Why do we think titanium alloy is a difficult material to process?Because of the lack of deep understanding of its processing mechanism and phenomenon.
1.Physical phenomenon of titanium processing
The cutting force of titanium alloy is only slightly higher than that of steel of the same hardness.
Why do we think titanium alloy is a difficult material to process?Because of the lack of understanding of its processing mechanism
Most titanium alloys have very low thermal conductivity, 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 produced in the cutting process destroys the surface integrity of titanium alloy parts at the same time, resulting in the reduction of geometric accuracy of parts and the serious reduction of their fatigue strength.
The elasticity of titanium alloy may be beneficial to the performance of parts, but the elastic deformation of the workpiece is an important cause of vibration during the cutting process.Cutting pressure causes the "elastic" workpiece to leave the tool and rebound, thus making the friction between the tool and the workpiece greater than the cutting effect.The friction process also generates heat, aggravating the thermal conductivity of titanium alloy.
This problem is more serious when processing thin-walled or ring-shaped parts. It is not easy to process titanium alloy thin-walled parts to the expected size accuracy.As the workpiece material is pushed 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 have increased significantly.At this point, according to the original determined cutting speed processing becomes too high, further leading to sharp tool wear.
"Heat" is difficult to process titanium alloy "culprit"!
2. Process knowhow for processing titanium alloy
On the basis of understanding the processing mechanism of titanium alloy and previous experience, the main processing techniques of titanium alloy are as follows:
(1) positive Angle geometric blade is adopted to reduce cutting force, cutting heat and deformation of workpiece.
(2) maintain a constant feed to avoid hardening of the workpiece, the cutter should always be in the feed state during the cutting process, the radial draft a e should be 30% of the radius in milling.
(3) high pressure and large flow cutting fluid is adopted to ensure the thermal stability of the processing process and prevent the surface denaturation of workpiece and tool damage due to high temperature.
(4) keep the blade edge sharp, blunt tool is the cause of hot build-up and wear, easy to cause tool failure.
(5) as far as possible, the titanium alloy should be processed in the softest state, because the hardened material becomes more difficult to process, and the heat treatment improves the strength of the material and increases the wear of the blade.
(6) use large tip radius or chamfer cut, as much as possible into the cutting blade.This reduces the cutting force and heat at each point and prevents local damage.In milling titanium alloy, the influence of cutting speed on tool life vc was the greatest, followed by radial draft (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.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.During processing, titanium molecules in the workpiece accumulate in the front of the blade and are "welded" to the blade under high pressure and high temperature, forming a debris tumor.When the debris is removed from the blade, the carbide coating of the blade is removed. Therefore, the processing of titanium alloy requires special blade materials and geometric shapes.
4. Suitable for titanium processing tool structure
The focus of titanium alloy processing is heat, a large amount of high pressure cutting fluid to timely and accurate injection on the cutting edge, in order to be able to quickly remove the heat.There is a special market for titanium alloy milling cutter unique structure.