Optimised Design Parameters for Twice Shrink-Fitted Dies in Plane Stress Conditions

摘要

Twice shrink-fitted dies are rather expensive and complex to build, in comparison with single shrink fitted ones, but are necessary in those applications where high compaction loads would otherwise lead to a too much large single shrink fitted die. Bearing this in mind, it is very important, especially for the twice shrink-fitted dies, to design them in order to minimize dimensions and reduce the stress states. In other words, for fixed compacting loads, it is useful to try to attain the minimum outer dimension of the insert, the intermediate diameter and, then, the shrink-fitting interferences so that the maximum tension on each item of the die is lower than the allowable ones for the insert and ring materials. In analogous mode, for a fixed outside dimension of the die, it is useful to try to find the intermediate diameters and the shrink-fitting interferences apt to maximise the allowable compaction loads, obviously taking in account the allowable maximum stresses on each die material. In this paper, for simple cylindrical shapes, some design parameters, like dimensions, shrink-fitting interferences, stress-strain states, have been evaluated, by analytical methods, in order to structurally optimise any twice shrink-fitted dies in the above mentioned sense.