Research On Surface Quality And Tool Wear In High-Speed Milling Of SiCp/Al Composites

Due to the high specific strength and stiffness, the SiCp/Al composites are widely used in the aviation and automobile industry. There are two main problems in the machining of SiCp/Al composite, one is the severe tool wear, and the other is the poor quality of machined surface. Few papers are related with the cutting of SiCp/Al composites with high volume fraction which are involved with the high-tech field. Thus the high-speed milling technology for cutting SiCp/Al composite, which is investigated to solve the above two questions, is very meaningful.Tool wear is a net problem for the machining of SiCp/Al composites. The selection of tool material and the mechanism of tool wear is the foundation in high-speed milling of this material. The tool wear mode and mechanism of TiN coated tool, TiALN coated tool, the CVD coated diamond tool and the PCD tool is investigated through the high-speed milling experiments for cutting SiCp/Al composites. Based on the tool wear mode, the standard of tool failure is determined. Then the variations of tool wear with the cutting parameters are investigated through cutting experiments. The results show that the increase of feed rate is helpful to reduce the tool wear and there are an optimist cutting speed range for the reduction of tool wear for different tool. Due to the least tool wear, the PCD tool is considered to be the best choice for high-speed milling of SiCp/Al composites. Finally, the rupture model of PCD tool is established to seek for the mechanism of the tool rupture. The concept of limit cutting speed is proposed. The rupture model is proved to be right by the results of cutting experiments.The investigation of the types and the forming mechanisms of machined surface defects are very critical because the machined surface defects severely affect the machined surface quality. The two-phrase Fem model of high-speed cutting of SiCp/Al composites is established to seek for the types and forming mechanisms of machined surface defects. The results show that the behavior of particle caused by the stress induced in the cutting process is the main reason for the formation of machined surface defects. There are four type machined surface defect, i.e., the small pit, the big hole, the plough groove and the raised particle above the surface. For the purpose of investigation of affection of cutting parameters on machined surface defects, the algorithm of reorganization and reconstruction based on the lifting wavelet is utilized to further investigation.Due to the existence of periodical feed mark and random surface defects on the machined surface of SiCp/Al composites, the appropriate characterization method is necessary to describe and appreciate the character of the machined surface of SiCp/Al composites. The applicability of two-dimensional roughness is analyzed because the Ra is unstable. The results show when the feed rate is small the existence of machined surface defects is the main reason to affect the surface roughness. Thus the three-dimensional roughness characterization method is investigated. Through the investigation of the stability of the parameters of three-dimensional roughness, the Sq is selected to be the characterization parameters for the machined surface of SiCp/Al composites. The construction of characterization parameters for the machined surface of SiCp/Al composites is constructed by the Sq parameter and Hk (the depth of big hole on the machined surface).The machined surface quality of SiCp/Al composites is closely related with the selection of cutting parameters.Firstly, the extent to affection of cutting parameters for the characterization parameters (Hk and Sq) is investigated by the orthogonal experiments of the high-speed milling of SiCp/Al composites. Then to seek for the affection law of cutting parameters for the characterization parameters, the limit energy damage theory is proposed to explain the affection law of cutting parameters for the Hk. Finally the cutting parameters are optimized for acquiring a good surface quality.