Titanium Alloy Development History
"Since the discovery of titanium in 1790, mankind has carried out a hundred years of arduous exploration in order to obtain its extraordinary properties."
In 1910, human beings made titanium metal for the first time, but it was not until 1951, 40 years later, that the industrial production of titanium was finally realized. In the 1960s, my country began to manufacture and apply titanium alloys.
Titanium Alloy Processing Difficulty
Today, titanium alloys have become one of the main structural materials for contemporary aircraft and engines because of their high specific strength, corrosion resistance, high temperature resistance, and fatigue resistance. They are widely used in aircraft structural parts and heat-resistant parts. , Therefore, titanium alloy is called "space metal" again.
However, titanium alloys also have 4 fatal shortcomings: low thermal conductivity, severe work hardening, high affinity with tools, and small plastic deformation. These properties make titanium alloys extremely difficult to machine. Among them, the cutting index of titanium alloy is only 20% of that of free-cutting steel!
1. Low thermal conductivity
Neither turning nor boring are particularly difficult operations, and carbide tools are often used for continuous cutting, mass production, or cutting for high volume metal removal. When forming cutting, turning or cutting, a cermet tool can be used to avoid cutting interruption with a constant forced feed, and the cutting process should not be stopped or decelerated.
2. Serious work hardening
When drilling deep holes, a short and sharp drill bit and low-speed forced feed should be used, and the support frame should be repeatedly tightened and fully cooled; and the drill bit should not be rotated in the hole, and should be drilled at a constant speed in the hole; each drilling Before drilling, the drill bit is first retracted, then the drill bit is cleaned, drilled and chips removed; when the hole is finally broken, forced feed can be used.
3. High affinity with knives
Try to avoid machining blind holes or too long through holes to prevent the surface roughness of the internal thread from becoming larger or breaking the tap; at the same time, the taps with surface oxidation, oxidation or chrome plating can also reduce seizure and wear.
4. Small plastic deformation
The springback is serious, which is half of the elastic modulus of 45 steel, causing serious friction and easy clamping and deformation of the workpiece.
Titanium Alloy Processing Technology
In order to deal with the problem of difficult machining of titanium alloys, the main methods of machining titanium alloys include: turning, milling, boring, drilling, grinding, tapping, sawing, EDM, etc.
1. Turning and boring
Neither turning nor boring are particularly difficult operations, and carbide tools are often used for continuous cutting, mass production, or cutting for high volume metal removal. When forming cutting, turning or cutting, a cermet tool can be used to avoid cutting interruption with a constant forced feed, and the cutting process should not be stopped or decelerated.
2. Drilling
When drilling deep holes, a short and sharp drill bit and low-speed forced feed should be used, and the support frame should be repeatedly tightened and fully cooled; and the drill bit should not be rotated in the hole, and should be drilled at a constant speed in the hole; each drilling Before drilling, the drill bit is first retracted, then the drill bit is cleaned, drilled and chips removed; when the hole is finally broken, forced feed can be used.
3. Tap
Try to avoid machining blind holes or too long through holes to prevent the surface roughness of the internal thread from becoming larger or breaking the tap; at the same time, the taps with surface oxidation, oxidation or chrome plating can also reduce seizure and wear.
4. Sawing processing
When sawing, low surface speed, continuous forced feed, and coarse-toothed high-speed steel saw blades with a pitch of 4.2 mm ~ 8.5 mm are suitable for sawing titanium alloys; if a band saw titanium alloy is used, the saw blade pitch is determined by the workpiece. The thickness is determined, generally 2.5 mm ~ 25.4 mm. The thicker the material, the larger the pitch. During the process, it is necessary to maintain the forced supply capacity and prepare the required coolant.
5. Low cost
Develop alloys that contain no or less precious metal elements, and add cheap elements such as iron, oxygen, and nitrogen, and develop titanium alloys that are easy to form, easy to cut, and cheap in alloying elements and master alloys, which are crucial to reducing the cost of civil titanium alloys. ;
6. EDM
Generally, copper and zinc are the best electrode materials. EDM of titanium alloy requires an operating gap between the tool and the workpiece, and the range is preferably 0.005mm ± 0.4mm; a smaller gap is usually used for finishing that requires a smooth surface, while Larger clearances are used for roughing operations that require rapid metal removal.
Titanium Alloy Future Prospects
With the maturity of titanium alloy processing technology and the continuous improvement of processing equipment and tools, the stable processing of super-large structural parts and precision and complex parts has been achieved. The processing efficiency of titanium alloys has been significantly improved compared with the previous ones.
According to the current development trend, in the future, the titanium alloy processing technology at home and abroad may develop in the following directions:
1. High performance
That is to develop alloys with higher service temperature, higher specific strength, higher specific modulus, and better corrosion resistance and wear resistance;
2. Multifunctional
That is to develop titanium alloys with various special functions and uses to further expand the application of titanium and titanium alloys;
3. Practicality
Improve the practical properties of existing alloys and expand the scope of use of traditional alloys through equipment and process improvements;
4. New technology
Adopt new processing technologies, such as cold forming technology, to improve the production efficiency, yield and product performance of titanium alloys;
5. Low cost
Develop alloys that contain no or less precious metal elements, and add cheap elements such as iron, oxygen, and nitrogen, and develop titanium alloys that are easy to form, easy to cut, and cheap in alloying elements and master alloys, which are crucial to reducing the cost of civil titanium alloys. ;
6. High tech
Advanced computer technology is used to simulate the deformation and processing process of the workpiece, predict the evolution of the metal microstructure, and even predict the mechanical properties of the final product, improve work efficiency and reduce development costs.
It is believed that with the continuous research and exploration of the majority of scientific and technological workers in the aviation industry, our understanding of titanium alloys has gradually deepened, and more technical means will emerge for the processing of titanium alloys, making greater contributions to my country's aviation industry!
