A predictive tool for delaying wrinkling and tearing failures in sheet metal forming

In the sheet metalforming industry, there is increasing demand to lower manufacturing costs while also providing a decrease in product development turnaround period as well as lighter weight products. These demands have put increasing pressure on the development and use of predictive numerical simulations and in the design and optimization of new forming technologies. In this paper, two of the primary in-process failure modes of sheet metal, wrinkling and tearing, are examined followed by construction of an advanced forming technology-Variable Binder Force-using numerical tools. Specifically, a methodology of capturing the onset of wrinkling and postbuckling behavior proposed in Cao and Boyce (1997) is used to predict wrinkling failure in conical and square cup forming. The results obtained from simulations and experiments demonstrate that the proposed method is not only accurate, but also robust. A tearing criterion based on Forming Limit Diagrams of non-proportional loading paths is then developed and again shows excellent predictability. Finally, a Variable Binder Force (VBF) trajectory for conical cup forming is designed using simulations which incorporate feedback control to the binder based on the predictions of wrinkling and tearing of the sheet. Experiments using this predefined VBF trajectory show a 16 percent increase informing height over the best conventional forming method, that is, constant binder force. The uniqueness of this paper is that numerical simulation is no longer utilized only as a verification tool, but as a design tool for advanced manufacturing process with the help of the predictive tools incorporated directly into the numerical model.