Numerical Simulation of Molten Metal Droplet Impinging in Uniform Droplet Spray Rapid Prototyping

A two-dimensional mathematical model has been developed to simulate the impinging and solidification process of a single droplet onto substrate in uniform droplet spray rapid prototyping. Droplet free surface is tracked by volume-of-fluid (VOF) algorithm. The effect of surface tension on the droplet is taken into consideration by means of considering surface tension to be a component of the body force. The governing equations are solved using a finite volume formulation. The calculation results predicted the final shape of a molten droplet impacting onto a solid substrate, and revealed that the solidification process began at the leading edge with the spread process of droplet. The simulation results provide insight and information not easy available from experimental. Keywords: numerical simulation, droplet, rapid prototyping

Thermal Modeling of Deposit Solidification in Uniform Droplet Spray Forming

In spray forming, the deposit thermal state is a key parameter which influences the microstructural evolution upon and after droplet impact onto the deposit. The uniform droplet spray (UDS) forming process has been developed to enable precise control of the droplet and deposit thermal state and the resultant material microstructure. By having a uniform droplet size throughout the spray, all the droplets deposited onto the substrate will have the same thermal state upon impact, allowing for precise control of the solidification process. This paper describes a one-dimensional, finite difference model that predicts the temperature and liquid fraction of the deposit during the UDS process. The model employs an explicit temperature-enthalpy method to incorporate a variety of solidification models. Experiments were conducted using Sn-15 wt percent Pb binary alloy. Temperatures were measured in the deposit and acceptable agreement with the simulation was obtained. Modeling has shown that the deposit thermal state is highly dependent on variations in spray conditions, which are predicted using droplet trajectory and droplet thermal models. Using the droplet and deposit models, the relationship between UDS process parameters and material microstructure can be understood.