Oil Screw Compressor,Oil Injected Rotary Screw Compressor,Oil-Flooded Screw Compressors,Oil Flooded Rotary Screw Compressor Yantai Weisheng Machinery&Electric Engineering Co.,Ltd , https://www.wilson-airpart.com
0 INTRODUCTION The final processing of hardened rolls was often completed by grinding. The grinding process is not only inefficient, but also the cutting fluid used will pollute the environment and affect the operator's health. Therefore, the use of dry The hard dry machining of hardened rolls by cutting tools has become a hot topic of research and application. The dry cutting of hardened rolls achieves a vehicle-generation grinding process, which increases the machining efficiency by 5 to 10 times and avoids the environmental pollution. It is a highly efficient and clean process method that is compatible with green manufacturing and clean production modes. Application prospects. 1 Dry cutting hardened roll tool material and its selection of ceramic material ceramic tool with high hardness (HRA91 ~ 95), high strength (bending strength of 750 ~ 1 000 MPa), good wear resistance, chemical stability, Good anti-adhesive properties, low friction coefficient and low cost. The ceramic tool also has a very high temperature hardness, which reaches HRA80 at 1,200°C. In normal use, ceramic tools have a high degree of durability, and the speed can be increased by 2 to 5 times than that of cemented carbide. It is especially suitable for high-hardness materials processing, finishing and high-speed machining, and various hardness steels and hardened cast irons with hardness up to HRC65 can be processed. . Commonly used alumina-based ceramics, silicon nitride-based ceramics, metal ceramics and whisker toughened ceramics. Alumina-based ceramic tools have higher red hardness than hard alloys. In high-speed cutting, the cutting edge generally does not undergo plastic deformation, but its strength and toughness are very low. To improve its toughness and improve its impact resistance, it is usually Zirconium oxide or a mixture of TiC and TiN can be added to the process. Another method is to add silicon carbide whiskers. Silicon nitride-based ceramics have a high toughness in addition to red, but also have good toughness, compared with alumina-based ceramics, its drawback is that when the processing of steel is easy to produce high temperature diffusion, exacerbated tool wear, silicon nitride-based ceramics are mainly used Discontinuously turning grey cast iron and milling grey cast iron. The cermet is a carbide based material with TiC as the main hard phase (0.5-2 μm). They are bonded together with Co or Ti binders and are similar to cemented carbide tools, but it Has low affinity, good friction and good abrasion resistance. It can withstand higher cutting temperatures than conventional cemented carbides, but it lacks the impact resistance of hard alloys, toughness during heavy processing, and strength at low feed rates. In recent years, through a great deal of research, improvement, and adoption of new manufacturing processes, the bending strength and toughness of ceramic materials have been greatly improved, such as the development of a new type of metal ceramic NX2525 developed by Mitsubishi Metals of Japan and developed by Sandvik Sweden. The new CT series of ceramic metal inserts and coated metal ceramic inserts series, the diameter of its grain structure is as small as less than 1μm, bending strength and wear resistance are much higher than ordinary cermets, greatly broadening the application of ceramic materials . The hardness and wear resistance of CBN CBN is second only to diamond, and it has excellent high-temperature hardness. Compared with ceramic tools, its heat resistance and chemical stability are slightly inferior, but impact strength and crush resistance are better. It is widely used in the cutting of hardened steels (above HRC50), pearlite grey cast irons, chilled cast irons and superalloys. Compared with cemented carbide tools, the cutting speed can be increased by an order of magnitude. The 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 inertness. They are suitable for cutting heat-resistant alloys, cast irons and iron-based sintered metals. . The composite PCBN tool has a lower content of CBN particles, and uses ceramics as a binder, which has a low hardness, but makes up for the poor thermal stability and low chemical inertness of the former material, and is suitable for the cutting and processing of hardened steel. The use of PCBN tools dry cutting hardened rolls should also follow the following principles: When the rigidity of the machine allows, choose a large depth of cut as possible, so that the heat generated in the cutting area makes the metal in the front area soften, which can effectively reduce the wear of PCBN tools. In the case of small depth of cut, the thermal conductivity of the PCBN tool should also be taken into account so that the heat in the cutting zone is too late for diffusion, and the shear zone can also produce a significant metal softening effect and reduce the wear of the cutting edge. The proper configuration of the blade geometry and geometric parameters to determine the shape of the blade and the geometric parameters are critical to the full play of the cutting performance of the tool. In terms of tool strength, the blade tip strengths of various blade shapes were: round, 100° diamond, square, 80° diamond, triangle, 55° diamond, and 35° diamond. After the blade material is selected, the blade shape with the highest possible strength should be selected. Hard turning inserts should also select the largest possible tip arc radius, rough machining with round and large radius blades, and the radius of the tool tip during finishing is approximately 0.8 μm. Hardened steel cuttings are red and soft forging belts, brittle, easy to break, do not stick, generally do not produce built-up edge on the cutting surface, the surface quality of processing is high, but the hardened steel cutting force is relatively large, especially The radial cutting force is even larger than the main cutting force, so the tool should adopt negative rake angle (g0≥-5°) and large relief angle (a0=10～15°). The main deviation angle depends on the rigidity of the machine tool. Take 45 ~ 60 °, to reduce workpiece and tool chatter. 2 Dry cutting hardened roll cutting parameters and its requirements for the processing system cutting parameters selection Hardened roll material hardness is higher, the cutting speed should be smaller. The suitable cutting speed range for hard turning finishing using dry cutting tools is 80 to 200 m/min, and the usual range is 100 to 150 m/min. When using deep cutting depth or strong intermittent cutting, the cutting speed should be maintained at 80-100m/min. Under normal circumstances, the back knife is between 0.1 and 0.3mm. When machining surface roughness is high, a small cutting depth can be selected, but it should not be too small. The feed rate can usually be selected between 0.05 and 0.25mm/r, depending on the surface roughness value and productivity requirements. When the surface roughness is Ra0.6 ~ 0.8μm, hard cutting using a dry cutting tool is much more economical than grinding. The requirements of the process system In addition to the choice of a reasonable tool, the use of dry cutting tools for hard turning of the lathe or turning center has no special requirements, if the lathe or turning center is sufficiently rigid, and the soft workpiece can be processed when required Accuracy and surface roughness can be used for hard cutting. Due to the large radial force when machining hardened rolls, this requires a larger machine power and a better rigidity of the machine system, which can both protect the dry cutting tools and obtain satisfactory machining results. In order to ensure a smooth and continuous turning operation, a common method is to use a rigid clamping device and a medium front angle tool. If the roll is positioned, supported, and rotated under cutting forces, it can remain fairly smooth. Existing equipment can use dry cutting tools for hard turning. 3 Problems to be Noted in Dry Cutting Hardened Rolls Dry cutting Hardened rolls do not use cutting fluid because a large amount of heat will be carried away by the chips during the cutting process, and thermal damage and thermal deformation will rarely occur on the surface of the workpiece. Conversely, using coolant can adversely affect tool life and surface quality. The fine-grained inserts are preferably made of high-strength square and circular inserts. Although the cutting force is increased, the roughness value is smaller and the surface quality is better. After grinding blunt, change the blade to change position. A diamond blade can also be used with a nose radius of 0.5 to 1 mm. Dry cutting tools for low-speed cutting (such as v <50m/min), not only similar to the cutting performance of cemented carbide, but also easily cause the vibration of the process system, so that the tool chipping, or even cutting. When high speed cutting is performed within a certain speed range, the increase of cutting temperature will also change the performance of the workpiece material and increase the toughness of the dry cutting tool, thereby reducing its damage. However, if the cutting speed is increased too much during intermittent cutting, the temperature difference will be great, and the resulting thermal stress can also cause the tool to break. The influence of the feed rate on the tool breakage is greater than the cutting speed. Selecting a smaller feedrate will help prevent or reduce the damage to the tool. Therefore, a smaller feed rate and the highest possible cutting speed should be used for dry cutting tools. When the dry cutting tool is installed, the tool's overhang length must be as short as possible to prevent chatter and deformation of the cutter bar, so that the dry cutting tool can maintain a good machining state. For high hardness and irregular workpieces, dry cutting tools are fragile and afraid of impact. When the cutting tool is cut into and cut out from the end face of the workpiece, especially the surface has irregularities, the impact is most likely to occur, the cutting edge is broken, and the durability is reduced. Therefore, before using the dry cutting tool, it is better to chamfer the cutting end of the workpiece to reduce the tool impact force. The chamfering of the blank cut-in can avoid excessive impact load when the tool just touches the workpiece. The chamfering at the cut-out of the blank is mainly to prevent the tool edge from being broken when the tool cuts away from the part. In order to use the dry cutting tool very well, it is important to control the workpiece quality stably and accurately determine the durability of the dry cutting tool. If a tool with severe wear has been used, the cutting force and cutting temperature increase, and the cutting is not smooth, it is difficult to control the size of the workpiece and the surface integrity, even if the dry cutting tool can not continue grinding and scrapped. In order to ensure the normal use of the tool, it is recommended that the flank wear of the dry cutting tool be 0.3 to 0.6 mm (small value when finishing the car). However, re-grinding requires a certain amount of equipment and techniques. Most factory machines do not have suitable conditions. The re-grinding of general dry-cutting tools should be done by a professional factory.