DIE CASTING ENGINEERING A Hydraulic, Thermal, and Mechanical Process DIE CASTING ENGINEERING A Hydraulic, Thermal, and Mechanical Process Bill Andresen M ARCEL D EKKER N EW Y ORK Although great care has been taken to provide accurate and current information, neither the author(s) nor the publisher, nor anyone else associated with this publica- tion, shall be liable for any loss, damage, or liability directly or indirectly caused or alleged to be caused by this book. The material contained herein is not intended to provide specific advice or recommendations for any specific situation. Trademark notice: Product or corporate names may be trademarks or registered tra- demarks and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress.
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Current printing (last digit): 10 9 8 7 6 5 4 3 2 1 PRINTED IN THE UNITED STATES OF AMERICA Preface This is a broad technical presentation for participants in the die casting process. It is intended that the material presented will help to reduce manufacturing costs, increase productiv- ity, and enhance quality through failure avoidance. While the scope is broad and covers the many facets of casting, the focus is on function, problem identification and solution, and strategic logic. All casting processing are a function of velocity and pres- sure.
Die casting is at the high level of both, a fact that presents unique challenges discussed in this book. Die casting is the shortest route between raw material and near net shape. Acknowledgment To Barb, who totally supports a hectic career in die casting, which is so enjoyable that it can hardly be considered work. Bill Andresen iii About the Author BILL ANDRESEN is the President of Hi Tech International, Inc.
An international technical and management consultant, he has a wide breadth of experience in the field ranging from hands-on engineering to the man- agement of manufacturing facilities and service as Technical Director of the American Trade Association. v vi About the Author Bill Andresen has held the positions of Production Control Manager, Chief Engineer, Plant Manager, and Man- ufacturing Vice President, and was a member of the board of directors and executive committee for Du-Wel Products. He was the founding manager of the aluminum plant in Dowagiac, Michigan that historically returned one-half of cor- porate earnings on one-third of the sales. He also served as the Executive Vice President of Viking Die Casting Corpora- tion, where he introduced new technologies that grew produc- tivity and sales.
Bill became a disciple of the world class developments by CSIRO in Australia for die casting technol- ogy. As a result of the gap between this and actual die casting practice, he formed Hi-Tech International, Inc. This firm offers measuring, analyzing, designing, and verifying for both new and existing projects to establish true value streams. Quality and productivity enhancement, mechanical die design, flow analysis, and thermal management are avail- able to clients worldwide that are engaged in high pressure die casting.
Andresen has been a longstanding and active mem- ber of the North American Die Casting Association. He served as Technical Director for the American Die Casting Institute where his responsibilities included the management of techni- cal research and worldwide interaction with die casting firms. Considerable public speaking and many published articles on die casting have also left his mark on the industry. He has represented the industry in negotiating more reasonable environmental regulations with various agencies of the United States government.
He has served as chairman of the Die Casting Research Foundation and received the Nysellius Award, the highest recognition by the industry for technical contributions. Andresen has taught die casting courses at the University of Wisconsin, Western Michigan University, Southwestern Michigan College, and NADCA, as well as teaching the die casting process to individual companies. Andresen graduated from Purdue University in West Lafayette, Indiana. iii About the Author.
Terms Used in Die Casting. The Die Casting Machine. Concepts of Cavity Fill. Metal Feed System.
209 vii viii Contents 9. Designing the Value Stream. Mechanical Die Design. Die Set Up Techniques.
Die and Plunger Lubrication. 379 Introduction WHAT IS DIE CASTING? Die casting is a manufacturing process for producing accu- rately dimensioned, sharply defined, smooth or textured sur- face metal parts. It is accomplished by injecting liquid metal at fast velocity and under high pressure into reusable steel dies. Compared to other casting processes, die casting is at the top end of both velocity and pressure.
The high velocity translates into a very turbulent flow condition. The process is often described as the shortest distance between raw mate- rial and the finished product. The term die casting is also used to identify the cast product. HOW ARE DIE CASTINGS PRODUCED? First, a steel mold, which is usually called the die and con- tains the cavities that form the castings, is made into two halves to permit removal of the castings.
This die is capable of producing thousands of parts in rapid succession. The die is then mounted securely in a die casting machine with the ix x Introduction Figure 1 individual halves arranged so that one is stationary (cover die) while the other is moveable (ejector die). The casting cycle starts when the two dies are clamped tightly together by the closing mechanism of the machine. Liquid casting alloy is then injected into the die in an extre- mely short period of time and at very high pressures, where it solidifies rapidly.
The die halves are then drawn apart when the machine opens, and the shot which includes the castings is ejected. Die casting dies range from simple to complex and have moveable slides and cores as determined by the configuration of the part. They consist of mechanical features; a metal flow system called runners, gates and vents; and a thermal system because the die also acts as a heat exchanger. Introduction xi The complete cycle of the die casting process is by far the fastest method known for producing precise nonferrous metal castings.
This is in marked contrast to sand casting which requires a new sand mold for each casting cycle. While the permanent mold process uses steel molds instead of sand, it is considerably slower and, like sand casting, not as precise as die casting. BASIC TO THE PROCESS The die casting process is fundamentally simple but it is com- plicated by a massive array of ancillary equipment and details. There are only three basic factors (see below) that affect the final product that results from the rapid conversion of metal in the ingot form to a net shape.
Some assumptions are usually made when dealing with die casting that help to visualize the logical chain of events that occur during each cycle. These assumptions are: Since the casting alloy is injected into the die cavity at a superheated temperature, it behaves like a hydrau- lic fluid during the very brief period of cavity fill. The metal travels in a straight line until it meets an obstruction and then the stream splashes and breaks up into turbulent eddies. During cavity fill, it follows the path of least resistance.
Die casting is a turbulent process since liquid casting alloy travels through the system at extremely high rates of speed. The three fundamental factors are: The thermal behavior of the casting alloy that can be quantified by the thermal constants. The shot end of the casting machine and the shot sleeve or goose neck that provide the liquid metal required to fill the die cavity. The shape of the part that defines the flow path of the liquid metal as it travels through the cavity.
The xii Introduction surface area to volume ratios and the distance that the metal must travel are important mathematical characteristics of each net shape. This text will attempt to present the details of die casting process in a logical manner. It is definitely predictable and controllable. AUTHOR’S NOTE The data presented in this text have been collected by the author from experience and many sources believed to be reli- able.
However, no expressed or implied warranty can be made to its accuracy or completeness. No responsibility or liability is assumed by Hi Tech International, Inc. or the author or the publisher for any loss or damage suffered through reli- ance on any information presented or included here. The final determination of the suitability of any information for the use contemplated for a given application remains the sole respon- sibility of the user.
No part or portion of this text may be reproduced without the expressed written consent of the author and the publisher. 5935-4 Andresen Ch01 R3 092904 1 Terms Used in Die Casting Many texts place this topic at the end or in a separate appen- dix, but it is addressed here at the beginning so that everyone referencing the subject of die casting may speak the same language. Clear communication is sometimes difficult, yet it is critical to successful die casting. This is a partial list of the more commonly used terms and is not intended as a comprehensive, totally inclusive glos- sary.
It is intended only to help introduce the subject and, as a convenient reference. Accumulator: A reservoir in the hydraulic system that holds the shot pressure at a constant level and reduces nor- mal fluctuations. This is a cylinder that is usually located at the shot end of the die casting machine. Aging: A change in the metallurgical structure, physical properties, and dimensions of an alloy that takes place over an extended period of time after a part is die cast.
Aging time is compressed with heat. Alloy: A metallic material that consists of two or more chemical elements whose physical properties are normally different than those of the separate ingredients. 1 5935-4 Andresen Ch01 R3 092904 2 Chapter 1 Anodizing: A process that utilizes the casting as the anode in an electrolytic cell so that a protective or decorative film can be applied to the surface. ANSI: American National Standards Institute.
AQL: Acceptable Quality Level as agreed upon between the die caster and customer. Area (projected): The area of the cavity and metal feed system that is visible when viewing the die at an angle perpendicular to the basic parting plane. Area (surface): The area of the cavity surface that comes into contact with the casting alloy in both die halves. ASQC: American Society for Quality Control.
ASTM: American Society for Testing and Materials. Australian metal feed system: A series of tapered tan- gential runners that are designed to generate constant gate speeds as the casting alloy exits the runner and enters the die cavity. The spurt of energy that occurs at the end of each runner branch is controlled with a shock absorber at this point in the system. Austenite: A Phase that Iron-carbon steels reach during heat treating that is relatively ductile with a low work hard- ening rate.
Back scrap: Runners, gates, biscuits, overflows, trim- mings, and defective castings that are normally remelted for another try at production. BHN: A number that quantifies hardness in the Brinell system.