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.
