Abstract
A cone-type piercing mill has been developed for piercing the materials with poor hot workability. This piercing mill is called "the super piercing mill" in Europe and America. This mill has cone-type main rolls supported at both ends with their roll axes inclined and crossed so as to enable piercing at a high feed and cross angle. This configuration is based on the following principles: by rendering the material more ductile than its mother material in front of the plug, any possible cause of the initiation of inside bore defects can be eliminated; and, at the same time, by releasing the redundant shear stress field during piercing process, it is possible to eliminate any possible cause of the propagation of inside bore defects. In order to ensure the best performance of the rotary piercing, disc rolls have been adopted instead of plate guide shoes. Piercing experiments were carried out using test materials with poor hot workability, such as continuously cast round billet, stainless steel, high alloy steel and Pb-S free cutting steel, with the feed and cross angle changed in various ways. The influences of the feed and cross angle on the inside bore and lamination defects were studied in detail. Furthermore, piercing experiments under high feed and cross angles were carried out with titanium, titanium alloy, zirconium alloy, nickel and nickel alloy in order to confirm the effects of such a high-angles piercing.
