Machining properties of titanium and titanium alloy

1. Cutting performance

According to the properties of titanium alloy and the characteristics of cutting process, the following aspects should be considered in machining:


As far as possible to use cemented carbide tools, such as tungsten cobalt cemented carbide and titanium alloy chemical affinity is small, good thermal conductivity, high strength. Shock-resistant superfine grain cemented carbides can be used for interrupted cutting at low speed. High speed steels with good high temperature performance can be used for forming and complex cutting tools.


A smaller front Angle and a larger back Angle are used to increase the contact length between the chip and the front cutter surface, reduce the friction between the workpiece and the back cutter surface, and the circular arc transition blade is used at the tool tip to improve the strength, so as to avoid burning and breaking of the sharp Angle. Keep the blade sharp to ensure smooth chip removal and avoid chip breakage. Cutting speed should be low to avoid excessive cutting temperature; Moderate feed, too much easy to burn the knife, too small because the knife edge in the process of hardening layer work and wear too fast; Cutting depth can be larger, so that the tip of the tool in the hardened layer under the work, is conducive to improve the durability of the tool. Cooling fluid must be added to fully cool during processing. When cutting titanium alloy, the blade resistance is large, so the process system needs to ensure that there is enough stiffness. Because titanium alloy is easy to deformation, so the cutting clamping force can not be large, especially in some finishing processes, when necessary, some auxiliary support can be used.


2. Grinding performance

Titanium alloy is characterized by active chemical properties, easy affinity and adhesion with abrasive at high temperature, blockage of grinding wheel, resulting in intensified wear of grinding wheel, reduced grinding performance, grinding accuracy is not easy to guarantee. Grinding wheel wear also increases the contact area between the grinding wheel and the workpiece, resulting in deterioration of heat dissipation conditions, grinding zone temperature sharply increased, in the grinding surface layer formed a large thermal stress, resulting in local burns of the workpiece, grinding cracks. The high strength and toughness of titanium alloy make it difficult to separate the grinding chips, increase the grinding force and increase the grinding power consumption. Titanium alloy has low thermal conductivity, small specific heat, and slow heat conduction during grinding, resulting in heat accumulation in the grinding arc area, resulting in a sharp rise in the temperature of the grinding area.


3. Extrusion processing performance

During the extrusion process of titanium and titanium alloy, high extrusion temperature and fast extrusion speed are required to prevent the temperature drop too fast. Meanwhile, the contact time between high \ temperature billet and mold should be shortened as far as possible. Therefore, the extrusion mold should choose new heat-resistant mold material, the billet from the heating furnace to the extrusion cylinder of the conveying speed is also fast. Proper protective measures should be taken in view of the fact that metals are easily contaminated by gases during heating and extrusion. Proper lubricants should be selected during extrusion to prevent adhesion of the mold, such as jacketed extrusion and glass lubrication extrusion. Due to the large deformation heat effect and poor thermal conductivity of titanium and titanium alloy, special attention should be paid to prevent overheating during extrusion deformation. The extrusion process of titanium alloy is more complicated than that of aluminum alloy, copper alloy and even steel, which is determined by the special physical and chemical properties of titanium alloy. When titanium alloy is formed by conventional thermal reverse extrusion, the temperature of the die is low, the surface temperature of the billet in contact with the die drops rapidly, while the internal temperature of the billet increases due to deformation heat. Due to the low thermal conductivity of titanium alloy, after the surface temperature drops, the heat of the inner billet cannot be transferred to the surface timely to supplement, and the surface hardening layer will occur, making it difficult to continue the deformation. At the same time, the surface layer and the inner layer will produce a large temperature gradient, even if it can form, it is easy to cause deformation and uneven organization.


4, Forging processing performance

Titanium alloy is very sensitive to forging process parameters, and the change of forging temperature, deformation, deformation and cooling speed will lead to the change of microstructure and properties of titanium alloy. In order to better control the microstructure and properties of forgings, advanced forging technologies such as hot die forging and isothermal forging have been widely used in the production of titanium alloys in recent years.


Titanium alloy plasticity increases with temperature and, in 1000-1200 ℃ temperature range, reach maximum plasticity, allow the deformation degree of 70% - 80%. Titanium alloy forging temperature range is narrow, should be strictly in accordance with the (alpha + beta)/ beta transition temperature to master (except ingot billet), otherwise the beta grains will grow dramatically, reduce the room temperature plasticity; Alpha titanium alloy are usually (alpha + beta) two-phase area forging, because (alpha + beta)/beta subroutine above forging temperature is too high, will lead to the beta phase, a beta titanium alloy ending forging and finish forging must be higher than (alpha + beta)/beta transition temperature. The deformation resistance of titanium alloy increases rapidly with the increase of deformation speed, and the forging temperature has a greater impact on the deformation resistance of titanium alloy, so the conventional forging must be completed with the least cooling in the forging die. The content of interstitial elements (such as O, N, C) also has a significant effect on the forging properties of titanium alloys.


5.Casting process performance

Due to the high chemical activity of titanium and titanium alloy, it is easy to have violent chemical reaction with N, O and N in the air, and easy to have chemical reaction with the refractories commonly used in casting. Titanium and titanium alloy casting, especially investment casting is much more difficult than aluminum and steel investment casting, need special means to achieve. Casting titanium development initial period, the result of the development of casting technology lags behind that of the pressure processing technology, therefore, first choose a certain deformation of titanium alloy, such as Ti 6 al Ο Ο 4 v, Ti Ο 5 al Ο 2.5 Sn as casting alloy material, etc. These alloys are still widely used today. However, with the development of titanium casting process and the improvement of the performance requirements of casting titanium alloy in various aspects and the increase of the complexity of casting structure, the argument that "all deformed titanium alloy is suitable for casting alloy" should be corrected. With the increase of the temperature and working strength of the alloy, the number and amount of added elements in the alloy also increase correspondingly, but at the same time, the casting performance of the alloy, crystallization structure of fluidity solidification interval, mechanical properties and so on must be taken into account, that is, the chemical composition of the alloy must be adjusted according to the requirements of the casting process.


To sum up, titanium alloy has been widely used in aerospace and other fields due to its excellent performance, but it is also restricted by its processing efficiency and production cost. Titanium smelting technology once a breakthrough, its price will be significantly reduced. With the development of titanium alloy, the increase of titanium material variety and the decrease of price, the application of titanium in civil industry will be multiplied, especially in shipbuilding, automobile manufacturing, chemical industry, electronics, Marine development, seawater desalination, geothermal power generation, sewage corrosion protection and other civil fields will be widely used. At the same time, the market demand will also accelerate the development of titanium industry and titanium material processing technology.

 Xi'an Ocean Trading Co., Ltd.