why machining aerospace parts must use titanium alloy materials?
why machining aerospace parts must use titanium alloy materials?
|We often hear titanium alloy products, and we often hear people mention that aerospace will use titanium alloy materials for processing parts. In fact, titanium has an unusual relationship with aerospace, as early as 1953, in the United States. The first use of titanium in the DC-T engine pods and fire walls produced by Douglas has unveiled the history of titanium application to aviation. Since then, titanium has been used in the aerospace industry for more than half a century. Titanium is widely used in aerospace because of its many valuable features for aircraft applications. PTJ Manufacturing Shop specializes in the custom processing and mass production of aerospace components. Today, we will provide you with an in-depth analysis of why aerospace uses titanium materials.|
The origin of titanium
In 1948, DuPont of the United States used magnesium to produce titanium sponge in tons. This marked the beginning of industrial production of titanium sponge, titanium. Titanium alloys are widely used in various fields due to their good corrosion resistance, high strength and high heat resistance.
The content of titanium in the earth's crust can be said to be very rich, much higher than common metals such as copper, zinc and tin, and the content is ranked ninth. It is widely found in many rocks, especially in sand and clay.
Characteristics of titanium
- High heat intensity: The use temperature is several hundred degrees higher than that of aluminum alloy, and it can work for a long time at 450~500 °C.
- High strength: 1.3 times of aluminum alloy, 1.6 times of magnesium alloy, 3.5 times of stainless steel, champion in metal materials.
- Good low temperature performance: Titanium alloy TA7 with extremely low interstitial element can maintain a certain plasticity at -253 °C.
- Good corrosion resistance: acid resistance, alkali resistance, atmospheric corrosion resistance, and strong resistance to pitting and stress corrosion.
- Large chemical activity: high chemical activity at high temperature, easy to chemically react with gaseous impurities such as hydrogen and oxygen in the air to form a hardened layer.
Small thermal conductivity and small elastic modulus: thermal
conductivity is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and
the thermal conductivity of various titanium alloys is about 50% lower
than that of titanium. . The modulus of elasticity of titanium alloy is
about 1/2 of that of steel.
Classification and use of titanium alloys
Titanium alloys can be classified into high-strength alloys, heat-resistant alloys, corrosion-resistant alloys (titanium-molybdenum, titanium-palladium alloys, etc.), low-temperature alloys, and special-function alloys (titanium-iron hydrogen storage materials and titanium-nickel memory alloys). Wait.
Although the history of titanium and its alloys is not long, it has won several honorable titles due to its superior performance. The title that was first won was “space metal”. It is lightweight, strong and resistant to high temperatures, making it ideal for aircraft and various spacecraft. About three-quarters of the world's titanium and titanium alloys are used in the aerospace industry. Many of the parts that originally used aluminum alloys have been replaced with titanium alloys.
The reason why titanium alloy is widely used in aviation
When the thrust ratio of the aero-engine is increased from 4 to 6 to 8 to 10, and the compressor outlet temperature is increased from 200 to 300 ° C to 500 to 600 ° C, the low-pressure compressor disc and blade originally made of aluminum must be used instead. Titanium alloy.
In recent years, scientists have made new progress in the research on the performance of titanium alloys. The original titanium alloy consisting of titanium, aluminum and vanadium has a maximum working temperature of 550 ° C to 600 ° C. The newly developed titanium aluminum (TiAl) alloy has a maximum operating temperature of 1040 ° C.
The use of titanium alloy instead of stainless steel to manufacture high-pressure compressor discs and blades can reduce the structural weight. Each 10% reduction in aircraft can save 4% of fuel. For the rocket, for every 1kg of weight, you can increase the range of 15km.
Aerospace applications of titanium alloys
Titanium alloys are mainly used in the manufacture of aircraft and engines, such as forged titanium fans, compressor discs and blades, hoods, exhausts and other structural components such as aircraft beam frame. The spacecraft mainly utilizes the high specific strength, corrosion resistance and low temperature resistance of titanium alloys to manufacture various pressure vessels, fuel tanks, fasteners, instrument straps, frames and rocket casings. Titanium alloy sheet welded parts are also used in artificial earth satellites, lunar modules, manned spacecraft and space shuttles.
In the United States in 1950, it was used for the first time on the F-84 fighter-bomber as a non-bearing member such as a rear fuselage insulation panel, an air hood, and a tail hood. In the 1960s, the use of titanium alloys moved from the rear fuselage to the middle fuselage, partially replacing structural steel to make important load-bearing components such as bulkheads, beams, and flaps. Since the 1970s, civilian machines have begun to use titanium alloys in large quantities. For example, Boeing 747 passenger aircraft uses more than 3,640 kilograms of titanium and accounts for 28% of the aircraft. With the development of processing technology, a large number of titanium alloys are also used on rockets, satellites and spacecraft.
The more advanced the aircraft, the more titanium is used. The titanium alloy used by the US F-14A fighters accounts for about 25% of the aircraft weight; the F-15A fighter is 25.8%; the fourth generation of American fighters uses 41% of titanium, and the F119 engine uses 39% of titanium. Use the aircraft with the highest amount of titanium.
Analysis of Machining Characteristics of Titanium Alloy
Secondly, the thermal conductivity of the titanium alloy is low, so that the heat of cutting is not easily dissipated in a small area near the cutting blade, the frictional force of the rake face is increased, the chip removal is not easy, the cutting heat is not easily dissipated, and the tool wear is accelerated. Finally, the titanium alloy has high chemical activity, and it is easy to react with the tool material at high temperature to form dissolution and diffusion, causing sticking, burning, and cutting.
cnc machining center processing titanium alloy characteristics
Improve the processing accuracy of parts and product consistency. The machining center has a tool compensation function that can obtain the machining accuracy of the machine itself.
Wide range of adaptability and greater flexibility. Such as arc machining, chamfering and transition fillet of this part.
Can achieve a multi-functional machine. The machining center can perform a series of machining such as milling, drilling, boring and tapping.
Accurate costing can be performed to control production schedules.
No special fixtures are needed, saving a lot of cost and shortening the production cycle.
Greatly reduced the labor intensity of workers.
Multi-axis machining is possible with machining software such as UG.
Tool and coolant material selection
The processing characteristics of titanium alloys determine that the geometric parameters of the tool are quite different from those of ordinary tools.
The helix angle β selects a smaller helix angle, the chip flute is increased, the chip removal is easy, the heat dissipation is fast, and the cutting resistance during the cutting process is also reduced.
The rake angle of the rake angle is sharp when cutting, and the cutting is light, avoiding excessive heat of cutting of the titanium alloy, thereby avoiding secondary hardening.
The back angle α reduces the wear rate of the blade, which is advantageous for heat dissipation and the durability is also greatly improved.
2. The selection of tool materials should meet the following requirements
Sufficient hardness. The hardness of the tool must be much greater than the hardness of the titanium alloy.
Sufficient strength and toughness. Since the tool is subjected to a large amount of torque and cutting force when cutting the titanium alloy, it must have sufficient strength and toughness.
Sufficient wear resistance. Due to the good toughness of the titanium alloy and the sharpness of the cutting edge during machining, the tool material must have sufficient wear resistance to reduce work hardening. This is the most important parameter for choosing a titanium tool.
Tool materials have a poor affinity with titanium alloys. Since the titanium alloy has high chemical activity, it is necessary to avoid the formation of alloys by melting and diffusion of the tool material and the titanium alloy, resulting in sticking and burning.
Tests on common tool materials and foreign tool materials in China show that the effect of using high-cobalt tools is ideal. The main role of cobalt can enhance the secondary hardening effect, improve the hardness of red hardness and heat treatment, and have high toughness and wear resistance. Sexual, good heat dissipation.
3. cooling fluid
Titanium alloy processing is best not to use chlorine-containing coolant to avoid toxic substances and cause hydrogen embrittlement, but also to prevent high-temperature stress corrosion cracking of titanium alloy.
The synthetic water-soluble emulsion can be used, and the coolant can also be used.
The coolant should be sufficient during the cutting process, the coolant circulation speed should be fast, the cutting fluid flow rate and pressure should be large, and the machining center is equipped with a dedicated cooling nozzle, as long as the adjustment can achieve the desired effect.
4.cutting parameter selection
Titanium alloy machining should choose a lower cutting speed, a suitable large feed rate, a reasonable depth of cut and a finishing amount, and sufficient cooling.
Cutting speed VcVc=30～50m/min
The feed amount f takes a large feed amount for rough machining, and the medium feed amount for finishing and semi-finishing.
The cutting depth aap==1/3d is suitable, the titanium alloy has good affinity, the chip removal is difficult, and the cutting depth is too large, which will cause the tool sticking knife, burning knife and breaking phenomenon.
Finishing allowance αc moderate titanium alloy surface hardened layer about 0.1~0.15mm, the margin is too small, the cutting edge is cut on the hardened layer, the tool is easy to wear, the hardened layer should be avoided, but the cutting allowance should not be too large.
PTJ Manufacturing Shop specializes in custom machining and mass production of aerospace parts. The company has imported turning and milling machine tools, core-type CNC lathes, fully automatic CNC lathes and cnc machining centers, which can meet the precision manufacturing tasks of precision parts up to 0.01mm. Collaborative precision CNC machine tools are also equipped with the company's precision testing center, using advanced projectors, coordinate measuring instruments, spectrometers, etc., PTJ to serve customers with perfect product solutions, welcome to call us.
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