pattern Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is the Filling Pattern? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow in Complex Molds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Overpack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Racetrack Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Varying Injection Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Underflow Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hesitation Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weld Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meld Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sink Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multidirectional Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unstable Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simple Flow Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow-front Velocity and Flow-front Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What are FFV and FFA? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow-front Velocity Influences Filling Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow to Determine the Filling Pattern . . . . . . . . . . . . . . . . . . . . . . . Computer Simulation Can Eliminate Molding Trials . . . . . . . . . . . . . . . . . . . . . Using a Flow Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow to Achieve Constant FFV . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controlling the FFV Through Ram Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Moldflow Design Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5

Product Design and Moldflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sequence of Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part Filling Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molding Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling Optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packing Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warpage Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Moldflow Flow Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unidirectional and Controlled Flow Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant Pressure Gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum Shear Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uniform Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33 33 34 34 35 35 36 37 38 38 38 39 40 41 41 41 41 42 43 43 43 44 44

47 47 48 48 48 49 49 49 49 50 51 52 53 54

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Contents

XIII

4.3.6 4.3.7 4.3.8 4.3.9 4.3.10 4.3.11 4.3.12

Positioning Weld and Meld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Avoid Hesitation Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Avoid Underflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Balancing with Flow Leaders and Flow Deflectors . . . . . . . . . . . . . . . . . . . . . . Controlled Frictional Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Shutoff of Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acceptable Runner/Cavity Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55 55 55 57 58 58 59

5

Meshes Used In Moldflow Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

5.1 5.1.1 5.1.2 5.1.3 5.2 5.2.1 5.2.2 5.3 5.4 5.5 5.5.1 5.5.2

Mesh Types Used by Moldflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Finite Elements Used in Moldflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesh Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solver Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesh Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesh Density Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geometry Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Importing Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Different Mesh Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Door Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Product Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.2 6.2.1 6.2.2 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.4 6.4.1 6.4.2

Material Properties for Product Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastics Are Sensitive to Operating Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . Stress-Strain Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Creep and Stress Relaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design for Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Predicting Part Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Loading/Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part Thickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part Thickness Drives Quality and Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cycle Time Increases with Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thick Parts Tend to Warp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thin, Uniform Parts Improve Surface Quality . . . . . . . . . . . . . . . . . . . . . . . . . . Reducing Part Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boosting Structural Integrity with Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural Integrity: the Goal of Every Design. . . . . . . . . . . . . . . . . . . . . . . . . . Designing Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

61 61 62 63 64 64 67 68 69 69 69 70

71 71 72 77 79 80 80 82 82 82 86 86 86 86 87 87 88 88 88

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XIV

Contents

6.5 6.5.1 6.5.2 6.5.3 6.5.4 6.5.5 6.5.6 6.5.7 6.5.8 6.5.9

Design for Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Molding One Part vs. Separate Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Tolerances: Fit between Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Press-fit Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Snap-fit Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Cantilever Snap Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Torsion Snap-fit Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Inserts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Welding Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

7

Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

7.1 7.1.1 7.1.2 7.1.3 7.1.4 7.2 7.2.1 7.2.2 7.3 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.3.7 7.4 7.4.1 7.4.2 7.4.3 7.4.4

Gate Design Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is a Gate? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single vs. Multiple Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manually Trimmed Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Automatically Trimmed Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determining the Number of Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Avoiding Common Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Freeze-off Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow for Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molding Window Size for the Three Gate Locations. . . . . . . . . . . . . . . . . . . . Filling Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Size Based on Shear Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Runner System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

8.1 8.1.1 8.1.2 8.1.3 8.1.4 8.1.5 8.1.6 8.1.7

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold Runner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Runner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sprue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

103 103 103 103 104 104 104 110 113 113 115 116 122 122 122 123 123 123 124 125 125

127 127 127 127 128 128 128 128

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Contents

XV

8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.2.5 8.2.6 8.2.7 8.2.8 8.2.9 8.2.10 8.3 8.3.1 8.3.2 8.4 8.4.1 8.4.2 8.4.3 8.4.4 8.5 8.5.1 8.5.2 8.5.3 8.6 8.6.1 8.6.2 8.6.3 8.6.4 8.7 8.7.1 8.7.2 8.7.3

Runner System Design Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Benefits of Good Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Design Philosophy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frictional Heating in Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Shutoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System and Runner Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant Pressure Gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold Slug Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Easy Ejection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Runner Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determining the Number of Cavities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Planning the Runner System Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Partially Balanced Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geometrically Balanced Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Runner Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determining Sprue Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Designing Runner Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determining Runner Diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How Runner Balancing Works. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . When Are the Runner Sizes Optimized?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Validating the Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Processing Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow for Runner Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Balancing a 48-cavity Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Balancing for a Family Mold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Runner Balancing for a Multigated Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

129 129 129 130 130 132 132 132 133 133 134 134 134 135 136 136 138 139 141 141 141 142 145 147 147 147 147 148 149 149 151 152

9

Cooling System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

9.1 9.1.1 9.1.2 9.2 9.2.1 9.3 9.3.1 9.3.2 9.3.3 9.3.4

Mold Cooling System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Importance of Cooling System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mold Cooling System Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling-channel Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Cooling Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alternative Cooling Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Do They Do? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baffles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bubblers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

153 153 154 156 156 157 157 158 159 159

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XVI

Contents

9.3.5 9.3.6 9.3.7 9.4 9.4.1 9.4.2 9.5 9.5.1 9.5.2 9.5.3 9.6 9.6.1 9.6.2

Cooling Slender Cores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling Large Cores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling Cylinder Cores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling System Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reynolds Number and Coolant Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mold Cooling Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Location and Size of Channels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Rate and Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow for Cooling System Design . . . . . . . . . . . . . . . . . . . . . . . . . . Example Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cycle Time Determined by Design and Processing Parameters . . . . . . . . . . .

10

Shrinkage and Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

10.1 10.1.1 10.1.2 10.1.3 10.1.4 10.1.5 10.2 10.2.1 10.2.2 10.2.3 10.3 10.3.1 10.3.2 10.3.3 10.3.4 10.3.5

Injection Molding and Shrinkage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Shrinkage and Warpage? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shrinkage and Machine Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mold Filling and Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How Pressure and Time Affect Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermally Unstable Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Causes of Shrinkage and Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relating Orientation and Area Shrinkage to Warpage . . . . . . . . . . . . . . . . . . . Designing Accurate Parts Considering Warpage . . . . . . . . . . . . . . . . . . . . . . . Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wall Thickness Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate Position and Runner Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molding Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling Line Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

Moldflow Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

11.1 11.2 11.2.1 11.2.2 11.2.3 11.2.4 11.2.5 11.2.6 11.3 11.3.1

Determine Analysis Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Moldflow Analysis Steps Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Whole Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimize Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Balance and Size the Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimize Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimize the Packing Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimize Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow to Evaluate an Initial Design . . . . . . . . . . . . . . . . . . . . . . . . . Description of this Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

160 161 162 162 162 163 163 163 164 166 167 168 169

173 173 173 174 175 176 177 177 181 182 183 184 184 185 187 190

191 192 192 192 197 199 200 201 205 205

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Contents

XVII

11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.3.7 11.4 11.4.1 11.4.2 11.4.3

Molding Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Filling Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gate and Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cooling System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packing Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warpage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Moldflow to Optimize the Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Determine the Cause of Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Investigating Different Gate Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Validating the Best Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

205 206 206 207 209 209 210 210 210 211

12

Part Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

12.1 12.1.1 12.1.2 12.1.3 12.2 12.2.1 12.2.2 12.2.3 12.3 12.3.1 12.3.2 12.3.3 12.4 12.4.1 12.4.2 12.4.3 12.5 12.5.1 12.5.2 12.5.3 12.6 12.6.1 12.6.2 12.6.3 12.7 12.7.1 12.7.2 12.7.3 12.8 12.8.1 12.8.2 12.8.3

Air Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is an Air Trap? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems Caused by Air Traps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Black Specks and Black Streaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Black Specks and Black Streaks?. . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Black Specks and Black Streaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brittleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Brittleness? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Brittleness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is a Burn Mark? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Delamination?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dimensional Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Dimensional Variation? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Dimensional Variation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discoloration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Discoloration?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Discoloration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fish Eyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Fish Eyes? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Fish Eyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

215 215 216 216 217 217 217 218 219 219 219 219 220 220 221 222 222 222 223 223 224 224 224 224 225 225 225 226 227 227 227 227

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XVIII

Contents

12.9 12.9.1 12.9.2 12.9.3 12.10 12.10.1 12.10.2 12.10.3 12.11 12.11.1 12.11.2 12.11.3 12.12 12.12.1 12.12.2 12.12.3 12.13 12.13.1 12.13.2 12.13.3 12.14 12.14.1 12.14.2 12.14.3 12.15 12.15.1 12.15.2 12.15.3 12.16 12.16.1 12.16.2 12.16.3 12.17 12.17.1 12.17.2 12.17.3 12.17.4

Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Flash? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flow Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is A Flow Mark? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Flow Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hesitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Hesitation? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems Caused by Hesitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is Jetting?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems Caused by Jetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ripples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Ripples? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cause of Ripples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is a Short Shot?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silver Streaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Silver Streaks? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Silver Streaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sink Marks and Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Sink Marks and Voids? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Sink Marks and Voids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weld Lines and Meld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Are Weld Lines and Meld Lines? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems Caused by Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength of Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

228 228 228 229 230 230 230 230 231 231 231 232 232 232 233 233 235 235 235 236 236 236 237 237 238 238 239 239 240 240 240 241 243 243 243 244 245

Appendix A: Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 A.1 A.1.1 A.1.2 A.2 A.2.1

Injection-molding Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Development of the Injection-molding Machine . . . . . . . . . . . . . . . . . . . . . . . Benefits of the Reciprocating Screw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

247 247 248 248 248

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A.3 A.4 A.4.1 A.4.2 A.4.3 A.4.4 A.4.5 A.4.6 A.4.7 A.4.8 A.4.9 A.4.10 A.4.11

Development of the Injection-molding Process. . . . . . . . . . . . . . . . . . . . . . . . Alternative Injection-molding Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Co-injection (Sandwich) Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fusible Core Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas-assisted Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Injection-compression Molding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lamellar (Microlayer) Injection Molding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Live-feed Injection Molding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Low-pressure Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Push-pull Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reactive Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural Foam Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thin-wall Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

XIX

249 249 249 250 251 252 253 253 254 254 255 256 256

Appendix B: Injection-molding Machine: System and Operations . . . . . . . . . . . .259 B.1 B.1.1 B.1.2 B.1.3 B.1.4 B.2 B.2.1 B.2.2 B.2.3 B.2.4 B.2.5 B.3 B.3.1 B.4 B.4.1 B.5 B.5.1 B.5.2 B.5.3 B.5.4 B.6 B.6.1 B.6.2 B.6.3

Injection-molding Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auxiliary Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Injection System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mold System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clamping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molded System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Delivery System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Operating Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Process Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Screw Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Injection Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Screw Rotation Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Secondary Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Decoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Secondary Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

259 259 260 260 260 261 261 263 264 264 264 265 265 266 266 268 268 268 268 269 269 269 269 270

Appendix C: Injection-molding Process Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 C.1 C.1.1

Importance of Process Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Setting Machine Process Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

XX

Contents

Moldflow Design Guide downloaded from www.hanser-elibrary.com by 190.235.14.195 on August 30, 2012 For personal use only.

Appendix D: Plastic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .281 D.1 D.1.1 D.1.2 D.1.3 D.1.4 D.2 D.2.1 D.2.2 D.3 D.3.1 D.3.2 D.3.3 D.3.4 D.4 D.5 D.5.1 D.5.2 D.5.3 D.5.4 D.5.5 D.5.6 D.5.7 D.5.8 D.5.9 D.5.10 D.5.11 D.5.12 D.5.13 D.5.14 D.5.15 D.5.16 D.5.17 D.5.18 D.5.19 D.5.20 D.5.21 D.5.22 D.5.23 D.5.24

What Are Plastics? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polymerization Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure of Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polymer Alloys and Blends. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polymer Composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classes of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structures and Properties of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Market Share Distribution of Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . . Structures and Properties of Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . . . Amorphous Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Semicrystalline Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermosets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Properties and Applications of Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PA 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PA 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PA 66 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PBT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PC/ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PC/PBT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HDPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LDPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PEI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PETG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PMMA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PPE/PPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PVC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additives, Fillers, and Reinforcements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modifying Polymer Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Low-aspect Fillers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-aspect Fillers: Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

281 281 281 283 283 283 284 284 285 285 286 286 287 288 289 290 291 293 294 296 297 299 300 301 303 304 305 306 307 309 310 312 313 314 316 317 318 319 319

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321