Before the Boeing 787 and Airbus's A350XWB, aluminum was the main material for modern aircraft.This material has one outstanding feature -- it welds very poorly.

After using the traditional welding method, the metal will become brittle, and it is easy to produce sand holes, bubbles, micro-cracks and other defects, so that the performance of the structure in these positions is lower than that of the non-welded area.This is not acceptable in aircraft manufacturing.

Although there are some special welding processes, such as friction stir welding and laser welding, they are too complex and difficult to ensure process stability.For the same material, the thinner it is, the harder it is to weld.Aircraft skin thickness is generally only about 2 mm, even if it can be welded, the difficulty will be very large, not the general operators can be competent, is not conducive to the mass production of aircraft.

The Boeing 787 and Airbus A350XWB are built mainly of composite materials, which are made from a variety of single materials that are combined by a special process that is harder to weld than aluminum alloy and is rarely used by manufacturers.When an airplane is flying at high altitude and high speed, the fuselage is subjected to tension.The engine vibrates when it works, and the aircraft itself vibrates.The forces that an aircraft experiences on each flight are constantly changing, and fatigue can be a problem.Tension, vibration and fatigue are the main reasons for the degradation of welding performance.

Aircraft working in such conditions for long periods of time can develop tiny cracks in the welds.What's more, the next crack will expand along the weld, and even cause the aircraft to disintegrate in the air, causing the tragedy of aircraft destruction and death.And riveting and screw joint has a good anti-vibration, anti-fatigue and other characteristics, and because of the existence of the connecting hole, naturally has the ability to continue to expand the crack.

The service life of the aircraft is generally more than 20 years, and there are many complex and precise instruments in the body. In the long use process, all kinds of devices may be damaged to different degrees, and riveting is easy to repair and replace.