Studies on maximum extrusion pressure in hot extrusion of aluminum

Abstract

In general, the maximum extrusion pressure in hot extrusion depends on yield strength, billet diameter, billet length, extrusion ratio, extrusion temperature, and extrusion rate.
The object of this work was to derive a formula for calculating the maximum extrusion pressure as a function of the above factors in hot extrusion of round aluminum rods.
A number of extrusion experiments were conducted and an empirical formula was derived by analysis of the experimental results.
Since the experiments were done using 600 ton vertical type extrusion press with has the capacity of production scale, it could eliminate the scale effect usually encountered by small size experiments mainly due to the small heat capacity.
The yield strength having a great effect on the maximum extrusion pressure was determined by each experiment of extrusion. At elevated temperatures, it was little affected by the strain, but greatly depended upon the strain rate, on the contrary to the case in cold extrusion.
The strain rate varied according to the point of billet and it was important to know how to determine the average strain rate. This method was established by analysis of the experimental results for calculating the maximum extrusion pressure.
In hot extrusion, the yield strength usually decreased owing to the temperature rise caused by the heat which had been generated during extrusion by the conversion of a part of extrusion energy.
It should be also noted that the yield strength increased by the work hardening during extrusion.
As the results of the above studies, the empirical formula was derived to calculate the maximum extrusion pressure.