Drawbeads control the flow of material into the die cavity during pressing operations. The tribological and forming properties of aluminium necessitate specific frictional and drawbead geometry requirements that are different from those established over many years for steels. Academic research on this topic is limited, requiring industry to rely on trial and error methods to determine the coefficient of friction and drawbead geometry. This research project focused on developing an innovative, scientific and holistic methodology to determine the optimum drawbead geometry and an appropriate coefficient of friction value to be used in forming feasibility simulations for aluminium panels. Special attention was given to the ease with which this research could be implemented in an industrial environment. Hence, extensive experiments to gather material properties such as plane strain and pure shear tests, complex material models, or optimisation models based on artificial neural networks (ANN), and non-linear friction models were avoided. Three approaches identified in the literature for designing drawbeads, namely, experimental, analytical and numerical modelling were investigated to test the underlying assumptions, strengths and limits of each. For example, analytical models assumed symmetric material flow passing over the drawbeads, which in reality does not occur. Based on these findings a systematic, hybrid approach has been developed which uses a combination of physical drawbead tests and numerical modelling, to determine the coefficient of friction which is then used to obtain the drawbead restraining force. Using a novel criterion, different drawbead geometry conditions have been ranked to aid selection of an optimised drawbead geometry. The optimised drawbead geometry obtained from the hybrid approach was validated by stamping of rectangular pans. The rectangular pan, when stamped using the optimised geometry obtained from the hybrid approach, did not show defects such as severe thinning and wrinkles. The numerical stamping model with geometric drawbead predicted the punch force with a 4.5% error, thinning with a 5% error and draw-in with an 8% error. An innovative hybrid approach has been proposed which is capable of accurately predicting the coefficient of friction, the drawbead restraining force and the drawbead geometry. The same coefficient of friction and the drawbead geometry when used in the forming simulation accurately predicted the punch force, thinning and draw-in. As a direct application of innovation, Jaguar Land Rover can use the novel criteria for selecting the drawbead geometry to use effectively the drawbead geometry generation feature in the commercial sheet metal forming software package during forming feasibility simulations. The hybrid approach can potentially save 34% of the die tryout time and provide average cost savings of £34,400 per die set per tryout attempt.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:737727 |
| Date | January 2017 |
| Creators | Joshi, Yogendra K. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/99564/ |
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