Influence of process parameters on the correlation between in-situ process monitoring data and the mechanical properties of Ti-6Al-4V non-stochastic cellular structures

Abstract

Selective Laser Melting (SLM) facilitates the formation of complex, stochastic or non-stochastic, metallic cellular structures. There is a high level of interest in these structures recently, particularly due to their high strength to weight ratios and osteoconductive properties. While the ability to in-situ monitor the SLM process is of key importance for future quality control methods.In this work lattice structures were fabricated, using the single exposure scanning strategy, on a Renishaw 500M SLM machine. The build process was also monitored using a co-axial in-situ process monitoring system.It was found that by increasing the energy input, through increasing the laser power and/or exposure time, the lattice strut diameters, within the 1.5 mm diamond unit cells, increased from 119 to 293 μm, resulting in the major pore diameter decreasing from 1106 to 932 μm. The effect of systematically altering the laser beam spot size on the cellular structures was also evaluated. It was observed that by doubling the laser beam spot size, that there was a 17% reduction in strut diameter and a 22% reduction in mechanical strength of the structures. It was also observed that at constant energy input levels, the lattice structures created using a focused laser exhibited an 81% lower mechanical strength than the structures created using a de-focused laser. Thus, demonstrating that the mode of energy input is critical to achieving the desired strength in these structures.Based on the outputs from the in-situ monitoring system, a broadly linear correlation was obtained between the laser input energy, the associated process monitoring data generated and the mechanical strength of the lattice structures.