Assessing the lubrication performance of vegetable oil-based nano-lubricants for environmentally conscious metal forming processes

In metal forming processes, employing lubricants for providing desirable tribological circumstances at tool-workpiece interface is essential to increase the material formability, prolonging tool life and suppressing energy loss. With increasing the awareness and concerns towards the substantial hazardous effects of conventional metal forming lubricants a step forward is crucial to replace them with benign and compatible lubricants with environment. Despite the fact that vegetable oils have an immense potential to be utilized as green lubricants, but the limited tribological characteristics of them restrict their applications. Hence, the biodegradability and non-toxicity privileges of vegetable oils have been incorporated with friction reduction and extreme pressure capabilities of nanoparticle additives in this study, to develop a high performance lubricant with environmentally friendly feature. The CuO and SiO2 nanoparticles were dispersed in soybean and rapeseed oils in diverse concentrations and their lubrication performance were compared with two conventional metal forming lubricants, CM202A press drawing oil and solid lubricant of zinc phosphate plus sodium soap. The standard ring compression test was utilized to evaluate the efficiency of considered lubricants. The performance comparison was made using two key factors of friction coefficient and deformation load. The necessary friction calibration curves for estimating friction coefficient were provided employing finite element simulation. The acquired results convey that the lubricity of vegetable oil is dependent on its chemical structure. With increasing the concentration of nanoparticles, the friction factor and deformation load reach to a minimum for a certain amount of concentration. According to obtained results, the most efficient concentration of nanoparticles was determined within the range of 0.5-0.7 wt%, which provides 21-31% enhancement. It is demonstrated that the vegetable oil-based nano-lubricants which are enriched with optimum amounts of nanoparticles have the friction reduction capability comparable to conventional lubricants. The outcomes of this study can be fruitful in developing more environmentally conscious metal forming processes. (C) 2016 Elsevier Ltd. All rights reserved.