Smith & Associates
Die Maintenance Handbook
Features a wealth of design and troubleshooting information in a compact easily searchable format
400 Pages · Many illustrations · With tables & equations
You will find instant on-the-job answers, proven die maintenance and troubleshooting procedures, and practical advice for every class of sheetmetal pressworking.
Plus, major topics not found elsewhere in print such as...
Die Maintenance Handbook
"What a great reference book! David Smith has an uncanny way of breaking down complicated tooling practices into simple, easy to follow explanations. Every aspect of die maintenance is covered in this book. It will surely improve the work efficiency of both new and experienced die builders. I have already ordered a copy for each of our toolroom employees, and I know the time and money we'll save will quickly recoup the cost."
"Extremely informative, subject matter presented in a clear and concise manner consistent with this authors' style of writing. (Author David Smith) pulls together and organizes all technical and financial aspects of die maintenance. Anyone in the metal stamping business should have a copy in their reference library."
"Die Maintenance Handbook is an excellent reference for smaller press shops without a large staff of die specialists. It addresses the full spectrum of contributing factors of poor press shop practices and tool wear and failure, such as tool design, the press, metal components, and lubricants. And happily, this practical book doesn't overdo the theory and mathematics."
Dr. Stuart P. Keeler, Ph.D....
"I was pleased to see that it is not limited to just die maintenance. It's very useful information for the die designer to contemplate before the die is even built. Smith understands that when certain guidelines, presented in the Handbook, are applied during the design stage, dies will be much easier to maintain.
I have been involved with progressive dies for over twenty-five years, mostly in the area of design. The Handbook does an excellent job of describing and explaining principles and concepts of the cutting, blanking, forming and drawing processes. It should be required reading for all personnel involved with dies, regardless of experience.
I plan to help make this Handbook available to all of our tool makers and every one else who is involved in all aspects of designing, building and maintaining dies."
Jim Martellotti President
Nascal Interplex, Inc.
"Die Maintenance Handbook is a welcome addition to David Smith's other great resources which have tremendously helped the my career and that of my colleagues. I'm impressed by the way he explains not just what to do, but what not to do, and I appreciate his focus on safe work practices. Clearly, the contents of this book could have only been written someone with a superior level of experience."
My opinion is that Mr. Smith has taken the approach of focusing on the basics of die maintenance. Many die related problems can be traced to a misunderstanding of basic principles. Basic principles of die construction and proper maintenance are often over looked and many dollars are spent chasing issues that are simply effects of the true problem. The Die Maintenance Handbook provides the knowledge of "what to do" along with "what not to do". Knowing what not to do is often a better lesson since it was learned from experience. Mr. Smith's experience provides the reader with a realistic view of how to detect, diagnose and repair problems that are encountered daily. As indicated in the book, proper die maintenance along with a functional tracking system is what ensures that production goals can be achieved each time that a die is set in a press.
I found it to be a great resource for press and die
work fundamentals. It is well written and I
would highly recommend the book to anyone who wants a better understanding of good die design and practical maintenance
techniques. Dave has consulted us at
La-Z-Boy on press working issues and I continue to be impressed with his technical expertise and practical
This book addresses more than just Die Maintenance. It covers a wide range of essential information necessary for achieving optimum results in any stamping operation."
Table of Contents
By D. Smith,
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Detailed Die Maintenance Handbook Table of Contents
1 An Overview of Basic Die Operations........................................ 1
Understanding the basic die operations is a foundation for troubleshooting the stamping process. In presswork, metal is cut by punching perforating and shearing. Other processes include bending, unbending and forming. This involves bending and straightening as well as stretching the metal. Biaxial stretch forming and true cup drawing are also common operations that give shape to metal goods. The squeezing or coining operations are a very old type of metalworking that includes cold and warm forging. Finally, we point out that there are analytical tools to simulate and aid in understanding how to improve the processes.
2 Troubleshooting Punching and Cutting Operations............ 11
Understanding the sequence of events during the cutting operation explains the effect of die clearance on the roughness of fracture. This understanding helps define and achieve the correct clearance for each job. A case study of a strategy explains how to maximize tool life.
Calculating cutting force requirements based on American and Metric systems of length, area, and force measurement are used to determine the length of cut theoretical peak cutting force and cutting energy required The effect of cutting speed on the required force and the effect of side-thrust or lateral forces and effect of die clearance are explained.
3 Designing Large EDM Die Sections for Repairability.......... 27
The application of EDM technology has raised the economics of throwaway versus repairable die sections. Issues to resolve are die section location and retention including the limitation of shifting with screws and keys.
Good punch and die-steel design considers the economics of making fragile sections replaceable. Maintaining correct clearance may require robust sections and well designed screw placement.
4 Die-shaving Operations.......................................................... 33
Die shaving is related to machining operations. The punch to die clearance and size of the shave punch versus part hole size correctly chosen provide straight smooth holes and edge features by the shaving process. Close work may require multiple shaving operations. The application of the of the hollow-ground concept.
5 Solving Punch Head Breakage Problems............................ 39
Addressing the root causes of punch head breakage includes the contributing factors punch head flexure leading to crack formation.
Head Modifications including applying a stress-reducing head radius and Increasing the head to the point ratio is an expensive solution. Ironworker-and bulldozer-style punches are old proven solutions for heavy punching work. The safety of personnel is an issue in the event of punch failure.
6 The Cost of Punch and Die Maintenance.............................. 49
To accurately know your cost of punch and die maintenance, you must record all causal factors based on cause codes and then make use of this data to reduce your repair costs. The real cost of die damage may surprise you and the value of good workmanship will become apparent.
7 Good Maintenance Practice................................................... 53
Following a good grinding practice when sharpening a die starts with proper wheel selection. Understanding the wheel nomenclature printed on the paper washer on the wheel assists in proper selection. Safe wheel usage and proper wheel dressing is essential.
Good workmanship includes removing grinding burrs and smoothing sharp edges using the correct edge-stoning procedure. The grinding procedure used to sharpen die sections and punches is gentle to avoid overheating the tool steel. Stress-relieving cutting and forming tools by redrawing is recommended.
After reworking the die on the bench, the die components may require shimming to maintain die timing and the correct shut height. Shimming progressive dies must assure that form stations have the correct relationship to embossments etc.
Proper shimming materials are used and the shim is laid out and cut to shape carefully. All burrs are removed. If more than three shims are required, a hardened solid shim is fabricated. Spare shims are stored correctly.
Ball lock punches and die buttons also require care in their use. if a teardrop must be ground or modified this too must be done properly. One must always be sure that the ball locks properly.
8 Compound Dies ...................................................................... 73
Compound blank and piercing dies still are extensively used for precise work varying from small washers and shims to lawnmower deck blanks. The problem of part removal can be addressed by using cut-and-carry or pushback operations. Here, there are success factors and process control variables discussed in detail.
9 Pressure Pad and Stripper Selection.................................... 79
Positive or tunnel strippers are the most economical if they are satisfactory for the application. Movable strippers provide better stock control but require pressure systems--typically springs or nitrogen cylinders. Elastomer strippers are recommended for short run work where cost id a major factor. Stripping forces and the factors that determine them are discussed in detail
10 Anti-slug Pulling Methods.................................................... 89
Solving slug pulling problems is essential to dependable progressive die operation. Proven methods vary from spring-loaded pusher pin to blow-off devices using a hole through the punch. Reverse taper in the die button, electrical etching and metal deposition in the die opening all find application in controlling slug pulling problems. Punch shear angles,
vacuum ejectors and external vacuum systems are detailed.
11 Cutting Force and Snap-through Reduction .................... 101
The role of punch shear includes simple angular shear, balanced-Vee shear and balanced pointed shear. One case study presents successfully punching thick medium carbon steel. Here, the importance of timing is critical to not exceeding the press reverse load capacity.
There is a proven square law relationship that means a small timing improvement greatly reduces snap-through energy release. Combined cutting and bending is a special case covered in the text. providing angular shear on the d and maintaining records of correct timing are essential to continued success.
12 Bending of Metals ............................................................... 111
Accurate bending of metals requires bend allowances for the amount of flat metal required to actually complete the bend. Over the years many tables of empirical data have been developed. A simple but accurate method of calculation the amount of metal in a bend is provided along with the factors that cause variation.
Springback or elastic recovery often requires compensation The factors affecting springback including causes and cures for bend-angle variation such as coining the bend in press brake press-brake work is a major topic.
Wipe-bending and wipe flanging springback is best controlled with optimum flange steel geometry.
Rotary-action die bending operations including fine adjustment of the bend angle is important and explained.
How some bend angles vary because of adjustments of pad pressures can provide a means to control bend angles although practical applications has limitations.
13 Forming Flanges and Hems............................................... 129
Analysis of flanging operations and choice of tooling for flange types each of which have minimum bend radii limitations is important. Maximum strain and metal formability limits stretch flanging operations. Hemming is useful for providing smoothness and strength to metal edges. Using hems to assembey stampings is very useful. This chapter has many aids to troubleshoot flanging and hemming processes.
14 Drawing and Stretching of Metals..................................... 141
Success in deep drawing of cylindrical cups is aided by understand and analyzing the metal flow during the process. Why and how deep-drawn cup-shaped shells fail can vary from exceeding process limits for the material drawability to simply failing to provide a proper draw radius.
Most drawing failures result in excessive thinning of the part and fractures. Measuring wall thickness and determining material quality together with the stamping analysis techniques discussed in the next chapter all aid in troubleshooting.
Drawing requires Energy which is converted in to heat, a process success issue.
Drawing box-shaped parts involves simple plane strain stretching, bending and straightening, as well as cup drawing and bending. Providing proper shape and clearance in the blankholder
Providing enough clearance in the blankholder avoids fracture by allowing the metal to thicken at the corners.
Simple biaxial stretch forming is not true drawing but a good process for providing shape and rigidity to stampings such as automotive hoods, roofs and many smaller stampings.
15 Stamping Analysis Techniques......................................... 157
Computerized stamping analysis takes most of the guesswork out of stamping and tooling design. Simple sectional analysis programs as well as general analysis programs are being developed to the point that the part and die can literally be tried out in a computer.
Circle grid analysis is an intuitively simple way to measure stamping deformation. Press shop applications to measure forming severity using the deformed circles and plotting the measurements using CGA is an excellent process control tool. It is possible to lightly scribe circles in order to make do without etching equipment in an emergency.
16 Die Maintenance Documentation and Tracking............... 167
A systematic die maintenance system can use a simple die repair work cycle step-by-step as follows:
A simple paper request for maintenance form designed to suit your needs has many advantages. Properly designed, the form mirrors the repair process. In case studies this is an effective way to institute computerized die history and cause/cost code data. Tracking and reducing costs is a basis for continuous improvement.
17 Effective Die Maintenance Program Strategy.................... 183
Understanding that a die maintenance facility is a place where dies are repaired and a die maintenance program versus a Die Maintenance Area. Production scheduling planning is essential to die maintenance.
Tracking the cost of maintenance and downtime and shop-floor involvement is essential in order to achieve continuous improvement. Showing employee appreciation aids correct entry of maintenance work records for computerization and accurate document control.
Maintaining an affordable inventory of spare parts for planned and emergency maintenance requires common sense rather than traditional crib part float levels. A good rule is to have the die owner pay for the spare parts inventory.
Putting numbers on die repair cost includes unanticipated downtime cost, run ahead any disruption production cost, excess shipping cost and all parts and labor at the shop load rate. By knowing the cost for each piece for die maintenance and establishing the dieroom as a cost or profit center it is often found that repairs done in-house are less costly than dealing with an outside vendor.
In chapter 6 we discussed assigning cause codes to all repairs. Pareto charting the major cost items and involving everyone in their reduction will lower maintenance costs.
When taking in a used die it must be established who pays for refurbishing the die and determining any extra costs due to the die not being built according to good engineering practice. You must also accurately know your shop equipment load and additional auxiliary equipment requirements.
18 Metallic Springs as Die Pressure Devices....................... 211
Types of Metal Springs
Materials Used to Make Metal Springs
Processing Die Spring Steels
Seven step procedure for selecting the correct springs.
Considerations when Repairing Dies
Nitrogen Cylinders and Hydraulic Pressure Systems
Spring Mounting and Care
Analysis of Spring Failures.
Winding Springs in-house
19 Gas and Hydraulic Die-pressure Systems....................... 227
Many types of pneumatic cylinders are used in die automation systems. They are seldom used for pad pressure in new die designs.
Nitrogen die-pressure systems are used in both piped and self contained cylinder systems. Nitrogen systems require care in filling and repair of wear and any leaks. Rebuilding nitrogen manifold systems as well as self contained cylinders requires systematic work--never patchwork maintenance.
Inverted draw-dies, cam return applications and floating draw-die punches all may make use of gas pressure systems.
Hydraulic die-pressure systems have many advantages where pad return timing and high forces are required.
20 Press Selection and Maintenance..................................... 247
Understanding press terminology including shut height bed and bolster, gears, pitman, press slide connections, connection strength and slide adjustment are all important terms.
Types of presses include gap-frame presses, open-back Inclinable, open-back stationary type and straightside presses. In these basic frame types both mechanical and hydraulic machines features and applications are explained.
Understanding and measuring gap-frame press stiffness and the purpose of adding tie-rods to the front of the press.
Production of Precision Stampings.
Mechanical Press Drives.
Direct-drive Mechanical Press Applications.
Single-gear Reduction Presses.
Angular Misalignment Due to Crankshaft Twist
Twin-end Drive Presses.
Double-gear Reduction Presses
Single Connection Presses
Two- and Four-point Presses
Speed Reduction and Torque Capacity
Mechanical Versus Hydraulic Presses
Ram Tipping Controls.
Upgrading Existing Presses.
Die cushions and application of both pneumatic and hydraulic die cushions correct usage and troubleshooting is featured.
How to center the load in the press and the problems created by unbalanced loading and mishit damage is illustrated.
21 Troubleshooting Large Panel Stamping Dies.................. 283
The first step in trying out a large stamping die is to make sure it will bolt up correctly in the production press. Correcting any misalignment is essential if automatic quick die change clamps are used.
Nitrogen Pressure Systems
Marking Nitrogen Pressure
A Systematic Approach to Die Tryout
Measuring with an Ultrasonic Thickness Gage
Blank Holders without Draw Beads
Bending and Unbending .
Commercial Steel Draw Beads..
Cast Draw Beads.
Multiple Draw Beads
Double-action Press Operations
Dirt Problems ..
Sources of Contamination
Forming Ribs and Embossments
22 Waveform Signature Analysis........................................... 301
Charting Tensile-Testing Machine Waveforms
Case Study: Webster Industries.
Chart Recorder Selection
Diagnosing Hydraulic Overload Problems.
Triple-action Toggle Press Case Studies..
Detecting Waveform Changes.
Die- and Press-protection systems
Hydraulic Overload Protection.
Shear Collars and Stretch-links.
23 Repairing Damaged Die Steels and Castings.................. 323
When a one of a kind die shoe or other casting is broken making correct repair decision quickly is essential. Lasting repairs can often be achieved most rapidly with mechanical repair techniques
. Preparation of a cracked or broken casting by hand chipping, grinding and careful fitting is more intriguing than any jig saw puzzle. Using tie-rods to hold the broken castings in assembly as well as adding a steel plate to reinforce the casting are simple repair techniques if approached in a systematic way. Applying clamping force to a crack with a dutchman and other cold crack repair techniques can get production running quickly.
Electrical and gas welded repairs are used for both iron and steel die parts. Choosing wisely from the available welding materials and techniques will save money while assuring good repairs..
24 Die Materials and Treatments ........................................... 339
Understanding the characteristics of tool and die steels and choosing the best tool steel for your application is important. Types covered include:
The heat treatment of die steels with simplified theory is explained. Proper quenching and tempering of tool steels and its influence of heat treatment on die life and cannot be neglected. Cold and cryogenic treatment is discussed as an adjunct to proper heat treatment, not a cure-all for problems. The control of surface chemistry and dimensional change.
Tool steel production methods covered include the wrought ingot process, refining by electroslag and vacuum arc remelting as well as powder metallurgy tool steels.
Die surface coatings and treatments are increasingly used to increase wear life and lubricity. Old processes include chromium plating, gas nitriding with newer processes such as ion nitriding as well as titanium nitride and titanium carbide.
Wrought low-carbon steels and cast irons as well as cast carbon and low-alloy steels are used for die shoes, fixtures backing plates and the working surfaces of some dies. Cast and ductile irons are widely employed in large die shoes and drawing dies.
Nonferrous and nonmetallic die materials, nonferrous cast materials, zinc-based alloys, cast beryllium, Copper, and bismuth alloys are an important class of tooling materials discussed.
Carbide die materials are widely employed in long run cutting dies especially for hard and abrasive materials.
Appendix A: Generic Die Standards....................................... 371
Appendix B: Case Study—
This case study examines the plant culture and capabilities of the dieroom that supports a custom contract stampers pressroom operation. This study documents order entry procedure, machine shop capabilities, spare parts storage, ergonomic aluminum die sets.
Quick die change capabilities accurate bench die buildup, standardized tooling and an eye to the future make this case study a fitting conclusion for this work.
By D. Smith,