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I. Introduction titanium

1948 DuPont did with Magnesium tons of titanium sponge production - which marks the beginning of the industrialization of titanium sponge titanium production. And because of its high strength titanium ratio, corrosion resistance, and high heat resistance and are widely used in various fields.

Titanium content in the crust than the rich, ranked ninth in the content, much higher than the common metals copper, zinc and tin. Titanium is widely present in many rocks, particularly sand and clay.

Second, the characteristics of titanium

High intensity: aluminum is 1.3 times, 1.6 times the magnesium alloy, stainless steel, 3.5 times champion metallic materials.

High thermal strength: Temperature several hundred degrees higher than aluminum, can be long-term work at a temperature of 450 ~ 500 íŠ.

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

Good low temperature performance: low interstitial elements titanium TA7, at -253 íŠ still maintain a certain plasticity.

Large chemical activity: high chemical activity at high temperatures, easily react with hydrogen in the air, gaseous impurities such as oxygen, to generate a hardened layer.

Thermal conductivity, low elastic modulus: thermal conductivity of about 1/4 of nickel, iron 1/5, 1/14 of aluminum, while the thermal conductivity of various titanium alloys decreased by 50% than the thermal conductivity of titanium. Elastic modulus was about 1/2 of the titanium alloy steel.

Third, the classification and use of titanium alloys

Titanium-use can be divided into: heat-resistant alloys, high-strength alloys, corrosion resistant alloy (Ti - molybdenum, titanium - palladium alloy, etc.), low temperature alloys and special features alloy (Ti - Fe hydrogen storage materials and titanium - nickel shape memory alloy) and so on.

Although the history of the application of titanium and its alloys is not long, but because it was over the public performance, has won numerous glorious title. First won the title is the "space metal." Its light weight, high strength and high temperature, especially suitable for the manufacture of aircraft and spacecraft. The world production of titanium and titanium alloys, about three-quarters of all for the aerospace industry. Many of the original aluminum alloy components are switched to titanium alloys.

Fourth, titanium alloys for aerospace applications

Titanium is mainly used in aircraft and engine manufacturing materials, such as titanium forging structural frame members fan, compressor disk and blades, engine covers, exhaust and other parts, and every box girders and other aircraft. Spacecraft main use of high strength titanium alloy, corrosion resistance and low temperature performance to produce all kinds of pressure vessels, fuel tanks, fasteners, instrument straps, architecture and rocket casing. Sputnik, the lunar module, manned spacecraft and space shuttle are also using titanium plates welded.

In 1950 the United States for the first time in the F-84 fighter-bombers later used as the fuselage insulation panels, wind shield, tail cover other non-load-bearing components. 1960s began using parts from titanium alloy fuselage toward the rear of the fuselage, in part, instead of structural steel bulkheads, beams, flap tracks and other important bearing components. Since the 1970s, civilian aircraft began extensive use of titanium alloys, such as the Boeing 747 with a capacity of 3640 kg titanium Weight accounted for more than 28%. With the development of process technology, the rockets, satellites and spacecraft, but also with a lot of titanium.

The more advanced aircraft, the use of more titanium. US F-14A fighter titanium, about 25% of the weight of the machine; F-15A fighter was 25.8%; US fourth-generation fighter with titanium content of 41%, the F119 engine with titanium content of 39%, which is currently Titanium highest aircraft.

Five, titanium been widely used in aviation reason

Sailing a top speed of modern aircraft has reached more than 2.7 times the speed of sound. So fast supersonic flight, aircraft and air friction will generate a lot of heat. When the flight speed of 2.2 times the speed of sound, aluminum can withstand a. Must use high temperature titanium alloy.

When the aircraft engine thrust to weight ratio increased from 4 to 6 to 8 to 10, the compressor outlet temperature accordingly from 200 ~ 300 íŠ to 500 ~ 600 íŠ, the original manufacturer of aluminum low pressure compressor disk and blades must use Titanium.

In recent years, scientists have to study the performance of titanium, continue to make new progress. The original is made of titanium, aluminum, titanium vanadium component, the maximum operating temperature of 550 íŠ ~ 600 íŠ, while the newly developed titanium aluminum (TiAl) alloys, the maximum operating temperature has been increased to 1040 íŠ.

With titanium instead of stainless steel plate and high-pressure compressor blades, can reduce the structural weight. Reduce the weight of 10% per aircraft, fuel savings of 4%. Rockets, every 1kg of weight reduction, you can increase the range of 15km.

Titanium alloy aircraft landing gear parts

Six Characteristics of Titanium Machining

First, the low thermal conductivity of titanium alloy, is only 1/4 of steel, aluminum, 1/13, 1/25 copper. Due to slow cooling the cutting zone, is not conducive to thermal equilibrium, in the cutting process, the heat and poor cooling effect, is easy to form a high temperature in the cutting zone, springback deformation after machining large parts, resulting in increased torque cutting tools, rapid blade wear, durability decrease.

Second, the low thermal conductivity of titanium, so cutting heat accumulated in the small area near the cutter easy to distribute, rake increased friction, easy chip removal, cutting heat easy to distribute and accelerate tool wear. Finally, the high chemical activity of titanium alloys at high temperature processing easy and tool material reacts to form soluble dressing, diffusion, resulting in stick knives, burning knife, cutting knife and so on.

Seven characteristics of titanium machining center

Processing center can process multiple parts at the same time, improve production efficiency.

Improve machining accuracy, product consistency. Machining center tool compensation function, you can get the machine itself precision.

There are a wide range of adaptability and greater flexibility. This part of the process, such as arcs, chamfer and fillet.

You can achieve a machine can. Machining centers can be milling, drilling, boring, tapping a series of processing.

You can calculate the exact cost, control the production schedule.

Does not require special fixtures, significant cost savings funds, shorten the production cycle.

Greatly reducing the labor intensity.

UG and other processing software with multi-axis machining.

Eight, select the tool and coolant materials

1, the tool material selection should meet the following requirements:

Sufficient hardness. The tool must be much larger than the hardness of the alloy hardness.

Sufficient strength and toughness. Because under a lot of torque and cutting force when cutting tool alloy, it is necessary to have sufficient strength and toughness.

Sufficient wear resistance. Because of good toughness titanium alloy, the processing to be sharp cutting edge, so the tool material must have sufficient wear resistance, so as to reduce the work hardening. This is a selection of the most important parameters machining titanium knives.

Tool material and titanium affinity ability to be worse. Due to the high chemical activity of titanium, tool material and so to avoid the formation of soluble titanium cladding, made of alloy diffusion caused stick knives, burning knife phenomenon.

After cutting tool materials used for domestic and foreign tool materials tested showed that the effect of high cobalt ideal tool, the main role of cobalt can strengthen the secondary hardening effect, raise the red hardness and hardness after heat treatment, but also has high toughness, wear , good heat dissipation.

2, cutter geometry

Processing characteristics of titanium decision tool geometry and common tool there is a big difference.

Choose a smaller helix angle β helix angle, flutes increases, chip easily, heat dissipation, but also reducing the cutting process of cutting resistance.

When the rake angle γ sharp cutting edge, cutting light, avoid excessive cutting titanium heat, thus avoiding secondary hardening.

After the blade angle α decreases the wear rate is conducive to heat, durability has also been greatly improved.

3, cutting parameter selection

Titanium machining should choose a lower cutting speed, suitably large amount of feed, depth of cut and finishing a reasonable amount of cooling to be sufficient.

Cutting VcVc = 30 ~ 50m / min

Take feed f large amount of feed roughing, semi-finishing and finishing to take a moderate amount of feed.

Cutting depth apap = 1 / 3d appropriate, titanium affinity good, Chip difficulties, the depth of cut is too large will cause the tool to stick knives, knife burning, breakage.

Finishing allowance αc moderate titanium surface hardened layer of about 0.1 ~ 0.15mm, margin is too small, hardened layer on the cutting edge, the tool is easy to wear, machining hardened layer should be avoided, but it should not be too large cutting margin.

4, coolant

Titanium machining coolant better not chlorine, to avoid toxic substances and cause hydrogen embrittlement can also prevent heat stress corrosion cracking of titanium alloy.

Selection of synthetic water-soluble emulsion can also be equipped with self-cooling fluid.

When cutting coolant to ensure adequate coolant circulation faster, cutting fluid flow and pressure should be large, machining centers are equipped with special cooling nozzles, as long as you can to adjust to achieve the desired effect.
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