Why Titanium Alloy Is A Difficult Material To Process?

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

Physical Phenomena of Titanium Alloy Processing

The cutting force during titanium alloy processing is only slightly higher than that of steel with the same hardness, but the physical phenomenon of processing titanium alloy is much more complicated than processing steel, which makes titanium alloy processing face huge difficulties.

The thermal conductivity of most titanium alloys is very low, only 1/7 that of steel and 1/16 that 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 the chips but will be concentrated in the cutting area. The temperature generated can be as high as 1,000 ℃, causing the cutting edge of the tool to wear, chip, and crack quickly. Generate built-up edge, and quickly appear worn edge, which causes more heat to be generated in the cutting area, further shortening the life of the tool.

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

Titanium Alloy

The elasticity of titanium alloy may be beneficial to the performance of parts, but during the cutting process, the elastic deformation of the 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. The friction process also generates heat, which aggravates the problem of poor thermal conductivity of titanium alloys.

This problem is even more serious when machining thin-walled or ring-shaped and other easily deformable parts. It is not an easy task to process thin-walled titanium alloy parts to the expected 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.

“Hot” is the “culprit” in the difficult processing of titanium alloys.

Process Technique for Processing Titanium Alloys

On the basis of understanding the processing mechanism of titanium alloys, plus previous experience, the main process know-how for processing titanium alloys is as follows:

  • Use positive-angle geometry inserts to reduce the cutting force, cutting heat, and workpiece deformation.
  • keep constant feed to avoid workpiece hardening, in the cutting process the tool should always be in the feed state, the milling radial tool ae should be 30% of the radius.
  • 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.
  • Keep the blade edge sharp. Blunt cutting tools are the cause of thermal aggregation and wear, which can easily lead to tool failure.
  • The titanium alloy is machined at its softest possible since the material becomes more difficult to work after hardening, and heat treatment increases the strength of the material and increases blade wear.
  • Use a large arc radius or chamfer to cut in, and put as much cutting edge as possible into the cutting. This can reduce the cutting force and heat at every point and prevent local damage. When milling titanium alloys, among the cutting parameters, the cutting speed has the greatest influence on the tool life VC, followed by the radial tool engagement (milling depth) ae.

Solve the Problem of Titanium Processing From the Blade

The blade groove wear during titanium alloy processing is the local wear along with the depth of cut at the back and front, and it is often caused by the hardened layer left by the previous processing. The chemical reaction and diffusion between the tool and the workpiece material at the processing temperature above 800℃ are also one of the reasons for the formation of groove wear. Because during the machining process, the titanium molecules of the workpiece accumulate on the front area of the blade and under high pressure and high temperature “welding” to the blade, forming a chip tumor.

Tool Structure Suitable for Titanium Machining

The focus of titanium alloy processing is heat, a large amount of high pressure cutting fluid for timely and accurate injection on the cutting edge can quickly remove the heat. There is a unique structure of milling cutter specially used for titanium alloy processing on the market.

Thank you for reading! Any questions, contact our team members freely.

 

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