Optimizing quality of additively manufactured Inconel 718 using powder bed laser melting process

Abstract

Inconel 718, a widely used nickel based super alloy, is of special interest to the aerospace and automotive fields for its highly desirable and consistent material properties over a large range of temperatures. The objective of this research is to understand the effect of process parameters of a Direct Metal Laser Sintering (DMLS) machine, concerning mainly beam power between 40W and 300W and scan line speed between 200mm/s and 2500mm/s on scan line quality, line geometry and dimensions, and melt pool geometry in laser melted Inconel 718 line scans. A beam power that is too low (40W) does not provide enough energy to maintain a continuous line. It was shown that mid-range beam powers (100W and 150W) result in the best and most uniform scan lines with minimal voids and shallower melt volumes. Higher power runs resulted in voids forming in the bottom of the melt pool and were consistent with either electron beam welding or melting processes operating at higher temperatures. Laser energy density (LED), a method of correlating the effects of scan speed and beam power into one characteristic process parameter, was also investigated. This ratio of beam power to scan speed follows a second order polynomial trend line for melt pool width and a logarithmic trend for average line width. LED values for melt pool depth are separated to show two trend lines as two mechanisms operate at low values below 0.25J/mm and high values above 0.25J/mm. LED values above 0.21J/mm are desired for a continuous fill percentage in the formed lines, however dimensional accuracy of the line is sacrificed significantly at values over 0.2J/mm.