A strip-drawing simulator with computer-controlled drawbead penetration and blankholder pressure

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Failure in the stretch-drawing of sheet metal panels is caused predominantly by either wrinkling or splitting. Wrinkling, which can occur in the flange inside the blankholder or in the unsupported side wall of the stamping part, is due to compressive circumferential stresses that result in buckling of the sheet. Splitting, on the other hand, is caused by excessive tensile stresses. Both modes of failure are influenced by blankholder force (BHF). Material flow is often modified locally by the insertion of drawbeads into the tooling. In industrial practice, drawbeads are a fixed component of the tooling and thus exercise their controlling function with a set penetration. A multiple-action hydraulic sheet-metal strip-drawing test apparatus has been constructed for the purpose of studying the effectiveness of feedback controls in sheet-metal forming. This device simulates the flow of sheet-metal in the blankholder and over the die shoulder in the stamping of sheet-metal panels. Its special features consist of the ability to adjust both the BHF and the drawbead penetration while the strip is being drawn and to measure forces in the sheet on either side of the die shoulder. Feedback control of the strip-drawing process using a proportional plus integral controller is demonstrated and the results are presented in the paper. The controller adjusts the drawbead position to eliminate the deviation of the punch force from the desired force. The results indicate that the addition of feedback control to the process reduces the effects of undesirable input variations as well as of disturbances on the output. © 1994.

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Journal of Materials Processing Tech.