The processing of difficult-to-machine materials has always been a bottleneck restricting the efficiency of machining processing. To improve the processing efficiency, it is necessary to first understand what is difficult to process materials and some characteristics of difficult-to-machine materials.
In the processing of niobium alloys, we mainly use welding tools. The grades of the tools are generally selected from YD series and YW series carbide turning tools. Niobium alloy materials have the characteristics of low thermal conductivity, and the heat generated during cutting is difficult to spread, resulting in a high temperature at the tip of the tool and a significant influence on the cutting edge. As a result of this effect, the bond strength of the binder in the tool material is lowered at high temperatures, and particles such as WC (tungsten carbide) are easily separated, thereby accelerating tool wear.
Secondly, the niobium alloy material is strong in plasticity, and the chips are not easy to be broken. If the chip removal is not smooth during the processing, the chips will accumulate on the rake face of the tool. Under severe friction conditions, the strength and hardness of the material will increase rapidly, plus The high temperature generated by a large amount of heat can damage the tool in an instant. In addition, the composition of the bismuth alloy material and some of the components of the tool material react under high temperature cutting conditions, and appear to be analyzed, detached, or other compounds are formed, which also accelerates the formation of tool wear such as chipping.
For these phenomena generated during cutting, we mainly change the machining effect by adjusting the sharpening angle and cutting amount of the tool. Because the heat generated by the niobium alloy during cutting is not suitable for diffusion, we chose a rake angle of 5° when sharpening the turning tool. The chipbreaker is sharpened in a circular arc shape, with a small feed rate, using lard as the The lubricating fluid can make the iron scraps flow smoothly, which can greatly extend the service life of the cutter and improve the processing efficiency. A sharper carbide end mill is suitable for milling.
Titanium alloy is also considered to be difficult to process due to its high strength and low thermal conductivity. Because the material has a low thermal conductivity, it needs to be filled with sufficient coolant, otherwise the cutting heat will easily accumulate in the cutter head to make the tip of the tool overheat and wear quickly. In addition, titanium alloys require a high degree of sharpness to the tool. The tool generally has a front angle of about 20°. The main and auxiliary back angles and the main and auxiliary declinations are generally not required. The main and auxiliary flank surfaces can be finely ground in the tool grinding machine. If there are no conditions, the ordinary light cyan silicon carbide grinding wheel is carefully trimmed and then sharpened, and then the main and auxiliary flank surfaces are carefully polished with fine silicon carbide whetstone. Until the fingernail is scraped along the blade, the blade is smooth and the resistance is very uniform. There is no gap. If it is scratched on the serrations, the gap in the blade will expand rapidly during use until the tool is damaged. When turning a titanium alloy with a carbide tool, the cutting speed should not exceed 80m/min, and the high speed steel tool should be lower. When milling titanium alloy, the most suitable tool is the super-hard straight shank end mill HSS-AL, which is produced by Guiyang Southwest Tool CNC Tool Co., Ltd., and needs sufficient cooling when used.
There are also many grades of superalloys. We have contacted GH202, GH169, and GH131. In general, their commonality is high hardness, high strength, and poor heat dissipation. Therefore, we usually process such materials using YT, YD, YW welded carbide tools, with low speed, large knife depth to process, the efficiency is still ideal. If the machine tool is used for machining, the cutting speed can be improved, but the depth of the knife can't exceed 3mm. In comparison, the efficiency is not improved, and the cost is gone up.
There are also some non-ferrous metals in difficult-to-machine materials that change their processing properties by adding some rare metals. For example, beryllium bronze, because of the addition of rare metal crucibles, its processing performance is manifested by the accelerated wear of the tool and the difficulty of controlling the size of the part. To this end, we work hard on the sharpening of the tool. According to the characteristics of the beryllium bronze, the front angle of the tool is ground to 2°. In order to further improve the wear resistance of the tool, the minor declination and the relief angle are sharpened. . And a lower cutting speed and a smaller knife depth were chosen. In order to reduce the heat of cutting during machining, a large amount of cutting fluid can be used to reduce the heat of cutting, and a large amount of iron scraps can be washed away, so that the processing is smooth, the sharpness of the tool is maintained, thereby prolonging the service life of the tool and improving the production of the tool. effectiveness.
Through the summary of practice, we have some experience in the processing of difficult-to-machine materials, that is, we must first summarize the characteristics of the material, and seek processing methods according to the material characteristics.
In the processing of niobium alloys, we mainly use welding tools. The grades of the tools are generally selected from YD series and YW series carbide turning tools. Niobium alloy materials have the characteristics of low thermal conductivity, and the heat generated during cutting is difficult to spread, resulting in a high temperature at the tip of the tool and a significant influence on the cutting edge. As a result of this effect, the bond strength of the binder in the tool material is lowered at high temperatures, and particles such as WC (tungsten carbide) are easily separated, thereby accelerating tool wear.
Secondly, the niobium alloy material is strong in plasticity, and the chips are not easy to be broken. If the chip removal is not smooth during the processing, the chips will accumulate on the rake face of the tool. Under severe friction conditions, the strength and hardness of the material will increase rapidly, plus The high temperature generated by a large amount of heat can damage the tool in an instant. In addition, the composition of the bismuth alloy material and some of the components of the tool material react under high temperature cutting conditions, and appear to be analyzed, detached, or other compounds are formed, which also accelerates the formation of tool wear such as chipping.
For these phenomena generated during cutting, we mainly change the machining effect by adjusting the sharpening angle and cutting amount of the tool. Because the heat generated by the niobium alloy during cutting is not suitable for diffusion, we chose a rake angle of 5° when sharpening the turning tool. The chipbreaker is sharpened in a circular arc shape, with a small feed rate, using lard as the The lubricating fluid can make the iron scraps flow smoothly, which can greatly extend the service life of the cutter and improve the processing efficiency. A sharper carbide end mill is suitable for milling.
Titanium alloy is also considered to be difficult to process due to its high strength and low thermal conductivity. Because the material has a low thermal conductivity, it needs to be filled with sufficient coolant, otherwise the cutting heat will easily accumulate in the cutter head to make the tip of the tool overheat and wear quickly. In addition, titanium alloys require a high degree of sharpness to the tool. The tool generally has a front angle of about 20°. The main and auxiliary back angles and the main and auxiliary declinations are generally not required. The main and auxiliary flank surfaces can be finely ground in the tool grinding machine. If there are no conditions, the ordinary light cyan silicon carbide grinding wheel is carefully trimmed and then sharpened, and then the main and auxiliary flank surfaces are carefully polished with fine silicon carbide whetstone. Until the fingernail is scraped along the blade, the blade is smooth and the resistance is very uniform. There is no gap. If it is scratched on the serrations, the gap in the blade will expand rapidly during use until the tool is damaged. When turning a titanium alloy with a carbide tool, the cutting speed should not exceed 80m/min, and the high speed steel tool should be lower. When milling titanium alloy, the most suitable tool is the super-hard straight shank end mill HSS-AL, which is produced by Guiyang Southwest Tool CNC Tool Co., Ltd., and needs sufficient cooling when used.
There are also many grades of superalloys. We have contacted GH202, GH169, and GH131. In general, their commonality is high hardness, high strength, and poor heat dissipation. Therefore, we usually process such materials using YT, YD, YW welded carbide tools, with low speed, large knife depth to process, the efficiency is still ideal. If the machine tool is used for machining, the cutting speed can be improved, but the depth of the knife can't exceed 3mm. In comparison, the efficiency is not improved, and the cost is gone up.
There are also some non-ferrous metals in difficult-to-machine materials that change their processing properties by adding some rare metals. For example, beryllium bronze, because of the addition of rare metal crucibles, its processing performance is manifested by the accelerated wear of the tool and the difficulty of controlling the size of the part. To this end, we work hard on the sharpening of the tool. According to the characteristics of the beryllium bronze, the front angle of the tool is ground to 2°. In order to further improve the wear resistance of the tool, the minor declination and the relief angle are sharpened. . And a lower cutting speed and a smaller knife depth were chosen. In order to reduce the heat of cutting during machining, a large amount of cutting fluid can be used to reduce the heat of cutting, and a large amount of iron scraps can be washed away, so that the processing is smooth, the sharpness of the tool is maintained, thereby prolonging the service life of the tool and improving the production of the tool. effectiveness.
Through the summary of practice, we have some experience in the processing of difficult-to-machine materials, that is, we must first summarize the characteristics of the material, and seek processing methods according to the material characteristics.
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