Investigation of the Influence of Anti-Wear Coatings on the Surface Quality and Dimensional Accuracy during Finish Turning of the Inconel 718 Alloy

Abstract

This piece of work deals with the influence assessment of the kind of coating of the cutting inserts and their wear on the dimensional accuracy and the top layer microstructure and roughness of the surface machined with constant cutting parameters vc = 85 m/min, f = 0.14 mm/obr and ap = 0.2 mm. The tests were performed on shafts made of Inconel 718 material under the conditions of finish turning, requiring a tool life of more than 20 min. The cutting inserts of identical geometry made of fine-grained carbide covered with coatings were applied by the PVD and CVD method. The values of the obtained diameter dimensions were assessed in reference to the assumed ones, as well as the values of the surface roughness and stereometry and the microstructure of the top layer. The nature and mechanisms of edge wear and its value expressed by the VBC parameter were also assessed. It was determined in the tests that the machined surface quality defined by the Ra and Sa roughness parameters and the dimensional accuracy were influenced not only by the coating microhardness but also by the method of applying the given coating. The lowest values of the tested roughness parameters were observed for the surface machined with an edge, with the S205 coating applied by the CVD method, which was characterized by the lowest microhardness. The edge with this coating also showed the lowest wear, defined by the VBC parameter, which translated into dimensional accuracy. Furthermore, the edge with the S205 coating also provided the best results with regard to the surface layer microstructure. The least favorable results, both in terms of dimensional accuracy and surface roughness, were obtained for the surface machined with a 1115-PVD-coated edge. The highest wear value was also recorded for this edge.

Keywords

• Inconel 718
• turning
• surface roughness
• tool wear
• microstructure