Liquid LCO2 Assisted Machining of Martensitic Stainless Steel with TiAlSiN PVD Coated Tools

Abstract

Sustainable machining involves the use of environmentally friendly cooling and lubrication fluids. A novel approach of lubricated liquid carbon dioxide (LCO2) can be used to replace conventional cutting fluids while promising benefits such as cleaner machining and higher productivity. In this study, milling of martensitic stainless steel was performed under different cooling and lubrication conditions (dry, flood, LCO2, LCO2 + MQL). Cutting tool (ball end mill, d = 8mm) was protected by a TiAlSiN PVD hard coating, while the same uncoated tool was used as a reference. Tool life time measurements were taken under different cooling and lubrication conditions at pre-determined time intervals, until the critical tool wear of 0.2 mm was reached on the flank face. At the same time, thermocouples were inserted into the workpiece to measure the temperature directly below the cutting zone. The influence of different cooling and lubrication conditions on surface roughness parameters was also investigated. From the experimental results, surprisingly, conventional flooding machining outperformed LCO2 and LCO2 + MQL assisted machining in terms of surface roughness. Moreover, the TiAlSiN coated tool exhibited roughly three times longer tool life time when compared to the uncoated tool at the same machining conditions. Whereas both, LCO2 and LCO2 + MQL cooling/lubricating strategies significantly reduce the temperature in the cutting zone, dry machining strategy provides the longest tool life time.