Development of a Laboratory Test Method for Assessment of Crater Wear Volume on Inserts for Steel Turning

Abstract: This thesis project was carried out at Sandvik Coromant in Västberga, Sweden with the purpose of developing a new laboratory test method for volumetric assessment of crater wear on inserts for steel turning. The test method was developed with the Sandvik Coromant´s existing crater wear measurement method as a starting point. Crater wear is currently measured as the projected area of exposed substrate, meaning where all coating layers have been removed. Based on earlier research on volume wear assessment, a focus variation microscope was selected to carry out 3D scans. To accurately measure the removed volume, an initial reference scan is required to capture individual variations existing on samples. The insert is then scanned after turning and compared with its reference. Factors affecting accuracy as well as possible improvements were identified as: Sample preparation, scan settings (resolution, quality) and data processing (alignment of scans, volume calculation etc.). Guiding alignment markers were created by laser ablation to help with alignment.  CloudCompare software was used to process the scanned 3D point clouds. A step by step routine was developed to ensure consistent results. The repeatability was assessed showing 8% standard deviation in volume for a shallow crater within the coating to 2% for a large crater worn into the substrate. The new method provides the possibility to measure wear while still inside the coating, which has been previously unavailable data. This enables measurement of the contribution of each specific coating layer on the wear resistance such as wear rate of a single layer instead of a combined wear rate for all layers. Detailed coating wear analysis is a valuable tool for development of optimized coatings. The developed wear measurement method was implemented on a case study which demonstrated the capabilities regarding its ability to resolve performance differences in experimental coatings. Additional wear parameters were used beside crater volume to support wear rate analysis and novel ways of representing volume wear parameters were presented.