The Effect of Vibration on Plastic Flow in Coining

Abstract

Coining with a superimposed vibrational load of 800 lb and with a relatively low frequency of 130 cps was investigated. The materials were commercially pure lead and aluminum which were chosen to give an indication of the coinability during hot-working and cold-working, respectively. All blanks had a constant diameter d0 = 1 in. and three initial thicknesses h0 to give ratios h0 /d0 , of 0.250, 0.125, and 0.0625. The definition or degree of coining and surface finish was examined when coining these materials with three punches which were provided with different grooves of equal width. The shapes of the grooves had the following cross section: square, triangular, and semicircular. It was found that superimposed vibration upon static loading reduces the peak pressure required for the same degree of coining (measure of definition) significantly for dry lead, but to a lesser degree for dry aluminum. The improvements for h0 /d0 = 0.0625 were 30 to 35 per cent for lead and 5 to 7 per cent for aluminum. It was also found that unlubricated specimens give a better surface finish and that the tendency to form folds, as is observed at times with lubricated blanks, at the point of coring, apparently is eliminated.