Modelling of spray forming process

• Main Author: Muhamad, N.
• Published: Swansea University 1994
• Subjects: 669
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638270

This thesis reports the results of a theoretical investigation into the <i>Osprey Preform Process</i>. It focuses on the fluid and heat transfer phenomena associated with the liquid metal spray, the billet buildup and the solidification behaviour of the metal as the preform is produced. In the first part of the study, a nonlinear lumped parameter numerical model has been developed to model the physical processes taking place in the two phase spray and both fluid and thermal influences have been addressed. The analyses show the importance of the momentum exchange with the entrained gas on both velocity profiles and the temperature histories of the spray and this reflects the need to consider the total thermal design of the deposition chamber. The effect of a small amount of undercooling was also included where it was found to result in a wetter spray arriving at the deposit. The above model was incorporated in the buildup simulation for a cylindrical billet deposited onto a substrate having an axis in the horizontal plane. A series of sensitivity studies were carried out to assess the influence of some of the important chamber parameters which are mainly concerned with the position and movement of the scanner and the substrate under the spray. Although a direct comparison between the predicted billet shape and those manufactured was not posible due to the absence of data, the analyses confirmed the significant parameters which influence the billet shape produced and which have to be optimised in actual practice. These findings are compatible with the experience of <i>Osprey Metal Ltd</i>. Finally, the solidification history of the billet preform was analysed using a two dimensional thermal network method. It was found that the thermal history of the billet is sensitive to the thermal boundary conditions applied. Therefore, an appropriate choice of the spraying conditions needs to be established to produce uniform material properties throughout the billet extent.