The Effect of Surface Finish on the Drawing Characteristics of Chromium-Plated Sheet Metal Forming Tools

Experience in stamping plants has suggested that there are considerable differences in the ability of different chromium-plated dies to form sheet metal. Earlier laboratory work indicated that differences in friction resulting from different surface finishes among chromium-plated dies might be an important factor in the observed behavior. The effect of surface roughness was studied by measuring the friction of sheet metal drawn through chromium-plated drawbeads in a drawbead simulator. Surface roughness was varied by polishing the as-plated surface to smoother finishes, step-by-step, and measuring the friction at each step. It was found that rough finishes exhibited the highest friction. As the finish became smoother, friction was reduced. However, friction reached a minimum and began to rise as the finish became still finer. This suggests that in production tools there is an optimum surface roughness which will give the best forming for sheet metal stamping.