CV黒鉛鋳鉄切削における工具損傷に及ぼす諸因子の影響

抄録

  Compacted vermicular graphite cast iron (FCV) has poorer machinability than gray cast iron (FC), and thus requires higher production costs in many cases. For this reason, high efficiency machining methods are required for FCV. In this study, we investigated the effects of various factors, chemical compositions, and mechanical properties of cast iron, cutting speed (V_c) etc., on tool failure in FCV machining compared with FC and ductile cast iron (FCD). The results showed that tool life in FCV machining is substantially shorter than FC and slightly longer than FCD under the same cutting conditions. In the case of FC machining, the tool life of several cBN tools increased with increasing V_c, because Si and Al oxidation occurred at the bottom area of the flank wear surface, after which this oxidation contributed to improving wear resistance. However, tool life in FCV machining decreased with increasing V_c, because the Al oxides, which improve wear resistance, reacted with the Mg in FCV, resulting in the generation of Mg-Al reaction products. These Mg-Al reaction products did not contribute to improving wear resistance. In the case of FCV machining, large flank wear was observed on the cBN tool and peeling off of the coating on the cutting edge was observed on the Ti(C, N)-Al₂O₃ coated CVD cemented carbide tool. The cutting force in FCV machining was larger than that in FC machining. In the measurement of high temperature tensile strength, FCV had higher strength than FC.
  These results suggest that the cutting edge temperature in FCV machining is higher than FC machining, therefore tool life in FCV machining is shorter than FC machining due to decreasing cutting edge strength and growing reaction wear.