Experimental Study of Direct Metal Laser Sintering: High Cycle Fatigue Life and Process Parameters

Direct Metal Laser Sintering (DMLS) is a relatively new manufacturing process in additive manufacturing (AM) that fuses powdered metal by using a high-powered laser. This process works by laying down a thin layer of metal powder and sintering that layer to the previous layer and then repeating the process to build a part. Once a layer sinters to the previous layer, a recoating blade adds a new layer of metal powder, and the process repeats until the build process is complete. DMLS provides a substantial reduction in material waste and can mitigate tooling wear during production. These characteristics along with substantial automation result in less production time and labor as compared to many conventional manufacturing methods. The DMLS process allows for manufacturing much more intricate designs and the intricate designs can consist of internal geometries that may not be possible through a conventional machining or forging processes. Although this process allows manufacturing prototypes without requiring specific tooling, it is challenging to use this process for manufacturing production parts since complex shapes can take a significant amount of build time. Furthermore, manufactured parts also need some amount of post-processing to remove the support material.

This study investigates three process parameters that could be changed to reduce production time. These three parameters are as follows: build layer thickness, laser scan speed, and laser hatch distance. The values chosen for laser scan speed are 1083 mm/s for the low value and 1245 mm/s for the high value. The high value for laser scan speed is 15% above the default scan speed of 1083 mm/s. The low value for layer thickness is also the default of the DMLS machine at 0.02 mm. The high value for layer thickness is 100% higher than the default, at a value of 0.04 mm thickness. The low value for hatch distance in this study is chosen to be the default setting, 0.09 mm. The high setting for laser hatch distance is 0.1 mm. These values have been finalized such that the specific energy density is maintained as per the guidelines of the manufacturer. The M 290 machine manufactured by EOS has been used for this study. In order to evaluate the influence of process parameters, the manufactured parts are tested for structural integrity by testing fatigue life and static strength. While none of the three parameters is seen to significantly influence tensile strength, results indicate that build layer thickness is a significant process parameter that directly affects fatigue life. Furthermore, the interaction between build layer thickness and laser scan speed is found to be statistically significant for high cycle fatigue. However, laser scan speed and laser hatch distance are seen to be statistically insignificant. The initial results of this study indicate that process parameters of DMLS need to be selected judiciously in order to strike a balance between build time and structural integrity.