Scholars at home and abroad have conducted preliminary […]
Scholars at home and abroad have conducted preliminary analysis and research on the formation and propagation of cracks, the shape and size of chips, and the interaction between the tool and the workpiece material during chip formation in graphite ordinary cutting and high-speed machining. Experts believe that when a positive rake angle tool is used for graphite turning, a large chip will be generated first, and 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 chips; while a negative rake angle During tool processing, due to the simultaneous expansion of multiple sliding surfaces, the generated chips are mainly small particles.
When studying the turning process and characteristics of carbon-graphite materials, it is pointed out that the cutting tool does not simply peel off the graphite blank, but according to the nature of the cutting tool and the blank, the cutting factor of the cutting tool and the sharpness of the cutting edge, etc. Respectively play the role of "cutting and peeling" or "crushing and peeling" on the particles on the cutting surface: the cutting force during the cutting process of carbon-graphite material is irregular and intermittent high-frequency impact force; in addition, in high-speed relative motion There is considerable friction between the carbon particles and the cutting edge. It is believed that the cutting process of graphite material is mainly the surface of the processed material being crushed (crushed) by the pressing force of the cutting edge of the tool. The pressing force is actually the friction between the edge 1:3 and the processed material. It is mentioned that the chip particles during turning of sintered graphite are concave and convex. The shape of the new sharpened tool chips is severely irregular, the surface is angular, and the size is tens to hundreds of microns. As the tool wear increases, the chip particles are average The diameter is approximately spherical, and the unevenness of the powder surface is reduced by 14".
Experts observed through high-speed photography during the high-speed turning of graphite material that the initial cracks generated inside the graphite material expanded along the cutting direction, causing the graphite material to fragment, and most of the chips slipped along the rake surface, resulting in tool crescent craters. Wear. The graphite chips in the high-speed turning process of sintered graphite are divided into four grades: 500m, 250 pm, 125m and 63 ttm, among which the particle size is less than 250 I. The weight of tm graphite chips occupies most of the total weight of chips, and as the feed rate increases, the proportion of large chips will increase.
After studying the high-speed milling process of graphite, it is believed that the formation process of graphite chips is very similar to that of brittle materials such as ceramics; graphite materials are crushed at the tool tip to form fine chips, and the cracks generated by cutting will first move forward to the tool tip. The bottom extends and then expands to the free surface to form a large piece of chip breaking, and form a fracture pit on the processed surface of the graphite; the contact state of the chip and the rake face of the tool is divided into the cutting contact impact zone and the chip sliding along the rake face Shift zone, they respectively lead to different tool wear patterns. The cutting force and its fluctuation amplitude of graphite electrode material turning increase with the increase of the feed rate. The ratio of the cutting force to the average cutting force can reach 2.0, which fully reflects the fluctuation characteristics of the cutting force during the processing of brittle materials.