The hottest dry cutting tool and its application i

Dry cutting tools and their application in processing rollers

preface

the final processing of hardened rollers used to be completed by grinding. Grinding is not only inefficient, but also the cutting fluid used will pollute the environment and affect the health of the author who has the practical value of application. Therefore, The use of dry cutting tools to measure the adhesion of two different materials has become a hot spot of research and application at present. The dry cutting of hardened roll realizes the replacement of grinding with turning, the processing efficiency is increased by 5 ~ 10 times, and environmental pollution can be avoided. It is an efficient and clean process method, which conforms to the mode of green manufacturing and cleaner production, and has a wide application prospect

1 dry cutting hardened roll tools

1) tool materials and their selection

a. ceramic materials

ceramic tools have the advantages of high hardness (hra91 ~ 95), high strength (bending strength of 750 ~ 1000 MPa), good wear resistance, good chemical stability, good adhesion resistance, low friction coefficient and low price. Ceramic cutting tools also have high high temperature hardness, reaching hra80 at 1200 ℃. When in normal use, ceramic tools are extremely durable, and the speed can be 2 ~ 5 times higher than that of cemented carbide. They are especially suitable for processing high hardness materials, finishing and high-speed processing, and processing all kinds of hardened steel and hardened cast iron with hardness up to HRC65. Alumina based ceramics, silicon nitride based ceramics, cermets and whisker toughened ceramics are commonly used. Alumina based ceramic tools have higher red hardness than cemented carbide. Generally, the cutting edge will not produce plastic deformation under high-speed cutting, but its strength and toughness are very low. In order to improve its toughness and impact resistance, zirconia or a mixture of tic and tin can be added on the one hand, and silicon carbide whiskers can be added on the other. 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 easy to produce high-temperature diffusion when machining steel, which intensifies tool wear. Silicon nitride based ceramics are mainly used in intermittent turning and milling gray cast iron. Cermet is a kind of carbide based material, in which tic is the main hard phase (0.5 ~ 2 m). They are combined by CO or Ti binder. It is a tool similar to cemented carbide, but it has low affinity, good friction and good wear resistance. It can withstand higher cutting temperature than conventional cemented carbide, but it lacks the impact resistance of cemented carbide, the toughness during heavy machining and the strength during low-speed and large feed. In recent years, through a lot of research, improvement and adoption of new manufacturing processes, the bending strength and toughness of ceramic materials have been greatly improved, such as the new type of cermet nx2525 developed by Mitsubishi metal company in Japan and the new CT series and coated cermet blade series developed by Sandvik company in Sweden. The diameter of grain structure is smaller than 1 m, and the bending strength and wear resistance are much higher than ordinary cermet, The application scope of ceramic materials has been greatly expanded

b. CBN

the hardness and wear resistance of CBN are second only to diamond, and it has excellent high-temperature hardness. Compared with ceramic tools, its heat resistance and chemical stability are slightly poor, but its impact strength and crushing resistance are better. It is widely used for cutting hardened steel (above HRC50), pearlitic gray cast iron, chilled cast iron and superalloys. Compared with cemented carbide tools, its cutting speed can be increased by an order of magnitude

the dry cutting of hardened rolls 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 softens the metal in the front edge area 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

2) determination of blade structure and geometric parameters

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 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. For hard turning blades, the radius of the tool tip arc should also be as large as possible. Rough machining with circular and large radius blades, and the radius of the tool tip during finish machining is about 0.8 M. Hardened steel chips are red and soft forged bands, which are brittle, easy to break, and non cohesive. Generally, there is no chip buildup on the cutting surface, and the machined surface quality is high. However, the cutting force of hardened steel is relatively large, especially the radial cutting force is larger than the main cutting force, so the tool should adopt a negative rake angle (G0 ≥ -5) and a large rake angle (a0=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

2 dry cutting hardened roll cutting parameters and their requirements for the process system

1) selection of cutting parameters

the higher the hardness of hardened roll material, the smaller the cutting speed should be. The suitable cutting speed range for hard turning finishing with dry cutting tools is 80 ~ 200m/min, and the common range is 100 ~ 150m/min. When using large cutting depth or strong intermittent cutting, the cutting speed should be maintained at 80 ~ 100M/min. In general, the amount of back cutting is between 0.1 ~ 0.3mm. The machining surface treatment efficiency is low, and when the roughness requirement is high, 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 is ra0.6 ~ 0.8 m, hard turning with dry cutting tools is much more economical than grinding

2) requirements for process system

in addition to selecting reasonable tools, there are no special requirements for lathes or turning centers to use dry cutting tools for hard turning rollers. If the rigidity of lathes or turning centers is sufficient and the required accuracy and surface roughness can be obtained when machining soft workpieces, they can be used for hard cutting. Because the radial force is very large when Machining Hardened rolls, it requires that the machine tool power should be large and the machine tool system should be rigid, which can not only protect the dry cutting tools, but also obtain satisfactory machining results. In order to ensure the stability and continuity of turning operation, the common method is to use rigid clamping device and medium rake tool. If the plastic of the roll under the action of cutting force has been more and more widely used, and the positioning, support and rotation in the medical field can be kept quite stable, the existing equipment can use dry cutting tools for hard turning

3 problems needing attention in dry cutting hardened rolls

dry cutting hardened rolls do not use cutting fluid, because a large amount of heat will be taken away by chips in the cutting process, and thermal damage and deformation will rarely occur on the workpiece surface. On the contrary, the use of coolant will adversely affect the tool life and surface quality

it is better to choose square and round blades with high strength for fine turning. Although the cutting force is increased, the roughness value is smaller and the surface quality is better. After blunt grinding, it is enough to rotate and change the blade. Diamond blade can also be selected, and the radius of the blade tip is between 0.5 ~ 1mm

when the dry cutting tool performs low-speed cutting (such as V