Electro-magnetic blank restrainer.

Abstract

Electro-magnetic blank restrainer (EMBR) is a new method of controlling blank movement in the sheet metal forming process. The proposed method controls ferrous blanks using electromagnetic force and can vary the force with high accuracy and speed during forming of sheet metal. In this dissertation, the magnetic force was theoretically estimated and compared with conventional forces. Extensive experiments were conducted with electromagnets made of two different magnetic alloys, 1020 steel and Fe-Co alloy. In the experiments, magnetic forces were measured on armature and sheet metal specimen. The electromagnet of Fe-Co alloy showed high energy efficiency and superior magnetic performance when compared with the electromagnet of 1020 steel. Nonlinear finite element analysis was carried out for electromagnets. From the analysis, the magnetic field distributions were plotted and analyzed to study the effects on the magnetic force. The magnetic force in the sheet metal was also estimated in the analysis and used with the experimental forces to determine the coefficient of friction in the magnetic field. The sheet metal force is very difficult to measure in the experiment. An experimental die was built to prove the feasibility of EMBR in production. The die was designed such that the restraining force could be applied by either of blankholder, drawbead or EMBR. The parts from each method were compared in the strain distribution and springback. From the comparisons, it was clearly verified that EMBR can produce a sufficient restraining force on the blank and can be combined with the conventional blankholder to increase the restraining force close to drawbeads. From all the analyses and experimental results with EMBR, and its comparisons with the conventional methods, it became evident that EMBR can be implemented in a stamping die with the possibility of active force control and variation. Therefore, EMBR can further develop the advanced forming concepts that have not been possible or very difficult with the conventional methods in production settings, and could lead to substantial savings in the manufacturing cost.