Why is titanium alloy difficult to work?

Release time：2022-04-13 00:41:36 丨 Number of visits：

Why do we think titanium alloy is a difficult material to work with? Because of the lack of deep understanding of its processing mechanism and phenomenon.

1. Physical phenomena of titanium processing

The cutting force of titanium alloy is only slightly higher than that of steel with the same hardness, but the physical phenomenon of processing titanium alloy is much more complex than that of steel, so that titanium alloy processing is faced with great difficulties.

Most titanium alloys have very low thermal conductivities, only 1/7 of steel and 1/16 of aluminum. Therefore, in the process of cutting of titanium alloy heat will not quickly passed to the artifact or taken away by chip, and agglomeration in cutting area, the temperature can be as high as 1 000 ℃ above, make the cutter blade quickly wear, cracks, and generate the devolop tumor, rapid wear of the blade, and make the cutting area produces more heat and further shorten the life of cutting tools.

The high temperature in the cutting process destroys the surface integrity of titanium alloy parts, resulting in the decrease of geometric accuracy and the phenomenon of work hardening which reduces the fatigue strength seriously.

The elasticity of titanium alloy may be beneficial to the performance of parts, but in the cutting process, the elastic deformation of workpiece is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to move away from the tool and rebound, resulting in greater friction between the tool and the workpiece than the cutting action. Friction process will also generate heat, aggravating the problem of poor thermal conductivity of titanium alloys.

This problem is more serious when machining thin wall or ring parts which are easy to deform. It is not easy to process titanium alloy thin wall parts to the desired dimensional accuracy. Because when the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and produced plastic deformation, the strength and hardness of the material at the cutting point increase significantly. At this point, machining at the original cutting speed becomes too high, which further leads to sharp tool wear.

"Heat" is difficult to process titanium alloy "culprit"!

2. Technical know-how for processing titanium alloy

On the basis of understanding the processing mechanism of titanium alloy and previous experience, the main process tips for processing titanium alloy are as follows:

(1) The use of positive Angle geometric shape of the blade, to reduce the cutting force, cutting heat and workpiece deformation.

(2) keep constant feed to avoid workpiece hardening, in the cutting process the tool should always be in the feed state, milling radial tool ae should be 30% of the radius.

(3) The use of high pressure and large flow cutting fluid, in order to ensure the thermal stability of the processing process, to prevent the workpiece surface degeneration and tool damage due to high temperature.

(4) Keep the blade edge sharp, blunt tool is the cause of thermal aggregation and wear, easy to lead to tool failure.

(5) The titanium alloy should be processed in the softest state possible, because the material becomes more difficult to process after hardening, and heat treatment improves the strength of the material and increases the wear of the blade.

(6) Use a large tip arc radius or chamfering cut to bring as much of the blade into the cutting as possible. This reduces cutting force and heat at each point and prevents local damage. In the milling of titanium alloy, the cutting speed has the greatest influence on tool life VC, and the radial cutting depth (milling depth) ae is the second.

3. Solve the problem of titanium processing from the blade

The blade groove wear in titanium alloy machining is the local wear in the back and front along the direction of cutting depth, which is often caused by the hardening layer left by the early processing. The chemical reaction and diffusion between the tool and the workpiece material at the processing temperature above 800℃ is also one of the reasons for the formation of groove wear. Because in the process of processing, titanium molecules of the workpiece accumulate in front of the blade, under high pressure and high temperature "welding" to the blade, forming a chip tumor. When the nodules are removed from the blade, the carbide coating of the blade is carried away, so titanium alloy machining requires special blade materials and geometry.

4. Tool structure suitable for titanium processing

Titanium alloy processing parts manufacturer said: the focus of titanium alloy processing is heat, a large number of high pressure cutting fluid to timely and accurate injection on the cutting edge, can quickly remove the heat. On the market there are special milling cutters for titanium alloy processing unique structure.