Die Science: Thinking like sheet metal

If you have ever attended one of my public or custom on-site training courses, you’ve heard me emphasize the importance of understanding your sheet metal’s behavior before you try to cut or form it. Chances are that sometime during the course, I said, “You must think like the sheet metal or ‘become the metal.’”

As we move steadily into the use of new, advanced material types, this concept becomes even more important. As materials change, so must the cutting and forming processes.

Experience Is Not Always the Best Teacher

Many die building shops and stampers have a lot of experience with different metal types, processes, and part shapes. The problem is that they often fail to record or learn from those experiences. And even if they do learn from those experiences, they often fail to understand why a process was or was not successful.

I often am asked to find a die building shop or stamper to manufacture a given part or produce the tooling for it. For the sake of explanation, let’s say the part is a deep-drawn shell made from 0.060-in.-thick, 3003 O-temper aluminum. Obviously, I want to find a shop with a great deal of experience in designing and building dies for deep drawing aluminum shells.

After finding a shop, I approach the sales rep or shop floor manager and ask a few questions: “What types of aluminum have you dealt with? Can you show me some samples of parts you’ve made? Can you tell me why you processed this part this way?”

In a typical response, he tells me the shop has dealt with many types of aluminum. As he is showing me some sample parts, he says that many of them were a real challenge. “We found we needed to put a very large radius in this area or else it would split. We processed the part this way because after trying many different approaches, we have discovered that this way works best.”

At this point I’m thinking that this shop has a great deal of experience but still doesn’t know why certain methods were necessary to achieve the specified part geometry. The shop obviously has had success, but I must question if this success was the result of simple trial and error and a great deal of luck, or the result of a true understanding of the metal’s behavior. To be honest, I’m leaning toward the trial and error and luck.

What responses did I want to hear?

“Yes! We have dealt with many different types of aluminum, including 3003, 5052, 6061, and 1001. We have processed many different tempers, including O, T, and H. For deep drawing, we prefer using a fully annealed O temper. It’s typically better for deep drawing.”

When showing me parts, a shop floor manager might have a good response: “Because this part was designed to be made of H-temper aluminum, which has poor elongation percentage and poor stretch distribution, it was a real challenge. We were able to eliminate the potential splitting problem by increasing the radius, thus distributing the stretch over a large area.”

And what is the manager’s preferred response when explaining why he processed the part a certain way? “Given the height of the feature and the location of it to the blank edge, we knew that it was necessary to use this particular punch shape to obtain the required surface area for the following reduction.”

Learn From Your Experiences

Experience is not always the best teacher, but evaluated experience is. Take time to study the metal’s behavior and discover why.

Don’t be satisfied that doing a certain thing to a die resulted in success. Find out what really happened. Positive results are great, but if you truly understand why you got a positive outcome, you can use that understanding to solve similar problems.

Become the Metal

Keep in mind the importance of understanding the material’s behavior when making a tooling decision. In other words, don’t think like aluminum if you’re forming steel. It just won’t work.

Thousands of types of materials are stamped today. Some might require annealing after forming; others may be formed multiple times without annealing. Some metals stretch a great deal, while others stretch very little. Some are hard and abrasive; others are soft and ductile. Some metals exhibit a great deal of springback while others may have very little. Some metals even might not be able to take the shape needed in a conventional stamping process and may require a completely different process, such as casting or forging.

As each metal has its own behavior, you need to create the die geometry with respect to this behavior. If you don’t know the metal’s type or behavior, find out before you attempt to develop the die geometry and process. Consider the material’s thickness, elongation, chemistry, and hardness. You can find most of this information in a metallurgical handbook or online.

Also keep in mind that the metal being formed will affect your judgment with respect to the tool steel or die material necessary to form the part. In any case, don’t attempt to develop a die or a forming process without this critical data. Think like your metal.