Minimization of sheet thickness variation and other defects of mini drawn parts using a blank holder plate made from concentric rings

Thickness variation is a major defect of the drawn parts made from sheet metals, which influences the intensity of part defects and may cause part failure. In the case of mini deep drawing, sheet thickness variation along part's profile has the following effects on the drawn part geometry: increased non-uniformity of diameter variation, variation of springback parameters (part edge radius deviations and angle of wall inclination), different wrinkling intensities, and part cracking and fracture. The present paper analyses the experimental results of the investigations concerning the sheet thickness variation in the case of mini cylindrical drawn parts made from a copper alloy. Some constructive solutions of tool components that allow the control and minimization of sheet thickness variation by controlling the blank holder force, contact and friction forces (especially in the part flange zone) are also proposed and tested by simulation and experiment. The constructive solutions of the new tools were obtained by constructing the blank holder plate from two concentric rings made from different materials with equal or unequal widths.