Why do we think titanium alloy is such 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 machining titanium alloy is much more complex than that of steel, which makes the machining of titanium alloy face great difficulties.
Why do we think titanium alloy is such a difficult material to work with? Because of the lack of understanding of its processing mechanism
Most titanium alloys have very low thermal conductivity, only 1/7 of that of steel and 1/16 of that of aluminum. Therefore, the heat generated in the process of cutting titanium alloy will not be quickly transferred to the workpiece or chip away, and gathered in the cutting area, the temperature generated can be up to 1 000℃ above, so that the cutting edge of the tool rapidly wear, crack and debris tumor, rapid wear of the blade, and make the cutting area produce more heat, further shorten the life of the tool.
The high temperature generated during the cutting process also damages the surface integrity of the titanium alloy parts, resulting in a decrease in the geometric accuracy of the parts and a work hardening phenomenon that severely reduces the fatigue strength of the parts.
The elasticity of titanium alloy may be beneficial to the performance of parts, but in the cutting process, the elastic deformation of the workpiece is an important cause of vibration. Cutting pressure causes the "elastic" workpiece to move away from the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, which aggravates the problem of poor thermal conductivity of titanium alloy.
This problem is more serious when processing thin-walled or ring parts that are easily deformed. It is not easy to process thin-walled titanium alloy parts to the desired dimensional accuracy. Because when the workpiece material is pushed 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 increased significantly. At this point, machining at the previously determined cutting speed becomes too high, further leading to sharp tool wear.
"Heat" is the titanium alloy difficult to process the "culprit"!
2. Technical know-how of processing titanium alloy
On the basis of understanding the processing mechanism of titanium alloy and previous experience, the main technological know-how of processing titanium alloy is as follows:
(1) Adopt blade with positive Angle geometry to reduce cutting force, cutting heat and workpiece deformation.
(2) Keep a constant feed to avoid hardening of the workpiece. The cutting tool should always be in the feed state during the cutting process. The radial cutting quantity A and e should be 30% of the radius during milling.
(3) High pressure and large flow cutting fluid is adopted to ensure the thermal stability of the processing process and prevent surface denaturation of the workpiece and tool damage due to high temperature.
(4) Keep the cutting edge of the blade sharp, blunt tool is the cause of heat accumulation and wear, easy to lead to tool failure.
(5) Machining the titanium alloy in the softest state possible, because after hardening the material becomes more difficult to work, heat treatment increases the strength of the material and increases blade wear.
(6) Use large tool tip radius or chamfering to cut, as much as possible into the cutting edge. This reduces cutting force and heat at every point, preventing local breakage. In the milling of titanium alloy, the cutting speed has the greatest influence on the tool life vc, followed by the radial cutting amount (milling depth) ae.
3. Solve the titanium processing problem from the blade
The blade groove wear in titanium alloy machining is the local wear in the back and front along the cutting depth direction, which is often caused by the hardening layer left by the early machining. The chemical reaction and diffusion between the tool and the 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 process of processing, titanium molecules in the workpiece accumulate in the front of the blade, under high pressure and high temperature "welding" to the blade, the formation of debris nodules. When chip nodules are removed from the blade, they take the hard alloy coating away from the blade, so machining titanium alloys requires special blade materials and geometry.
4. Tool structure suitable for titanium processing
The focus of titanium alloy processing is heat, a large number of high pressure cutting fluid to timely and accurate injection to the cutting edge, in order to quickly remove the heat. There are special milling cutters on the market for titanium alloy processing with unique structures.
Contact us for more information. Thank you
Nicole
Company: Baoji Jimiyun Dynamic Co., Ltd
Cuntry:China
Add:Baoti road,Jintai,Baoji city,Shaanxi,China
Cel:+86 13369210920
Website:www.jm-titanium.com
