AN INVESTIGATION OF NEW TRIBOLOGICAL VARIABLES IN FRICTION MODELING OF BULK METAL-FORMING

The present ''realistic'' fiction model is examined by a series of ups etting tests. Specimens made of different aluminum alloys and prepared by various processes display diverse results. Severe surface rougheni ng takes place in some cases using A6061T4 bar manufactured by hot ext rusion. It results in a lubrication condition which is very different from the theoretical prediction. From hardness tests and microstructur e observations, it is found that there is no obvious correlation betwe en the hardness and the roughening process for A6061T4 alloy. The seve re roughening is attributed to the distortion of the coarse grains rec rystallized during the preprocess, that is, the hot extrusion. This is rare in sheet metal forming where most workpieces are prepared from c old rolled sheet metals. The orange peel appearance not only changes t he lubrication mechanics, but also makes the surface finish of the pro duct unacceptable. Since the existing friction model fails to predict such phenomena, surface roughening and all its related factors must be considered as new, important tribological variables in the friction m odeling of bulk metal forming.