Why is titanium alloy so difficult to machine?
Why do we think titanium alloy is a difficult material to machine? Because of the lack of deep understanding of its processing mechanism and phenomenon.
Physical phenomena of titanium processing
Table of Contents
The cutting force of titanium alloy processing is only slightly higher than that of steel with the same hardness, but the physical phenomenon of titanium alloy processing is much more complex than that of steel, which makes titanium alloy processing face great difficulties.
The thermal conductivity of most titanium alloys is very low, only 1 / 7 of steel and 1 / 16 of aluminum. Therefore, the heat generated in the process of cutting titanium alloy will not be quickly transferred to the workpiece or taken away by chips, but will gather in the cutting area, and the generated temperature can be as high as more than 1000 ℃, which will make the cutting edge of the tool wear, crack and form chip tumor rapidly, and the rapidly worn cutting edge will generate more heat in the cutting area and further shorten the service life of the tool.
The high temperature produced in the cutting process destroys the surface integrity of titanium alloy parts at the same time, resulting in the decline of geometric accuracy and work hardening that seriously reduces its fatigue strength.
The elasticity of titanium alloy may be beneficial to the performance of parts, but the elastic deformation of workpiece is an important reason for vibration in the cutting process. The cutting pressure makes the “elastic” workpiece leave the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting effect. The friction process will also produce heat, which aggravates the poor thermal conductivity of titanium alloy.
This problem is more serious when machining thin-walled or ring-shaped parts. It is not easy to process titanium alloy thin-walled parts to the expected dimensional accuracy. As 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, and the material strength and hardness of the cutting point increase significantly. At this time, machining at the originally determined cutting speed becomes too high, which further leads to sharp tool wear.
“Heat” is the “culprit” of titanium alloy difficult to process!
Process know-how for processing titanium alloy
On the basis of understanding the processing mechanism of titanium alloy and previous experience, the main process know-how for processing titanium alloy is as follows:
- (1) The blade with positive angle geometry is adopted to reduce the cutting force, cutting heat and workpiece deformation.
- (2) Keep a constant feed to avoid hardening of the workpiece. The tool should always be in the feed state in the cutting process. During milling, the radial tool draft AE should be 30% of the radius.
- (3) High pressure and large flow cutting fluid is used to ensure the thermal stability of the machining process and prevent workpiece surface degeneration and tool damage due to high temperature.
- (4) Keeping the blade edge sharp and blunt is the cause of heat accumulation and wear, which is easy to lead to tool failure.
- (5) As far as possible, it is processed in the softest state of titanium alloy, 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 chamfer cut in to put as many blades into the cutting as possible. This can reduce the cutting force and heat at each point and prevent local damage. In the milling of titanium alloy, the cutting speed has the greatest influence on the tool life VC, and the radial feed (milling depth) AE takes the second place.
Solve the problem of titanium processing from the blade
The wear of blade groove in titanium alloy machining is the local wear along the cutting depth in the back and front, which is often caused by the hardened layer left by early machining. The chemical reaction and diffusion of cutting tool and workpiece material at the processing temperature of more than 800 ℃ is also one of the reasons for the formation of groove wear. Because in the processing process, the titanium molecules of the workpiece accumulate in front of the blade and are “welded” to the blade under high pressure and high temperature to form chip nodules. When the chip deposit is stripped from the blade, the cemented carbide coating of the blade will be taken away. Therefore, titanium alloy processing requires special blade material and geometry.
Tool structure suitable for titanium machining
The focus of titanium alloy processing is heat. A large amount of high-pressure cutting fluid should be sprayed on the cutting edge in time and accurately, so that the heat can be removed quickly. There is a unique structure of milling cutter specially used for titanium alloy processing on the market.
Source: Network Arrangement – China Pipe Sleeves Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]
Please notice that you might be interested in the other technical articles we’ve published:
- Fixture design for turning thin walled pipe sleeve parts
- What is a flange
- What is a butterfly valve
- What is a safety valve
- What is a ball valve
- What is pipe fitting
- Manufacturing and quality control of 800H alloy seamless butt welded pipe fittings
- Improving the processing technology of stainless steel thin-wall pipe sleeves