Theoretical analysis of technological possibilities of reducing surface roughness at abrasive processing

Abstract

The paper presents analytical dependences for determining the parameters of surface roughness at abrasive machining with cutting grains positioned spherically at the same height on the working surface of the tool and overlapping mutually in the process of forming the roughness of the processed surface. The calculations established that, provided that the cutting grains are located at the same height on the working surface of the tool as applied to the free abrasive finishing process, it becomes possible to significantly reduce the surface roughness parameters Ra and Rmax. The calculations also stated that these parameters are the less, the less the granularity of the abrasive or diamond grains is at processing. With an increase in the grain size of the diamond powder, in order to achieve the specified values of the surface roughness parameters Ra and Rmax, it is necessary to increase the number of the cutting grains forming the surface roughness. However, this leads to reduced processing performance. It has also been shown that it is not possible to put into practice the processing conditions under which the surface roughness parameters Ra and Rmax, established theoretically, become very small due to the difficulty of providing the same arrangement of abrasive grains on the working surface of the tool. Based on the theoretical solutions obtained, specific practical recommendations have been developed to reduce the surface roughness. So, an effective method of internal grinding has been developed using a soft felt (felt) wheel with a glued layer of abrasive powder 63C. This method can significantly reduce the surface roughness parameter Ra without increasing the complexity and reducing processing productivity. For its practical implementation, it is proposed to use abrasive powder with granularity F80-F150. In doing so, it is effective to grind by setting the axis of rotation of the grinding wheel with an individual drive perpendicular to the axis of rotation of the hole being machined. As a result, the number of simultaneously working abrasive grains significantly increases as compared to conventional internal grinding due to an increase in the contact area of the grinding wheel with the workpiece. Also, a certain different-height arrangement of cutting grains on the working surface of the tool, which takes place under real processing conditions, also decreases, which results in a decrease in the roughness of the machined surface