Research On Processing Mechanism Of Rotary Ultrasonic Machining Of SiCp/Al Composites And Processing Stability Of Thin-walled Workpiece

SiCp/Al composites have many excellent characteristics and have been widely used in many fields. However, the machining property of SiCp/Al composites is poor due to the reinforced particles existing in matrix. How to improve processing quality of SiCp/Al composites and satisfy economic demands have become a key problem for its application. The traditional machining methods and some non-traditional machining methods used at present could not fully satisfy the requirements of high accuracy, high efficiency, and low cost in machining of SiCp/Al composites parts.Rotary Ultrasonic Machining(RUM) is a method of combining ultrasonic-assisted machining and grinding which has many outstanding processing characteristics and it is very fit for machining SiCp/Al composites of medium and high volume fraction. The processing quality and processing efficiency could be improved greatly. SiCp/Al composites have been used to manufacture thin-walled workpiece, but the chatter is appeared easily due to low stiffness in machining process and it will affect tool life and processing quality seriously.The research on processing mechanism of RUM of SiCp/Al composites is a basis of realizing high efficiency and precision maching of this material. On account of the differient physical characteristics of matrix and reinforced particles of SiCp/Al composites, the material removal mechanism is differ from single phase brittle material or single phase ductile material and the influences of matrix and renforced particles should be considered synthetically. In this thesis, the effects of ultrasonic vibration on machining process were analyzed. The analysis results indicate that ultrasoinc vibration could reduce cutting force value in removal process of SiCp/Al composites, improve machining surface quality, and improve material removal rate. Based on the observed results of scratching surface topography and chip morphology, the removal mechanism of RUM of SiCp/Al composites was analyzed. The results show that the aluminium matrix mixed with reinforced particles is removed in the way of plastic deformation and a part of residual matrix material coats on machining surface. Owing to ultrasonic vibration, the instantaneous cutting depth of the abrasive grain on tool possesses time variability and it results in the Si C particle is removed in the way of brittle mode and plastic mode. In the removal process, there exist particle displacement, particle detachment and particle pullout.In order to study the effect of technological parameters on machining process in RUM of SiCp/Al composites and provide the experimental basis for exploring technological approach of restraining chatter effectively in machining thin-walled workpiece, the processing performance experiments of RUM were performed for the SiCp/Al composites reinforced with 45% volume fraction of 3μm silicon carbide particles in aluminium matrix(2A12). The effects of processing parameters on cutting force and surface roughness were studied. The experimental results indicate that RUM could obviously reduce the values of cutting force and surface roughness, lower tool wear, restrain the grinding blockage. Based on the experimental research, the typical thin-walled workpieces were machined by RUM and the improper selection of cutting parameters would lead to chatter appearing.For restraining the chatter in machining process, the chatter mechanism of RUM of SiCp/Al composites was analyzed. On the basis of the ordinary grinding processing model and the stability analysis method proposed by Budak, the stability analysis mathematical model of RUM of SiCp/Al thin-walled workpiece was built with synthetically consideration of characteristics of RUM and SiCp/Al composites. Based on the model, the processing stability analysis method was determined.On the basis of the above research, the modal parameters and the cutting force coefficient were determined by modal experiments and cutting experiments. The processing stability Lobe diagrams of the typical thin-walled workpice were obtained by the stability analysis method. The processing points on different area of Lobe diagram of thin-walled plate were selected and the cutting experiments were carried out according to the cutting parameters of the selecting points. When the workpiece was machined with cutting parameters of stability points, the machining process is stable, the cutting force and surface roughness values were low, and the chatter mark and damage were not appeared on workpiece surface. The above research results show that the processing parameters could be selected properly according to this stability analysis method to avoid machining chatter and enhance processing quality and processing efficiency.