Every punch and die set will wear, slowly but constantly, and cost you quality before they eventually fail completely. Here are the checks to find signs of wear early enough.
Check the Punch Tip for Damage
When inspecting the punch tip for wear and tear after each production run, the cutting edge of the punch should be of a sharp uniform edge, with no signs of chipping or a flat area on the edge. A rounded tip to the edge of the punch indicates wear and the punch will need to be re-grinded or even replaced depending on the extent of wear.
Measure Punch Length Regularly
The allowed tolerance for the length of a punch is generally less than 1mm, and it is wise to use a digital calliper or a good quality micrometer to measure this. Most punch manufacturers will have a maximum re-grind dimension after which the punch should be retired.
Inspect the Die Edge and Clearance
Feel any roughness, chipping or rollover on the die edge with a fingernail? Also check the punch clearance against the die, to ensure it is set for the material thickness being cut (typically about ten to fifteen percent above the material thickness). As the punch and die wear, the cut quality will deteriorate until the tooling can no longer be used.
Watch Burr Height on Finished Parts
Burr height must be measured on finished parts and compared to the set burr height using a burr gauge. If the burr is longer than approximately 10% of the material thickness then either the punch or die edge is wearing. This must be dealt with before it gets any worse.
Check Lubrication at the Punch Guide
Punch guides are also prone to wear, particularly if they are not adequately lubricated. Ideally the guides should be smeared with a thin film of the correct machine oil before each shift. This will help prevent wear and also help to remove any metal particles that may have accumulated in the guides’ area.
A useful reference for CNC Punching Machines is https://www.cotswold-machinery-sales.co.uk/euromac-bending-machines/punching-machines/. The HSE guidance on the safe use of work equipment and machinery is worth keeping alongside your maintenance log.
Catching wear early will help to keep your product to the best quality and prevent excessive costs for wear and tear of your tooling.