Effective Remedies for Punch and Die Chipping Problems

May 15, 2019

A material-dense punch and die combo can absorb a great deal of punishment. Pushed to its limits, however, even a high-quality tool combo will chip. The overall piston-rolling strength of the tool holds out for a while longer. The impact-driven backbone crashes down resolutely, but the chipping effect propagates. Left like this, the output coming off a production line will look shoddy and cheap. Let’s remedy this frustrating problem.

Punch and Die Chipping: The Causative Factors

As an operator issue, the punch hasn’t been loaded properly. It’s misfeeding the die, not striking “true,” or it’s angularly adrift for some other, as yet, unknown reason. Looking down at the sheet metal retainment mechanism, a cheap and nasty feeder isn’t holding the workpiece properly. As the metal moves, the die falls at an angle; the impact hits the punch at a weakened strike point, and chipping flakes away. Essentially, no matter how strong a carbide or tungsten strengthen tool is, that tool will chip if its surrounding components aren’t operating properly. All tool parts, including the punch and die, must interact correctly. Considering the small parts clearances and heavy forces in play, anything less than this perfectly aligned setup is going to produce tool chipping.

Determining Punch and Die Remedies

Experimental testing routines take the equipment offline. That’s an unfortunate development, but this move is necessary if a repair engineer is to reduce the number of parts rejections coming off the line. A finite element model is one option. The numerical methodology that defines this error checking approach uses all production data and tool specs to determine a likely cause. Of course, there’s always common sense. If the same tool parts are chipping, then a certain heat treatment process or metal gauge isn’t up to the job at hand. If, on the other hand, tool misalignments and/or sheet metal strippers are performing sub-optimally, then the operator receives more training, the stripper gets replaced, or the punch/die miss-hit cause gets identified by that finite element modelling strategy.

As that last tidbit of information suggests, the best solutions come to those who are willing to use all available diagnostic tools. Computer simulations are powerful aids, but the human brain and its cognitive functions can be just as effective. A truly capable repair operative adopts a full-service approach. There’s the sheet metal thickness to examine, plus the composition of the alloy. The clearances between the punch and die sections, the angle of strike, the sheet stripper retainment mechanism, all of those many moving parts are analysed, both physically and by simulated computer work, to narrow down the cause of the tool chipping problem.

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