Investigation of Heat Transfer and Bonding During Material Jetting Additive Manufacturing

Abstract

Optimum process parameters are critical to achieve deposits of high metallurgical integrity during material jetting additive manufacturing. The most important process parameters include deposition temperature, substrate temperature, mass deposition rate, velocity of material jetting and the level of oxygen. This document describes experiments and analyses to determine these parameters using pure tin as a model deposition material. Molten tin at 4000C was deposited through a 250µm diameter nozzle at a velocity of 1m/s onto a tin substrate maintained at either 1500C, 1750C or 1950C. The deposition experiments were carried out under ambient air and inert gas (N2) environments. The experimental results showed that better metallurgical bonding was obtained at 1950C substrate temperature in N2 gas environment and these parameters also gave consistent results during shear tests. A simple heat transfer model is presented to describe the heat flow from a deposition to the substrate. Hypothesized Newtonian cooling agreed with the experimental temperature results which enabled experimental determination of the interfacial heat transfer coefficient hi. In addition 2-D axisymmetric transient numerical simulations have been carried out using the empirical hi data and the results agreed with experiments. This work demonstrated use of appropriate process parameters to get good metallurgical bonding.