Study On The Evaluation Method Of Machined Surface Roughness Of C/C Composite

Carbon reinforced carbon (C/C) composite have much good properties, such as high specific modulus, high specific strength, abrasion resistance and so on, which is widely used in aeronautics & astronautics. Because of the inhomogeneous structure and anisotropy performance for fiber reinforced composite, its cutting mechanism is different from that of common engineering material, which leads to much special surface topography. Therefore, 2-D evaluation of traditional surface topography is not suitable for composite any more. However, at present 2-D evaluation is also adopted by the design and application of composite, which cannot reflect the machined surface topographical characteristic of composite authentically. So, it is necessary to study on assessing the machined surface topography of composite, so as to reflect it more authentically, by which the surface performance can be predicted more reasonable.Based on the analysis above, 3-D non-contact measurement is carried out on the machined surface of C/C composite and LY12 duralumin by surface roughness measure instrument TalyScan150. And conclusions can be drawn that:(1) With studying on 2-D evaluation, 3-D evaluation and magnitude parameters of machined surface roughness of C/C composite and LY12 duralumin, the results show that: only with 3-D evaluation, can the surface roughness of composite be reflected more comprehensively and more authentically. Root-mean-square deviation (S_q) parameter of the surface is more suitable than arithmetic-mean-deviation (S_a) parameter for composite. And S_q is recommended as the first evaluating parameter of 3-D surface roughness assessment.(2) By the area auto-correlation function and power spectrum density function, the texture characteristic of C/C composite is analyzed. The results indicate that: the machined surface of C/C composite is isotropy. With the help of image processing, the fractal attribute is studied, which indicate that: the machined surface of C/C composite appears fractal. And by fractal dimension surface bearing, friction, abrasion and so on can be quantified.(3) The factors affecting the machined surface roughness of C/C composite is studied by 3-D evaluation method and S_q. Outcomes show that: when milling surface roughness increases and later decreases with cutting speed increasing; decreases with cutting depth increasing; increases with feed rate increasing. But when turning, it increases with cutting speed increasing, cutting depth increasing or feed rate increasing. The influence of feed rateon surface roughness of C/C composite is greatest of three factors. Furthermore, fiber angle and structure are the most significantly influential factors.(4) The CBN tools are not suitable for machining C/C composite, compared with coated tools and diamond tools when improving the surface quality of C/C composite. The influence of corner radium on composite is the same as that on metal. That is to say, there is a best scale of corner radium to make the surface roughness of C/C composite minimal. Furthermore, cutting composite also reflects the pattern of cutting tools, the different of which from metal is that the reflecting extent of composite is less important than that of metal.