Machining of sintered steel under different lubrication conditions

Cutting experiments of sintered steel Fe–2Cu–0.8C under different lubrication/cooling conditions and with different tool materials were performed in order to clarify the reasons for the low machinability of the sintered steel, and investigate the applicability of minimum quantity of lubricant (MQL) to the machining of sintered steel. As a theoretical approach to the short tool life in machining sintered steel, the impacts to the cutting edge caused by micro-voids were theoretically modeled, and it was revealed that the cutting edge suffered from impacts at a very short interval causing high cycle fatigue. Extremely short tool life in dry machining of sintered steel already used for wet machining proved that coolant definitely increased the stress amplitude in high cycle fatigue. Application of the air jet to a tool showed the positive effect in reducing tool wear. This indicated the possibility that micro-cracks nucleated by high cycle fatigue were healed by oxidation. MQL cutting with small amount of oil and air jet is proved to be acceptable for machining sintered steel from the results of cutting experiments using uncoated and coated carbide and cermet tools. Finally, it is confirmed that thick coating of a carbide tool is effective for dramatically improving the machinability.