Last month, the scrap rates on a stamping line suddenly lurched upward and have remained there. The department supervisor says the problem is oscillations in the feed system. Curious as to what this means, you visited the operator.

The way the machine works is the feedstock stops on top of the die, the machine stamps the feedstock twice, and then the feedstock advances to the next blank section to make the next part. An operator showed you stamped stock that had double impressions, one slightly off from the other. But on a good part, it looks like a single impression.

What should you do?

First, talk with a tool designer about this process. Stamping twice is one way some manufacturers try to extend the life of worn dies. A single stamp process, if applicable, will save energy and increase output.

Control system problems might allow the part to move while being stamped, thus accelerating die wear. Get the mechanics out there with micrometers, and have them check the stops and other mechanical items. You will need to examine the electrical controls.

Check the limit switches to ensure they don't wobble, and use a digital multimeter to test operation. A single limit switch could be causing this scrap problem.

Consider changing the function of limit switches. Use photo switches in their place in the control scheme, and have the limit switches "back up" the photo switches. This reduces mechanical drift and increases reliability.

Review the PLC logic for further improvement opportunities.