A new lubrication approach in the SPIF process: Evaluation of the applicability and tribological performance of MQL

Abstract

The abrupt changes in the customer demands and the need to achieve versatility in production for satisfying the different needs of consumers have resulted in the development of rapid prototyping processes. Single Point Incremental Forming (SPIF) is a forming method which doesn't require dies for production and thus enables to greatly reduce the manufacturing costs for low to medium batch productions while enabling versatile manufacturability. One of the major disadvantages of this process is the poor surface quality of formed parts due to friction between tool and sheet interfaces. For this reason, suitable lubrication techniques and the use of lubricants are of great importance in obtaining the desired surface quality. In this study, the Minimum Quantity Lubrication (MQL) technique, which provides significant improvements in metal cutting processes with its effective lubricating feature, has been applied for SPIF process to investigate its effectiveness in SPIF processes. For this purpose, a series of experiments have been carried out by forming 7128 sheet metals with SPIF process in a CNC vertical machining center. In the experiments, SPIF parameters (feed rate, tool stepdown, etc.) have been kept constant and the effects of MQL parameters on surface roughness/topography, thickness distribution, roundness deviation, angular deviation have been focused. Three different pressures (4, 6, and 8 bar), three different flow rates (50, 75, and 100 mL/h) and three different vegetable-based oils with different viscosities have been selected as MQL parameters. In addition, 7128 sheet metal has been formed with the SPIF process by using a paste lubricant for the comparison of paste lubricated and MQL assisted SPIF process. Finally, friction tests have been carried out in a ball-on-disk device to determine the friction coefficients of the oils. Experimental results have shown that the increase in pressure has greatly increased the surface quality and dimensional accuracy, while the increased flow rate level improved the surface quality and dimensional accuracy up to a certain value (75 mL/h). It has been concluded that the surface quality can be improved by 14.60% with the MQL assisted SPIF process over the paste lubricated SPIF process, which has proved the applicability and superiority of MQL technique for SPIF processes.