A PREDICTIVE TOOL FOR DELAYING WRINKLING AND TEARING FAILURES IN SHEET-METAL FORMING

In the sheet metalforming industry, there is increasing demand to lowe r manufacturing costs while also providing a decrease in product devel opment turnaround period as well as lighter weight products. These dem ands have put increasing pressure on the development and use of predic tive numerical simulations and in the design and optimization of new f orming technologies. In this paper, two of the primary in-process fail ure modes of sheet metal, wrinkling and tearing, are examined followed by construction of an advanced forming technology-Variable Binder For ce-using numerical tools. Specifically, a methodology of capturing the onset of wrinkling and postbuckling behavior proposed in Cao and Boyc e (1997) is used to predict wrinkling failure in conical and square cu p forming. The results obtained from simulations and experiments demon strate that the proposed method is not only accurate, but also robust. A tearing criterion based on Forming Limit Diagrams of non-proportion al loading paths is then developed and again shows excellent predictab ility. Finally, a Variable Binder Force (VBF) trajectory for conical c up forming is designed using simulations which incorporate feedback co ntrol 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 formin g method, that is, constant binder force. The uniqueness of this paper is that numerical simulation is no longer utilized only as a verifica tion tool, but as a design tool for advanced manufacturing process wit h the help of the predictive tools incorporated directly into the nume rical model.