Electromagnetic blank restrainer in sheet metal forming processes

Electromagnetic blank restrainer (EMBR) is a new technology that was recently developed to control material movement in sheet metal forming processes. Magnetic attraction on the ferrous sheet metal is the intrinsic property of EMBR. Such magnetic force is quantified using Maxwell's stress tensor to assess the feasibility of EMBR in the sheet metal forming process. The 3D finite element analysis (FEA) of an electromagnetic system is conducted to determine the distribution of magnetic flux density on contacting surfaces of the sheet metal. The distribution is then used to estimate the magnetic force. Experiments have been conducted to measure the magnetic force and compare with results from the FEA. Biaxial-loading apparatus has been built to measure restraining forces on the sheet metal with blankholder, drawbead, and EMBR. All the restraining forces are put together in a chart to see where each method stands with respect to one another. In order to evaluate the quality of forming with each method, an experimental die has been built. The die forms a channel in a single stroke and provides a direct indication of how each restraining method controls blank movement in the die. The real advantage of EMBR lies in the effectiveness of force control and its flexible location in a sheet metal forming die. To prove this, a prototype has been built in a tryout die where house appliance panel is formed with blankholder and EMBR. EMBRs are locally installed in the die and actively controlled during the forming process. The part formed with EMBR shows a significant improvement in the forming quality. At the end of this paper, two immediate impacts that EMBR can bring to the sheet metal forming industry are also discussed.