Titanium alloys are divided into a phase, b phase, and a + b phase according to the metal structure, with TA, T, and TC indicating their brand and type. The materials used in a new engine of our company are T and TC. Generally, TA series is used for casting and forging, and TC series is used for bar.
Features and machinability
Titanium alloy has the following advantages over general alloy steel:
The specific strength becomes higher: The density of titanium alloy is only 4.5g / cm3, which is much smaller than iron, and its strength is similar to that of ordinary carbon steel. Good mechanical properties: The melting point of titanium alloy is 1660 ℃, which is higher than that of iron and has higher thermal strength. It can work below 550 ℃, and usually shows good toughness at low temperatures.
Good corrosion resistance: in
It is easy to form a dense oxide film on the surface of titanium alloy below 550 ℃, so it is not easy to be further oxidized, and it has high corrosion resistance to the atmosphere, seawater, steam, and some acid, alkali, salt media.
On the other hand, the machinability of titanium alloys is relatively poor. The main reasons are:
Poor thermal conductivity, resulting in high cutting temperature and reduced tool durability. At temperatures above 600 ° C, an oxidized hard layer is formed on the surface, which has a strong abrasive effect on the knife. Low plasticity and high hardness increase the shear angle, the length of contact between the chip and the rake face is very small, the stress on the rake face is very large, and the blade is prone to breakage.
The elastic modulus is low, the elastic deformation is large, and the workpiece surface near the flank face has a large amount of springback, so the contact area between the processed surface and the flank face is large, and the wear is serious.
The characteristics of the titanium alloy cutting process make it very difficult to process, resulting in low processing efficiency and high tool consumption.
General principles of cutting
According to the nature of the titanium alloy and the characteristics of the cutting process, the following aspects should be considered during processing:
Use hard alloy tools as much as possible, such as tungsten-cobalt hard alloys and titanium alloys have small chemical affinity, good thermal conductivity, and high strength. Intermittent cutting at low speeds can use impact-resistant ultra-fine grained cemented carbide, and high-speed steel with good high-temperature performance can be used for forming and complex tools.
Use a smaller rake angle and a larger rake angle to increase the contact length between the chip and the rake face, reduce the friction between the workpiece and the rake face, and use a circular transition edge to increase the strength and avoid burnt sharp corners And blade. It is necessary to keep the blade sharp to ensure smooth chip evacuation and avoid chipping of sticky chips.
The cutting speed should be low to avoid cutting temperature too high; the feed rate is moderate, too large, easy to burn the knife, too small, because the cutting edge works in the work hardened layer and wears too fast; the cutting depth can be large, so that the tip is in the hardened layer The following work will help improve the durability of the tool. Cooling fluid must be added to cool down during processing.
Cutting titanium alloy has a high resistance to knife eating, so the process system needs to ensure sufficient rigidity. Because the titanium alloy is easily deformed, the cutting clamping force cannot be large, especially in certain finishing processes, certain auxiliary supports can be used when necessary.
The above are the general principles that need to be considered when processing titanium alloys. In fact, when using different processing methods and under different conditions, there are different contradiction highlights and focus on solving problems.