Titanium alloy is difficult to machine, cutting fluid is selected in this way to extend tool life by 8 times.
September 30, 2021
Titanium alloy is difficult to machine, cutting fluid is selected in this way to extend tool life by 8 times. The cutting force during titanium alloy processing is only slightly higher than that of steel with the same hardness, but the physical phenomenon of processing titanium alloy is much more complicated than processing steel, which makes titanium alloy processing face huge difficulties. The thermal conductivity of most titanium alloys is very low, only 1/7 that of steel and 1/16 that of aluminum. Therefore, the heat generated in the process of cutting titanium alloy will not be quickly transferred to the workpiece or be taken away by the chips, but will be concentrated in the cutting area, and the temperature generated can be as high as 1000 ℃, causing the cutting edge of the tool to wear, chip and generate rapidly The built-up edge, the rapid appearance of worn blades, causes more heat in the cutting area, and further shortens the life of the tool. The high temperature generated during the cutting process also destroys the surface integrity of the titanium alloy parts, resulting in a decrease in the geometric accuracy of the parts and a work hardening phenomenon that severely reduces its fatigue strength.
The elasticity of titanium alloy may be beneficial to the performance of parts, but during the cutting process, the elastic deformation of the workpiece is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to leave the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, which aggravates the problem of poor thermal conductivity of titanium alloys. This problem is even more serious when processing thin-walled or ring-shaped parts that are easily deformed. It is not an easy task to process thin-walled titanium alloy parts to the expected dimensional accuracy. Because when the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and plastic deformation occurs, and the material strength and hardness of the cutting point increase significantly. At this time, machining according to the originally determined cutting speed becomes too high, which further leads to sharp tool wear.
"Hot" is the "culprit" that is difficult to process titanium alloys! Selection of Titanium Alloy Cutting Fluid When cutting titanium alloys, in order to reduce the cutting temperature, a large amount of cutting fluid with cooling effect should be poured into the cutting area. The requirements for cutting fluids include large thermal conductivity, large specific heat capacity, large heat capacity, large heat of vaporization, high vaporization speed, large flow rate, and fast flow rate. Generally speaking, the thermal conductivity of water is 3 to 5 times greater than that of oil, the specific heat capacity is 1 time, and the heat of vaporization is almost 10 times greater, so water-soluble cutting fluid is more suitable. The above is a conventional view, but also limited to the factors of processing equipment. The latest research results show that the heat of titanium alloy processing particles is extremely high, and the local heat formed is very large. Although the cooling performance of water-soluble cutting fluid is preferred, it has vaporized before reaching the cooling area. In fact, water-soluble cutting fluid is used The average temperature in the center area of the slab is more than 2 times higher than that of the oil-based cutting fluid, and the cutting process results are not ideal.
However, pure oil cutting fluid is obviously not suitable for high-speed machining due to its viscosity, flash point, etc. It is difficult to control the risk of fire. In the titanium alloy cutting fluid, chlorine, which is a halogen substance with fire extinguishing properties, cannot be used. Because the high temperature will decompose and release hydrogen during the cutting process, it will be absorbed by titanium to cause hydrogen embrittlement, and it may also cause high temperature stress corrosion cracking of titanium alloy. Also, because the chloride in the cutting fluid may decompose or volatilize toxic gas during use, safety measures must be taken when using it, otherwise it should be strictly prohibited. After cutting, the parts should be thoroughly cleaned with a chlorine-free cleaning agent in time to remove chlorine residues. Therefore, cutting titanium alloys should require suppliers to avoid chlorine in the cutting fluid components.
