DMRC Research Examines Properties of SLM Components

The effective use of AM in manufacturing demands repeatability, full use of AM properties and the production of functional parts that meet specifications. The Direct Manufacturing Research Center (DMRC) of the University of Paderborn, Germany, was founded five years ago as a joint effort between academia and industry to advance existing additive technologies into dependable production manufacturing technologies. Fused deposition modeling (FDM), selected laser sintering (SLS) and selective laser melting (SLM) are being examined, analyzed and compared by DMRC to better understand how each can be optimized in applications.

Recent projects at the DMRC have focused on product optimization with SLM. Researchers are looking at material qualification, which consists of regular checks of particle dispersions and particle micrographics; product qualification that will consider quasi static and fatigue behavior under high temperature atmosphere; process qualification that includes the analysis of optimal process parameters and heat treatment; and quality management by testing the part’s powder, mechanical and geometrical qualities.

“One project focused on the comparison between the SLM 250HL and the SLM 280HL from SLM Solutions with respect to the build-up rate and the resulting component quality,” explains Dr. Eric Klemp, director of the DMRC. “The main objective was to compare two fundamentally different SLM systems in terms of cycle time and component properties.”

“Test samples were manufactured on each of these two machines to measure the process cycle time of both systems, using three layer thicknesses: 50 microns, 100 microns and 150 microns,” says Klemp. According to the project report, in order to obtain detailed values for exposure and recoating times, a real-time data collection script was developed that scanned the SLM-log files of the time data required for recoating and exposure in each layer.

Part properties were evaluated closely to measure any improvements. This process included characterization and comparison of the mechanical properties of the SLM materials with regard to process cycle time improvements. Testing revealed the possibility to increase the build-up rate by about 39 percent using the SLM 280HL compared to the previous generation SLM 250HL system. In experiments using stainless steel 316L, “The SLM system 280HL assured a significant increase in the build-up rate of the material,” says Klemp.

Klemp explained that the tests included the influence of production parameters of the new exposure strategy on the mechanical properties, measuring the variation of the energy density as well as exposure parameters and quantification of the impact on the component properties. Optimization of the lattice structures manufactured by the SLM method involved examining the microstructure characterization and the influence of processing and heat treatment on the resulting microstructure. Then, mechanical testing was performed to determine the structure performance under diverse loading conditions in the monotonic and cyclic loading regime.

“Structurally, they were found to be comparable to machined metal parts, and able to contribute to the development of lightweight structures if you design the lattice grid to different strengths,” says Klemp.

The two DMRC departments responsible for the research project, Automotive Lightweight Construction and Institute of Applied Mechanics, transferred the results regarding optimal balance between build-up rate and component quality to an actual component in order to demonstrate the performance of this AM technology. This data will be used in development of the next generation SLM systems, taking production to the next level for end-use components.