Made from hardened tungsten carbide alloys, tool punches should last for ages. That may be the case in an ideal world, but we clearly don’t live there. Punch life issues occur, they frustrate equipment operators, and they cause periods of machine downtime to accumulate. A productivity loss graph could probably chart the problem. Or, better yet, all of that valuable company time could be spent coming up with a punch life boosting strategy.
Working with HSLA Steels
Let’s pick the second option, the punch life extension approach. Now, even if the previous generation of punches, as made by a state-of-the-art tooling service, have proven themselves time and again, that doesn’t mean much if the materials they’re processing are growing stronger. And that’s exactly what’s happened. High-Strength, Low-Alloy (HSLA) steels are bringing new challenges into the industry. To compensate for those challenges, punch tools require an edge. And we’re not talking metaphorically; punching tools need to be kept sharp and clean. A properly scheduled maintenance program can take care of this aspect of things. Punches with asynchronously applied concavities and convex elements require special attention here. Otherwise, shear angle issues will be that much harder to offset.
Utilizing Evolving Tooling Technologies
Sure, conventional life-extending techniques do yield positive results. For instance, by managing the Rockwell Hardness of a punches tool head, brittleness problems and multiple breakage incidents become things of the past. By making the tool pins and bushing larger and harder, the same life boosting goals are realized. Beyond conventional repair overtures and maintenance methods, though, there are other avenues to explore. Granted, the short-term gains may not seem obvious, but the long-term savings will ensure a substantial pay-off. To begin with, push the upfront costs aside for the moment. A far-sighted designer looks instead for the following system adaptations:
- Back tapered profiles to reduce side galling
- Harder, more fatigue-resistant tool alloys
- Special friction-minimising coatings
- Powder metallurgy research and development
Looking at that bulleted list, back tapered punch sides aren’t too hard to incorporate into a production system. With the tool metal, A2 carbon chrome alloys can no longer cut it in sheet metal punching operations, not when HSLA sheets are becoming so popular. A switch to M2, M4 or some other high-toughness tool alloy is recommended.
Even coatings technologies can extend punch tool lifespans. That film-like finish combines with powder metallurgy-derived punches that are as chip-proof as they are wear-resistant. Remember, powdered metals are still part of a relatively new field of alloy strengthening technology, so new developments are always cropping up there. As for the coatings, TiCN (Titanium Carbon Nitride) thin films can greatly boost punch life. The coatings feature low-friction coefficients, which facilitate fast punch operations and hassle-free tool spring-back strokes.