Computational study on structures of vertical columns formed by successive droplets

Abstract

• The positive enthalpy was developed to investigate the heat accumulation effect. • Shape parameters were established for modeling bonding states. • The ideal bonding structure was obtained by linear interpolation of shape parameters. • The average length of ravine was proposed to evaluate the surface quality. • The effects of superheat and Weber numbers on surface quality were investigated. Components fabricated by the deposition and solidification of molten droplets have the common defect of rough surface, which are mainly caused by the poor bonding and inadequate evolution of the interface. To address such a problem, the pileup process of vertical column by successive droplets was simulated under an axisymmetric system, where the evolution of interface was captured by Front Tracking Method (FTM). The positive enthalpy was calculated to investigate the heat accumulation effect on the structure of vertical column. Shape parameters were established for modeling bonding states, and the ideal bonding was obtained by linear interpolation of these parameters. The average length of ravine was proposed to evaluate the surface quality, and the effects of superheat and Weber numbers on surface quality of ideal structure were investigated. The results show that the positive enthalpy increases gradually under constant deposition rate, and the excessive bonding occurs on the head of vertical column due to the heat accumulation. The mathematic calculation model proposed to acquire the ideal bonding state and the variation rules of surface quality for ideal structure, which is affected by superheat numbers and Weber numbers, can provide access to improve the forming precision in droplet based manufacture.