Mechanism of high speed machining of graphite

2020-12-17186

        Some scholars at home and abroad have carried out preliminary analysis and Research on the crack formation and propagation, chip morphology and size, and the interaction between tool and workpiece material in common cutting and high-speed machining of graphite. Das thinks that when using positive rake angle tool for graphite turning, a large chip will be generated first, and then an arc groove will be left on the surface of the workpiece to be processed, and then it will be removed in the form of fine chip; while when using negative rake angle tool, due to the simultaneous expansion of multiple slip surfaces, the chip will be generated

        The chips are mainly small particles. When studying the turning process and characteristics of carbon graphite materials, it is pointed out that cutting tools do not peel off the surface of graphite blank, but "cut and peel" or "crush and peel" the particles on the cutting surface according to the properties of cutting tools and blanks, cutting factors of cutting tools and the sharpness of cutting edge In addition, there is considerable friction between the carbon particles and the cutting edge in the high-speed relative motion. It is considered that the cutting process of graphite material is mainly the surface of the material to be processed is cracked (crushed) by the extrusion force of the tool edge. The extrusion force is actually the friction between the cutting edge 1:3 and the processed material. It is mentioned that the chip particles in stone burning ink turning are concave and convex. The chip shape of the new edge grinding tool is very irregular, and the surface is multi angular, with the size of tens to hundreds of microns. With the increase of tool wear, the average diameter of chip particles is approximately spherical, and the concave convex degree of chip surface is reduced by 14 ".

        Masuda observed by high-speed photography during the high-speed turning of graphite materials that the initial cracks generated in the graphite materials propagated along the cutting direction, resulting in the fragmentation of graphite materials. Most of the chips slide along the rake face, resulting in tool crescent wear. Sato divides the graphite chips in the high-speed turning process of sintered graphite into four grades: 500 "m, 250 PM, 125? M and 63 TTM. The weight of graphite chips with particle size less than 250 i.tm accounts for most of the total chip weight, and with the increase of feed rate, the proportion of large particles will increase [. K6nig studied the high-speed milling process of graphite, and considered that the formation process of graphite chips was very similar to that of brittle materials such as ceramics; graphite materials were crushed at the tool tip, forming fine chips, and the cracks generated in cutting would extend to the front and bottom of the tool tip first, and then spread to the free surface, forming large pieces of broken chips and forming fracture pits on the machined surface of graphite The contact state with tool rake face is divided into cutting contact impact zone and chip slip zone along rake face, which lead to different tool wear patterns. The cutting force and its fluctuation amplitude increase with the increase of feed rate, and the ratio of the maximum cutting force to the average cutting force can reach 2.0, which fully reflects the fluctuation characteristics of cutting force in machining brittle materials.