The Use Effect Of Coating Tools

The use effect of coating tools

In addition to coating methods and equipment, coating process, and coating materials, the use effect of coating tools should be noted as follows:

1. The surface quality of the tool before coating. The surface of the tool to be coated should be a bright polished surface. There should be no defects such as rust spots, abrasion, oxidation, chipping, etc. on the working surface of the tool, and no burrs on the cutting edge. The surface roughness on the front and flank surfaces should reach Ra<0.8~1.25µm. The smaller the surface roughness value, the better the bonding of the coating. In addition, the cleaning quality of the tool surface is also very important.

2. Tool base material. The base material and coating material of the coated tool should be reasonably matched, and it must be selected according to different processing requirements. The substrate of the coated high-speed steel tool can be made of W6Mo5Cr4V2 (M2) general-purpose high-speed steel, cobalt-containing super-hard high-speed steel, and powder metallurgical high-speed steel (PM HSS), or made of cemented carbide tungsten steel as a whole Tungsten steel blade. Due to the uniform matrix of powder metallurgy, the use effect is good. When processing titanium alloys, it is recommended to use cobalt-containing super-hard high-speed steel such as W2Mo9Cr4VCo8 (M42) as the base material of the tool. For coated hobs, when gears are processed at normal cutting speeds (less than 45m/min), chipping is the main cause of hob wear. Therefore, W6Mo5Cr4V2 high-speed steel with better toughness should be selected as the base material of the tool; When hobbing (cutting speed is greater than 100m/min), crescent crater wear is the main cause of hob wear. Therefore, cobalt-containing super-hard high-speed steel or CW9Mo3Cr4VN high-speed steel with higher heat resistance and wear resistance should be used as the tool matrix Material. For the matrix of coated cemented carbide tools, when processing steel, it is advisable to choose the cemented carbide of the processed steel, such as WC-TiC-Co or WC-TiC-TaC-Co alloys (P30 is used more); for processing cast iron and For 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 effect on the use of coated tools. Tests have confirmed that coated tools are most suitable for cutting difficult-to-machine materials such as high-hardness and wear-resistant alloys.

Third, the geometric angle of the tool. Due to the good lubricity of the coating, the coated tool will often slip on the surface of the workpiece when working. For this reason, the relief angle on the coated tool should be slightly larger than that of the uncoated tool. The practice has shown that for a class of finishing tools such as reamers, after increasing the relief angle, the cutting edge can be sharpened, chip formation is easy, the slipping phenomenon is significantly reduced, and the use performance of the tool is improved.

4. Cutting amount and cutting fluid. In order to give full play to the performance of the coated tool, the cutting amount and cutting fluid must be selected correctly. Coated tools have good heat resistance and strong anti-crescent wearability, so they can work with a larger feed rate and cutting speed, but a larger feed rate should be selected first. Generally, the feed rate of coated high-speed steel tools is increased by 10% to 100% than that of uncoated tools, and it is appropriate to increase the cutting speed by 20% to 30%. In order to improve work efficiency, coated carbide tools can also be cut at a cutting speed that is 25% to 70% higher than that of uncoated tools. The cutting speed when machining medium carbon structural steel with coated carbide general-purpose tools is 100~150m/min for end mills, 80~100m/min for drills, and 20~40m/min for taps for cast iron. The practice has proved that when using No. 20 machine oil and 10% kerosene for cooling, the life of the coated high-speed steel boring tool can be increased by 1 to 2 times. When machining 20CrMnTi (197HBS) steel helical cylindrical gears (modulus m=5) with TiN-coated high-speed steel hobs, using 20# mechanical oil and kerosene mixed lubrication, the tool life can be increased by about 5 times, even after regrinding It can be increased by 2 to 3 times, and the life span during dry cutting is only increased by 1 time. [pre] The use of coated tools also requires the machine tool to have good precision, high rigidity, and low vibration, and the clamping of the tool or blade should also be firm.

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