We often come into contact with air transportation, such as sending air cargo or taking a plane. When you see an airplane, you may have a question: What is an airplane made of? Why can we load so many and so heavy goods

Can you fly so high? Let's look down with questions.

1、 Introduction to Titanium

In 1948, DuPont Company in the United States used the magnesium method to produce sponge titanium by ton, marking the beginning of industrial production of sponge titanium, also known as titanium. Titanium alloys are widely used in various fields due to their high specific strength, good corrosion resistance, and high heat resistance.

Titanium is abundant in the Earth's crust, ranking ninth in content, far higher than common metals such as copper, zinc, and tin. Titanium is widely present in many rocks, especially in sand and clay.

2、 The characteristics of titanium

High strength: 1.3 times that of aluminum alloy, 1.6 times that of magnesium alloy, and 3.5 times that of stainless steel, ranking first among metal materials.

High thermal strength: The usage temperature is several hundred degrees higher than that of aluminum alloy, and it can work for a long time at a temperature of 450-500 ℃.

Good corrosion resistance: resistant to acid, alkali, and atmospheric corrosion, with particularly strong resistance to pitting and stress corrosion.

Good low-temperature performance: Titanium alloy TA7 with extremely low interstitial elements can maintain a certain degree of plasticity at -253 ℃.

High chemical activity: At high temperatures, the chemical activity is very high, easily reacting with gas impurities such as hydrogen and oxygen in the air to form a hardened layer.

Low thermal conductivity and elastic modulus: The thermal conductivity is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about half of that of steel.

3、 Classification and uses of titanium alloys

Titanium alloys can be divided into heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium molybdenum, titanium palladium alloys, etc.), low-temperature alloys, and special functional alloys (titanium iron hydrogen storage materials and titanium nickel memory alloys) according to their uses.

Although titanium and its alloys have a short history of application, they have earned multiple honorable titles due to their outstanding performance. The first title awarded is "Space Metal". It is lightweight, strong, and resistant to high temperatures, making it particularly suitable for manufacturing airplanes

And various spacecraft. Currently, about three-quarters of the titanium and titanium alloys produced worldwide are used in the aerospace industry. Many components that were originally made of aluminum alloy have switched to titanium alloy.

4、 Aerospace applications of titanium alloys

Titanium alloy is mainly used as a manufacturing material for aircraft and engines, such as forged titanium fans, compressor discs and blades, engine covers, exhaust devices and other parts, as well as structural framework components such as aircraft beams and frames. Spacecraft mainly utilize the high ratio of titanium alloy

To manufacture various pressure vessels, fuel tanks, fasteners, instrument straps, structures, and rocket shells with strength, corrosion resistance, and low temperature resistance. Artificial Earth satellites, lunar modules, manned spacecraft, and space shuttles also use titanium alloy plate welding components.

Why does it have to use titanium alloy for the materials of air transport aircraft?

In 1950, the United States first used non load bearing components such as rear fuselage heat shields, wind shields, and tail shields on F-84 fighter bombers. Since the 1960s, the use of titanium alloy has shifted from the rear fuselage to the center fuselage, partially replacing structural steel in the manufacture of partition frames

Important load-bearing components such as beams and wing slides. Since the 1970s, civilian aircraft have started to use a large amount of titanium alloy, such as the Boeing 747 aircraft, which uses over 3640 kilograms of titanium, accounting for 28% of the aircraft weight. With the development of processing technology, in rockets, artificial satellites, and the universe

On the spacecraft, a large amount of titanium alloy was also used.

The more advanced the aircraft, the more titanium it uses. The titanium alloy used in the F-14A fighter jet in the United States accounts for approximately 25% of the aircraft weight; The F-15A fighter jet is 25.8%; The fourth generation fighter jet in the United States uses 41% titanium, and its F119 engine uses 39% titanium, which is

The aircraft currently uses the highest amount of titanium.

5、 The reasons why titanium alloys are widely used in aviation

The maximum speed of modern aircraft has reached over 2.7 times the speed of sound. Such rapid supersonic flight will generate a large amount of heat due to friction between the aircraft and the air. When the flight speed reaches 2.2 times the speed of sound, aluminum alloy cannot withstand it anymore. have to

High temperature resistant titanium alloy must be used.

When the thrust to weight ratio of aircraft engines increases from 4-6 to 8-10, and the outlet temperature of the compressor correspondingly increases from 200-300 ℃ to 500-600 ℃, the low-pressure compressor discs and blades originally made of aluminum must be replaced with titanium alloy.

In recent years, scientists have made new progress in their research on the properties of titanium alloys. The titanium alloy originally composed of titanium, aluminum, and vanadium has a maximum working temperature of 550 ℃ to 600 ℃, while the newly developed titanium aluminum (TiAl) alloy has a maximum working temperature of 550 ℃ to 600 ℃

The working temperature has been raised to 1040 ℃.

Replacing stainless steel with titanium alloy to manufacture high-pressure compressor discs and blades can reduce structural weight. For every 10% reduction in aircraft weight, fuel can be saved by 4%. For rockets, for every 1kg reduction in weight, they can increase their range by 15km.

Why does it have to use titanium alloy for the materials of air transport aircraft?

Titanium alloy material aircraft landing gear parts

6、 Analysis of machining characteristics of titanium alloy

Firstly, titanium alloy has a low thermal conductivity, only 1/4 of steel, 1/13 of aluminum, and 1/25 of copper. Due to slow heat dissipation in the cutting area, it is not conducive to thermal balance. During the cutting process, the heat dissipation and cooling effects are poor, making it easy to form high temperatures in the cutting area

After work, the deformation and rebound of the parts are large, causing an increase in cutting tool torque, fast blade wear, and reduced durability.

Secondly, the thermal conductivity of titanium alloy is low, making it difficult to dissipate cutting heat in a small area near the cutting tool. This increases the friction force on the front cutting surface, making it difficult to remove chips and reducing cutting heat, accelerating tool wear. Finally, the chemical activity of titanium alloys

At high temperatures, it is easy to react with the tool material during processing, forming dissolution and diffusion, resulting in phenomena such as sticking, burning, and breakage of the tool.

7、 Characteristics of titanium alloy processing in machining centers

The machining center can process multiple parts simultaneously, improving production efficiency.

Improve the machining accuracy of parts and achieve good product consistency. The machining center has a tool compensation function, which can obtain the machining accuracy of the machine tool itself.

Has extensive adaptability and greater flexibility. Such as the arc machining, chamfering, and transition fillet of this part.

It can achieve multiple functions for one machine. The machining center can perform a series of processing such as milling, drilling, boring, and tapping.

Accurate cost calculation can be performed to control production progress.

No need for specialized fixtures, saving a lot of cost and expenses, and shortening the production cycle.

Greatly reduces the labor intensity of workers.

It can perform multi axis machining with processing software such as UG.

Why does it have to use titanium alloy for the materials of air transport aircraft?

8、 Selection of cutting tools and coolant materials

1. The selection of cutting tool materials should meet the following requirements:

Sufficient hardness. The hardness of the cutting tool must be much greater than that of titanium alloy.

Sufficient strength and toughness. Due to the high torque and cutting force that cutting tools bear when cutting titanium alloys, they must have sufficient strength and toughness.

Sufficient wear resistance. Due to the good toughness of titanium alloy, the cutting edge needs to be sharp during machining. Therefore, the tool material must have sufficient wear resistance to reduce work hardening. This is the most important parameter for selecting titanium alloy cutting tools for machining.

The affinity between tool materials and titanium alloys is poor. Due to the high chemical activity of titanium alloy, it is necessary to avoid the formation of alloy deposits and diffusion between the tool material and titanium alloy, which may cause sticking and burning of the tool.

After conducting experiments on commonly used domestic and foreign tool materials, it has been shown that using high cobalt tools has ideal effects. The main function of cobalt is to strengthen the secondary hardening effect, improve the red hardness and hardness after heat treatment, and have high toughness

Wear resistance and good heat dissipation.

2. Geometric parameters of milling cutters

The processing characteristics of titanium alloy determine that there are significant differences in the geometric parameters of cutting tools compared to ordinary cutting tools.

Spiral angle β Choosing a smaller spiral angle increases the chip removal groove, making it easier to remove chips and faster to dissipate heat. At the same time, it also reduces the cutting resistance during the cutting process.

Anterior horn γ When cutting, the cutting edge is sharp and the cutting is light and fast, avoiding excessive cutting heat generated by titanium alloy and thus avoiding secondary hardening.

Rear corner α Reducing the wear rate of the blade is beneficial for heat dissipation and greatly improves its durability.

3. Cutting parameter selection

Titanium alloy machining should choose a lower cutting speed, appropriate large feed rate, reasonable cutting depth and precision machining amount, and sufficient cooling.

Cutting speed VcVc=30~50m/min

For rough machining, a larger feed rate is taken, while for precision and semi precision machining, a moderate feed rate is taken.

The optimal cutting depth is apap=1/3d. Titanium alloy has good affinity and is difficult to remove chips. If the cutting depth is too large, it can cause tool sticking, burning, and fracture.

Precision machining allowance α The surface hardening layer of moderate titanium alloy is about 0.1-0.15mm, and the allowance is too small. The cutting edge cuts on the hardening layer, making the tool easy to wear. It should be avoided to work on the hardening layer, but the cutting allowance should not be too large.

4. Coolant

It is best not to use chlorine containing coolant during titanium alloy processing to avoid the generation of toxic substances and hydrogen embrittlement, and to prevent high-temperature stress corrosion cracking of titanium alloys.

Choose a synthetic water-soluble emulsion, or you can use your own coolant.

During cutting, the coolant should be sufficient, the coolant circulation speed should be fast, the cutting fluid flow rate and pressure should be large, and the machining center should be equipped with dedicated cooling nozzles. As long as attention is paid to adjustment, the expected effect can be achieved.