Spray forming: A numerical investigation of the influence of the gas to melt ratio on the billet surface temperature

The relationship between the Gas to Melt Ratio (GMR) and the surface temperature of an evolving billet surface in spray forming is investigated numerically. The basis for the analysis is an integrated approach for modelling the entire spray forming process. This model includes the droplet atomisation taking thermal coupling into consideration and the deposition of material at the surface of the billet taking geometrical aspects such as shading into account. The coupling between these two models is accomplished by ensuring that the total droplet size distribution of the spray is the summation of "local" droplet size distributions along the r-axis of the spray cone. The criterion for a successful process has been a predefined process window characterised by a desired fraction solid range at a certain distance from the atomizer. Inside this process window, the gas and melt flows have been varied and the influence of the gas and metal flow rates on the surface temperature of the billet has been analysed. Based on this, a relationship for the surface temperature as function of the GMR has been suggested for the spray forming of a 100Cr6 billet.