2021 Volume 62 Issue 723 Pages 48-53
Difficulties in press forming, such as the occurrence of fractures, wrinkles, and springback, are more severe when using ultrahigh-strength steel (UHSS) than when using mild steel owing to the poor formability of UHSS. To make matters worse, the shape of a frame part, for which UHSS is often used, is, in many cases, complex and curved in the top and/or side view. Countermeasures against defects in a UHSS part are, therefore, so specialized that it would be highly advantageous in the press forming of a UHSS sheet if a new forming technology with wider applicability to curved shapes could be developed. In this study, a new forming technology that is effective in the press forming of curved-in-top-view parts was developed. The new forming technology consists of two processes. The 1st process is preforming and the 2nd process is cam bending. The key in this technology is the optimum design of the preformed shape to obtain an accurate final shape after the 2nd process. The new technology was applied to forming a curved-in-top-view hat shape of steel of 590 to 1470 MPa grade, and its suppression effects on the above-mentioned problems was confirmed by both CAE and trial pressing.
