December 14, 2008
Effective stamping professionals rely on scientific principles and not magic to determine and correct production problems. Find out how to troubleshoot wrinkles and rips and take corrective action by following a basic procedure that can be modified to troubleshoot almost any stamping issue.
If you've ever attended one of my die troubleshooting clinics or seminars, chances are you heard me vent my frustration about how the United States views the tool and die industry. All too often, the process of designing, building, and troubleshooting a die is portrayed as an art form. This portrayal elevates my blood pressure. I hope you are not making die-related decisions based on an inspiration you had on your way to work, but are making these decisions based on the laws of physics.
Besides hearing me vent my frustration regarding this misperception, chances are attendees saw a little magic show during the training session. I perform the magic demonstration for a couple of reasons. First, tooling professionals often are viewed as magicians. A problem occurs; we are asked to go to the press and work our magic to make it go away. Also, magic makes the training session fun. I believe we learn more when we enjoy the training. Following the magic, I usually reveal how the simpler tricks were done. Why? To demonstrate that there is no such thing as magic, and despite what you think you see, it's nothing more than simple physics. Once you understand the physics, the magic goes away. Die troubleshooting is a physics-based science.
Dr. Edward Deming, the father of statistical process control, once said "In God we trust; everybody else, bring data." That's good advice.
To troubleshoot a stamping operation successfully, you must approach the operation scientifically and lose the black-art, trial-and-error techniques that have plagued the tooling industries for centuries. To do this, you must use a systematic process based on data to help solve problems, and you must have a good understanding of physics.
In our industry, assumptions can lead to disaster. Don't change tooling permanently simply because that's the way it worked on a previous job. Find out why the technique worked. Collect data to help you arrive at the root cause. There is nothing wrong with tricks of the trade as long as you understand why they work. Take the time to understand your material's unique behavior. What works for steel may not work for aluminum.
Is there such a term or profession as a dieologist? No, but there should be. I define a dieologist as someone who solves sheet metal stamping die problems through a systematic process of collecting data, using applied physics, and conducting data-based experimentation.
In other words, approach die-related problems as a dieologist—not a black-art specialist.
Step 1—Identify the Problem with the Part. Obviously, this is one of the easiest steps in the process. Some questions to ask are:
Step 2—Check Process Parameters to See if They Comply with the Setup "Recipe" or Control Plan.
Every die/press/feeder should have documented guidelines for setup. Before making any changes in the tooling, make sure that the die/tooling is set up correctly and that all of the incoming variables are correct. Some questions to ask are:
Step 3—Reassess and Qualify Setup. Simply verify setup parameters. If parameters are OK, proceed to Step 4. If process parameters are not correct, readjust and qualify to recipe.
Step 4—Look for Interactive/interrelated Problems. Physically examine the defective product. Some questions to ask are:
Step 5—Prioritize Work. Decide the basic item to be addressed first. If rips are causing wrinkles, address the rip first, and the wrinkle most likely will go away. If wrinkles are causing rips, address the wrinkle, and the rip most likely will disappear.
Step 6—Determine Corrective Action through Experimentation. Remember, you must act as a scientist. Scientists conduct experiments and derive solutions based on the result of their experimentation. Also, keep in mind that at this point, you still haven't made any permanent changes to the tooling. Permanent changes do not take place until you have completed your experimentation.
The following experiments are for data collection only. By conducting them, you can determine where in the die you may have to make permanent changes. You also can reasonably approximate how close you are to failure. If the following experiments do not yield concrete conclusions, they at least will enable you to come up with good hypotheses.
Wrinkles—too much metal present in a given area.
Rips or tears—insufficient metal present in fractured area.
Step 7—Implement Permanent Corrective Action. In this step, you make changes to the tooling and/or process.
Solving for wrinkles. You must now find a permanent way to increase friction in a given area. Permanent solutions may be:
Solving for rips or tears. Permanent solutions may be:
Step 8—Fine-Tune Your Corrective Action. In this step, make fine adjustments to your process changes, If you are using circle-grid analysis, verify and fine-tune it to be robust.
Step 9—Adjust Control Plan and Recipe.
Document any changes that you have made to the setup process, recipe, or control plan. This helps prevent setting up the job to outdated parameters in the future. (QS-9000 people love this step.)
Troubleshooting matrices won't reveal solutions for all drawing problems, but they may give you an idea of the science that some perceive as a black art. Meet with your toolroom professionals to discuss—as a team—developing a data-based troubleshooting process. Fit it to your company's resources and time constraints. Remember that people will support a world that they are allowed to create.
Above all, use data to make your decisions. Lose the magic.