A study on process parameters in end milling of AISI-304 stainless steel under electrostatic minimum quantity lubrication conditions

Effective lubrication and cooling are very critical to control friction and heat generation in metal-cutting processes. Conventionally, cutting fluids in flood form are employed during the processes; however, their usage is frequently seen to raise major environmental, economic, and employees' health concerns. All these factors have urged researchers to search for alternatives to minimize or even eliminate cutting fluid usage. To serve that purpose, a new near-dry machining technique called "electrostatic minimum quantity lubrication" (EMQL) has been innovated and developed. EMQL is a technique using the synergetic effects between electrostatic spraying (ES) and minimum quantity lubrication (MQL), wherein a very small amount of lubricant, negatively charged by the electrostatically contact charged method, is directed into the machining area in the form of a fine, uniform, and highly penetrable and wettable oil mist. The focus of this study is to evaluate the performance of EMQL in end milling of AISI-304 stainless steel in terms of tool wear, cutting force, tool life, and surface roughness. The influence of EMQL process parameters such as charging voltage, air pressure, lubricant flow rate, and cutting speed is determined based on an experimental study. A comparison with the results obtained in completely dry, wet, and MQL machining is also provided. The experimental results show the effectiveness of EMQL as a viable alternative to conventional wet and MQL machining through the reduction in the friction at the tool-chip interface. It is found that the charging voltage is an important factor influencing the effective application of EMQL oil mist. EMQL with -5 kV voltage is recommended because it provides not only lower tool wear and cutting force but also higher tool life and better surface finish. In addition, it is found that there are the optimum lubricant flow rate and air pressure in end milling of AISI-304 stainless steel with EMQL. The proper selection of the above parameters can lead to a low-cost and eco-friendly machining.