Laser line scanner aptitude for the measurement of Selective Laser Melting parts

Abstract

When looking for any metrological verification of parts manufactured by metal laser printing with optical equipment, it is necessary to ensure the traceability of the measurements that can be obtained. The difficulty of this process lies in the fact that these measurements are obtained on point clouds captured from surfaces with high form errors and poor surface finishes, even when this type of surface usually undergoes processes to improve the surface finish, such as sandblasting. This research focuses precisely on the analysis of the metrological suitability of a laser line scanner (laser triangulation sensor) on parts manufactured by Selective Laser Melting (SLM).The study starts from the design of a test part specifically oriented to the printing process with SLM metal powder bed. This test part was printed in 17-4PH stainless steel and then sandblasted. The test part was measured in a Coordinate Measuring Machine (CMM), obtaining reference GD&T values. The measurement was carried out under pre-sandblasting ("as built") and post-sandblasting conditions, thus providing interesting information about the erosion rate of this post process. A state-of-the-art laser sensor was employed for the metrological comparison, mounted on the same available CMM that was used for contact measurements.In this research three analyses were carried out: the quality of 3D metal printed parts with respect to CAD model, the effect of the sandblasting post-process, and the accuracy of the measurements obtained with the laser line sensor. In addition, this work conducts an in-depth study about the influence of point cloud treatment and filtering procedures, by comparing the filtering methods applied by different reverse engineering software packages. The study leads to the conclusion that filters based on the standard deviation of the point cloud are the best candidates in order to obtain laser measurements closer to the contact measurements.