Shape design of the deep-drawing preform for manufacturing of automobile drum clutch hubs

A large variety of metal forming processes is required in manufacturing for automotive applications. Traditionally, the design process for metal forming tools is based on trial-and-error and on the skill of experienced die-makers. This approach results in high development cost and long lead-times. Especially, the drum clutch requires tight dimensional accuracy in inside diameter and gear shape because it is used as the main component for the automatic transmission. The drum clutch investigated in this study is formed in five forming steps, which are first deep drawing, second deep drawing, restriking, embossing, and Grob processes. Dimensional accuracy of the final products greatly depends upon how much more accurate pre-form is manufactured in the previous forming processes before the Grob process. The deep drawing, restriking, and embossing processes in which the pre-form is formed are very important and decisive steps. Thus in some cases, excessive strain by these operations causes dimensional inaccuracy and cracks initiated from the base and wall of the product. Based on the above background, the objective of this study is to optimize the pre-form shape and tooling so that excessive thinning and crack formation are avoided while a sharp corner radius and flatness are obtained. Process variables such as the punch shapes both of first and second deep drawing, and punch angle were selected to evaluate the deformation characteristics. The optimum parameters were determined from forming simulations using commercial finite element method codes, DEFORM-2D, specifically developed for metal forming simulation. Finally, experiments for the whole drum clutch forming processes were carried out to verify the optimized forming parameters and the analytical results.