Discussion and Application of Production and Processing of Aviation Titanium Alloy Forgings
Entering the 21st century, aerospace has shown a broader development prospect. High-level or ultra-high-level aerospace activities will become more frequent, and its 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 more far-reaching effects.
It should be pointed out that the great achievements of the aerospace industry are inseparable from the development and breakthrough of aerospace material technology, and titanium alloy has an irreplaceable position in the aerospace field due to its advantages such as high strength and light surface quality.
Grade 5 titanium forging generally requires solution aging heat treatment to ensure that it meets the requirements for shear strength of 660MPa and tensile strength of 1100MPa.
Fasteners made of titanium alloy should be inspected in detail. In addition to observing whether there is damage in the appearance, mechanical properties and metallurgy inspections should also be carried out. 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 (wire, annealed, forgings and rings, heat-treatable titanium alloy rods). There are clear standard requirements and performance requirements in terms of phase, appearance, defect control, and mechanical properties.
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 the surface coating will flow in between the metal air strikes, which makes the fasteners vulnerable to damage during the production process. During subsequent use, 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 its surface. This layer of film can effectively protect the titanium alloy inside the material from oxidation, thereby improving the corrosion resistance of the titanium alloy material.
Problems in turning processing. Titanium alloy materials are difficult to machine and have poor thermal conductivity. The heat generated during machining does not diffuse through the part and machine structure, but is concentrated in the cutting zone, where there is a strong notch sensitivity, which can lead to chipping and deformation; while dulling of the cutting edge generates even higher heat And further reduce tool life The high temperature generated during the cutting process will also cause continuous hardening of the workpiece. This phenomenon will affect the surface integrity of titanium and may lead to inaccurate geometric accuracy of the part and seriously reduce its fatigue strength. Generally speaking, in In reasonable mechanical processing conditions, the turning process is not difficult. If it is for mass production, continuous cutting, and cutting with a relatively large amount of metal removal, it is necessary to use cemented carbide tools; and for forming cutting or cutting, it is necessary to use steel tools. Make reasonable adjustments and use cermet knives if necessary.
The precision of machining of titanium alloy fasteners. The precision requirements for machinery will be higher. During mechanical production, because the tool is in a state of work wear during each production process, and it is calibrated according to the program, the density of titanium alloy fasteners is higher, and the tool is easily worn during the processing process. In this state, the tool is still processed according to the program, which can easily cause the precision of the compact parts to be affected during the processing. If the precision of the fasteners is not strictly controlled within the error range during the entire processing process, the titanium alloy and other materials cannot be tightly 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 craft product shown in the picture is a product made in a high-precision production workshop, and the connection performance of this product is better.
2. Technological know-how for processing titanium alloy fasteners
Adopt positive-angle geometric inserts to reduce cutting force, cutting heat and deformation of the workpiece; keep the cutting edge of the inserts sharp, blunt tools are the cause of heat buildup and wear, which can easily lead to tool failure.
Keep a constant feed to avoid hardening of the workpiece. During the cutting process, the tool should always be in the feed state. The radial cutting ae should be 30% of the radius during milling.
High-pressure and large-flow cutting fluid is used to ensure the thermal stability of the machining process and prevent the workpiece surface from degeneration and tool damage due to excessive temperature.
Try to process titanium alloy in the softest state, because the material becomes more difficult to process after hardening, and heat treatment improves the strength of the material.
Plunge in with a large nose radius or chamfer to get as much of the cutting edge into the cut as possible. This can reduce the cutting force and heat at each point and prevent local breakage. When milling titanium alloys, among the cutting parameters, the cutting speed has the greatest influence on the tool life vc, followed by the radial cutting amount (milling depth) ae.
3. Application in aviation
According to the data, titanium alloy fasteners are widely used on aircraft.
Each Chinese-made 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 planned annual production of 150 large aircraft in 2018, 30 million pieces of titanium alloy fasteners are needed every year. The development potential of titanium alloy fasteners is huge, and the market development prospect is very promising.
In recent years, with the rapid development of China's aerospace industry, the demand for aviation fasteners has increased dramatically.
In addition, China's large aircraft manufacturing has made great progress. Although there is still some time before the first flight in 2014, 100 start-up orders have been obtained at the air show at the end of 2010. To complete these orders is very important 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 equipment, the requirements for titanium fasteners are extremely high. In particular, commercial aircraft will operate for 20 to 30 years after they are put into operation, and fly continuously for more than ten hours a day. The requirements for fasteners are even higher than the aerospace standards. Titanium alloy fasteners can meet the above requirements.
In addition, titanium alloy fasteners can greatly reduce the weight of the aircraft itself, which can not only improve the performance of the aircraft, but also reduce the cost of use. The most important thing is to reduce fuel consumption.
Such excellent performance is bound to be widely used in aircraft manufacturing. The main problem that currently plagues its development is the titanium alloy material.
The analysis of the machinery industry pointed out that China is a big fastener producing country, and its output has ranked first in the world for many years, but China is not a strong fastener producing country.
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 decrease, its application in aircraft structures will become more and more extensive in the future.
With the rapid development of China's aviation industry and the continuous improvement of aircraft performance requirements, future high-performance aerospace fasteners will require higher strength, higher fracture toughness, and higher fatigue performance for titanium alloy materials.
