2020 年 59 巻 1 号 p. 309-313
In the past, leaded brass has been used in various applications because its micro cutting is easy due to good machinability. However, leaded brass cannot be used under the EU RoHs Directive；thus unleaded brass is supposed to be used. The machinability of unleaded brass is poor compared with that of leaded brass. In order to improve machinability, cutting fluid is used. The cutting fluids contain oily additives, preservatives, rust inhibitors, and extreme–pressure agents in the base oil. The extreme–pressure agent achieves lubrication under high pressure. There are a few extreme–pressure agents；among them, chlorinated paraffins have the highest lubrication capability. However, the abolition of short–chain chlorinated paraffins has been decided in the COP8 （Eighth session of the Conference of the Parties）. Medium–chain chlorinated paraffins （MCCPs） generate short–chain chlorinated paraffins as byproducts thus their use also has some issues. Hence, the development of extreme–pressure agents that can achieve comparable machinability to that of chlorinated paraffins has been awaited. However, the efficiency of new extreme–pressure agents is difficult to investigate because the effect of chlorinated paraffins has not been clarified in the drilling of fine holes with a micro drill.
In this study, wet drilling of fine holes was carried out with a micro drill using cutting fluids. The cutting fluids contained two kinds of MCCP and a long–chain chlorinated paraffin （LCCP） as the extreme–pressure agent. We investigated the effect of these chlorinated paraffins on cutting behavior. The tool life of micro drills became longer with an increase the amount of added LCCP. When the added LCCP was 50 weight％, more than 500 fine holes could be drilled. It was also clarified that the cutting resistance was higher for MCCP than for LCCP；however, the tool life of the micro drill was longer for MCCP than for LCCP.