Extreme nitriding limits in aluminium extrusion

Abstract

Extrusion of aluminium is an efficient manufacturing process which allows long continuous production. The heated billet (aluminium material) is squeezed through the opening of a metal die in order to shape the desired aluminium profile. A long continuous production increases aging of the die and hampers its capability to yield homogeneously shaped profiles. Hence the dies are usually removed from production lines before their breaking point and only go back into production after receiving a layer coat for protection of the metal. This paper consists of a preliminary analysis of the extrusion amounts between consecutive maintenance procedures of the dies. A maintenance procedure in its whole encompasses an immersion bath of the die in caustic soda, a polishing operation and possibly a subsequent coat layering process in a nitriding chamber. The main goal here is to find the optimal life cycle for a die, in the sense that we are looking for a risk level (an extrusion amount) above which die-damage occurs with a certain high probability. We shall rely on extreme value statistics to answer the question of how long can we go on at each continuous operation of aluminium extrusion.