Jak se vyrábějí listy rotoru vysokotlakých turbín leteckých motorů? Česká republika

The principle of how aircraft engine high-pressure turbine rotor blades are manufactured is very simple, but the various parameters in this process require a lot of experiments to obtain the parameters of each node, the composition of auxiliary materials, and a lot of luck.

First, the high-pressure turbine rotor blades require complex internal cooling air ducts (see the figure below). First, the internal cooling air ducts are made (excluding cooling air holes, which will be discussed later). The wax mold is then cast with a special ceramic to form the air ducts.

After having this ceramic airway mold, put it together with the blade outer mold and put it into the casting furnace. The molten super alloy* enters the mold cavity from top to bottom (including the ceramic airway inner mold and the wax outer mold). It is very troublesome to make countless layers of coatings between each mold making. German companies use robots to do it, and it seems that Russia still uses aunt's brushes. These coatings directly determine the casting quality, and the tolerance rate is extremely low.

At this time, the casting machine will strictly control the temperature of the molten super alloy, and then let it solidify on a horizontal plane (that is, the growth of the crystal), from bottom to top, when the crystal grows in the spiral (crystal selector), it squeezes and selects each other, and finally only one crystal that is closest to the preset direction will be left, and this crystal will continue to grow upward.

Because the high-pressure shaft has to rotate more than 10,000 times, each piece is subjected to more than 10 tons of centrifugal force, and the strength of nickel crystals in each direction is different, so its diagonal (the strongest direction) needs to be within 10 degrees of the centrifugal force direction. (One more thing to say, the unidirectional nickel-based alloy used in the low-pressure turbine rotor requires the crystal direction but not only one crystal, because the melting point of single crystal is 50K higher than that of polycrystalline (including unidirectional crystal))

The yield rate is not high. As far as I know, many excellent precision casting factories in Germany have challenged this process and finally went bankrupt. The threshold is really too high.

Finally, the finished product is obtained and a special alkali is used to dissolve the ceramic airway mold left in the airway to make cooling holes. There are electro-dissolution holes and electrochemical holes. The most common holes are made by laser. The shape of the holes is also very complicated. Then there is electroplating coating, which is also a huge knowledge.

The picture below shows polycrystalline on the left, unidirectional crystal in the middle, and single crystal on the right.

However, after the casting, the blades do not have the air holes connecting the inner cooling air duct and the blade surface. This is generally done by laser. Because the cooling air has lost a lot of pressure when it is extracted from the high-pressure compressor and flows from the hollow shaft to the high-pressure turbine, although the core airflow also loses pressure when it passes through the combustion, and the process from the shaft to the blade has a certain centrifugal compression and pressure-boosting effect, it still requires a higher static pressure to hit the cooling air to the blade surface. At this time, a hole with an expanded cross-section is needed to handle the cooling air, reduce the dynamic pressure and increase the static pressure, and then the cooling air pushes the hot core airflow away from the blade surface (a lot of nonsense). Moreover, too fast a speed will cause the cooling to be directly injected into the core airflow, and it has another job, which is to form a layer of cooling air film on the blade surface to protect the blade, which requires deceleration and pressure increase.

Therefore, this type of hole needs to optimize its geometric shape for different positions. Laser drilling can be easily automated, but the disadvantage is that there will be internal surface stress.

The tail of the turbine stator (unidirectional crystal, off topic) needs to be punched with wake cooling holes to serve the subsequent turbine rotor. This hole is extremely slender and cannot withstand internal stress, so it is made using electrochemical corrosion. Of course, these are not absolute, and different companies have different processing methods.

After doing this, a single crystal turbine blade has been obtained, but it has not been coated yet. Modern turbine blades require a layer of zirconia thermal barrier coating, a zirconia oxide ceramic. Because it is ceramic, it is brittle to a certain extent. When the turbine is working, if there is a slight deformation, the entire piece may peel off, and the turbine blades will melt immediately. This is absolutely unacceptable within Hangfa.

Then there is the EB-PVD process (Electron-beam physical vapor deposition), vapor deposition method.

Of course, there are many layers of other materials before making it, such as platinum plating (platinum), plasma spraying, etc. There is also a layer to reinforce the zirconia and stick it like glue. Of course, there are slight differences between each company, and they are not static.

First, the electron gun emits an electron beam, which is guided by the magnetic field and hits the zirconia substrate. The substrate bombarded by the electrons will turn into a gaseous state, and the gaseous zirconia is guided to the surface of the blade to start growing. Zirconia will grow into small sticks with a diameter of 1 micron and a length of 50 microns, densely covering the surface of the leaves without the pores being coated. Because it is not a whole piece of ceramic, the small sticks can move slightly relative to each other without peeling off the whole piece, which solves the problem of failure caused by deformation.

Zirconia has extremely high hardness and extremely low thermal conductivity, which can achieve a very steep temperature gradient between the nickel substrate and the hot core airflow. With internal cooling and air film cooling, the blade can work for a long time with high strength and high reliability in an environment far higher than its own melting temperature.

At this point, the blade surface is completed. In order to fit into the turbine wheel, the blade also needs a pine-shaped or mortise and tenon structure blade root

As mentioned above, each turbine blade withstands more than ten tons of centrifugal force when working, and the blade heel also needs to be processed very finely. Nickel-based super alloy is very hard, high temperature resistant, and very difficult to process.

The blade heel is ground out. The blade is clamped by a special fixture, and the upper and lower grinding wheels with opposite geometry (female mold) grind inwards.

This will cause the grinding wheel to fail quickly, so a positive diamond grinding wheel is added to the outside of the two grinding wheels to continuously grind the grinding wheel to keep it working. The industrial diamonds on the diamond wheel are glued on by robots.

After these processes and inspection, the blade is ready to work. It is just a part of an aircraft engine, and an aircraft engine is just a module on an aircraft.