Influence of wear on particle emission in aluminum blanking

Abstract

The pollution of blanked parts with particles emitted by the blanking operation itself can be encountered in different cases of blanking, in particular aluminum blanking. The consequences of this pollution are a degradation of the quality of the parts produced (appearance, function) and, possibly, a degradation of the behavior of the blanking tool. In this context, we studied the effect of the wear of the punch in the case of AW5754 H111 blanking. Press tests were conducted with a complex part shape and with different press test configurations. The results highlighted two types of wear. The first one is called “run-in” (punch surface accommodation) and leads to a reduction of the emission of particles. On the contrary, the second type of wear, called “pick-up” (material transfer from the sheet), leads to increase particle emission. The mechanisms corresponding to the two particle emission modes are studied. The first mechanism is well known and results from the transition from a blanked edge geometry with secondary shear zone to a more conventional geometry without this secondary shear zone. The second mechanism is new, with sheet material being picked up by the punch and then the picked up material being scraped off, eventually leading to particles being deposited on the die and the part. The study also focuses on the effect of lubrication, clearance and punch shape on these mechanisms. The two mechanisms differ by the influence of lubrication: The second mechanism becomes preponderant as soon as lubrication becomes insufficient, and a solution must be found rapidly because of the larger particle emission and the risk of galling of the punch.