خصوصیات سطحی در ماشینکاری فوق العاده دقیق از SIC/AL به کامپوزیت های زمینه فلزی با استفاده از تجزیه و تحلیل سیستم های وابسته به داده

This paper presents a data dependent systems (DDSs) method for the analysis of surface generation in ultra-precision machining of Al/SiC metal matrix composites (MMCs). The DDS analysis provides a component by component wavelength decomposition of the surface roughness profile of the machined surface. A series of face cutting experiments was done on Al6061/15SiCp MMCs under different cutting conditions. The cutting results indicate that the characteristics of the wavelength components analyzed by the DDS analysis method are correlated well with the surface generation mechanisms. Since the relative powers of the wavelength components are used to measure the contributions of the cutting mechanisms to the total roughness, this resolves the shortcomings of the conventional spectrum analysis method in characterizing the surface properties such as pits and cracks in ultra-precision machining of MMCs.

Over the past decades, the machinability of silicon carbide reinforced aluminum alloy (Al/SiC) composites has attracted much scientific and public attention. The Al/SiC composites are promising as structural materials because of their high specific modules and specific strength, good wear resistance and high temperature resistance [1]. However, it is well known that the metal matrix composites (MMCs) are difficult to machine to a good surface finish. This is due to the fact that the hard SiC reinforcement in the Al/SiC MMC is embedded in the soft ductile aluminum matrix. The mechanism in the cutting of SiC reinforcement depends largely on the deformation of the Al matrix during cutting [2]. Some research work has been reported on the surface characteristics of machined Al/SiC MMCs. In the study of Looney et al. [3], the influence of tool materials on surface finish has been reported. El-Gallab and Sklad [4] have further examined the microstructures of chips, and observed the formation of shear bands, where reinforcement particles align themselves. By developing an improved quick-stop device, Lin et al. [5] are able to examine the cutting mechanisms more effectively. Although extensive studies can be found in literature on the machinability of MMCs, most of these studies focus only on the conventional turning process, relatively little research work has been done on studying the surface generation in ultra-precision machining of MMCs, such as single-point diamond turning (SPDT). In SPDT, the cutting edge radius of the diamond tool is usually in the same order as the average size of the reinforcement in the Al/SiC MMC. There is a significantly thick layer of undeformed chip (i.e. with the same order as the average size of the SiC reinforcement) at which complicated plastic and elastic deformation are taking place. The current understanding on the cutting mechanics, deformation behavior and its relation to the surface generation mechanisms is still limited. In this paper, the mechanisms of surface generation in ultra-precision machining of an Al/SiC MMC are analyzed based on a data dependent systems (DDS) analysis [6]. The DDS analysis provides a component by component wavelength decomposition of the surface roughness profiles of the machined surfaces. The characteristics of these wavelength components are correlated with different surface generation mechanisms. Their relative powers are used to measure the contributions of the mechanisms to the total roughness.

In this paper, a DDS analysis method is used to characterize the surface generation in ultra-precision machining of Al/SiC MMCs. The metal cutting dynamics are characterized by the natural frequency, the damping ratio, and the relative contribution of the central wavelength components which make up the roughness profile of the workpiece. The characteristics of these wavelength components are correlated with the cutting mechanism. A series of cutting tests was carried out on Al6061/15SiCp MMCs under different cutting conditions. The results indicate that the cutting dynamics of the surface roughness possess a strong correlation with the surface generation mechanisms of the MMCs. Moreover, the DDS analysis method provides an effective way to characterize quantitatively the effect of cutting phenomena such as the cut through and pulled out mechanisms on the surface generation in ultra-precision machining of Al/SiC MMCs.