Machinability of titanium alloys
Under the same technological conditions (cutting speed 100-180 m/min, dry cutting), the main cutting force of Ti-6Al-4V and normalized 45 steel turning is equivalent, and the radial cutting force corresponding to the former is 15%-30% higher , the cutting temperature (700 ~ 800 ℃) is about 7% higher. In contrast, wet cutting (5% emulsion) reduces cutting forces by about 10% and cutting temperatures by about 5%, while improving surface quality.
In order to obtain good surface integrity, the cutting amount should be selected reasonably. In general, the higher the cutting speed, the more severe the case hardening; the feed rate has no significant effect on the degree of hardening. Increases in cutting speed, depth of cut and feed rate can all lead to increased surface roughness.
The cutting surface is prone to a certain degree of residual tensile stress, while the subsurface is mostly residual compressive stress; increasing the feed and depth of cut, the surface tensile stress level and the subsurface compressive stress level are higher. For the consideration of cutting temperature, generally lower cutting speed and larger depth of cut should be used, and suitable cutting fluid should be selected at the same time.
Selection of titanium alloy cutting tools
Rapid tool wear caused by high cutting temperature is the main problem in the cutting process of titanium alloys. Therefore, the development of high-performance tools for titanium alloy cutting is an important topic that needs to be studied in the future.
When machining titanium alloys, coated carbide tools and polycrystalline diamond (PCD) tools show excellent cutting performance, especially PCD tools are the best; polycrystalline cubic boron nitride (PCBN) tools are second; TiC-based hard Solid alloy tools and ceramic tools are considered unsuitable for titanium alloy cutting due to low durability and other reasons.
The high matching between PCD tools and titanium alloy cutting is mainly due to its good thermal conductivity and extremely high hardness: the thermal conductivity of diamond is several times that of cemented carbide, and more cutting heat can be conducted out of the cutting area through the tool; extremely high The hardness of the tool ensures the wear resistance of the tool.
The tool life of PCD tools for cutting titanium alloys can reach dozens of times that of cemented carbide tools. In the future, we should start from tool preparation (welding, cutting and sharpening, etc.) and cutting process optimization (cutting amount selection and cutting fluid supply, etc.) to reduce the tool cost of PCD tools for cutting titanium alloys and further expand its application range.
In terms of tool angle, a smaller rake angle is generally selected to cut titanium alloys to increase the contact length between the chip and the rake face; at the same time, a larger relief angle is selected to reduce the friction between the flank and the machined surface.
Titanium alloy high-speed cutting technology
The main feature of high-speed cutting is to greatly increase the cutting speed on the basis of conventional cutting. "High speed" is a relative concept, and the specific value depends on the mechanical properties of the workpiece material, etc. For titanium alloys, the general cutting speed exceeds 100 m/min can be regarded as high-speed cutting. High-speed cutting has the following advantages:
(1) High processing efficiency. High-speed cutting generally uses high spindle speed and fast feed rate at the same time, so that the material removal rate is doubled, up to 5 times or even higher than conventional cutting.
(2) It can improve the surface quality and machining accuracy of the workpiece. During high-speed cutting, due to factors such as the narrowing of the shear deformation area, the cutting force is smaller than that in conventional cutting, which is beneficial to ensure the machining accuracy of parts, especially thin-walled parts; The workpiece has a lower proportion of heat, which helps to improve its surface quality and machining accuracy.
(3)The relative tool life is long. Under high-speed cutting conditions, although the use time of the tool decreases, the improvement of cutting efficiency is more obvious, that is, the same amount of tool wear can complete more cutting tasks. In other words, the relative life of the tool is increased.
(4) Under the condition of high cutting speed, the heat generation in the cutting process increases. This is a challenge for the cooling system of the machine tool and the wear resistance and thermal strength of the tool. In addition, high-speed cutting also requires the machine tool to have high rigidity and precision, etc., in order to give full play to its technological advantages. At present, the United States, Japan, Germany and other countries are in the leading position in the above-mentioned development level.
---EDITOR: Miya Ma/Cynthia Lee
---POST: Cynthia Lee