Experimental results of MQL assisted by cold air flow in turning operations

This paper deals with minimal quantity lubrication (MQL), a technique recently introduced in machining to reduce the lubricant consumption and, as a consequence, the machining costs. Using this technique it is possible to lubricate the cutting zone by a low lubricant flow (ml/hour) instead of flooding as during traditional machining operation, so reducing, as showed by some authors, the cost of lubricant till 30% of the total machining costs. In the present research a modified MQL equipment which uses an external cold air flow obtained by using a vortex tube is considered. The objective of this work was to study the influence of the temperature of the cold air flow during the cutting operation when applying the MQL technique. Turning tests of normalized 100Cr6 steel were performed using commercial triple coated carbide tips. During the tests the variables evaluated were the lubrication type and the air flow temperature. All the other cutting parameters were kept constant in order to obtain a segmented chip A SEM study on the worn tips was conducted with the aims of evaluating the tip wear geometry and of finding, using EDS microanalysis, traces of lubricant or lubricant compounds on the worn surfaces. This analysis showed that the lubricant reaches the cutting surfaces and chemically reacts with the workpiece and the tool tip, so reducing the tool wear. The geometry of the final workpieces was analysed too. Dimensional deviation and roughness were measured at the end of the tool life. Residual stresses were measured on the workpieces surface by using the X-ray diffraction method both in cutting and feed direction in order to evaluate how this new lubrication technique affects the fatigue life of the workpiece. Interesting results were obtained, showing several advantages due to the application of MQL technique in cutting, especially in comparison with dry cutting operation.