In this paper, we describe a drawing method for improving the dimensional accuracy of bars. The proposed method improves the straightness of the bars drawn with the initial curvature and drawing angle. The straightness of the bars is improved using eccentric path line. The eccentric path line is achieved by offsetting the guide installed on the entry side of the die in a direction perpendicular to the drawing direction. The effects of die geometry on the relationship between the amount of guide offset and the curvature of the drawn bar were investigated through experiments and finite element analysis. The results showed that the smaller the contact length between the bar and the die at the approach portion, the more effective the path line eccentricity, and a contact length of about 0.25 relative to a die hole is desirable. From these results, high straightness was obtained when bars with the initial curvature and drawing angle were drawn with path line eccentricity using a contact length of 0.24 relative to a die hole. On the basis of these results, it is possible to produce very straight bars with a small amount of path line eccentricity by selecting the appropriate die geometry.

Tensile specimens with equivalent plastic strains of 5 %, 10 %, 15 %, and 20 % were prepared for four specimen types: SS400, A1070-O, SUS304, and AZ31. The relationship between equivalent plastic strain and KAM (kernel average misorientation) was visualized and formulated from the results of EBSD (electron backscattered diffraction pattern) and OIM (orientation imaging microscopy) analyses. The results obtained in this study enabled quantitative understanding of the local strain introduced at each location during fabrication and deformation.