Application analysis of the hottest superhard tool

Application analysis of superhard tools in hard turning (II)

continuously extending the industrial chain, composite polycrystalline cubic boron nitride (PCBN) tools with high CBN content have high hardness, good wear resistance, high compressive strength and good impact toughness. Their disadvantages are poor thermal stability and low chemical inertia, which are suitable for cutting heat-resistant alloys, cast iron and iron series sintered metals. The content of CBN particles in PCBN tools is low. Using ceramics as binder, its hardness is low, but it makes up for the poor thermal stability and low chemical inertia of the former material, and is suitable for cutting hardened steel

residual stress of ceramic and PCBN tools in cutting hardened steel when cutting gray cast iron and hardened steel, ceramic tools or CBN tools can be selected. Therefore, cost-benefit and processing quality analysis should be carried out to determine which one to choose. Figure 3 shows the wear of the tool surface after machining gray cast iron with Al2O3, Si3N4 and CBN tools. The cutting performance of PCBN tool material is better than that of Al2O3 and Si3N4. However, in dry cutting hardened steel, the cost of Al2O3 ceramics is lower than that of PCBN materials. Ceramic tools have good thermochemical stability, but they are not as tough and hard as PCBN tools. When the cutting hardness is lower than HRC60 and small feed rate is adopted, ceramic tool is a better choice. PCBN tools are suitable for cutting workpieces with hardness higher than HRC60, especially in automatic machining and high-precision machining

in addition, under the same flank wear, the residual stress on the workpiece surface after cutting by PCBN tool is also relatively stable than that of ceramic tool. The dry cutting of hardened steel with PCBN tools should also follow the following principles: choose a large cutting depth as far as possible when the rigidity of the machine tool allows, so that the heat generated in the cutting area makes the metal in the front edge area soften locally, which can effectively reduce the wear of PCBN tools. In addition, when using a small cutting depth, it should also consider the poor thermal conductivity of PCBN tools, which makes it too late for the heat in the cutting area to diffuse, and the shear area can also produce obvious metal softening effect, Reduce the wear of cutting edge

the blade structure and geometric parameters of superhard tools. The reasonable determination of blade shape and geometric parameters is very important to give full play to the cutting performance of tools. In terms of the strength of the tool that can print experimental reports, the tip strength of various blade shapes from high to low is: round, 100 diamond, square, 80 diamond, triangle, 55 diamond, 35 diamond. After the blade material is selected, the blade shape with the highest strength should be selected. Hard turning blades should also choose as large a tip arc radius as possible, rough machining with circular and large tip arc radius blades, and the tip arc radius during finish machining is about 0.8 M. Hardened steel chips are red and soft ribbons, brittle, easy to break, and non cohesive. Hardened steel has high cutting surface quality, and generally does not produce chip nodules, but the cutting force is large, especially the radial cutting force is larger than the main cutting force. Therefore, the tool should adopt a negative rake angle (go -5) and a large rake angle (ao=10~15). The main deflection angle depends on the rigidity of the machine tool, which is generally 45 ~ 60 to reduce the chatter of the workpiece and tool. Cutting parameters of superhard tools and requirements for process system the higher the hardness of workpiece material, the lower the cutting speed should be in accordance with the requirements of the food safety law, but it is responsible for purchasing qualified food contact materials and verifying their compliance. The suitable cutting speed range for hard turning finishing with superhard tools is 80 ~ 200m/min, and the common range is 10 ~ 150m/min; Large cutting depth or strong intermittent cutting of high hardness materials shall be adopted, and the cutting speed shall be maintained at 80 ~ 100m/min after regular power on. Generally, the cutting depth is between 0.1 ~ 0.3mm. For the workpiece with low surface roughness, a small cutting depth can be selected, but it should not be too small, and it should be appropriate. The feed rate can usually be selected between 0.05 ~ 0.25mm/r, and the specific value depends on the surface roughness value and productivity requirements. When the surface roughness ra=0.3 ~ 0.4 m, hard turning with superhard tools is much more economical than grinding