Tooling by Design
Die Damage at Coil Change
If you could create a list of the top-10 stamping-related problems in your press shop, die damage at coil change likely scores high on the list for most shops running progressive dies. There are many causes of die damage at coil change; here are three.
Short feeds (or misfeeds) cause most of the die damage that occurs in press shops. Care must be taken to ensure that the strip starts correctly into the die. Improper positioning of the leading end of the strip will do more damage to the die in the first 10 strokes of the press than the next 10,000 strokes.
Be sure that the strip does not sag between any of the lifters. If not corrected, the strip will be pulled out of its correct die position. Again, rail systems generally provide better support and usually perform better than spring lift pins or round lifters that are notched on one side.
Unbalanced forming or cutting can result when starting the lead edge of the strip, which can tilt forming pads and stripper plates. This can be particularly problematic when stamping thick materials. Ensure that forming and cutting stations have heels to absorb side thrusts when stamping thick materials (Fig. 2).
Starting a strip out of position (off-progression) will likely cause die damage. Many parts require the edge of the blank to flow inward during flanging, forming or drawing operations. This requires blank material to move sides or flex vertically, or both, during the die operation. Here, use a flexible part carrier to allow flexing and movement of the blank without pulling adjacent parts out of position.Often, the most misunderstood part of die setup is setting feed-release timing. The strip material may slide backwards after the feed releases the material and before the pilots have entered the pilot hole. To prevent this, make the first pilot with an undersized nose longer than the other pilots (Fig. 3). MF
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