In situ punch wear measurement in a blanking tool, by means of thin layer activation

The improvement in the productivity of the leadframe blanking industry of is a key for its competitiveness. Consequently the challenge for researchers covers a wide range of scientific areas (materials, lubrication, process, etc.). Among others the improvement of the punch wear resistance is one of the most important parameters in the blanking process. Consequently punch wear understanding is the topic of this paper. Because of the strong influence of the centering of the punch-die clearance upon the burr amount, it is crucial to directly measure punch wear in the blanking press without disassembling the tool. In this paper a new method for a direct measurement of the punch wear, selective activation technique, which has never been applied in the field of blanking is described. With the help of this technique, a precise relation between the loss of activity and the worn volume on the punch has been established. In addition this method allows the influence of the blanking process parameters, like lubrication or nature of the blanked material, to be quantified in real time. The measured wear volumes by this method have been confirmed by means of measurements of the profile of the worn punch carried out after completion of a large amount of blanked parts. These geometrical results exhibit a good agreement with the selective activation technique.