Surface quality analysis of the hottest coated cut

2022-08-04
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Surface quality analysis of coated tools

the coated tool surface shall be a bright polished surface, and each working surface of the tool shall be free of rust, grinding paste, oxidation, edge collapse and other defects, and the edge shall be free of burrs. The surface roughness on the front and rear cutting surfaces shall reach RA 0.8~1.25 μ m。 The smaller the surface roughness, the better the adhesion of the coating. In addition, the cleaning quality of the tool surface is also very important

tool base material

the base material and coating material of coated tools shall be reasonably matched and selected according to different processing requirements. The matrix of coated high-speed steel tools can be either general-purpose high-speed steel W6Mo5Cr4V2 (M2), superhard high-speed steel containing cobalt and powder metallurgy high-speed steel (PM HSS). Because the matrix of powder metallurgy is uniform, the application effect is good. When machining titanium alloy, it is recommended to use cobalt containing superhard high speed steel such as w2mo9cr4vco8 (M42) as the base material of cutting tools. For the coated hob, when the gear is processed at the normal cutting speed (45m/min), the main reason for the wear of the hob is the broken edge. Therefore, W6Mo5Cr4V2 high speed steel with good toughness should be selected as the foundation for Zhongwang to enter the aircraft manufacturing field; Base material of cutting tools in 2015; In high-speed gear hobbing (cutting speed is greater than 100m/min), the main cause of hob wear is crescent wear. Therefore, cobalt containing superhard high-speed steel or cw9mo3cr4vn high-speed steel with high heat resistance and wear resistance should be selected as the base material of the tool

for the matrix of coated cemented carbide tools, when processing steel, it is appropriate to select cemented carbide for processing steel, such as WC tic Co or WC tic tac Co alloys (P30 is more used 98.07); When processing cast iron and non-ferrous metals, WC Co alloys should be selected (K20 is used more)

the hardness and machinability of the processed material also have a certain impact on the use effect of coated tools. It is proved that the coated tool is most suitable for cutting difficult to machine materials such as high hardness and wear-resistant alloys

geometric angle of the tool

due to the good lubricity of the coating, the coated tool often slips on the surface of the workpiece. Therefore, the back angle of the coated tool should be slightly larger than that of the uncoated tool. The practice shows that for reamers and other finishing tools, increasing the back angle can make the cutting edge sharp, the chip formation easy, the slip phenomenon is obviously reduced, and the service performance of the tools is improved

cutting parameters and cutting fluid

in order to give full play to the performance of coated tools, cutting parameters and cutting fluid must be selected correctly. Because the coated tool has good heat resistance and strong ability to resist crater wear, it can work with a large feed rate and cutting speed, but a large feed rate should be selected first. Generally, the feed rate of coated high-speed steel tools is 10%~100% higher than that of uncoated tools, and the cutting speed of 20%~30% higher is appropriate. In order to improve work efficiency, coated carbide tools can also be cut at a cutting speed 25%~70% higher than uncoated tools. At present, when machining medium carbon structural steel with coated carbide general-purpose tools, the cutting speed of end mills can reach 100~150m/mi, and the pulling force range of 100 Newton is enough n, and the drill bit can reach 80~100m/min; Cast iron processed by tap is 20~40m/min

practice has proved that the service life of coated high-speed steel boring cutter can be increased by 1~2 times when using No. 20 machine oil and 10% kerosene for cooling. When tin coated high-speed steel hob is used to process 20CrMnTi (197hbs) steel helical cylindrical gear (modulus m=5), using No. 20 mechanical oil and kerosene for mixed lubrication, the service life of the tool can be increased by about 5 times, even after regrinding, it can be increased by 2~3 times, and the service life can only be increased by 1 time during dry cutting

when using coated tools, it is also required that the machine tool should have good accuracy, high rigidity and low vibration, and the clamping of tools or blades should also be firm

Regrinding and recoating of coated tools regrinding must be carried out after the coated tools are worn. When regrinding the coated tool, all the worn parts on the tool must be worn off. For tools that only need to regrind the front face (such as broach, gear hob and gear shaper cutter) or tools that only need to regrind the back face (such as drill bit and reamer), if the coating on the other face adjacent to the cutting edge (such as the spiral chip discharge groove of the drill bit) is not damaged, the tool wear resistance can be improved. Compared with developing countries, the service life of coated tools after regrinding can reach about 50% or more of the service life of new coated tools, which is still higher than that of uncoated tools

diamond wheel can be used for grinding coated carbide tools. However, cubic boron nitride (CBN) grinding wheel has better effect when grinding coated high speed steel tools. The worn parts of the tool shall be completely removed, and the coating shall not peel off, nor shall the tool be annealed

an important problem in using coated tools is the restoration of cutting performance of the tool after regrinding, that is, whether the tool can be coated (recoated) again after each grinding (opening). For regrinding forming tools, only recoating can ensure that the total service life of the tool is increased by more than 3~5 times. All recoated cutters must first be ground according to the process requirements, and the polished part is not allowed to have various quality defects, such as grinding paste, burr, etc. During recoating, local shielding technology can be used to coat only the grinding surface. For recoating without shielding technology, after recoating for 4~6 times, the coating thickness of the non grinding surface of the tool will be too large, which will affect the accuracy of the tool and produce local peeling phenomenon. At this time, the tool shall be recoated after the film removal treatment. The cutting performance of the tool after recoating is generally not lower than that of the tool newly coated for the first time. The tool can be recoated many times until it is scrapped

it can be seen from the above that recoating has great potential to improve tool wear resistance and productivity. However, whether the tool needs to be repainted after regrinding depends on whether the tool can be repainted technically and economically

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