What are the fabrication techniques of the titanium?
Thermal conductivity of titanium alloy is small, about 1/3 of iron, the heat generated during machining is difficult to be released through the workpiece; at the same time, due to the small specific heat of titanium alloy, the local temperature rises quickly during machining, therefore. It is easy to cause the tool temperature is very high, so that the tip of the tool sharp wear, service life is reduced. Experiments have proved that the temperature of the front end of the cutting tool of cutting titanium alloy is 2-3 times higher than the temperature of cutting steel. Titanium alloy low modulus of elasticity, so that the processed surface is prone to rebound, especially the processing of thin-walled parts rebound is more serious, easy to cause strong friction between the back face and the processed surface, thereby wearing the tool and chipping. Titanium alloy chemical activity is very strong, high temperature is very easy to interact with oxygen, hydrogen, nitrogen, so that its hardness increases, plasticity decreases, in the heating and forging process of the formation of oxygen-rich layer of machining difficulties.
Titanium alloy machining methods are many, mainly including: turning, milling, boring, drilling, grinding, tapping, sawing, EDM, etc..
1. Titanium alloy turning and boring
The main problems of turning titanium alloy are: high cutting temperature; more serious tool wear; large cutting rebound. Under suitable machining conditions. Turning and boring is not a particularly difficult process. For continuous cutting, mass production or large metal removal cutting, generally use carbide tools, when the molding cutting, turning groove or cut off, suitable for adjusting steel tooling, metal ceramic tools are also used. As with other machining operations, cutting interruptions can be avoided by always using a constant forced feed. Do not stop or slow down during cutting. Generally do not cut but cool sufficiently; the coolant can be 5% sodium nitrate aqueous solution or 1/20 soluble oil emulsion aqueous solution. Before forging, turning the original bar surface oxygen-rich layer using carbide tools, the depth of cut should be greater than the thickness of the oxygen-rich layer, cutting speed of 20 ~ 30m/min, feed 0.1 ~ 0.2mm / r. Boring is finishing, especially for thin-walled titanium alloy products in the boring process, should be prevented from burns and deformation of the parts clamping.
2. Titanium alloy drilling process
Titanium alloy drilling is easy to grow and thin curly chips, while drilling heat is large, easy to make excessive accumulation of chips or adhesion in the drilling edge, which is the main reason for the difficulty of drilling titanium alloy. Drilling should use a short and sharp drill bit and low-speed forced feed, the support bracket should be tight, and should be given to repeat adequate cooling, especially deep hole drilling. During drilling the drill bit should be kept in the hole and not allowed to idle in the hole, and a low and constant drilling speed should be maintained. Drill through the hole carefully, when about to drill through, in order to clean up the drill bit and drilling, and to remove drilling debris, it is best to return the drill bit, and finally break the hole when the use of forced feed, so that you can get a smooth hole.
3. Tapping of titanium alloy
Tapping of titanium alloy is probably the most difficult machining process. When tapping, limited titanium chip exclusion and severe galling tendencies will result in a poor thread fit, causing the tap to jam or break. At the completion of tapping, the titanium tends to dry and tighten on the tap. Therefore, should try to avoid the processing of blind holes or too long through-hole, in order to prevent the internal thread surface roughness becomes large or broken cone phenomenon. At the same time, the tapping method should be continuously improved, such as the back edge of the tap can be ground away. Along the length of the tooth edge at the top of the tooth grinding axial chip removal groove and so on. On the other hand, the tap with oxidized, oxidized or chrome-plated surface is used to reduce the bite and wear.
4.Sawing of titanium alloy
When sawing titanium alloy, low surface speed and continuous forced feeding should be used. Experiments have proved that the tooth spacing of 4.2mm ~ 8.5mm coarse tooth high-speed steel saw blade is suitable for sawing titanium alloy. If the band saw saw titanium alloy, the saw blade tooth pitch is determined by the thickness of the workpiece, generally 2.5mm ~ 25.4mm, the thicker the material thickness, the larger the tooth pitch. At the same time must maintain the forced feed capacity and the required coolant.
5. EDM of titanium
Titanium alloy electric discharge machining requirements of tools and workpieces between - an operating gap. The gap range is best taken in 0.005mm 0.4mm, smaller gap is commonly used in the requirements of smooth surface finishing, larger gap is used in the requirements of rapid removal of metal roughing. Copper and zinc electrode materials are preferred.