Study of Porosity and Build Rate of the Selective Laser Melting (SLM) of Titanium and Its Statistical Modelling for Optimization
K. Antony, T. C. Clint and T. R. Rakeshnath
Titanium and titanium alloys have unique properties such as high strength to modulus ratio corrosion resistance and exhibit similar characteristics for biomedical devices. It is, therefore, considered to be a potential material and have a wide range of application in the field of biomedics. Due to the difficulties in obtaining the optimized parameters required for the laser processing, the titanium is still used little. This study lays the foundations for better understanding and control of the selective laser melting (SLM) process parameters mainly laser power, scanning speed and beam diameter. Since, in SLM of titanium, controlling the degrees of porosity and increase the build rate is quite a challenge and, in this study, the commercially pure titanium (CP-Ti) formation is investigated by means of single layer track formation to understand the processing mechanism and the effect of SLM processing parameters on the resulting porosity of the final track. The optimized parameters based on optimum surface porosity which is mainly around 25 to 30% achieved are presented. The resulting surface morphology of the CP-Ti processed track was examined and explained. Balling phenomenon was observed at low laser energy density and the combined effect of lower scanning speed and higher laser power results in formation spatters. The chemical composition of the laser track surface is studied and it was found that formation of protective oxide coating occurred. The influence of SLM processing parameters on porosity is statistically modelled and analysed using regression analysis and analysis of variance (ANOVA). This study mainly focuses its attention on the increase in build rate and porosity of optimized selective laser process parameters. From this study, it is shown that scanning speed and laser beam diameter are the dominant factors which affects the porosity of selective laser melted track.
Keywords: Nd:YAG laser, commercially pure titanium (CP-Ti), selective laser melting (SLM), porosity, build rate, Taguchi methods, analysis of variance (ANOVA), response surface methodology (RSM), regression model analysis