Mechanical processing technology of titanium alloy materials
Titanium alloy materials have many advantages and disadvantages, and their disadvantages include high hardness, low plasticity, low thermal conductivity, large elastic deformation, and low elastic modulus. Therefore, in the processing of titanium alloy, the thermal conductivity is small, the cutting temperature of the material is too high; the specific temperature is too small, the local temperature rise of the material is too fast, and the service life of the tool is lowered; the low elastic modulus will aggravate the surface of the material. The processing rebounds, which leads to tool wear or chipping. In high temperature environments, chemical activity will intensify its chemical interaction with nitrogen, hydrogen and oxygen, which will increase the difficulty of machining. In addition, the processing of titanium alloys, cutting conditions, tool materials, and cutting time will affect the overall efficiency of the cutting process. Therefore, the cutting process of titanium alloy materials must be strictly controlled.
Mechanical processing technology of titanium alloy materials
Titanium alloys have a wide range of machining processes, such as EDM, milling, turning, grinding, drilling, tapping, etc. The machining process of titanium alloy materials, tool materials, cutting fluids, processing parameters, and tool geometry are important factors, so they must be highly valued.
- Cutting fluid. In the cutting process of titanium alloy materials, the use of cutting fluid can not only reduce the heat of the cutting edge, but also wash away the chips, thus reducing the cutting force. It can be seen that the use of cutting fluid must be reasonable, so that the surface quality and production of the parts can be realized. Improvement in efficiency. At present, commonly used cutting fluids include water-insoluble oily solution, water-based soluble oily solution, water or alkaline aqueous solution.
- Tool material. As can be seen from the foregoing, titanium alloy materials have the disadvantages of high hardness, low plasticity and low thermal conductivity. Therefore, the processing process is bound to exhibit high cutting temperature and high cutting force, which in turn aggravates the wear of the tool and reduces the service life of the tool. The tool material must be characterized by high wear resistance and strong hardness. At present, commonly used tool materials include high-speed steel grades, carbide grades, coated tools (strong anti-blocking properties, strong oxidation resistance, good wear resistance, etc.), cubic boron nitride tools (high heat hardness, high hardness, etc.) ), polycrystalline diamond tools (high hardness, high wear resistance, high thermal conductivity, low friction coefficient, etc.)
- The geometry of the tool. For the roughing process of titanium alloy materials, tools with small front and rear angles and high rigidity should be selected, such as rough machining of titanium alloy Gr.5(Ti-6al4v,chinese name TC4), and the front angle should be 0~3°. For the finishing process of titanium alloy materials, try to use tools with sharper cutting edges, dense cutter teeth, large front/rear angles and large spiral angles, small negative chamfering edges or no chamfering, such as finishing of titanium alloy (Ti-6al4v,chinese name TC4). The angle is 8 to 15°. If the boring tool or round turning tool is used to process the titanium alloy, the front/rear angles are respectively 10-15°, 8~14°, and the radius of the tool nose arc is 0.2-0.6mm. If the thread turning tool is used, the front/rear angles are respectively Take 0°, 10°; if using a forming turning tool, the front/rear angles are 5° and 10° respectively. The design of the drill bit must meet the requirements of the fluency of the chip, that is, the helix angle is 25 to 30°, the grinding groove of the drill bit is polished, and the thickness of the core is 1/4 of the drill diameter; according to the actual situation, the chisel is ground to ensure the grinding. The strength of the drill bit and the centering action are better. In addition, the apex angle of the drill bit is 135 to 140°, and the back angle of the drill bit is 12 to 15° to increase the width and thickness of the cutting. The design of the milling cutter must meet the cutting requirements of titanium alloys. In the case of an end mill, the front/rear angles are respectively 6-8°, 6-12°, the helix angle is 35-40° (the front section is 3°), and the tool nose arc radius is 0.5-0.6 mm. The cutting environment of the tapping is often kept semi-closed, so the cutting fluid is difficult to flow smoothly to the cutting area, and the lubrication and heat dissipation effects are poor. The titanium alloy has only a small elastic modulus, so that the tap is easily caused. Twist or disintegrate. For this situation, it is especially important to optimize the geometric parameters of the tapping, that is, the back angle of the cutting cone part is 6~12°, the front angle is 7~10°, the cutting cone angle is 5~7°30′, and the tooth surface is shovel Take 1° from the corner. The design of the reamer must conform to the characteristics of the small elastic modulus of the titanium alloy, that is, the front/rear angle of the reamer is 3 to 5° and 10°, respectively, and the width of the cutting edge is 0.15 mm.
- Cutting process parameters of titanium alloy materials. For the case of interrupted cutting and continuous cutting.During the drilling process of titanium alloy, there are often broken drills and burnt knives, and the causes of this phenomenon include poor bit sharpening, poor cooling, untimely chip removal, and poor process system rigidity. In view of the above situation, the following aspects must be strictly controlled: one is to retreat the knife and remove the chips in time, and to observe the color and shape of the chips; the second is to add enough cutting liquid; the third is to fix the drilling mold and the work table. At the same time, the guiding and machining surface of the drill should be as close as possible to shorten the drill bit; the fourth is the manual feeding process, and the drill bit should be moved back and forth to prevent the drill bit from becoming dull due to the friction of the drilled surface. Milling requires intermittent cutting. Therefore, milling cutters often have chipping, cutting and tooth bonding. In severe cases, even the teeth may be damaged or cause chipping. In this case, it is better to adopt the cutting method of the down-cut milling, because the cutting is smoother and the cutting path of the cutter is shorter, and the cutting sequence from thick to thin can effectively control the occurrence of the cutting and bonding phenomenon, so that it can be controlled. The amount of wear of the milling cutter increases the durability of the tool and reduces the roughness of the machined surface. The cutting cone angle is as large as possible, and the taper portion is preferably 3 to 4 thread length. In addition, the cutting cone should be ground as far as possible to facilitate chip removal; use a short tap as much as possible to achieve the increase in tap stiffness; the taper of the tap is as large as possible (more standard value), thereby controlling the workpiece and Friction between the taps. Titanium alloy grinding often causes surface burns or blockage of the grinding wheel due to the problem of sticking. Because the thermal conductivity of titanium alloy is poor, it will definitely increase the temperature rise of the grinding zone, which will cause the titanium alloy to bond with the abrasive or chemical reaction. Know the working surface of the burned workpiece and reduce the fatigue strength of the part. In view of the above situation, the common control method is to optimize the grinding process parameters, such as: grinding wheel material – green silicon carbide TL; grinding wheel hardness – ZRI; grinding wheel speed – 10 ~ 20m / s; grinding wheel granularity – 60, in addition The feed rate is controlled to a low level as much as possible while the emulsion is completely cooled. In the case of tapping of titanium alloy, the tapping tap should be preferred, and the number of teeth is 2 to 3 teeth.
In summary, titanium alloy materials have many advantages and disadvantages, and their shortcomings seriously affect the cutting process of titanium alloy materials. Therefore, the cutting process of titanium alloy materials must fully consider the possible influencing factors and the characteristic requirements that must be met. In particular, the cutting process of titanium alloy materials should be controlled from the aspects of tool materials, cutting fluids, machining process parameters and tool geometry parameters to improve the overall efficiency of titanium alloy material processing.
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