Heat flow in multi-pass arc spraying processes

Abstract

Arc spraying is a coating method in which an electric arc is employed as the heat source to fuse metal wire. In single-pass spraying, a high heat input is needed to produce a thick coating layer. However, the substrate is distorted and the bond strength is reduced by residual stresses if a high heat input is introduced to the workpiece. Moreover, it is impossible to use single- pass spraying on large workpieces, since the single-pass spraying area is limited. To produce thick coating layers and for large workpieces, therefore, a multi-pass arc spraying process should be used on the same or different paths. In this study the heat flow problem in multi-pass arc spraying was solved by using a numerical method, and a series of experiments was carried out to measure the temperature change. With the progression of multi-pass arc spraying, many pores were formed in the coating. A modified value of the thermal conductivity of porous metal is generally lower than because the thermal conductivity was therefore considered for the simulation, that of solid metal. Also, the forced convection effect was considered at the upper surface, since the heat loss by the working gas (compressed air) is much greater than that by natural convection. The simulation and experimental results were in good agreement. The adopted simulation model can therefore be considered to be sufficiently powerful for the analysis of processing parameters in the multi-pass arc spraying process.