The material requirements for the manufacture of jet engines must be very strict. Because it must withstand extreme heat and force, and as light and extremely reliable as possible.
The turbojet can be simply divided into three sections – the compressor, the combustion chamber and the turbine. Before the air enters the combustion chamber, the compressor pressurizes the air flowing through the engine; in the combustion chamber, the air mixes with the fuel, ignites and burns. The compressor components are primarily made of titanium alloy, while the combustion chamber and turbine components are typically made of a nickel-based superalloy, such as Inconel 718.
Nickel-based superalloys have excellent physical properties, making them ideal materials for the manufacture of aerospace components. Nickel-based superalloys are suitable for a wide range of applications and a wide temperature spectrum. The material has high yield strength, high ultimate tensile strength, high fatigue resistance, and maintains corrosion and oxidation resistance at high temperatures.
Nickel-based superalloys, with a Ni content of 35-75% and a Cr content of 15-22%; meet 30% of the total material requirements for aircraft engine manufacturing; and are also used as structural materials for different parts of the space shuttle’s main engine. Used in the manufacture of gas turbine rotating components, including discs, blades, housing components (such as turbine casings), engine mounts, rocket engine components and pumps, accounting for 80% of the total nickel-based superalloys consumed by the aerospace industry.
Nickel-based alloys offer a great choice for jet engine component materials due to their performance, but at the same time they bring great difficulties to machining. Due to the high shear stress generated during the processing of nickel-based alloys and the low heat transfer coefficient, the cutting force and cutting temperature in the cutting area are very high. In addition, the physicochemical reaction between the nickel-based superalloy and the tool material causes the scraping of the chip and the adhesion to the surface of the workpiece, resulting in excessive tool wear, which limits the cutting speed and reduces the tool life. These characteristics not only lower the material removal rate, shorten the tool life, but also increase the processing cost.
Two. Titanium based alloy
For advanced aerospace systems, titanium alloys have high strength-to-weight ratios and excellent corrosion resistance. Titanium alloy parts are very handy to use. The Ti-based alloy has a Ti content of 86-99.5% and an Al content of 5-8%, which is hardly affected by exposure to an aerospace environment. A large number of titanium alloy materials are used in jet engines, and titanium alloy parts account for 25-30% of the weight of jet engines, mainly for compressors. Efficient operation of the engine is inseparable from titanium alloy components such as fan blades, compressor blades, rotors, disc parts, hubs and other non-rotor components (such as air intake guide vanes).
The excellent performance and light weight of titanium alloys not only enable aerospace engineers to design aircraft that fly higher and faster, but also make the aircraft highly resistant to extreme environments. However, the physical properties, chemical properties and machinability of titanium have long been regarded as difficult materials.
The titanium material has relatively high temperature resistance and low thermal conductivity, so that the generated cutting heat is not easily dissipated from the cutting area of the tool, causing excessive deformation and excessive wear of the tool. At high temperatures, titanium alloys retain their strength, and the result is a relatively high plastic deformation of the cutting tool, resulting in deep groove wear. During the processing, due to the high chemical reaction of the titanium alloy, the chip is cold welded to the cutting tool, which causes the built-up edge, which causes the chip breaking problem.
In the past few years, Iskar has invested a lot of resources in research and development to break through these processing difficulties and optimize the processing of nickel-based superalloys and titanium-based superalloys. The solution includes the professional introduction of special grades; the promotion of high-pressure cooling technology to the cutting tool to solve the problem of cutting heat dissipation.
To achieve high metal removal rates, Iska developed the following ceramic grades that can be used to machine nickel-base alloys at cutting speeds of 200 – 400 m/min:
IW7 – Whisker ceramic grade, with high hardness and high toughness, can be roughed and semi-finished at a cutting speed 8-10 times faster than carbide grades;
IS25 – The strong SiAlON composite grade excels in continuous cutting and slightly interrupted machining of nickel-base superalloys;
IS35 – The strong SiAlON composite grade excels in light interrupted cutting and heavy interrupted machining of nickel-based superalloys.
The following alloy grades are used for the targeted development and processing of nickel-based alloys and titanium alloys:
IC806 – High strength ultrafine grain matrix, TiAlN (PVD) coating. Special coating processes, including special coating post-treatment techniques, make the coating thinner and smoother, giving the inserts better nickel-based alloy and titanium alloy processing characteristics;
IC804 – The same TiAlN (PVD) coating on a harder substrate, specially designed to process the latest nickel-base alloy parts of jet engines up to HRC40-47;
IC20 – Uncoated alloy grade, especially recommended for the processing of aluminum and titanium alloys. The IC20 is mainly used for continuous cutting and performs well.
Four. High pressure cooling tool
In the field of metal removal, high pressure cooling has been around for quite some time. Today, high pressure cooling tools play an increasingly important role in the process of setting up difficult-to-machine materials such as titanium alloys and nickel-based alloys because of their significant productivity and chip control. High-pressure cooling is the key to making the cooling jets accurately reach the cutting area and flush out the chips.
Iskar is one of the first cutting tool manufacturers to respond to market demand. Through research and development, manufacturing and cutting tools to reasonably use high pressure cooling to reduce cutting temperature, adjust chip flow, and provide customized high pressure including JETCUT. Cool the tool.
The aerospace component OEM/PMA division not only needs to continue to face the pressure of cost reduction, but also to ensure the quality and longevity of the components manufactured. And this is a huge challenge for all involved. Isa’s improved cutting tools enable jet engine manufacturers to produce high-quality components with the ideal materials, while minimizing losses and maximizing efficiency.
Post time: Jul-31-2018