Current Research Trends in Variants of Minimum Quantity Lubrication (MQL): A Review

Abstract In this paper, an extensive literature review of sustainable machining using different minimum quantity lubrication (MQL) variants is presented. Nowadays, sustainable development (SD) is referred as a common global issue. Sustainability concept in machining is linked with two major goals. The first goal is to reduce the environmental impact by reducing the energy consumption in the process. The second goal is to reduce the consumption of hazardous non-biodegradable materials. During machining, it was evident that when the cutting of material takes place, it increases the heat produced due to plastic shear deformation and friction. In dry machining, the tool wear and surface roughness are very high and it is not practical to use this method. So, there is a need to introduce a coolant or lubricant in the cutting zone to control or reduce the cutting temperature. Conventional cutting fluids are referred as non-biodegradable in nature and high disposal cost is associated with them as well. The researchers found that Minimum quality lubricant (MQL) is an appropriate way to remove the heat from the work material and chips formed in this case are almost dry. Minimum quantity lubrication (MQL) has been emerged as a potential solution for the second goal. MQL is being popular in the metal cutting sector because of its ability to provide improved machinability while being sustainable at the same time. The main topic discussed in this article is to reduce the quantity of lubricant for the machining usage to move forward towards a cleaner and greener machining process. The research community also observed that when moving towards the superalloys primarily used in the aerospace and aircraft industry MQL technique is not efficient. Using the MQL technique, the friction is reduced by this lubricant film, but it does not take away the heat generated from the work material and tool. Due to this reason, several variants of MQL were developed. These variants include advanced oil on water (OoW) droplet MQL, minimum quantity cooling lubricant (MQCL), and nano MQL etc. In MQCL coolant is used at the lower temperature, which is air or water, to remove the extra amount of heat from the work material. The current study compared performance of all these MQL variants. It has also been observed that MQL operating parameters and jet arrangements can significantly affect the machining performance. The current study will provide a detailed comprehensive review about the performance of these variants.