Application of the most popular dry cutting tool i

2022-08-05
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The application of dry cutting tools in the processing of roll

0 preface

the final processing of hardened roll used to be completed by grinding. Grinding is not only inefficient, but also the cutting fluid used will bring pollution to the environment and affect the health of the operator. Therefore, the use of dry cutting tools in the hard dry cutting of hardened roll has become a hot spot of research and application at present. The dry cutting of hardened roll has realized turning instead of grinding, the machining efficiency has been increased by 5 ~ 10 times, and environmental pollution can be avoided. It is an efficient and clean process method, which conforms to the green manufacturing and clean production mode, and has a wide application prospect

1 dry cutting hardened roll cutter

it is necessary to set the tensile speed in strict accordance with the test standard. The cutter material and its selection

ceramic material

ceramic cutter has 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 very high high temperature hardness, which reaches hra80 at 1200 ℃. When in normal use, the ceramic tool has a very high durability, and the speed can be 2 ~ 5 times higher than that of cemented carbide. It is especially suitable for machining high hardness materials, finishing and high-speed machining. It can process 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 of 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 in heavy machining and the strength in low speed and large feed. In recent years, the bending strength and toughness of ceramic materials have been greatly improved through a large number of research, improvement and adoption of new manufacturing processes. For example, the new type of cermet nx2525 developed by Mitsubishi metal company of Japan and the new type of cermet blade CT series and coated cermet blade series developed by Sandvik company of Sweden have a fine grain structure with a diameter of less than 1 m, and the bending strength and wear resistance are much higher than ordinary cermets, The application range of ceramic materials is greatly broadened

cbn

cbn is second only to diamond in hardness and wear resistance, and 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 high-temperature alloy. Compared with cemented carbide tools, its cutting speed can be increased by an order of magnitude

The PCBN tool with high CBN content has high hardness, good wear resistance, high compressive strength and impact toughness. Its disadvantages are poor thermal stability and low chemical inertia. It is suitable for cutting heat-resistant alloy, cast iron and iron series sintered oil return pipe without oil flowing out of metal. The content of CBN particles in the composite PCBN tool 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. It is suitable for cutting hardened steel

the dry cutting of hardened roll with PCBN tool should also follow the following principles: select a large cutting depth as far as possible under the condition that the rigidity of the machine tool allows, so that the heat generated in the cutting area will soften the metal in the front edge area, which can effectively reduce the wear of PCBN tool. In addition, in the case of a small cutting depth, it should also consider the poor thermal conductivity of PCBN tool, 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

determination of blade structure and geometric parameters

reasonable determination of blade shape and geometric parameters is very important to give full play to the cutting performance of the tool. In terms of tool strength, the tool tip strength of various blade shapes from high to low are: round, 100 diamond, square, 80 diamond, triangle, 55 diamond and 35 diamond. After the blade material is selected, the blade shape with the highest strength shall be selected. For hard turning blades, the radius of the tool tip arc should also be as large as possible. Rough machining should be carried out with circular and large radius blades. 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 greater than the main cutting force. Therefore, 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

selection of cutting parameters

the higher the hardness of the hardened roll material, the lower the cutting speed. A large number of scholars are still studying hard. 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 large cutting depth or strong intermittent cutting is adopted, the cutting speed shall be kept at 80 ~ 100m/min. In general, the back cutting distance is 0.1 ~ 0.3mm. When the machining surface roughness is required to be high, a small cutting depth can be selected, but it should not be too small, and it should be appropriate. Generally, the feed rate can 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

requirements for process system

in addition to selecting reasonable tools, there are no special requirements for the lathe or turning center to use dry cutting tools for hard turning rollers. If the rigidity of the lathe or turning center is sufficient and the required accuracy and surface roughness can be obtained when machining soft workpieces, it can be used for hard cutting. Due to the large radial force when Machining Hardened rolls, the machine tool power is required to be large and the machine tool system is 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 positioning, support and rotation of the roll can be kept quite stable under the action of cutting force, 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 select 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, the blade can be shifted. The diamond blade can also be selected, and the radius of the blade tip is between 0.5 ~ 1mm

when the dry cutting tool is used for low-speed cutting (e.g. V 50m/min), it is not only similar to the cutting performance of cemented carbide, but also easy to cause the vibration of the process system, causing the tool to collapse or even unable to cut. In a certain speed range of high-speed cutting, the increase of cutting temperature will also change the properties of workpiece materials, improve the toughness of dry cutting tools, and reduce their damage. However, in intermittent cutting, if the cutting speed is increased too much, the temperature difference will be large, and the thermal stress will also lead to tool damage

the feed rate has a greater impact on tool breakage than the cutting speed. Choosing a smaller feed rate is helpful to prevent or reduce tool breakage. Therefore, the dry cutting tool should be selected with small feed rate and as high cutting speed as possible

when clamping the dry cutting tool, the overhang length of the tool should be as short as possible to prevent the chatter and deformation of the tool bar and keep the dry cutting tool in a good processing state

for workpieces with high hardness and irregularity, the dry cutting tool is brittle and afraid of impact. When the cutter cuts in and out from the end face of the workpiece, especially when the surface is uneven, it is most likely to have impact, and the edge is broken, reducing the durability. Therefore, before using the dry cutting tool, it is best to chamfer the cutting end of the workpiece to reduce the impact of the tool. The chamfering at the blank cut-in can avoid the tool from bearing excessive impact load when it just contacts the workpiece. The chamfering at the cut-out part of the blank is mainly to avoid the damage of a circle of material edges left when the tool cuts away from the part

in order to use dry cutting tools well, it is very important to stably control the workpiece quality and accurately judge the durability of dry cutting tools. If the tool with serious wear as described above is used all the time to ensure the size of the outer diameter of the product cable, it will be difficult to control the size and surface integrity of the workpiece if the cutting force and cutting temperature increase and the cutting is not smooth, and even the dry cutting tool will be scrapped due to the inability to continue grinding. In order to ensure the normal use of the tool, it is recommended that regrinding should be carried out when the wear of the back face of the dry cutting tool reaches 0.3 ~ 0.6mm (the smaller value is taken during finishing). However, regrinding requires certain equipment and skills. The machine tools of most factories do not have appropriate conditions. Generally, regrinding of dry cutting tools should be completed by professional factories

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