Titanium alloy machining

The thermal conductivity of titanium alloy is small, and the heat generated during machining is difficult to be released through the workpiece; At the same time, because the specific heat of titanium alloy is small, the local temperature rises quickly during processing. It is easy to cause high tool temperature, sharp wear of tool tip and reduction of service life. Experiments show that the temperature of the tool tip for cutting titanium alloy is 2-3 times higher than that for cutting steel. The low elastic modulus of titanium alloy makes the machined surface easy to rebound, especially the machining rebound of thin-walled parts, which is easy to cause strong friction between the flank and the machined surface, so as to wear the tool and collapse edge. Titanium alloy has strong chemical activity. It is easy to interact with oxygen, hydrogen and nitrogen at high temperature, which increases its hardness and decreases its plasticity. It is difficult to machine the oxygen rich layer formed in the process of heating and forging.

There are many machining methods for titanium alloys, mainly including turning, milling, boring, drilling, grinding, tapping, sawing, EDM and so on.

1. Turning and boring of titanium alloy

The main problems in turning titanium alloy are: high cutting temperature; Serious tool wear; Large cutting rebound. Under suitable machining conditions. Turning and boring are not particularly difficult processes. For continuous cutting, mass production or cutting with large metal removal, cemented carbide tools are generally used. When forming cutting, grooving or cutting, adjusting steel tools are suitable, and cermet tools are also used. Like other machining operations, constant forced feed is always used to avoid cutting interruption.

2. Drilling of titanium alloy

When drilling titanium alloy, it is easy to produce long and thin curled chips. At the same time, the drilling heat is large, which is easy to cause the chips to accumulate or adhere to the drilling edge, which is the main reason for the difficulty of drilling titanium alloy. Short and sharp drill bits and low-speed forced feeding shall be used for drilling, and the support support shall be fastened and fully cooled repeatedly, especially for deep hole drilling. During drilling, the drill bit shall be kept in the drilling state in the hole without idling in the hole, and the low and constant drilling speed shall be maintained. The drill through hole shall be carefully drilled. When it is about to be drilled through, in order to clean the drill bit, drill hole and remove drill cuttings, it is best to return the drill bit. When the hole is finally broken, forced feed is adopted, so as to obtain a smooth hole.

3. Tapping of titanium alloy

Tapping of titanium alloy may be a difficult machining process. When tapping, the elimination of titanium chips is limited and the serious biting tendency will lead to poor thread fit and the tap will be stuck or broken. When tapping is completed, the titanium alloy tends to dry shrink on the tap. Therefore, the machining of blind holes or too long through holes should be avoided as far as possible to prevent the increase of internal thread surface roughness or cone breaking. At the same time, the tapping method should be continuously improved, such as grinding the trailing edge of the tap. Grind the axial chip removal groove at the tooth top along the length of the tooth edge. On the other hand, the tap with oxidized, oxidized or chrome plated surface is used to reduce bite and wear.

4. Sawing of titanium alloy

When sawing titanium alloy, low surface speed and continuous forced feeding shall be adopted. Experiments show that the coarse tooth high-speed hacksaw blade with tooth pitch of 4.2mm ~ 8.5mm is suitable for sawing titanium alloy. If a band saw is used to saw titanium alloy, the tooth pitch of the saw blade is determined by the thickness of the workpiece, which is generally 2.5mm ~ 25.4mm. The thicker the material thickness, the larger the tooth pitch. At the same time, the forced feed capacity and the required coolant must be maintained.

5. EDM of titanium and titanium

The EDM of titanium alloy requires an operating gap between the tool and the workpiece. The clearance range is 0.005mm 4mm, smaller clearance is often used for finish machining requiring smooth surface, and larger clearance is used for rough machining requiring rapid metal removal.