Formation of Self-lubricating Layer on Workpiece Surface Ground by Nano-encapsulated Grinding Wheel
Among the many machining methods available,grinding is one of the most important and is primarily used for the final processing of different machine parts.The grinding wheel rotates at a high speed,which creates an airflow barrier around the grinding area,preventing the grinding fluid from effectively cooling and lubricating the area during grinding.This leads to grinding burns and other surface quality problems of the workpiece and affects machining efficiency.To address this problem,this study proposes filling the cavity of carbon nanotubes(CNTs)with an oleic acid(OA)lubricant,which is used as a filler in resin-bonded grinding wheels.Using this nano-capsule as a filler could help improve the strength of the grinding wheel owing to the high strength and thermal stability of the CNTs.The most important benefit of this method is the release of oleic acid into the grinding area when the nano-capsules rupture,and the self-lubricating layer formed can directly lubricate the grinding area,thereby improving the performance of the grinding wheel.First,nano-capsules are prepared by widely used wet chemical methods and then characterized by Thermogravimetric Analysis(TG),Fourier Transform Infrared Spectroscopy(FTIR),and Transmission Electron Microscopy(TEM)to evaluate the material stability,surface functional groups,and morphology.In addition,we evaluate the presence of nano-capsules in the grinding wheel and the effect of the nano-capsule filling on the tensile strength and hardness of the grinding wheel.Finally,the effects of the nano-capsule content and grinding speed on the grinding force,grinding temperature,grinding ratio,and workpiece surface roughness during the grinding of GCr15 steel are studied.The release of OA in the grinding wheel during the grinding process is studied using X-ray photoelectron spectroscopy and scanning electron microscopy(SEM)analysis of the workpiece surface,based on which the formation mechanism of the self-lubricating film is further clarified.A mechanism for the lubrication effect of the self-lubricating film is also proposed.The nano-capsules were successfully prepared by wet chemical methods;they were found to have a filling rate of approximately 20％and were thermally stable.During the curing process,the nano-capsules could resist the curing temperature of the resin and effectively protect the oleic acid.According to the tensile test,the nano-capsules increased the strength of the grinding wheel by approximately 25％when the filling amount was approximately 8％.Further filling of the nano-capsules reduced the tensile strength of the grinding wheel,and the hardness of the grinding wheel continued to decrease with an increase in the nano-capsule content.Moreover,the mechanical properties of the grinding wheel satisfied the requirements of its intended use when the nano-capsule filling content was less than 16％.Compared with ordinary resin grinding wheels,the grinding force of the nano-capsule filled grinding wheels can be reduced by 40％,the grinding temperature can be reduced by 45％,the surface roughness value can be reduced by 15％,and the grinding ratio can be increased by 30％.The nano-capsules embedded in the grinding wheel continuously released OA within its cavity onto the grinding interface during the surface grinding process,forming a composite self-lubricating layer.Because of this lubricating layer,the grinding wheel achieved better lubrication performance,which in turn improves the grinding performance of the wheel.The research presented in this paper provides a viable technical solution for grinding lubrication problems,which is beneficial for improving the grinding efficiency and surface quality of workpieces.The grinding wheel developed in this study has significant potential for application in green machining conditions where a large amount of grinding fluid is not allowed.
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