CNC Cutter
The cutting performance of the coating is significantly better than that of the TiN coating. Tool life for machining Inconel178 Although PVD coatings show many advantages, some coatings such as Al2O3 and diamond tend to use CVD coating technology. Al2O3 is a heat- and oxidation-resistant coating that isolates the tool body from the heat generated by cutting. Through CVD coating technology, the advantages of various coatings can also be integrated to achieve the best cutting effect and meet the needs of cutting processing.
E.g. TiN has low friction characteristics, which can reduce the loss of coating structure, TiCN can reduce the wear of flank, TiC coating has higher hardness, and Al2O3 coating has excellent thermal insulation effect. Compared with cemented carbide cutting tools, coated carbide cutting tools are greatly improved in terms of strength, hardness and wear resistance. For workpieces with a hardness of HRC45~55, low-cost coated cemented carbide can realize high-speed turning. In recent years, some manufacturers have applied methods such as improving coating materials, which have greatly improved the performance of coated tools. For example, some manufacturers in the United States and Japan use the Swiss AlTiN coating material and the new coating patent technology to produce coated inserts with a hardness of HV4500~4900, which can cut die steel with a hardness of HRC47~58 at a speed of 498.56m/min. When the turning temperature is as high as 1500~1600°C, the hardness does not decrease or oxidize, and the blade life is 4 times that of the general coated blade, and the cost is only 30%, and the adhesion is good. Ceramic materials With the continuous improvement of its composition and pressing process, especially the progress of nanotechnology, the toughening of ceramic tools has become possible. In the near future, ceramics may cause cutting after high-speed steel and cemented carbide. The 3rd revolution in processing.
Ceramic cutting tools have the advantages of high hardness (HRA91~95), high strength (bending strength of 750~1000MPa), good wear resistance, good chemical stability, good anti-bonding performance, low friction coefficient and low price. Not only that, ceramic tools also have high high temperature hardness, reaching HRA80 at 1200°C. During normal cutting, the ceramic tool has extremely high durability, and the cutting speed can be increased by 2 to 5 times compared with cemented carbide. It is especially suitable for high-hardness material processing, finishing and high-speed machining. It can cut all kinds of hardened steel and hardened cast iron with a hardness of HRC65. Wait. Commonly used are: alumina-based ceramics, silicon nitride-based ceramics, cermets and whisker toughened ceramics.
Alumina-based ceramic tools have higher red hardness than cemented carbide. Under high-speed cutting, the cutting edge generally does not produce plastic deformation, but its strength and toughness are very low. In order to improve its toughness and impact resistance, it is usually possible to Add ZrO or a mixture of TiC and TiN, another way is to add pure metal or silicon carbide whiskers. In addition to high red hardness, silicon nitride-based ceramics also have good toughness. Compared with alumina-based ceramics, its disadvantage is that it is prone to high temperature diffusion when machining steel, which aggravates tool wear. Silicon nitride-based ceramics are mainly used in Intermittent turning of grey cast iron and milling of grey cast iron. Cermet is a carbide-based material, in which TiC is the main hard phase (0.5~2μm), which is combined by Co or Ti binder, and is a kind of tool similar to cemented carbide. But it has low affinity, good friction and good wear resistance. It can withstand higher cutting temperatures than conventional cemented carbide, but it lacks the impact resistance of cemented carbide, the toughness during strong cutting, and the strength at low speed and high feed.
In recent years, through a lot of research, improvement and the adoption of new production processes, its bending strength and toughness have been greatly improved. The new CT series and coated cermet blade series, the diameter of the grain structure is as small as 1μm, and the bending strength and wear resistance are much higher than ordinary cermets, which greatly broadens its application range. Cubic boron nitride (CBN) CBN is second only to diamond in hardness and wear resistance, and has excellent high temperature hardness. Compared with ceramics, its heat resistance and chemical stability are slightly worse, but its impact strength and crush resistance are better. Okay. It is widely used in the cutting of hardened steel (HRC≥50), pearlitic gray cast iron, chilled cast iron and superalloy, etc. Compared with cemented carbide tools, its cutting speed can be increased by an order of magnitude.
The composite polycrystalline cubic boron nitride (PCBN) tool with high CBN content has high hardness, good wear resistance, high compressive strength and good impact toughness. Its disadvantages are poor thermal stability and low chemical inertness. It is suitable for heat-resistant alloys, Machining of cast iron and iron-based sintered metals. The content of CBN particles in PCBN tools is low, and ceramics are used as binders, which have low hardness, but make up for the poor thermal stability and low chemical inertness of the former material, and are suitable for cutting hardened steel.
Residual stress in cutting hardened steel with ceramic and PCBN tools When cutting gray cast iron and hardened steel, ceramic tools or CBN tools can be selected. For this reason, a cost-benefit and machining quality analysis should be carried out to determine which one to choose. Figure 3 shows the flank wear of Al2O3, Si3N4 and CBN tools machining gray cast iron. The cutting performance of PCBN tool materials is better than that of Al2O3 and Si3N4. However, in dry cutting of hardened steel, the cost of Al2O3 ceramics is lower than that of PCBN materials. Ceramic knives have good thermochemical stability, but not the toughness and hardness of PCBN knives. When the cutting hardness is lower than HRC60 and the small feed rate is used, the ceramic tool is a better choice. PCBN tools are suitable for cutting workpieces with a hardness higher than HRC60, especially in automated machining and high-precision machining.
In addition, under the same flank wear condition, the residual stress on the workpiece surface after cutting by PCBN tool is also relatively stable than that of ceramic tool. Dry cutting of hardened steel with PCBN tools should also follow the following principles: select a large depth of cut as far as the rigidity of the machine tool allows, so that the heat generated in the cutting area can locally soften the metal in the front edge area, which can effectively reduce the wear of the PCBN tool. , When the depth of cut is small, it should also be considered that the PCBN tool has poor thermal conductivity, which makes the heat in the cutting zone too late to diffuse, and the shear zone can also produce a significant metal softening effect to reduce the wear of the cutting edge.
Blade structure and geometric parameters of superhard tool The reasonable determination of blade shape and geometric parameters is crucial to give full play to the cutting performance of the tool. In terms of tool strength, the cutting edge strengths of various blade shapes from high to low are: circle, 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 inserts should also choose the largest tool nose arc radius as possible, and use round and large nose arc radius inserts for rough machining. The tool nose arc radius during finishing is about 0.8 μm. Hardened steel chips are red and soft ribbon-like, brittle, easy to break, and non-stick. It is larger than the main cutting force, so the tool should adopt a negative rake angle (go≥-5°) and a larger clearance angle (ao=10°~15°). The entering angle depends on the rigidity of the machine tool, and is generally 45°~60° to reduce the chattering of the workpiece and the tool. The selection of cutting parameters of super-hard tool and the requirements of the process system The higher the hardness of the workpiece material, the smaller the cutting speed should be. The suitable cutting speed range for hard turning finishing with super-hard tools is 80-200m/min, and the common range is 10-150m/min; when using large depth of cut or strong intermittent cutting of high-hardness materials, the cutting speed should be maintained at 80-100m /min. Under normal circumstances, the depth of cut is between 0.1 and 0.3 mm. For workpieces with low surface roughness, a small depth of cut can be selected, but it should not be too small and should be appropriate. The feed rate can usually be selected between 0.05 and 0.25mm/r, and the specific value depends on the surface roughness value and productivity requirements. When the surface roughness Ra = 0.3 ~ 0.4μm, the use of superhard tools for hard turning is much more economical than grinding.
In addition to the selection of reasonable tools, the use of superhard tools for hard turning has no special requirements on lathes or turning centers. If the rigidity of the lathe or turning center is sufficient, and the required accuracy and Surface roughness, ready for hard cutting. In order to ensure a smooth and continuous turning operation, the usual method is to use a rigid clamping device and a medium rake angle tool. If the workpiece can be positioned, supported and rotated relatively smoothly under the action of cutting force, the existing equipment can use superhard tools for hard turning. The application of superhard tools in hard turning Superhard tools are used for hard turning. After more than ten years of development and popularization and application, this technology has obtained huge economic and social benefits. The following takes industries such as roll processing as an example to illustrate the popularization and application of superhard cutting tools in production.
In the roll processing industry, many large domestic roll enterprises have used superhard tools to carry out rough turning, rough turning and finishing turning of various types of rolls such as chilled cast iron and hardened steel, and have achieved good benefits. The average processing efficiency is increased by 2 to 6 times. , saving processing time and electricity by 50% to 80%. For example, when the roll factory of Wuhan Iron and Steel Company makes rough turning and semi-finishing of chilled cast iron rolls with a hardness of HS60-80, the cutting speed is increased by 3 times. One roll per car saves more than 400 yuan in electricity and labor costs, and saves tools. Cost nearly 100 yuan, and achieved huge economic benefits. For example, when our school uses FD22 cermet tool to turn 86CrMoV7 hardened steel rolls of HRC58～63 (Vc=60m/min, f=0.2mm/r, ap=0.8mm), the single-edge continuous cutting roll path reaches 15000m (tool tip The maximum width of the flank wear belt VBmax=0.2mm), which meets the requirements of turning grinding instead of grinding. In the industrial pump processing industry, 70% to 80% of the domestic ballast slurry pump manufacturers have adopted superhard tools.Ballast slurry pumps are widely used in mining, electric power and other industries, and are urgently needed products at home and abroad. In the past, due to the difficulty of turning this material with various tools, the process of annealing and softening, roughing, and then quenching was used. After adopting the super-hard tool, one-time hardening processing is successfully realized, which eliminates the two processes of annealing and quenching, and saves a lot of man-hours and electricity.
In the processing of crankshafts, camshafts, transmission shafts, cutting tools, measuring tools and equipment maintenance in the automobile, tractor and other industries, the automobile processing industry often encounters the processing problems of hardened workpieces. For example, a locomotive and rolling stock factory in my country needs to process the inner ring of the bearing during equipment maintenance. The hardness of the inner ring of the bearing (material GCr15 steel) is HRC60, and the diameter of the inner ring is f285mm. The grinding process is used, and the grinding allowance is uneven. It takes 2 hours to grind it well; and the superhard tool is used first, and it takes only 45 minutes to process an inner ring.