Abstract
This study examined the effects of the servo press's motion control and lubrication on the shape-freezing properties of hatshaped product of ultra-high strength steel formed by draw forming. Bending motion is effective in decreasing camber angle in shape freezing but is not effective in spring-back. Lubrication is effective in reducing camber angle in shape freezing but deteriorates shape freezing against spring-back. Shape freezing in draw forming of hat-shaped parts is affected by two factors: warpage due to unbending of the vertical wall and spring-back in bending on both sides of the web surface. In the case of the inching motion, friction between the die and the steel plate is suppressed, and the load during bending and unbending is reduced. When lubricant is used, friction is reduced due to the presence of an oil film between the work piece and the die. Therefore, warpage of the vertical wall is suppressed by the inching motion and lubrication. When bending is performed while tensile force is applied, spring-back decreases. The reason for the increase in spring-back due to lubrication is that the tensile force at the R shoulder of the die is reduced due to friction, and the effect of the tensile load on the bending of the R shoulder of the punch is reduced. The effects of press motion and lubrication on shape freezing were clarified by estimating the amount of strain that a steel plate undergoes during processing by measuring the half-value widths of the vertical wall and bending area from X-ray diffraction experiments.
