Improved SPIF performance through dynamic local heating

The limited accuracy of the single point incremental forming process [J. Jeswiet, F. Micari, G. Hirt, A. Bramley, J. Duflou, J. Allwood, Asymmetric single point incremental forming of sheet metal, Annals of CIRP 54(2) (2005) 623 - 650] has been identified as its major deficiency [J.M. Allwood, G.F. King, J. Duflou, A structured search for applications of the Incremental Sheet Forming process by product segmentation, Proceedings of the Institute of Mechanical Engineers, Part B, Journal of Engineering Manufacture 219(2) (2005) 239 - 244]. Improving the process by introducing either fixed [J.R. Duflou, B. Lauwers, J. Verbert, F. Gelaude, Y. Tunckol, Medical application of single point incremental forming: cranial plate manufacturing, in: Proceedings of the VRAP 2006 Conference, Leiria, September 2006, pp. 161 - 166] or programmable support structures [J.M. Allwood, N.E. Houghton, K.P. Jackson, The design of an incremental sheet forming machine, in: Proceedings of the Shemet 2005 Conference, Erlangen, April 2005, pp. 471 - 478; H. Meier, O. Dewald, J. Zhang, incremental forming of sheet metal by two industrial robots, in: AMST'05 Advanced Manufacturing Systems and Technology 2005, vol. 486, Springer, Wien, New York, pp. 437 - 444], tends to reduce the flexibility of the process and increases the complexity of the control system. In the presented research, the authors have opted for an alternative approach in which the material properties are differentiated by localised temperature variations. In this way, different zones can be created in the sheet metal part being processed. By means of a dynamic heat, input in the direct vicinity of the stylus, a ductile area with low-yield strength is generated. By synchronising the movement of the heat source over the sheet metal surface with the stylus feed rate and direction, and by using appropriate cooling of the surrounding area, a temperature gradient can be assured between this area and the workpiece zone where no deformation is envisaged. Effects of such strategy are reduced forces on the stylus and, in consequence, a better localised deformation and thus a higher precision. Furthermore, higher forming limit angles have been demonstrated for materials with low strainability at room temperature. An experimental setup has been built to test this dynamic, local heating principle and is described in the paper. The effects on the process performance are demonstrated by means of experimental results. (c) 2007 Elsevier Ltd. All rights reserved.