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Image of laser powder bed fusion with two lasers during printing (note effluent from each melt pool).
Metal LPBF systems with multiple lasers offer increased productivity over single laser systems. Parts that are uneconomical to produce with LPBF using a single laser system can be made cost competitive through the use of multiple lasers. While many manufacturers are offering commercially available equipment with two and four lasers, there is a gap in understanding potential material defects arising from the use of multiple laser systems. To accelerate industrialization of these multiple laser systems, it is critical to understand the material property implications resulting from these defects.
The objective of this effort was to understand the metallurgical defects in multiple laser LPBF systems and apply nondestructive evaluation (NDE) methods to identify potential defects in service. The goal was to deliver a test artifact, technical data package, and new standard as the foundation for end users to confidently implement higher productivity metal additive manufacturing (AM) equipment. The project sought to accelerate the introduction of multiple lasers for demanding applications.
A test artifact was designed to examine material defects caused by the use of multiple lasers. Defects included porosity due to overlap of laser paths, lack of fusion porosity from lack of laser overlap in the stitching region, additional spatter from multiple melt pools, and varying surface roughness due to variance in calibration. The artifact was also designed to examine tolerance issues in overlap of the individual lasers, as well as other factors affected by the use of multiple lasers. Melt pool monitoring was used to screen defects and micro-computed tomography (CT) to characterize these defects, identifying porosity and other microstructural features in the test artifacts. Using a Concept Laser M2 LPBF machine with two 400W lasers, Proto Precision Manufacturing Solutions printed the test artifact out of Inconel 718, an alloy of strong interest to the aerospace industry for AM.
The manufacture of INC718 via multiple lasers in the powder bed fusion process was successfully investigated. It was found that laser calibration and alignment play a significant factor in the end part quality of the multi-laser powder bed fusion (MLPBF) process. To address these issues, new methods and a set of standardized test artifacts were developed to assess laser calibration, alignment, and metallurgical quality of the stitched regions. These new methods are being incorporated into new standardization efforts that are now underway.
Through the investigation, multiple scan and build strategies were developed to have the best balance of productivity and end part quality. Additionally it was found that for a representative component, a 47% build time decrease was achieved by the addition of a second laser to the build. This added productivity was accomplished while producing material that after heat treatment had comparable or better density, hardness, tensile strength, and high cycle fatigue properties than the nominal