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(min) Surface roughness Ra
Îœm Vc
(m/min) f
Mm/r HB240
(annealing) 45 to 55 0.1 90 to 115 6.3 to 3.2 HRC 25 to 30
(conditioning) 45-55 0.1 95-110 3.2 HRC35-38
(Quenched and tempered) 45-55 0.1 60-75 3.2 Table 2 Cutting performance of several types of tool materials Comparison Material Hardness Cutting amount Tool durability T
(min) Surface roughness Ra
Îœm Vc
(m/min) f
Mm/r YG8 45-55 0.1 72-82 3.2 YT14 45-55 0.1 80-95 3.2 YW2 45-55 0.1 90-110 3.2
6.3 (cut off) TiC-TiCN-TiN 45 to 55 0.1 128 to 185 3.2 to 1.6 Use of heat treatment to change the hardness of the material Martensitic stainless steels have different hardness after heat treatment and have a great influence on turning. Table 1 shows the turning of different hardness 3Cr13 steels after heat treatment using a YW2 turning tool. It can be seen that the annealed martensitic stainless steel has low hardness but poor turning performance. This is due to the material's plasticity and toughness, non-uniform microstructure, strong adhesion, easy to produce cuttings in the cutting process, and difficult to obtain good surface quality. . The 3Cr13 material with a hardness below the HRC30 after quenching and tempering process has good processability and easy to achieve a good surface quality. However, if the hardness is greater than that of HRC30, the surface quality is better, but the tool is easy to wear. Therefore, after the material enters the factory, it is first quenched and tempered. The hardness reaches HRC 25 to 30, and then the cutting process is performed. The choice of tool material The cutting performance of the tool material is related to the tool's durability and productivity. The tool material's processability affects the tool's own manufacturing and sharpening quality. Therefore, the tool material should choose high hardness, good adhesion and toughness. Under the same cutting parameters, the author carried out comparative turning tests on several kinds of materials. From Table 2, it can be seen that the outer turning tool with TiC-TiCN-TiN composite coated blades has a high durability and a high surface quality. Well, productivity is high. This is because the coated hard alloy blade has better strength and toughness, and because the surface has higher hardness and wear resistance, smaller friction coefficient and higher heat resistance, and It is a good tool material for turning stainless steel on CNC lathes and it is the material of choice for turning 3Cr13 stainless steel turning tools. Since there is no cutting blade of this material, the comparison test of Table 2 shows that the cutting performance of YW2 cemented carbide is also good, so the blade of YW2 material can be selected as the cutting blade. Tool geometry and structure selection For good tool materials, choosing a reasonable geometric angle is especially important. When processing stainless steel, the geometry of the cutting part of the tool should generally be considered in terms of the choice of front and rear corners. When selecting the rake angle, factors such as the shape of the chip groove, the presence or absence of chamfering, and the angle of the positive and negative angles of the rake angle should be considered. Regardless of the type of tool, the larger rake angle must be used when machining stainless steel. Increasing the rake angle of the tool can reduce the resistance encountered during swarf separation and removal. The selection requirements for the relief angle are not very strict, but should not be too small. When the relief angle is too small, it can easily cause serious friction with the workpiece surface, which can worsen the surface roughness and accelerate tool wear. And because of the strong friction, the effect of strengthening the surface hardening of the stainless steel T tool back angle should not be too large, the back corner is too large, so that the tool wedge angle decreases, reducing the cutting edge strength, accelerated tool wear. In general, the relief angle should be larger than when processing ordinary carbon steel. When turning martensitic stainless steel generally, it is appropriate to take the tool angle g0 from 10° to 20°. The posterior angle a0 is preferably 5° to 8°, and the maximum is not more than 10°. In addition, the blade angle ls, the negative blade angle can protect the blade tip and increase the blade strength. Generally, g0 is selected to be -10° to 30°. The main declination angle kr should be selected according to the shape of the workpiece, the machining position and the loading conditions. The edge surface roughness should be Ra 0.4-0.2 μm. In the tool structure, the outer circular turning tool adopts an external oblique circular arc chip breaker, the curl radius of the chip at the tip is large, the curl radius of the chip at the outer edge is small, the chip is turned to the surface to be machined and broken, and the chip breaking condition is good. . For the cutting knife, the sub-deflection angle can be controlled within 1°, which can improve the chip removal conditions and prolong the service life of the tool. Reasonable choice of cutting amount The amount of cutting has a great influence on the surface quality of the workpiece, the tool durability and the processing productivity. The cutting theory holds that the cutting speed V has the greatest influence on the cutting temperature and the tool durability, the feed rate f is the next, and the ap is the smallest. On the surface of a single pass machining on a CNC lathe, the depth of cut ap is determined by the workpiece size. It is generally 0 to 3mm depending on the material blank size. The cutting speed of difficult-to-machine materials is often much lower than the cutting speed of ordinary steels, because the increase in speed will cause severe tool wear, and different stainless steel materials have their own different optimal cutting speeds. This optimal cutting speed is only Can be determined by testing or consulting relevant information. When machining with a carbide tool, cutting speed V = 60 to 80 m/min is generally recommended. Feed rate f does not affect the tool life as much as the cutting speed, but it will affect chip breaking and chip evacuation, thus affecting the surface of the workpiece on the scratch, scratches, affecting the surface quality of the processing. When the surface roughness is not high, f is 0.1 to 0.2 mm/r. In short, for difficult-to-machine materials, generally lower cutting speeds are used, and the medium amount of cutting is used. The use of a suitable cooling lubricant for turning stainless steel cooling lubricants should have high cooling performance, high lubricating properties and good permeability. The high cooling performance ensures that a large amount of cutting heat can be taken away. The toughness of stainless steel is large, and it is easy to generate built-up edge when cutting, which deteriorates the processing surface. This requires the cooling lubricant to have higher lubricating performance and better permeability. The commonly used stainless steel cooling lubricating fluids are vulcanized oil, vulcanized soybean oil, kerosene oleic acid or vegetable oil, carbon tetrachloride, mineral oil, and emulsion. Considering that sulfur has a certain corrosion effect on the machine tool, vegetable oils (such as soybean oil) are easily attached to the machine and result in degeneration and deterioration. I chose a mixture of four-grid carbon and oil at a weight ratio of 1:9. Among them, the carbon permeability of the four grippers is good, and the lubrication of the engine oil is good. Tests have proved that this type of cooling lubricant is suitable for semi-finishing and finishing of stainless steel parts with low surface roughness requirements, and is particularly suitable for turning of martensitic stainless steel parts. After taking the above processing measures, the machining of 3Cr13 stainless steel has been completely normal. The number of honing times is only 1/3 of that in trial production, and the production efficiency is greatly improved. The quality of the parts fully meets the pattern requirements.
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Research on CNC Turning Process of 3Cr13 Stainless Steel
0 Introduction Although rough machining, semi-finishing and finishing machining of stainless steel materials on ordinary lathes are not too difficult. However, on high-productivity CNC lathes, how to solve the problems of large cutting force, high temperature, severe tool wear, low durability, poor surface quality, and low productivity in stainless steel cutting can be achieved in one cutting process. The requirements of the drawings are still not easy to achieve. In the process of machining 3Cr13 stainless steel material, the author conducted trial and error from the aspects of tool material selection, tool geometry, structure determination, selection of cutting amount, blank supply status, lubrication and coolant selection, and achieved certain results. success experience. 1 3Cr13 stainless steel CNC turning characteristics and analysis of stainless steel parts in the trial processing, first of all, according to the turning method of ordinary carbon steel 3Cr13 steel turning test, the result is a serious tool wear, low productivity, the surface quality of the parts can not meet the requirements. Comparing the mechanical properties of carbon structural steels such as 3Cr13 steel, 40 steel, and 45 steel, the strength, elongation, reduction of area, and impact performance of 3Cr13 steel are higher than that of No. 40 steel and No. 45 steel. High strength, good plasticity, medium carbon martensitic stainless steel. Due to severe work hardening during cutting, large cutting resistance, high cutting temperature, severe tool wear, increased number of sharpening, increased downtime and machine adjustment time, and reduced productivity. Because it is easy to stick the knife and generate built-up edge, it causes the change of workpiece size and affects the surface roughness, and the chip is not easy to curl and break, and it also damages the processed surface of the workpiece and directly affects the quality of the part. Therefore, it is not possible to cut 3Cr13 steel by cutting 45 steel. Nor can you copy the processing method on a common lathe to a CNC lathe. Because the CNC lathe generally has fewer knives, it requires that the machining surface can reach the required size and surface roughness with a minimum number of passes to ensure higher productivity. In response to the above problems, the author took the following processing measures. 2 Main machining process measures for turning 3Cr13 stainless steel Table 1 Turning conditions for different hardness 3Cr13 steel Material hardness Cutting capacity Tool durability T