Entering the 21st century, aerospace has shown broader development prospects. High-level or ultra-high-level aerospace activities have become more frequent, and their role will go far beyond the field of science and technology itself, and will have an impact on politics, economy, military, and even human social life. Broader and far-reaching impact.
It should be pointed out that the tremendous achievements made in the aerospace industry are inseparable from the development and breakthrough of aerospace material technology, and titanium alloys have an irreplaceable position in the aerospace field due to their high strength and light surface quality.
Titanium alloy fasteners generally require solution aging heat treatment to ensure that they meet the requirements for shear strength of 660MPa and tensile strength of 1100MPa.
Fasteners made of titanium alloys must be inspected in detail. In addition to observing whether there is damage to the appearance, they must also be inspected for mechanical properties and metallurgy. Titanium alloy fasteners have strict material standards, quality, performance standards and requirements. ,
The processing technical conditions of titanium alloy fasteners must comply with the relevant requirements proposed in the AMS4967 standard (wires, annealing, forgings and ring parts, heat-treatable titanium alloy bars). Phase, appearance, defect control, and mechanical properties have clear standard requirements and performance requirements.
1. Problems in the processing of titanium alloy fasteners
Corrosion problem. When installing titanium alloy fasteners, it is easy to form a certain gap, so that surface paint will flow in between metal air strikes, which makes the fasteners susceptible to clothing during the production process. In the subsequent use process, the tightness of the connection will be affected. The main reason for the corrosion resistance of titanium alloy materials is that there is a protective oxide film on the surface. This film can effectively protect the titanium alloy inside the material from being oxidized, thereby improving the corrosion resistance of the titanium alloy material.
Problems in turning processing. Titanium alloy materials are difficult to process and have poor thermal conductivity. The heat generated during the machining process will not diffuse through the parts and the machine tool structure, but will be concentrated in the cutting area. There is a strong notch sensitivity, which may cause chipping and deformation; while the blunt blade will generate even higher heat And further reduce the life of the tool. The high temperature generated during the cutting process will also cause the workpiece to continue to harden. This phenomenon will affect the surface integrity of titanium, and may cause the geometric accuracy of the part to be inaccurate, and seriously reduce its fatigue strength. In reasonable machining conditions, the turning process is not difficult. If it is for mass production, continuous cutting, and cutting with a large amount of metal removal, cemented carbide tools are required; and steel tools are required for forming cutting or cutting. Make reasonable adjustments and use cermet knives when necessary.
The precision of machining of titanium alloy fasteners. The precision requirements for machinery will be higher. In mechanical production, because the tools are in a state of working wear during each production process, and are calibrated according to the program, the density of titanium alloy fasteners is higher, and the tools are easily worn during the machining process. In the state, the tool is still processed according to the program, it is easy to cause the precision of the compact part in the processing process to be affected. If the precision of the fastener is not strictly controlled within the error range during the entire processing process, the titanium alloy and other materials cannot be closely connected during the use process, which will have a certain impact on the subsequent use. The precision of titanium alloy fasteners in the machining production process is a major problem that needs to be overcome in the production process. For example, the fastener technology product shown in the figure is a product made in a high-precision production workshop, and the connection performance of this product is better.
2. Process know-how for processing titanium alloy fasteners
Use positive-angle geometry blades to reduce cutting force, cutting heat and workpiece deformation; keep the blade edge sharp, blunt tools are the cause of heat buildup and wear, and easily lead to tool failure.
Maintain a constant feed to avoid hardening of the workpiece. The tool must always be in the feed state during the cutting process. The radial tool engagement ae during milling should be 30% of the radius.
Using high-pressure and large-flow cutting fluid to ensure the thermal stability of the machining process and prevent surface degeneration and tool damage caused by excessive temperature.
It is possible to process the titanium alloy in the softest state, because the material becomes more difficult to process after hardening, and the heat treatment improves the strength of the material.
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.
3. Application in aviation
According to data, titanium alloy fasteners are widely used in aircraft.
My country's domestically produced C919 aircraft needs about 200,000 pieces of titanium alloy fasteners, and 20 million pieces of titanium alloy fasteners are needed to complete the first batch of 100 start-up orders.
According to the plan to produce 150 large aircraft in 2018, 30 million titanium alloy fasteners will be needed every year. Titanium alloy fasteners have huge development potential, and the market development prospects are very promising.
In recent years, with the rapid development of my country's aerospace industry, the demand for aviation fasteners has increased sharply.
In addition, the manufacturing of large aircraft in my country has made great progress. Although there is still a period of time before the first flight in 2014, the start-up order for 100 aircraft has been obtained at the air show at the end of 2010. These orders must be completed for titanium The demand for alloy fasteners is huge, and the market prospect of titanium alloy fasteners is very promising.
In order to ensure the continuous and safe flight of aerospace appliances, the requirements for titanium fasteners are extremely high. In particular, commercial aircraft will operate for 20 to 30 years after being put into operation, and will continue to fly continuously for more than ten hours a day. The requirements for fasteners are even higher than the standards for aerospace. Titanium alloy fasteners can meet the above requirements.
In addition, titanium alloy fasteners can greatly reduce the weight of the aircraft itself, not only can improve the performance of the aircraft, but also reduce the cost of use, Z is mainly to reduce fuel consumption.
Such excellent performance is bound to be widely used in aircraft manufacturing, and the main problem that currently plagues its development is titanium alloy materials.
The analysis of the machinery industry pointed out that my country is a large fastener manufacturer, and its output has ranked first in the world for many years, but my country is not a strong fastener manufacturer.
Most of the fasteners made in China are low-end and low-value-added products. The market share of high-end fasteners such as aviation fasteners is relatively low. The product types and specifications are very limited, and related technologies and production need to be improved.
The widespread use of titanium alloy materials in recent years is inseparable from the drive of innovation and the grand plan of the country.
As the cost of titanium alloy processing continues to drop, its application in aircraft structures will become more and more extensive in the future.
With the rapid development of my country's aviation industry and the continuous improvement of aircraft performance requirements, the future high-performance aviation fasteners put forward higher strength, higher fracture toughness, and higher fatigue performance requirements for their titanium alloy materials.
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