titanium metal
1948 years that DuPont produced tons of titanium sponge with magnesium method-this marked the beginning of the industrial production of titanium sponge. Titanium alloys are widely used in various fields because of their high specific strength, good corrosion resistance and high heat resistance. Titanium is rich in the earth's crust, ranking ninth in content, far higher than copper, zinc, tin and other common metals. Titanium is widely present in many rocks, especially in sand and clay.
Titanium
strength: is aluminum alloy1.3 times, 1.6 times of magnesium alloy, 3.5 times of stainless steel, the champion of metal materials.
thermal strength: The use temperature is several hundred degrees higher than that of aluminum alloy, which can be used in450~500 ℃ temperature for long-term work.
good corrosion resistance: Acid resistance, alkali resistance, atmospheric corrosion resistance, pitting corrosion, stress corrosion resistance is particularly strong.
good low temperature performance: titanium alloy with extremely low interstitial elementsTA7, it can maintain certain plasticity at -253 ℃.
chemical activity: high chemical activity at high temperature, easily with hydrogen, oxygen and other gas impurities in the air chemical reaction, the formation of hardened layer.
thermal conductivity, small elastic modulus: thermal conductivity of about 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 1/2 of that of steel.
Titanium Alloy
Titanium alloys can be divided into: heat-resistant alloys, high-strength alloys, and 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). Although the history of the application of titanium and its alloys is not long, it has won many honorable titles due to its superior performance. First won the title is "space metal" it is light weight, strength and high temperature resistance, especially suitable for the manufacture of aircraft and various spacecraft. At present, about 3/4 of the titanium and titanium alloys produced in the world are used in the aerospace industry. Many of the original parts of aluminum alloy, have switched to titanium alloy.
Titanium Alloys
Titanium alloys are mainly used in the manufacture of aircraft and engines, such as forged titanium fans, compressor discs and blades, engine hoods, exhaust devices and other parts, as well as structural frames such as aircraft girder frames. The spacecraft mainly uses the high specific strength, corrosion resistance and low temperature resistance of titanium alloy to manufacture various pressure vessels, fuel tanks, fasteners, instrument straps, frames and rocket shells. Artificial earth satellites, lunar modules, manned spacecraft and space shuttles also use titanium alloy sheet welds.
1950, the United States was first used as a non-bearing component such as a rear fuselage heat shield, a wind deflector, and a tail cover on a F-84 fighter-bomber. Since the 1960 s, the use of titanium alloy has moved from the rear fuselage to the middle fuselage, partially replacing structural steel to manufacture important load-bearing components such as bulkheads, beams, flap rails, etc. Since the 1970 s, civil aircraft began to use a large number of titanium alloys. For example, Boeing 747 passenger aircraft used more than 3640 kilograms of titanium, accounting for 28% of the aircraft's weight. With the development of processing technology, a large number of titanium alloys are also used in rockets, satellites and spacecraft. The more advanced the aircraft, the more titanium it uses. The titanium alloy used in the United States F-14A fighter aircraft accounts for about 25% of the weight of the aircraft; the F-15A fighter aircraft is 25.8 percent; the fourth-generation fighter aircraft uses 41% of titanium, and its F119 engine uses 39% of titanium, which is currently the highest amount of titanium. Aircraft.
titanium alloys
air transport aircraft have to use titanium alloy?
the top speed of modern aircraft has reached the speed of sound.more than 2.7 times. Flying at supersonic speeds so fast will cause the plane to rub against the air and generate a lot of heat. When the flight speed reaches 2.2 times the speed of sound, the aluminum alloy can not withstand, must use high temperature resistant titanium alloy. When the thrust-to-weight ratio of the aero-engine is increased from 4~6 to 8~10, and the compressor outlet temperature is correspondingly increased from 200~300 ℃ to 500~600 ℃, the low-pressure compressor discs and blades originally made of aluminum must be replaced by titanium alloys.
In recent years, scientists have made new progress in the research on the properties of titanium alloys. The original titanium alloy composed of titanium, aluminum and vanadium has a maximum working temperature550 ℃ ~ 600 ℃, and the newly developed titanium aluminum (TiAl) alloy, the maximum working temperature has been increased to 1040 ℃. The use of titanium alloy instead of stainless steel to manufacture high-pressure compressor discs and blades can reduce the weight of the structure. For every 10% weight reduction of the aircraft, fuel can be saved by 4%. For rockets, every 1kg weight reduction can increase the range by 15km.
titanium alloy
First of all, titanium alloy thermal conductivity is low, only steel1/4, aluminum 1/13, copper 1/25. Due to the slow heat dissipation in the cutting area, it is not conducive to thermal balance. In the cutting process, the heat dissipation and cooling effect is very poor, and it is easy to form high temperature in the cutting area. After processing, the deformation and rebound of the parts are large, resulting in increased torque of the cutting tool, fast edge wear, and reduced durability.
Secondly, the thermal conductivity of titanium alloy is low, so that the cutting heat is not easy to distribute in a small area near the cutting knife, the friction of the rake surface is increased, it is not easy to remove chips, the cutting heat is not easy to distribute, and the tool wear is accelerated. Finally, titanium alloy has high chemical activity, and it is easy to react with tool material at high temperature, forming dissolution and diffusion, resulting in knife sticking, knife burning, knife breaking and so on.
machining center
machining center can process multiple parts at the same time to improve production efficiency. Improve the machining accuracy of parts and have good product consistency. The machining center has a tool compensation function, which can obtain the machining accuracy of the machine tool itself. There is a wide range of adaptability and greater flexibility, such as parts of the arc processing, chamfering and transition fillet, can achieve a multi-functional. Machining center can be milling, drilling, boring, tapping and a series of processing. Accurate cost calculation can be carried out to control the production schedule. Do not need special fixture, save a lot of cost, shorten the production cycle. Greatly reduce the labor intensity of workers. can be associatedUG and other processing software for multi-axis machining.
tools and coolant materials
1. The selection of tool materials shall meet the following requirements:
enough hardness, the hardness of the tool must be much greater than the hardness of the titanium alloy.
sufficient strength and toughness, because the tool bears a large torque and cutting force when cutting titanium alloy, it must have sufficient strength and toughness.
sufficient abrasion resistance, due to the good toughness of titanium alloy, the cutting edge should be sharp, so the tool material must have sufficient wear resistance, so as to reduce the work hardening. This is the most important parameter for selecting titanium alloy cutting tools.
tool material and titanium alloy affinity is poor, due to the high chemical activity of titanium alloy, it is necessary to avoid the formation of tool materials and titanium alloy dissolution, diffusion and alloy, resulting in stick knife, knife burning phenomenon. After the domestic commonly used tool materials and foreign tool materials test shows that the use of high cobalt tool effect is ideal, the main role of cobalt can strengthen the secondary hardening effect, improve the red hardness and hardness after heat treatment, at the same time has a high toughness, wear resistance, good heat dissipation.
2, the geometric parameters of milling cutter
titanium alloy determine the geometric parameters of the tool and the ordinary tool there is a big difference. Helix angleβ selects a smaller spiral lift angle, the chip groove increases, the chip is easy to remove, the heat dissipation is fast, and the cutting resistance during the cutting process is also reduced. The rake angle & gamma; When cutting, the cutting edge is sharp and the cutting is light, avoiding excessive cutting heat of titanium alloy, thus avoiding secondary hardening. The back angle α reduces the wear rate of the blade, which is conducive to heat dissipation, and the durability is also greatly improved.
3, cutting parameters selection
Titanium alloy machining should choose a lower cutting speed, an appropriate amount of feed, a reasonable depth of cut and finishing, and sufficient cooling. Cutting speedVcVc = 30~50 m/min, the feed rate f takes a larger feed rate for rough machining, and a moderate feed rate for finishing and semi-finishing. Cutting depth apap = 1/3d is appropriate, titanium alloy affinity is good, chip removal is difficult, cutting depth is too large, will cause the tool stick, burning, fracture phenomenon. Finishing allowance alpha c moderate titanium alloy surface hardened layer of about 0.1~0.15mm, the allowance is too small, the blade cutting in the hardened layer, the tool is easy to wear, should avoid the hardened layer processing, but the cutting allowance should not be too large.
4. Coolant
titanium alloy processing is best without chlorine-containing coolant, to avoid toxic substances and cause hydrogen embrittlement, but also to prevent titanium alloy high temperature stress corrosion cracking. Synthetic water-soluble emulsion can also be used with coolant. When cutting, the coolant should be sufficient, the circulation speed of the coolant should be fast, the flow rate and pressure of the cutting fluid should be large, and the machining center is equipped with a special cooling nozzle, as long as you pay attention to the adjustment, you can achieve the desired effect
