Oxide formation in the Sprayform Tool Process

The Sprayform Tool Process is a novel alternative to CNC machining for the rapid manufacture of hard tooling. The process is based on the robot controlled sprayforming of molten steel droplets onto a ceramic master pattern to form a thick, dimensionally accurate steel shell. This paper describes the Sprayform Tool Process, and investigates the evolution of microstructure in thick steel shells in terms of the oxide fraction as a function of process parameters: (i) spray height; (ii) atomising gas pressure; (iii) wire feed rate; and (iv) manipulating robot velocity. Spray height had the strongest influence on oxide content; by reducing spray height from 160 to 120 mm the oxide fraction in the microstructure was halved. The role of droplet splashing on the subsequent oxidation of splash droplets has been revealed as an important phenomenon controlling sprayed microstructure and oxide fraction. On the basis of the presented experimental results, the implications for the manufacture of large steel shells by the Sprayform Tool Process are discussed.