Material Development of Aerospace Parts, Continuous Lightweight

Background of Aerospace Parts Industry:

The aviation industry has always been equipped with strict quality system certification and highly complex integration technologies. All countries in the world regard the aviation industry as an indicator of national industrial technical capabilities. In the next 20 years, the average annual growth rate of the air transport industry will be 4.7%, which will generate business opportunities for the aviation manufacturing industry. Therefore, it is estimated that the global demand for new passenger aircraft will be about 42,000 in the next two decades, with a market value of US$6.3 trillion, of which the demand for new aircraft in the Asia-Pacific region is the strongest. Under the promotion and guidance of relevant units of the Ministry of Economic Affairs, Taiwan's aviation industry has established a supply chain system for related civil aviation products, and established partnerships with world-renowned aerospace manufacturers. The government's plans to promote the national production of state-owned aircraft, self-made advanced trainers, and follow-up military aircraft have made the aviation industry a bright spot for development.

In terms of the cost of aircraft parts, the engine accounts for about 27%, which is only lower than 38% of the fuselage. The countries in the world that can fully independently develop advanced aero-engines are limited to the United States, Britain, France, Russia, and other countries. According to the driving principle, aero-engines include turbofans, turboprops, and turboshafts, which are respectively used in jets, propellers, and helicopters. Turbofan engines have the characteristics of high efficiency, low noise, small size, and high-reliability design. In terms of the cost of aircraft components, the engine accounts for about 27%, which is only 38% lower than the airframe. The engine of the Boeing 757 is mainly made of titanium and nickel. Without these materials, jet engines would not be able to operate in the required conditions. However, titanium alloys, nickel-based alloys, and other materials have good mechanical properties at high temperatures, so the materials have a large cutting force, slow heat dissipation, high tool temperature, and material work hardening during cutting. Therefore, it is difficult to carry out cutting efficiently, especially for superalloy impellers with complex torsion surfaces and thin plate features, the technical difficulty is deeper, so the relevant aerospace industry has an urgent demand for its cutting process technology.

The Material Development of Aviation Parts:

To make the aircraft lightweight, "Duralumin" is specially used in the body material. Duralumin is made of a mixture of aluminum, copper, magnesium, manganese, and other substances. Its characteristics are that its weight is lighter than iron, and its properties are strong and strong. It is an alloy that is very suitable as an aircraft material. As for the interior of the engine, which generates high temperature and pressure, magnesium alloys, titanium alloys, nickel alloys, and other materials are also used.

With the continuous advancement of aerospace technology, new manufacturing materials have begun to appear, and composite materials are one of them. This composite material is a combination of fiber material and plasticized products and is used to replace the old aluminum alloy material. Because of their excellent elasticity and durability, and lighter weight, composite materials are mostly used in aircraft landing gear, as well as in the flaps, and horizontal and vertical tail parts of aircraft wings.

The aviation industry has been using composite materials since the 1970s. Since 1985, it has been used to make tails, such as the Airbus A310 wide-body airliner. However, it was not until the past decade that composite materials made breakthroughs and were widely used in the Boeing 787 Dreamliner and Airbus A350. Almost half of the fuselage of the two aircraft is made of carbon fiber plastic and other composite materials. Lighter carbon fiber replaces most metal parts, saving fuel bills. Metals will have problems such as corrosion and fatigue, and they will need to be replaced after a certain time. Composite materials will not have such problems, which can prolong the life of the aircraft.

Material Introduction of Various Aviation Parts:

Taking the turbofan engine of Boeing 757 as an example, its materials include non-ferrous metals and alloys: titanium, nickel, chromium, cobalt, aluminum, niobium, and tantalum. Without these materials, jet engines would not be able to operate in the required conditions and kinetic energy.

Titanium alloys (a-type, a + b-type, b-type) have excellent strength-to-density ratio and corrosion resistance, but also because of their lightweight, corrosion resistance, high-temperature resistance, high fatigue strength, low thermal expansion coefficient, non-magnetic, and non-toxic metal materials, and can produce multiple colors by anodizing, so it is widely used in the aerospace industry and daily life. However, due to the physical properties of titanium alloy itself, such as high strength, difficulty to cut, easy to generate cutting chatter, low thermal conductivity, and small thermal expansion coefficient, resulting in high cutting temperature and high temperature during processing, the chemically reactive titanium The alloy reacts with the tool material chemically, resulting in tool wear and tear, which affects tool life.

In addition to the application of titanium alloys in the aerospace industry, vehicles, and sports equipment industries, emerging medical industries have developed rapidly in recent years, such as the processing and production of medical implants, bone nails, bone plates, and the production of artificial tooth roots. The materials are mainly SUS316LVM and Ti-6Al-4V ELI and Pure Ti. The main reason is that the material has a good affinity with the human body and is not easy to produce chemical changes. In particular, the current development trend of titanium alloys is increasing day by day. Because this material is defined as a difficult-to-cut material, there is an urgent need for its cutting parameters. It is expected to find the best condition factors and levels that meet the cutting process. When milling titanium and titanium alloys, climb milling should be used. It is advisable to use a milling cutter with a small diameter and a large number of teeth, which can reduce vibration. Usually, the clearance angle of the milling cutter teeth for milling titanium is 30-50% larger than that of ordinary milling cutters. For milling, the correct selection of lubricating coolant is very important. Generally, it is suitable to use lubricating coolant that is soluble in water, and it is better to add it by spraying.

Superalloys can be divided into four types: iron-based, iron-nickel-based, nickel-based, and cobalt-based. Among them, nickel-based superalloys contain more than 50% nickel, and the working temperature can reach 1000 °C. It can obtain ideal strength and thermal resistance, so it is widely used in aero-engines. Iron-based superalloys are based on iron and are suitable for parts with lower operating temperatures. The nickel content of iron-nickel-based superalloys is 30%-40%. These alloys have higher tensile strength than nickel-based and cobalt-based alloys and are suitable for slightly higher working temperature environments than iron-based alloys. Cobalt-based superalloys use cobalt as the base, accounting for about 45%-60%, and add Cr, Ni, C, W, Mo, Fe, etc. to improve the heat resistance.

Inconel 718 nickel-based superalloy still has good mechanical strength, fatigue limit, and high-temperature corrosion resistance at a high temperature of 700 °C, so it is widely used in high-temperature, high-load, and corrosion resistance environments. However, due to the small thermal conductivity and specific heat value of Inconel 718 nickel-based superalloy, and good mechanical properties at high temperatures, the material has a large cutting force and slow heat dissipation during cutting, resulting in high tool temperature. The Build-up edge phenomenon of chips and tools easily occurs when cutting nickel-based superalloys. In addition, the Inconel 718 nickel-based superalloy has a base of the vostian iron type, in which the content of Nb is higher than that of other alloys, and it is easy to precipitate hard Ni3Nb, resulting in work hardening during cutting. Makes the tool wear out quickly. The application of hard-to-cut materials for aerospace parts takes the impeller as an example. It is one of the important and novel components of modern aero-engines. It was first applied to the small engine of helicopters. In the 1980s, it was used in military aircraft engines and was rapidly adopted by commercial turbofan and turboprop aircraft.

• Lightweight: Due to the use of fewer blades, the weight can generally be reduced by 20-30%.
• The blade root is integrated with the disc.
• Higher aerodynamic efficiency.
• Improve the service life, and will not affect the fatigue strength of the joint due to corrosion. However, BLISK has its shortcomings, mainly in its manufacture and repair, complex torsion surfaces and difficult-to-cut materials are difficult to process and expensive. And to ensure its reliability, strict quality control is a necessary process.

Generally, the structure of the compressor impeller of aircraft engines and industrial gas turbines is that the independent blades are positioned on the disc in a welded or locked manner. The BLISK is also known as integrated bladed rotors (IBR), which means that the blade root geometry and positioning grooves are no longer required, and the disc rotor and blades are designed in one piece. The development status of integrated impeller compressor and BLISK manufacturing technology in today's engine structure, as well as the application of technology in BLISK manufacturing in the future and meeting the challenges of function, quality, and cost. The manufacturing feasibility of the bi-material BLISK is being developed for use in highly stressed turbine sections. In addition, in the design of BLISK, it is necessary to take into account the technology and method of future repair.