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

1. Physical phenomenon of titanium processing

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

Why do we think titanium is a difficult material? Lack of understanding of its processing mechanism

The thermal conductivity of most titanium alloys is very low, only 1/7 of steel and 1/16 of aluminum. Therefore, the heat generated during the cutting of the titanium alloy will not be quickly transferred to the workpiece or taken away by the chips. Instead, the heat generated in the cutting area can reach temperatures above 1 000 ° C, causing the cutting edge of the tool to quickly wear, crack and Debris formation is generated, and the worn blade quickly appears, which in turn generates more heat in the cutting area and further shortens the tool life.

The high temperature generated during the cutting process damages the surface integrity of titanium alloy parts at the same time, resulting in a decrease in the geometric accuracy of the part and a work hardening phenomenon that severely reduces its fatigue strength.

The elasticity of titanium alloy may be beneficial to the performance of the part, but during the cutting process, the elastic deformation of the workpiece is an important cause of vibration. Cutting pressure causes "elastic" workpieces to leave the tool and bounce, thereby making the friction between the tool and the workpiece greater than the cutting effect. The friction process also generates heat, which exacerbates the problem of poor thermal conductivity of titanium alloys.

This problem is even more serious when processing thin-walled or annular deformable parts, and it is not easy to process titanium-walled thin-walled parts to the expected dimensional accuracy. Because as the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and plastic deformation occurs, the material strength and hardness of the cutting point increase significantly. At this time, machining at the previously determined cutting speed becomes too high, further causing sharp tool wear.

"Hot" is the "culprit" of titanium alloys difficult to machine!

2. Technology know-how for processing titanium alloys

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

(1) Use positive-angle geometry inserts to reduce cutting forces, cutting heat, and workpiece deformation.

(2) Maintain a constant feed to avoid hardening of the workpiece. During cutting, the tool must always be in the feed state. The radial cutting amount a e during milling should be 30% of the radius.

(3) Use high pressure and high flow cutting fluid to ensure the thermal stability of the machining process and prevent workpiece surface degeneration and tool damage due to excessive temperature.

(4) Keep the cutting edge of the blade sharp. A blunt tool is the cause of thermal build-up and wear, which easily leads to tool failure.

(5) Work in the softest state of the titanium alloy as much as possible because the hardened material becomes harder to process. Heat treatment increases the strength of the material and increases the wear of the blade.

(6) Use a large tool nose arc radius or chamfer to cut in, and insert as many cutting edges as possible into the cutting. This can reduce the cutting force and heat at each point and prevent local damage. When milling titanium alloys, the cutting speed has the greatest influence on the tool life vc among the cutting parameters, followed by the radial cutting amount (milling depth) ae.

3. Starting from the blade to solve the problem of titanium processing

Blade groove wear during titanium alloy processing is local wear in the back and front along the cutting depth direction, and it is often caused by the hardened layer left in the previous processing. The chemical reaction and diffusion of the tool and the workpiece material at a processing temperature exceeding 800 ° C is also one of the reasons for the formation of groove wear. Because during the machining process, the titanium molecules of the workpiece gather in the front area of the blade and are "welded" to the blade under high pressure and high temperature, forming a chipping tumor. When the built-up edge is peeled from the blade, the carbide coating of the blade is taken away. Therefore, titanium alloy processing requires special blade materials and geometries.

4. Tool structure suitable for titanium machining

The focus of titanium alloy processing is heat, and a large amount of high-pressure cutting fluid must be accurately and timely sprayed onto the cutting edge to quickly remove heat. There are unique structures on the market for milling cutters specifically for titanium alloy machining.