INFLUENCES OF EXPANSION-RATIO ON INSIDE BORE AND LAMINATION DEFECTS IN EXPANSION PIERCING FOR MATERIALS WITH POOR HOT WORKABILITY

In addition to the super piercer, ''the new super piercer'' which allo ws expansion piercing has been developed by the authors. The developme nt of the skewing technology for disc roll axes and its application to the cone-type piercing technology results in remarkable increase in t he expansion ratio. And then, studied in detail were the influences of the expansion ratio, feed and cross angle on the rotary forging effec ts, and redundant shear deformations in the expansion piercing process . Noteworthy is that the larger the expansion ratio is, the more remar kable is the decrease in the number of rotary forging times, According ly, the larger the expansion ratio is, the more remarkable is the incr ease in the elongation value at the tip of the plug. Namely, when the expansion ratio becomes larger, any possible cause of the initiation o f inside bore defects can be eliminated. In order to confirm the above mentioned effects, the influences of the expansion ratio, heating tem perature, feed and cross angle on the inside bore defects in materials with poor hot workability were studied in this paper.