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Peter Ulintz Peter Ulintz
PMA Technical Consultant

Starting a Progressive Die Design

September 1, 2021

A typical progressive die design may start off like this: A customer sends a part print for a stamped part. In many cases, a 3D CAD model accompanies the drawing. The die designer creates a flat blank from the part drawing or CAD model and begins to orientate the blank to optimize material use while considering grain direction and accessibility for cams. He then determines the type and number of die stations, attaches part carriers, and designs the die structure and die details. Modern die design software automates much of this work.

However, dies designed in this way may increase the risk of producing nonconforming parts or generating high maintenance costs—for both the die and the press. To alleviate potential problems, designers must understand two important factors that can impact their die design: the influence of part material (sheet metal) and the press.

Influence of Part Material

Sheet metal type, grade and thickness greatly influence how a die should be designed and built. Of course, designers can determine material type and thickness from the part drawing. But they also must understand how different material properties influence the die design.

For example, designers commonly apply 10-percent-per-side cutting clearance to cutting and punching processes. Though perhaps an ideal cutting clearance for mild steel, it could be the worst choice for stainless steel in terms of burr height. Higher-strength steels require greater punch-to-die clearance to provide the mechanical leverage required to break the slug cleanly with a minimum burr. For example, research on advanced high-strength steels suggests required clearances exceeding 20 percent per side on some grades to provide for best edge-stretching capability.

Some aluminum grades have limiting draw ratios similar to those for steel, while others have much less. Draw-reduction ratios vary depending on the aluminum grade being formed. Die design handbooks usually contain draw-reduction tables for low-carbon steel. Due to differences in work hardening behavior, surface topography and other factors, do not use these tables for brass, aluminum or other nonferrous alloys.

Specifying sheet metal with little technical information also can affect die performance. For example, specifying Type 1008 steel allows for the supply of a wide range of properties. A low-carbon, vacuum-degassed (VD) steel could fall within this specification range as well as a Type 1006 drawing steel (DS) or a Type 1008 commercial steel (CS). All have less than a 0.10-percent weight of carbon and are aluminum-killed. And, all perform differently in the die.

In many shops, internal struggles persist around who decides on the material to be used for production. Is it the purchasing department (“we got the best price”), engineering department (“we want the most formable material”), estimating (“this is what we quoted”) or sales (“our competitor quoted a cheaper grade”)? The real answer: The die decides. 

If a stamping die could talk to its designer, it might say, “If you want me to produce this part to those specifications, using that lubricant and this die design, then I am going to need sheet metal with the following attributes…”

The problem that arises: The die speaks a language that most designers don’t understand. The language of the die is mechanical properties: strain, strain-rate, n-value, r-value, yield stress, elongation, coefficient of friction, etc. The die doesn’t understand tradenames, composition, Rockwell hardness or standards. To be successful, designers must learn the language of the die and how it applies to their designs.

Influence of the Press

Die designers also must understand that a centered ‘load’ and a centered ‘die’ are not the same. In a stamping die, forces distributed unevenly across the press slide cause the slide to tip and move laterally in the direction of the greatest force. A load not centered under the press ram may alter critical die clearances. If this movement occurs while punches are engaged with other die components, excessive wear or damage can occur. Rapid die wear increases die-maintenance costs and compromises the dimensional consistency of the stamped parts. 

Also important: the press tonnage rating. The available tonnage decreases in mechanical presses as the working distance above bottom dead center (BDC) increases. This ‘de-rating’ of tonnage occurs because the relationship between the crankshaft angle and the pitman has reduced mechanical advantage higher up in the stroke. This holds true for flywheel-drive mechanical presses and their servo-drive counterparts. Tonnage de-rating proves particularly important with deep drawing, where forming can begin several inches above BDC.

Cutting and blanking stresses all produce unloading forces in stamping presses—known as snapthrough or reverse tonnage. High-tensile snap-through forces introduce large downward accelerations that can damage the die and the press. 

A press factor not as well-understood as tonnage is working energy—a function of the press load and the distance through which the load must be applied. Energy expends with each stroke of the press, and must be replaced prior to the next stroke. In combination, the flywheel stores and delivers the required work energy while the electric motor restores depleted energy by maintaining flywheel speed and avoiding excessive slowdown. 

Forming and drawing processes can consume large amounts of press energy due to their long working distances. For example, pushing 50 tons through 1 in. of forming requires 50 in.-tons of energy. On the other hand, drawing 3 in. deep will require 150 in.-tons of energy. Changing to a high-strength material with twice the strength would require a press with at least 300 in.-tons of available energy. 

Want to learn more about progressive dies and deep drawing processes? Consider attending PMA’s Progressive Die Technology seminar (October 6-7, 2021) and our all-new Deep Draw Boot Camp (November 9-11, 2021). Both events will be held live in Cleveland, OH. Visit for more information or contact Marianne Sichi at MF

Industry-Related Terms: Blank, Blanking, Brass, Burr Height, Burr, CAD, Center, Die, Draw, Drawing, Forming, Grain Direction, Model, Ram, Rockwell Hardness, Slug, Stainless Steel, Stroke, Surface, Thickness, Work Hardening
View Glossary of Metalforming Terms

Technologies: Tooling


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