Numerical Simulation of Deposit Shape Evolution During the Spray-Rolling Process
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I.
INTRODUCTION
SPRAY rolling is a novel metallic semisolid near-netshape forming technique. It was proposed by E.J. Lavernia and K.M. McHugh in 2003 and may be traced back to A.R.E. Singer’s pioneering work in the 1970s.[1,2] Spray rolling combines the advantages of twin-roll casing and spray forming in a single operation and shows promise for providing a new method of plate and strip production resulting in energy and materials saving, a short production run, and high-performance process for the metal industry.[3–5] In spray rolling (Figure 1), the molten aluminum alloy metal stream is atomized into disintegrated, microsized droplets by an inert gas and deposited on the roller surface. Then, the deposited material is dragged into the roll gap and consolidated to a fully dense strip. The spray-rolling process has been under development in few industrial countries.[6–8] By controlling the process properly, especially the deposit shape and thickness, it is possible to control spray rolling yield in the manufacture of near-net-shape preforms of strips such as 7050 aluminum alloy. An inspection of the available literature demonstrates that the shape models have been developed and applied to describe the deposit shape evolution during spray forming process by dealing with a continuous droplet mass flux or individual droplets.[9–12] Moreover, it is evident that the droplet splashing, redeposition of materials, and topological features of deposition surface are important factors in governing the deposit FENGXIAN LI and XIA LUO, Ph.D. Candidates, and YUN ZHONG LIU, Professor, are with the National Engineering Research Center of Near-Net-Shape Forming Technology for Metallic Materials, South China University of Technology, Guangzhou 510640, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted December 30, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS A
shape.[13,14] However, it should be noted that the previous work on spray forming focused on deposits only in the shape of a billet, tube, or ring.[15] In spray rolling, two deposition surfaces are arranged closely next to each other. The rebounding of droplets from the surface of one wheel to another, namely the droplet rebounding and redeposition phenomenon, an important factor in governing the deposit shape, should be considered. The dynamics of the spray-rolling process presents a significant challenge for the development of meaningful models. Lin et al.[4,5] studied the transient to steady-state transition and the selection of the spray deposition rate during the spray-rolling process. However, little information has been obtained for the deposit shape evolution. This article provides a theoretical analysis of deposit shape evolution during spray rolling by considering the geometrical features of deposition surface and the droplet rebounding and redeposition phenomenon. We focus on determining the entry angle for spray-rolling process in order to obtain a continuous operation. The simulation results can be compared with the experimental re
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