On-Machine Measuring Method for the Reconstruction of Additively Manufactured Near-Net Shaped Parts

Additive manufacturing brings along many chances like functional integration or light-weight construction. Because of distortion and poor surface roughness, however, machining is required to produce high quality parts out of metal. Depending on the position on the build tray, there is a variation of the deformation so that the exact part geometry after the additive manufacturing process is unknown. Hence, there is a big challenge for the mechanical post-processing. In this paper, a strategy to measure additively manufactured parts made by Laser Beam Melting directly in a milling machine using the touch trigger probe was developed. Therefore, a test specimen was machined, that includes a selection of the most relevant geometric features like holes, cones, different chamfers and a free-form surface. Subsequently, a number of measuring points was chosen for every feature. In order to select the positions of the measuring points, different algorithms from literature were evaluated. As a result, the Hammersley algorithm was determined as the most suitable algorithm for this use case. A special measuring test cycle was implemented in a Computer Aided Manufacturing (CAM) software and tested on a five-axis milling machine. The measuring results were edited in the CAM so that an accurate geometric model of the real part could be created. Based on this model, an adaption of the tool paths is possible, with the effect of a reduction of the machining time and an optimized utilization of the tool. The results were also compared with an optical strip light projection. It was shown, that the discrepancy between the tactile and the optical measuring strategy was minimal. This means that the tactile measurement results have a sufficient accuracy. In a second step, the developed measuring strategy was applied to turbine blades made by Laser Beam Melting. Again, the turbine blades were measured using the touch trigger probe in a five-axis milling machine and the results were validated.     «

Additive manufacturing brings along many chances like functional integration or light-weight construction. Because of distortion and poor surface roughness, however, machining is required to produce high quality parts out of metal. Depending on the position on the build tray, there is a variation of the deformation so that the exact part geometry after the additive manufacturing process is unknown. Hence, there is a big challenge for the mechanical post-processing. In this paper, a strategy to m...     »