Die Design Fundamentals
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About this ebook
- Includes English and Metric systems.
- Covers new methods of producing blanks, such as waterjet cutting and laser cutting.
- Contains a glossary of terms for the first time.
- Illustrates each step in pictorial view and as a portion of an engineering drawing.
- Offers a completely revised chapter on presses and quick die-changing systems and includes the addition of “Quick Die Change Systems".
Vukota Boljanovic
Vukota Boljanovic, Ph.D., has nearly 50 years of experience in applied engineering in the aircraft and automotive industries, as well as academia. He has performed extensive research in manufacturing engineering, including the impact of design and modification on sheet metal dies, jigs and fixtures, and process selection, aircraft assembly, and inspection tool and dies. Dr. Boljanovic is the author of numerous technical papers and books, including such Industrial Press titles as Sheet Metal Forming Processes and Die Design; Die Design Fundamentals; Applied Mathematical and Physical Formulas Pocket Reference; Metal Shaping Processes; and Sheet Metal Stamping Dies. He has also contributed updated material on the topics of “Sheet Metal Working and Presses,” “Metal Casting, Molding, and Extrusion,” and “Powder Metallurgy” to the Machinery’s Handbook, 28th—32nd editions.
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Die Design Fundamentals - Vukota Boljanovic
PREFACE TO THIRD EDITION
The field of tool engineering and die design, a complex and fascinating subject, continues to advance rapidly. This broad and challenging topic continues to incorporate new concepts at an increasing rate, making tool and die design a dynamic and exciting field of study. In preparing this third edition, my most important goal has been to provide a comprehensive state-of-the-art textbook on die design fundamentals, which also encompasses the additional aims of motivating and challenging students.
This new edition provides balanced coverage of relevant fundamentals and real-world practices so that the student can understand the important and often complex interrelationships between die design and the economic factors involved in manufacturing sheet metal-forming products.
A groundbreaking and comprehensive reference with many thousands of copies sold since it first debuted in 1962 as J.R. Paquin’s Die Design Fundamentals, this new third edition of Die Design Fundamentals basically follows the same design philosophy: It is a step-by-step introduction to the design of stamping dies. However, the original book has been completely revised and updated, and the order of the chapters has been changed to follow the logical process of designing a die.
The plan of the book remains unique. After introductory material and a discussion of 20 types of dies, the design of a representative die is separated into 14 distinct steps. Each step is illustrated in two ways: first, as a portion of an engineering drawing, that is, as the component is actually drawn on the design; second, the die design is shown pictorially in order to improve the user’s visualization. In successive sections of the book, each step is detailed as it is applied to the design of the various types of dies listed in Chapter 2. In many figures a punch shank is shown because it is still in everyday use in many small stamping shops. However, according to the OSHA Standard 1910.217(7) it cannot be used for clamping the punch holder to the slide (ram) of a press, but can be used for aligning the die in the press. Slide (ram) mounting holes or another clamping system must be provided in the punch holder for fastening. The final chapter deals with presses and quick die-changing (QDC) systems.
The intent of this new edition is to provide students, instructors, and working professionals with graphically detailed assistance in understanding the underlying principles of designing single-station dies as well as small progressive dies of a type generally used once for short runs of parts manually cut from strip sheared from sheets.
For the first time, a dual (English and metric) system is included. New methods of producing blanks widely acknowledged within the industry, such as waterjet cutting and laser cutting are included, as well. The chapter 20 Presses and Quick Die-Change Systems
has been considerably revised, with the addition of a new subtopic, Quick Die-Change Systems.
To this third edition of the book has also been added a Glossary of the terms used.
In response to comments and suggestions by numerous reviewers, several major and minor changes have also been made throughout the text. A page-by-page comparison with the second edition will show that literally hundred of changes have been made for improved clarity and completeness.
It is hoped that by reading and studying this third edition of the book, students and other users will come to appreciate the vital nature of tool and die engineering as an academic subject that is as exciting, challenging, and as important as any other engineering and technology discipline.
The author of the third edition owes much to many people. I am grateful to my son Sasha for valuable contributions in the preparation of this edition. Finally, I wish to thank Em Turner Chitty for her competent proofreading of this new edition.
Vukota Boljanovic
Knoxville, Tennessee
1
INTRODUCTION TO DIE DESIGN
1.1 Basic Meanings
1.2 Die Components
1.3 Processing a Die
1.4 Die Operations
Die design, a large division of tool engineering, is a complex, fascinating subject. It is one of the most exacting of all the areas of the general field of tool designing.
How then shall we enter into the study of die design? Obviously, we shall have to begin cautiously, learning each principle thoroughly before proceeding to the next one. Otherwise it is quite likely that we should soon become hopelessly involved in the complexities of the subject and in the bewildering number and variety of principles that must be understood. What, then, is a die?
The word die
is a very general one and it may be well to define its meaning as it will be used in this text. It is used in two distinct ways. When employed in a general sense, it means an entire press tool with all components taken together. When used in a more limited manner, it refers to that component which is machined to receive the blank, as differentiated from the component called the punch,
which is its opposite member. The distinction will become clear as we proceed with the study.
The die designer originates designs of dies used to stamp and form parts from sheet metal, assemble parts together, and perform a variety of other operations.
In this introduction you will learn basic meanings and the names of various die components; then, operations that are performed in dies will be listed and illustrated. In other sections of the book, the design of dies and die components will be explained in a far more thorough manner, so that your understanding will be complete in every respect.
1.1 BASIC MEANINGS
1.1.1 Part Drawing
To begin our study of the various components that make up a complete die, let us consider the drawing of the link illustrated in Figure 1.1. This part is to be blanked from steel strip and a die is to be designed for producing it in quantity. The first step in designing any die is to make a careful study of the part print because the information given on it provides many clues for solving the design problem.
Figure 1.1 A typical part drawing.
Figure 1.2 A complete die drawing.
1.1.2 Die Drawing
Figure 1.2 is a complete die drawing ready to be printed in blueprint form. To the uninitiated it might appear to be just a confusing maze of lines. Actually, however, each line represents important information that the die makers must have to build the die successfully. In illustrations to follow, we will remove the individual parts from this assembly and see how they appear both as three- and as two-view drawings, and as pictorial views, to help you to visualize their shapes. As you study further, keep coming back to this illustration to see how each component fits in. When you are through, you should have a good idea of how the various parts go together to make up a complete die.
1.1.3 Blueprints
After a die has been designed on tracing paper using traditional techniques or AutoCAD, blueprints are produced for use in the die shop where the dies are actually built by die makers. This is how a blueprint of a die drawing appears. From such prints, die makers build the die exactly as the designer designed it. The drawing must be complete with all required views, dimensions, notes, and specifications. If the die maker is obliged to ask numerous questions, the drawing was poorly done. Figure 1.3 shows a typical blueprint.
Figure 1.3 A typical blueprint.
1.1.4 Bill of Material
The bill of material (Figure 1.4) is filled in last. This gives required information and specifications for ordering standard parts and for cutting steel to the correct dimensions. This material is cut and assembled in the stock room, then placed in a pan, along with a print of the die drawing. When filled, the pan must contain everything the die maker will require for building the die, including all fasteners and the die set.
Figure 1.4 A typical bill of material.
Figure 1.5 A pictorial view of an entire die.
1.1.5 Die Assembly
Figure 1.5 is a pictorial view of the entire die as shown in Figure 1.2. The die pierces two holes at the first station, and then the part is blanked out at the second station. The material from which the blanks are removed is a cold-rolled steel strip. Cold-rolled steel is a smooth, medium-hard steel, and it gets its name from the process by which it is produced. It is rolled, cold, between rollers under high pressure to provide a smooth surface. The strip A is shown entering the die at the right.
1.1.6 Scrap Strip
A scrap strip (Figure 1.6) is designed as a guide for laying out the views of the actual die. Figure 1.6a shows a typical scrap strip. This illustration shows the material strip as it will appear after holes have been pierced and the blank has been removed from it. We would first consider running the blank the wide way as shown at A. When blanks are positioned in this manner, the widest possible strip is employed and more blanks can be removed from each length of strip. In addition, the distance between blanks is short and little time is consumed in moving the strip from station to station. However, for this particular blank there is a serious disadvantage in this method of positioning. Because the grain in a metal strip runs along its length, the grain in each blank would run across the short width; the blanks would be weak and lacking in rigidity. This defect is important enough for the method to be discarded. Instead, the blanks should be positioned the long way in the strip as shown at B. The grain will then run along the length of each blank for maximum stiffness and strength.
Figure 1.6 Scrap strips: (a) Typical scrap strip layouts and (b) Three views of the scrap strip.
Three views of the material strip are shown in Figure 1.6b exactly as they appear in the die drawing in Figure 1.2. In addition, a pictorial view is supplied at the upper right corner to help in visualizing the strip. In other words, this is the way you would imagine the strip if you were to draw it in three views. The top or plan view shows the strip outline, as well as all openings. This would be made actual size on the drawing. The holes are represented by circles at the first station, and the blanked opening is shown at the second station. At the lower left, a side view of the strip is drawn. It is shown exactly as it would appear at the bottom of the press stroke, with the pierced slugs pushed out of the strip at the first station and the blank pushed out of the strip at the second station. The narrow end view at the lower right corner is shown as a section through the blanking station, and the blank is shown pushed out of the strip. The strip in many instances is often drawn shaded to differentiate it from the numerous lines that will represent die members. In the upper plan view, shading lines would appear on the surface of the metal. In the two lower views, the lines are shown in solid black to further differentiate the strip from the die members.
1.1.7 Stampings
Stampings are parts cut and formed from sheet material. Look around you! Wherever you may be, you will find stampings. Many are worn on your own person; the ring on your finger is probably a stamping. Most of the parts in old-fashioned wrist watches are stampings, including the wristband. Your belt buckle, the metal grommets through which your shoe laces pass, eyeglass frame, the clip on your ball point pen, and zipper—all these are stampings.
Look around the room, any room, and you will find products of the pressed-metal industry. Most of the parts in the lighting fixture are stampings; so are threaded portions of light bulbs, door knobs, and the radiator cover. The list is a long one indeed. In the home we find stampings by the score: pots and pans, knives, forks, and spoons, coffee pot, canister set, pie plates and muffin pans, cabinet handles, kettle, can opener, and more.
The refrigerator is almost entirely made of stampings. So are the stove, toaster, and other appliances. And each single part in all these requires an average of three to six dies to produce.
Every automobile contains hundreds of stampings. The largest are the roofs, hoods, quarter-panels, doors, etc. Even the wheels are stampings. There are hundreds of smaller parts, many of which are covered and seldom seen. For example, even the points require very complex dies with multiple stations each, costing thousands of dollars to build, in addition to assembly dies for joining the components.
Office machines and computers provide another big stamping field. So do adding machines, calculators, and dictating machines. We could go on and on; the list is almost endless. Radio and television components require thousands of dies. So do streamlined trains, aircraft, and missiles. All of these are improved from year to year, so an enormous number of new dies is constantly required.
The foregoing should give you some idea of the great size and importance of the pressed-metal industry.
Figure 1.7 A typical punch press.
1.1.8 Punch Press
Figure 1.7 is a photograph of a typical mechanical punch press in which dies are operated to produce stampings. The bolster plate A is a thick steel plate fastened to the press frame. The complete die is clamped securely on this bolster plate. The upper portion of the die is clamped in ram B, which is reciprocated up and down by a crank. As the material strip is run through the die, the upper punches, which are fastened to the moving ram B of the press, remove blanks from it.
1.2 DIE COMPONENTS
Figure 1.8 is an exploded drawing of the die shown in Figure 1.5 with the names of various die components listed. These names should be memorized because we will refer to them many times in future work.
Figure 1.8 An exploded view of the die shown in Figure 1.5.
Figure 1.9 A typical die set.
1.2.1 Die Set
Figure 1.9 shows a die set, and all parts the die assembly comprises are built within it. Die sets are made by several manufacturers and they may be purchased in a great variety of shapes and sizes. The center posts
A are called punch shanks
in the die set manufacturers’ jargon. And, no, they cannot be used for clamping the punch holder, but they can be used for aligning the die in the press. Ram mounting holes must be provided in the punch holder for mounting. In operation, the upper part of the die set B, called the punch holder,
moves up and down with the ram. Bushings C, pressed into the punch holder, slide on guide posts D to maintain precise alignment of cutting members of the die. The die holder E is clamped to the bolster plate of the press by bolts passing through slots F.
In Figure 1.10, the die set is drawn in four views. The lower left view shows a section through the entire die set. The side view, lower right, is a sectional view also, with a portion of the die set cut away to show internal holes more clearly. The upper left view is a plan view of the lower die holder with the punch holder removed from it.
The punch holder is shown at the upper right, and it is drawn inverted, or turned over, much like an opened book. In the complete die drawing, Figure 1.2, all punches are drawn with solid lines. If the punch holder were not inverted, most lines representing punches would be hidden and the drawing would contain a confusing maze of dotted lines.
Figure 1.10 A die set.
Another reason for inverting the punch holder is that this is actually the position assumed by the die holders and punch holders on the bench as the die makers assemble the die, and it is easier for die makers to read the drawing when the views have been drawn in the same position as the die on which they perform assembly motions.
1.2.2 The Die Block
Figure 1.11 shows the die block of the die shown in Figure 1.2. The die block is made of hardened tool steel into which holes have been machined, before hardening, at the piercing station and also at the blanking station. These are the same size and shape as the blank holes and contour. Other holes are tapped holes used to fasten the die block to the die holder, and reamed holes into which dowels are pressed to fix the block’s location relative to other die parts.
Figure 1.11 The die block.
The top view is a plan view of the die block. The lower left view is a section through the holes machined for piercing and blanking. Lines drawn at a 45-degree angle, called section lines,
indicate that the die block has been cut through the center, the lines representing the cut portion. Similarly, the end view is a section cut through the die block at the blanking station. A tapped hole is shown at the left and a reamed hole at the right side. These are for the screws and dowels that hold the die block to other die components. Sectioning a die, that is, showing the die as if portions were cut away to reveal the inside contours of die openings, is a very common practice. In fact, practically all dies are sectioned in this manner. The die maker can then read
the drawing far more easily than he could if outside views only were shown because these would contain many dotted or hidden lines.
Always remember that all drafting is, in a sense, a language. A die drawing is a sort of shorthand, which is used to convey a great deal of information to the die makers. Anything that can be done to make it easier for them to read the drawing will save considerable time in the shop.
Now refer back to Figure 1.2 and see how easily you can pick out the three views of the die block. That is exactly what the die maker has to do in order to make the die block.
1.2.3 The Blanking Punch
The blanking punch (Figure 1.12) removes the blank from the strip. The bottom, or cutting edge, is the shape and size of the part. A flange at the top provides metal for fastening the blanking punch to the punch holder of the die set with screws and dowels. Two holes are reamed all the way through the blanking punch for retaining the pilots, which locate the strip prior to the blanking operation. Locate the views of the blanking punch in the die drawing, Figure 1.2, to improve your ability to read a die drawing.
1.2.4 Piercing Punch
A piercing punch (Figure 1.13) pierces holes through the material strip or blank. It is usually round and provided with a shoulder to keep it in the punch plate. When a piercing punch penetrates the strip, the material clings very tightly around it. A way must be provided to strip or remove this material from around the punches. The means employed to remove such material is called a stripper.
Figure 1.12 The blanking punch.
Figure 1.13 A piercing punch.
1.2.5 Punch Plate
The punch plate (Figure 1.14) is a block of machine steel that retains punches by keeping the punch heads against the punch holder of the die set. The punches are held in counterbored holes into which they are pressed. Four screws and two dowels retain the punch plate to the punch holder of the die set. The screws prevent it from being pulled away from the punch holder. Dowels, which are accurately ground round pins, are pressed through both the punch plate and punch holder to prevent shifting. Locate the front view and plan view of the punch plate in the die drawing Figure 1.2.
Figure 1.14 A punch plate.
Figure 1.15 A pilot.
1.2.6 Pilot
Pilots (Figure 1.15) are provided with acorn-shaped heads, which enter previously pierced holes in the strip. The acorn shape causes the strip to shift to correct register before blanking occurs.
1.2.7 The Back Gage
The back gage (Figure 1.16) is a relatively thin steel member against which the material strip is held by the operator in its travel through the die. The front spacer is a shorter component of the same thickness. The strip is fed from right to left. It rests on the die block and is guided between the back gage and front spacer. The distance between the back gage and front spacer is greater than the strip width to allow for possible slight variations in width.
Figure 1.16 The back gage.
Figure 1.17 A finger stop.
1.2.8 The Finger Stops
The finger stop (Figure 1.17) locates the strip at the first station. In progressive dies having a number of stations, a finger stop may be applied at each station to register the strip before it contacts the automatic stop. Finger stops have slots machined in their lower surfaces to limit stop travel.
1.2.9 Automatic Stops
Automatic stops (Figure 1.18) locate the strip automatically while it is fed through the die. The operator simply keeps the strip pushed against the automatic stop toe, and the strip is stopped while the blank and pierced slugs are removed from it, then it is automatically allowed to move one station further and stopped again for the next cutting operation.
1.2.10 The Stripper Plate
The stripper plate (Figure 1.19) removes the material strip from around blanking and piercing punches. There are two types of stripper plates: spring-operated and solid. The one illustrated is solid. The stripper plate has a slot A machined into it in which the automatic stop operates. Another slot B at the right provides a shelf for easy insertion of a new strip when it is started through the die.
Figure 1.18 An automatic stop.
Figure 1.19 The stripper plate.
1.2.11 Fasteners
Fasteners hold the various components of the die together. Figure 1.20 shows the commonly used socket cap screw. These fasteners are available from various suppliers, and all have a threaded portion and a larger round head provided with an internal hexagon for wrenching. As you have been doing for previous illustrations, pick out the fasteners shown in the die drawing, Figure 1.2. Note that in section views, screws are shown on one side and dowels on the other.
Figure 1.20 Socket head cap screw for use as a fastener.
1.3 PROCESSING A DIE
Let us now consider the steps taken in designing, building, and inspecting a representative die. At the same time, you will gain an insight into the operation of press shops, tool rooms, and manufacturing plants so that your understanding of tooling and manufacturing will be better than average.
1.3.1 The Product
First, we will consider the product to be manufactured. The product engineering department designs the product. In most plants, the work consists in improving the product from year to year to meet changing styles and changing requirements of customers.
After management has decided upon the final form of the new or improved product, a directive is sent to the process planning department to route the various parts through the appropriate manufacturing departments. The process or methods engineers then plan the order of manufacturing operations and decide what operations will be used. They request that the tool design department produce designs of all jigs, fixtures, cutting tools, and dies needed for efficient production of the parts.
After a product designer has prepared layouts and assembly drawings of the product to be manufactured, the engineering department prepares detail drawings of each component the shop has to produce. These drawings contain all required views, dimensions, and explanatory notes to represent all detail features of the objects.
The part which is to be machined, formed, pressed, or inspected is called by one of the following terms:
•Part
•Work
•Workpiece
Part is the preferred term, but workpiece or, simply, work are often employed as alternate names; all three terms will be used interchangeably throughout this book.
The print on which this part, work, or work-piece is represented is called a part print. In designing a die for producing a stamping, the die designer works from a part print.
1.3.2 Process Planning
Prints of detail drawings are sent to the process planning department. When stampings are required, it is the function of this department’s employees to determine how the stampings are to be made. They decide how many operations will be required and what presses will be employed to make them. This department thus assumes the responsibility of determining the sequence of manufacturing operations. The information is noted on a series of forms:
a) Route Sheet
The route sheet (Figure 1.21) is designed to suit the requirements of the individual plant and, therefore, the information route sheets contain will vary. However, the following elements are usually included:
1.The heading. This is located at the top of the sheet and contains information such as:
•Part name
•Part number
•Drawing number
•Number of parts required
•Name of product engineer
•Date
In addition, the product name and model number may be included.
2.The number of each operation required to make and inspect the part. Numbers are most frequently listed in increments of 5, such as 5, 10, 15, 20, etc., to provide numbers in sequence for additional operations which may be found necessary in manufacture or when changes are made in the design of the product.
3.The name of each operation.
4.The name and number of the machine on which the operation is to be performed.
5.Estimates of the number of parts that will be completed per hour for every operation. These estimates are altered after production rates have been measured accurately by the time study department. Route sheets are supplied to the following departments:
•Tool design department
•Production department
•Inspection department
Of course, any machine or product will contain many components, which have been standardized and which can be purchased from outside suppliers or vendors. Such items would include screws and dowels, bearings, clutches, motors, and many others. The purchasing department would be supplied with a bill of material, and purchase orders would be issued for all parts to be bought.
Figure 1.21