2020 Volume 61 Issue 715 Pages 175-181
We have developed a new hydroforming sealing technique with flat tools. This forming technique using seal punches with a flat end face enables the deformation of both ends of a tube during die closure while applying internal pressure to the tube. We studied the effects of various forming conditions on the sealing performance of this technique. The sealing performance was more stable when tube end faces were ground with a milling machine than when they were cut with a band saw. The sealing performance was better when the seal punch end faces were milled surfaces rather than textured surfaces. When the seal length was too large, tube ends tended to buckle. When the seal length was too small, the hydraulic fluid tended to leak, because the tube ends were pulled into the dies during hydroforming. The sealing pressure limit became higher with increasing axial force of the seal punches during die closure. However, that pressure became lower when the axial force was increased excessively. Effective hydroforming results were obtained when the axial stress applied to the tube ends after die closure was at least equivalent to the proof stress of the tube material. By this new hydroforming seal technique, we successfully produced full-length, flanged hydroformed parts and full-length, bent hydroformed parts with a rectangular cross section.