Phenomena during Electrical Discharge Machining with Molybdenum Disulfide Powder Suspended in Working Oil

摘要

A problem for machines used in space environment is lubrication between sliding parts such as joints. Solid lubricants, such as molybdenum disulfide (MoS{sub}2), gold, silver or polytetrafluoroethylene (PTFE) are often used on the sliding parts exposed in the space environment instead of liquid ones because of evaporation and cosmic radiation. On the other hand, electrical discharge machining (EDM) has been used not only for removal process but also for deposition process. When MoS{sub}2 powder is mixed in the working oil, MoS{sub}2 layer can be deposited on stainless steel during the finishing EDM process. The deposition process must be clear to improve the endurance of the lubricant layer. In this report, the deposition process is discussed with the conditions such as the discharge location and the gap distance monitored during EDM and the influence of some other machining conditions investigated through the friction test. Because these phenomena are the same as those in EDM with Si powder, the main factors to make the surface smooth should be the discharge dispersion and the expansion of the gap distance. Then the reciprocating friction test in air was carried out to investigate the influence of machining time and measured point of the deposited layer. A low friction coefficient held out at the areas near the front edge and at the center of the deposit for long lubrication duration. The biased concentration in a gap between the electrode and the specimen caused the unstable the lubrication duration. Because the lubrication duration was saturated over 30 min, the deposited MoS{sub}2 was removed during deposition in the case of machining for a long time. The influence of the thermal properties of the specimen was also investigated. MoS{sub}2 could be deposited on the metals with lower melting point than MoS{sub}2.