Establishing a die setup recipe for progressive dies
Setting up a stamping die is one of the most critical steps in a successful stamping process. It's a fact: More damage is done to a die, especially a progressive die, in the first 10 hits than in the next 10,000 hits. Most die damage happens during initial setup, when the material is being fed into the die. Mistakes such as misfeeds, pilot piercing, double metal, sheared cutting sections, and stock hang-ups often occur.
To reduce the number of mistakes, it is important to have a good die setup recipe for each progressive tool. The special setup sheet should contain numerous items in checklist form.
All of the following items are crucial to your die-setup recipe. Although some of these items may seem very obvious, do not make assumptions that they will be performed automatically.
- Die placement- Make sure that the die is set so that the material feeds parallel to the tool. Parallel feed can be achieved several ways, such as stop pins, keyways, and conical locaters. Figure 1shows stop pins and keyways.
Only one type of locater is necessary. Avoid "sighting in" the tool as this process is difficult to repeat and inaccurate. When possible, try to place the center of the estimated tonnage in the center of the press and not the centerline of the die in the center of the bolster.
- Pitch and progression- Make sure the feed pitch and progression are set correctly. Overfeeding or underfeeding most likely will result in a misfeed and die damage.
- Coil width- Make sure the coil width is correct.
- Material thickness, type, mechanical properties- Verify the metal thickness, and, when possible, verify that it is the right type to be used in the die.
- Feed line height- Verify feed line height, the height at which the metal will be fed into the die.
- Lubrication- Verify the type of lubricant to be used, the application method, and the mixture ratio. Don't forget that it is important to lubricate both sides of the material correctly.
- Nitrogen pressure- Check the nitrogen pressure and make sure that it is set correctly.
- Scrap ejection- Make sure that all slug belts and shakers are in place and functioning properly.
- Shut height- Ensure that the shut height of the die is set correctly. Avoid using press counters to establish the finish shut height. Avoid hitting setup blocks. Because a press defects, it may be necessary to calibrate the finished shut height after the die is fully loaded.
- Tonnage monitors- Record your tonnage when the die is properly operating, and use this tonnage as a baseline for setup.
- Coil quality- Check coils for defects. Avoid running rusty or dirty stock through the tool because this can cause die damage, as well as defective parts. Figure 2shows various coil surface defects.
- Sever-edge camber- Check for sever-edge camber in the coil. Severely cambered material will be difficult to feed through the dies. Figure 3shows the process for checking for camber. The general standard for camber is that it be no more than 1/4 in. per 8 ft. of coil. The ratio can be measured easily using an 8-ft. piece of string and a scale.
- First-hit line- This is a very important step and requires careful attention. Starting the material in the wrong spot can cause half-hits of half-forms. Unbalanced cutting or forming can cause the upper and lower dies to misalign and shear. Also, incorrectly starting the material can leave loose scrap in the die. If the scrap is not removed, double metal results and is fed into the tool. This condition can cause severe die damage. A good die designer establishes a distinct first-hit line by placing a positive spring-loaded stop at this point, rather than a simple line with a message: Start strip here.
- Loose scrap- Despite efforts to avoid loose scrap in the tool, it often is produced, no matter where the first-hit line is located. Make sure that all of the loose scrap is removed manually.
- Bolts and fasteners- Double-check all of the bolts securing the die in the press, making sure that they are tightened and secure. Make no assumptions. Despite the fact that this seems obvious, it still helps to have a checklist reminder.
- Stock condition- Make sure the steel is properly straightened and feeds smoothly through the die.
- Die protection- Make sure all die protection equipment, such as sensors, proximity switches, and whiskers, are properly installed and functioning.
- Counterbalance- Make sure the press counterbalance pressure is set properly with respect to the upper-die weight. Not doing so can cause poor ram-to-bolster parallelism, unnecessary press loading, as well as excessive wear, die shearing, a tonnage loss, and a press energy loss.
- Slug ejection- Make sure that the scrap falls off the tool freely during all operations, including cutting and piercing.
- Feed acceleration, timing- Properly time the acceleration and deceleration of the stock-feeding system, and set the optimal time to feed.
- Feed and pilot release- Time the feed release so that the pilots are free to locate the strip. Usually this is done by inching the press down and releasing the feed roller after the lead of the pilots has entered the pilot hole.
Implementing the Setup Procedure
These setup factors are key items to think about when setting up a progressive die. I strongly suggest allowing the setup personnel to create (as a team) their own procedures based on the available recourses. Start with all of the factors listed previously and then have a die setup specialist add or subtract variables as needed. All too often tooling or production managers establish a die setup procedure and try to force the die setup personal to implement it. It's a simple fact: People will support a world that they are allowed to create. If you create it and try cramming it down their throats, well, good luck. You're gonna need it!
Haste Makes Waste
Neither the process of setting up dies nor should the tremendous responsibility of a die setter should be taken lightly. Tooling cost often is enormous, and one simple mistake can cost thousands of dollars. Try creating a simple checklist of critical items, and then take the time to check them off manually during the die setup procedure. Take nothing for granted, make no assumptions, and keep accurate records of each tool set's parameters.
Best of luck... Art