Machinability of laser heated silicon nitride ceramics during a turning process

Abstract

The Si3N4 ceramics are, due to their low density, very good wear, corrosion and heat resistance, an important material with many engineering and medical applications. However, the high hardness (2125HV) and brittleness of ceramics make for serious difficulties when machining. Laser Assisted Machining (LAM) is currently being developed as a research method for the machining of hard Si3N4 ceramics. It is a hybrid process of the machining, where the material is heated by laser irradiation and soft surface layer is machined by defined cutting edge of the cutting tool tips. In comparison with conventional machining this method significantly increases the tool durability.The research presented here shows the results of the hard Si3N4 ceramics machinability tests which were evaluated by a VBc wear indicator of the polycrystalline diamond (PCD) tool tips, and the geometric structure and Ra surface roughness parameters of the machined ceramics. The conventional turning and laser assisted turning (LAM) of Si3N4 ceramics with a special temperature control system at the tool tip of machined surface during this process was investigated. It was noticed that the wear intensity of PCD tool tips was significantly influenced by the temperature of the machined layer during the ceramics turning process. This was confirmed by 5 fold decrease in the tool insert wear rate during LAM process in comparison with conventional turning. A suitably high temperature at the machined surface is a guarantee of low tool insert wear rate and thus increasing their durability. In this case the economics of this process is significant improved. The possibilities of obtaining higher turning capacity via cutting speed increase without decreasing tool insert durability was confirmed. The machined surface roughness after LAM process in different range of temperatures compared with conventional turning shows improved results. The machined Si3N4 ceramic geometrical surface structure in the range of low feed values is random. However it is determined by tool insert feed in the range of the highest feed values.The Si3N4 ceramics are, due to their low density, very good wear, corrosion and heat resistance, an important material with many engineering and medical applications. However, the high hardness (2125HV) and brittleness of ceramics make for serious difficulties when machining. Laser Assisted Machining (LAM) is currently being developed as a research method for the machining of hard Si3N4 ceramics. It is a hybrid process of the machining, where the material is heated by laser irradiation and soft surface layer is machined by defined cutting edge of the cutting tool tips. In comparison with conventional machining this method significantly increases the tool durability.The research presented here shows the results of the hard Si3N4 ceramics machinability tests which were evaluated by a VBc wear indicator of the polycrystalline diamond (PCD) tool tips, and the geometric structure and Ra surface roughness parameters of the machined ceramics. The conventional turning and laser assisted turning (LAM) of Si3N4 cer...