Continuous dry cylindrical and rectangular deep drawing by electroconductive ceramic dies

Two types of electroconductive ceramic tools are employed in this study to describe the dry deep drawing behavior of cold rolled steel sheets into cylindrical and rectangular cups. Each of electroconductive ceramic tools is machined by die sinking electric discharge. Four experimental setups are also prepared to investigate the effect of the surface roughness on the quality of dry deep drawing: the unlapped and the lapped electroconductive ceramic dies in dry condition and the unlubricated and the lubricated SKD11 die. Even without lubricating oils, cylindrical and rectangular cups are successfully deep drawn over 10,000 by the present tooling. Furthermore, compared to the lubricated SKD11 tooling, surface roughness of deep drawn cups is reduced by the present ceramic tooling. Fine finishing in ceramic tooling never leads to low surface roughness in the deep drawn cups since the work materials make unconstrained plastic flow in the direction of thickness. Hence, the unlapped electroconductive ceramic tooling is favored for practical ceramic tooling to preserve well-defined contact interface between metallic work sheets and ceramic tools in dry deep drawing. In addition, the rectangular cup drawing is evaluated by more severe conditions than the cylindrical cup drawing because the stress concentrates on the corner parts. Through this test, it is demonstrated that the electroconductive ceramic tooling has a potential of practical dry deep drawing.