SOLUTIONS FOR YOUR GALLING HEADACHES
In order to troubleshoot and improve tool life when you experience galling, you must first determine the root cause – abrasive galling or adhesive galling. Material buildup on the surface of the punch tip will occur with both, but each has its own distinct method to reduce the problem.
Abrasive galling occurs when the cutting edge of the punch tip breaks down or fractures. Typically, the fractures are so small that abrasive galling is often mistaken for material adhesion. If not properly reviewed and diagnosed, the solutions you try may not be as effective as they could be.
Adhesive galling occurs when the material being punched has similar properties to the steel used in the punch. Material gets transferred from the work piece to the punch tip and then adheres to the tip. Don’t confused this with misalignment. Consistent wear seen only on one side most likely indicates a misaligned tool that would benefit from improving the strip alignment.
In both cases, once galling begins, it only continues to worsen by building up more material – and causing premature wear, out of tolerance product and eventually tool failure.
WHAT'S THE BEST SOLUTION?
In order to determine the best solution, inspect the tip under a microscope to see how the material is adhering. This is a simple, yet important step.
Next, check the material you are stamping. Is it an abrasive material? Does it have high yield or tensile strength? Is it ferrous or non-ferrous? All of these things play into the proper solution.
If the tool steel, or coating applied, is too similar to the material being stamped, you increase the potential for adhesion. If the tensile strength of the material is higher than the steel of the punch, it’s likely you will see micro-fracturing of the cutting edge that is leading to abrasive galling. This is the difference you should look for to determine the next steps. If you see micro-fractures, a change in tool steel may be your best solution, but a harder steel may not always be the right choice either.
If galling is due to adhesion, a change to the material could be warranted, but additional solutions to create a barrier between the steels include lubrication, coatings and surface treatments. The goal is to reduce friction and heat which is causing the adhesion.
- Lubrication: Some lubricants can become less effective as they breakdown, or even vanish throughout the progression, so it’s important to apply the right lubrication, in the right amount, at the right time.
- Coatings: Coating the punch is another way to create a barrier. This provides a different surface type than the tool steel and reduces steel-on-steel issues. Coatings often improve the coefficient of friction, and in some cases, quite substantially. Less friction equals less adhesion.
- Surface Treatments: The best way to reduce friction is to improve the surface finish of the tooling. This can be accomplished with some diamond paste and a little elbow grease. Reducing the RA not only creates a shiny part, it provides less resistance during the piercing and stripping motions. You can also change the grain structure of the tip to be in line with the motion of the piercing. Grinding linear, as opposed to cylindrically, often provides a considerable amount of friction reduction.
The best solution for Application A may not be the best solution for Application B. Sometimes it may take some combination of tool steel and coatings. Other times it may be lubricants and grinding methods. It may even take the whole kitchen sink. Whatever the solution may be, just remember that the best solution cannot be found without a little work on the front end to determine the real reason for the galling.
Watch our webinar "Prevent Galling and Increase Throughput in Stamping Applications" to learn more, or contact your local Sales Engineer to discuss solutions that are available for galling in your stamping applications.