In the 21st century with rapid industrial development, my country's aerospace industry has achieved unprecedented development. High-level aerospace activities are becoming more and more frequent. These activities not only affect science and technology, but also have a profound impact on politics, economy, military, and even human life. The great achievements of the aerospace industry are inseparable from the progress of aviation materials technology. Titanium alloys have an irreplaceable position in the aviation field because of their high strength and light weight.
In order to improve the shear strength and tensile strength of titanium alloy fasteners, titanium alloy fasteners need to be subjected to solid solution aging heat treatment. This treatment method can increase the shear strength of the fasteners to 660MPa, while the tensile strength can reach 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 subjected to mechanical properties and metallurgy
In the 21st century with rapid industrial development, my country's aerospace industry has achieved unprecedented development. The increasingly frequent aerospace activities have driven the development of aerospace science and accelerated the research and development of aerospace materials. Titanium alloys have gradually occupied the dominant position of aerospace materials because of their excellent high strength and low weight ratio. This has brought about tremendous changes in my country's economy, military and daily life.
In order to improve the shear strength and tensile strength of titanium alloy fasteners, titanium alloy fasteners need to be subjected to solid solution aging heat treatment. This treatment method can increase the shear strength of fasteners to 660MPa, while the tensile strength can reach 1100MPa. Titanium alloy fasteners must be strictly inspected for appearance, mechanical properties and metallurgical processes before leaving the factory. Titanium alloy fasteners have strict material standards and quality, performance standards and requirements. The processing technical conditions of titanium alloy fasteners must comply with the relevant requirements set forth in the AMS4967 standard (wire, annealing, forgings and rings, heat-treatable titanium alloy bars). This standard has clear standard requirements and performance requirements in terms of material tolerance, size, metallographic structure, appearance, defect control, and mechanical properties.
Problems in the processing of titanium alloy fasteners
Corrosion problem. It is easy to form a certain gap when installing titanium alloy fasteners, so that surface coatings will flow in between metal air strikes, which makes the fasteners vulnerable to clothing during the production process. In the subsequent use process, the tightness of the connection will be affected. The strong corrosion resistance of titanium alloy materials is mainly because titanium alloy is very active and will oxidize to form an oxide film. This oxide film is very corrosion-resistant and hardly reacts with other materials, protecting the interior from corrosion, thereby improving the corrosion resistance of titanium materials.
Problems in turning. Titanium alloy materials are difficult to process and have poor thermal conductivity. The heat generated during the processing will not diffuse through the parts and machine tool structure, but will be concentrated in the cutting area. There is a strong notch sensitivity, which may cause chipping and deformation; and the blunting of the blade will generate even higher heat and further reduce the tool life. 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 parts to be inaccurate and seriously reduce its fatigue strength. Generally speaking, under 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, carbide tools need to be used; and when forming cutting or cutting, the steel tool needs to be reasonably adjusted, and metal ceramic tools are used when necessary.
Precision issues in the machining of titanium alloy fasteners. The precision requirements for machinery will be higher. During mechanical production, since the tool is in a state of working wear during each production process and is calibrated according to the program, the density of titanium alloy fasteners is higher, and the tool is easily worn during the processing process. Under the state of wear, the tool is still processed according to the program, which can easily affect the precision of the fastener during the processing.
If the accuracy of the fastener is not strictly controlled within the allowable error range during the processing, then when used, the titanium alloy and other materials cannot be tightly connected, which will affect the subsequent use effect. Therefore, improving the accuracy of titanium alloy fasteners in mechanical processing is an important challenge that needs to be solved in the production process. For example, the fastener process product shown in the figure is a product made in a high-precision production workshop, and the connection performance of this product is better.
Process tips for processing titanium alloy fasteners
Use a blade with a positive angle geometry to reduce cutting force, cutting heat and deformation of the workpiece; keep the blade edge sharp, blunt tools are the cause of heat accumulation and wear, and are prone to tool failure. Maintain a constant feed to avoid hardening of the workpiece. The tool should always be in feed during the cutting process. The radial cutting depth ae should be 30% of the radius during milling. Use high-pressure and high-flow cutting fluid to ensure the thermal stability of the machining process and prevent surface denaturation and tool damage due to excessive temperature. Process titanium alloys in the softest state as much as possible, because the material becomes more difficult to process after hardening, and heat treatment increases the strength of the material.
Use a large tool tip radius or chamfer to cut in, and put as much of the blade into the cutting as possible. This can reduce the cutting force and heat at each point and prevent local breakage. When milling titanium alloys, the cutting speed has the greatest impact on the tool life vc among all cutting parameters, and the radial cutting depth (milling depth) ae is second.
Application in aviation
Titanium alloy fasteners are widely used in the fields of flight and shipbuilding. For example, each C919 airship delivered in my country requires about 200,000 titanium alloy bolts. To deliver 100 aircraft, a total of 20 million titanium bolts are required. If 150 behemoth transport ships are expected to be shipped annually in 2018, the total amount of titanium fasteners required each year will be as high as 30 million. It can be seen that titanium has extraordinary development potential and the prospects are surprisingly optimistic.
For a long time in the future, with the rapid advancement of my country's aviation industry, the demand for bolts will clearly extend. my country has made significant progress in the manufacture of large aircraft. Although there is still some time before the first flight in 2014, the action plan for the advancement of 100 aircraft has been determined in the dialogue at the end of 2010. Judging from the total amount of these orders, the demand for titanium fasteners is very huge and the market prospects are very broad.
In order to ensure the safety and robustness of the flight device, the requirements for titanium alloy bolts are very strict. Especially after commercial aircraft are put into operation, they generally need to work for 20 to 30 hours for a long time and fly more than ten hours a day, so the necessity of turbulence is actually higher than during normal flight. Although titanium alloy bolts cannot meet these high requirements, they can also completely reduce the weight of the aircraft, thereby improving the performance of the aircraft, reducing the loss of use, and most importantly, reducing fuel utilization.
