Experimental Research On Mechanism Of SiCp/Al Composites Thin-walled Workpiece In High Speed Milling

Due to their excellent comprehensive performance such as high specific strength and modulus, high temperature resistance, wear resistance, fatigue resistance, small thermal expansion coefficient and so on, high-volume SiCp/Al composites have a good promising applications in many the high-tech fields, for example, aerospace, advanced weapons manufacturing, automobile, optical precision instruments, electronic, etc. However, because of the totally different mechanical properties between SiC particles and Al alloy matrix, the machining of the composites is more difficult and the cutting mechanism is more complex compared to the simple metal and brittle materials. Especially, the SiCp/Al composites thin-walled pieces are poor rigidity as well, there are the deformation and vibration problems under the effect of cutting force and cutting heat. Therefore, the machining quality is hard to guarantee. At the same time, owing to the distribution of stress around SiC particles is uneven, the composites are vulnerable to stress concentration, generating crack and damage. As a result, it is of great theoretical and practical significant to research on the machining mechanism, deformation and damage of the thin-walled workpiece of high-volume SiCp/Al composites in high speed milling.In this paper, based on comprehensive analysis on the development conditions of SiCp/Al composite machining precisely in high speed, the researches, which are about the surface forming and surface quality, changing characteristics and influence factor of milling force, cutting temperature and temperature field, machining deformation and damage in high speed and precision milling of high-volume SiCp/Al composites thin-walled piece, are carried on thoroughly and systematically by the methods of theoretical analysis and experimental research. The main research contents and results are as follows:(1)Not only the mechanism of surface formation was studied but also surface feature of micro-morphology and macro-morphology in up and down milling ways were put forward; Chip morphology and formation mechanism of were proposed when SiCp/Al composites milled in high speed. Meanwhile, the defect’s characteristic and formation mechanism of the machined surface of SiCp/Al composite thin-walled workpiece were analyed in high speed milling; Variation characteristics of the machined surface roughness were proposed. As well as, the rule that milling ways, cutting parameters and tool geometry parameters influence on surface roughness in different cutting position of thin-walled was found out.The results of the study to reduce the cutting deformation, provides a theoretical and experimental basis for optimizing cutting parameter.(2)According to the characteristics of SiCp/Al composite thin-walled workpiece, the research proposed that the middle radial milling force is bigger than the both ends radial milling force on the whole cutting length. At the same time, the rule that the milling way influences on the milling force was researched also. The result shows the forces of up milling are greater than that of down milling in different cutting position. The rule that cutting parameters, tool geometry parameters and cutting path effect on was found out. The cutting force lied in entrance, middle part and exit, which is influenced on milling ways, cutting parameters, tool geometry parameters and cutting path was studied. At the same time, when the tool lied on the different position of workpiece, such as entrance, middle and exit, the cutting force varying characteristics were proposed. The characteristics of milling force’s time and frequency domain are analyzed, which points out that cutting into frequency of the blade plays a leading role in the force spectrum, so the cutting process is stability and without vibration. These results provide a theoretical and experimental basis for reducing cutting deformation and optimizing cutting parameters.(3)The regular that milling way, cutting parameters and tool geometry parameters influence on cutting temperature and temperature field’s distribution of SiCp/Al composites thin-walled workpiece in different cutting position was studied. Under the condition of up and down milling ways, the rules and characteristic of cutting temperature and temperature field varying in cutting process was put forward. That the milling speed, feed and radical depth influence on the temperature of workpiece surface and tool were proposed also. And the rake angle and edge inclination was also. For high-volume fraction SiCp/Al composites thin-walled workpiece, all of these provide theoretical guidance for reducing thermal deformation and selecting reasonable process parameters.(4)Characteristic of elastic deformation and damage mechanism of SiCp/Al composites thin-walled workpiece were studied. At the same time, the regular that cutting speed, feed and radical depth effect on elastic deformation of workpiece in milling process was obtained. Moreover, feature and mechanism of the inner damage, border defect and edge overcut of high-volume fraction SiCp/Al thin-walled workpiece in milling process were brought forward. Namely, It points out that the inner damage mainly included the ductile damage of matrix, the enhanced phase bursting and its debonding in the interface. Border defect is mainly supporting strength of cutting material lied the cut out end drops, which lead to the cutting material together with the workpiece edge shear and slip along the direction of the negative shear Angle; Meanwhile, In the cut into and cut out end of the workpiece, there is an obvious overcut phenomenon. Due to the tool cutting edge inclination is positive, overcut form of up milling is different from that of down milling. For high-volume fraction SiCp/Al composites thin-walled workpiece, all of these provide theoretical guidance for reducing machining deformation and damage.