Impact of die wear and punch surface textures on aluminium can wall

Aluminium can manufacturing uses a wide range of punch sleeve surface roughness and textures. The ironing die and the punch tooling both can vary in the roughness from 0.04 μm to 0.4 μm Ra during the can forming process. This, together with the roughness of the incoming can body sheet (from 0.3 μm to 0.6 μm Ra) creates a wide range of tool/metal interface coefficients of friction. Ironing dies become rougher and have to be replaced frequently once they lose their shape. Punches maintain a consistent roughness for periods of a week to a month and any surface wear is compensated for with die changes. The initial die and punch surface finish adopted by a manufacturing unit determines the long time plant productivity and punch life. A higher friction on the punch side, compared to the die side, is the preferred manufacturing operating condition. Departures from the preferred condition with ground, polished, cross-hatch and media textured punches are examined. Plants that prefer polished carbide punches over cross-hatched must have their lubrication and coolant parameters controlled within a very narrow operating window. A larger operating window and better performance is achieved with the cross-hatch and micro-textured punches having a Ra less than half that of the can body sheet. Above all, a random isotropic texture is identified as the ideal punch sleeve surface texture and the best performer for aluminium can manufacture.