When you sit on a commercial airliner and soar over the sea of clouds and the earth at an altitude of 10,000 meters, have you ever wondered how this huge "big bird" is assembled? How many mysteries are hidden under its smooth shell?
In fact, it takes millions of tiny rivets to connect a fuselage that is 60 meters wide and nearly 80 meters long to a two-sided wing.
They are like a seamstress who threads a needle, holding the behemoth firmly in place so that it can soar in the wind.
With so many nails, why not weld? Today we will uncover the mystery of aircraft manufacturing - the irreplaceable riveting process.
The lightweight body rests on it
When you fly over the oceans and mountains, do you worry about whether the fuselage of this "big bird" is strong enough? In fact, in order to reduce weight, commercial airliners widely use aluminum alloy and composite materials to make the fuselage and wings.
These metal materials are strong but low density, reducing weight and ensuring safety.
But the lightweight body is also more difficult to attach.
According to relevant information, at present, commercial aircraft mainly use aluminum alloys of the 2024, 7075 and other series, as well as fiberglass/carbon fiber reinforced composites.
The combined density of this type of material can be more than 30% lighter than that of steel.
The fuselage and wings are made of composite materials, which can reduce weight by more than 20% compared to all-metal construction.
It is the lightweight of the material that brings a huge increase in flight efficiency.
However, the common denominator of these advanced materials is that they are not easy to weld.
High-strength aluminum alloys such as 7075 can lose more than 50% of the strength in the heat-affected zone during welding, and glass composites are also prone to interface delamination and matrix ablation during the thermal process.
If welding is chosen, the aircraft structure loses the lightweight advantage of the material itself.
This is where small rivets come in handy.
Riveting is a mechanical joining that uses the stamping process to create a mating at the joints of the parts to achieve a secure locking effect.
This cold working process does not alter the metallographic structure inside the material and has little negative impact on strength.
A standard steel rivet weighs about 0.5 grams, but can withstand a shear load of about 500 kilograms.
In several key parts of the aircraft structure, connected in the form of rivet arrays, the connection strength is sufficient to support the fuselage and wings.
For example, the Airbus A380 uses around 5 million 2127 rivets, creating a reliable overall load path.
It is worth mentioning that the riveted connection also has a unique fracture suppression function.
When the connection is unevenly stressed, the peripheral rivets can play a role in load redistribution, which effectively inhibits crack propagation along the direction of the individual rivets and ensures structural integrity.
This makes it particularly suitable for the reliability design of aircraft structures.
Aircraft structures are designed to be lightweight, which relies on high-strength and low-density materials that are not easy to weld together.
This is where the small rivets come into play: dense arrays of rivets form a reliable connection, cold working processes do not damage material properties, and crack propagation inhibition.
It is their presence that allows the lightweight aircraft to soar safely in the sky.
Reliability trumps welding
Why does the aircraft industry prefer riveting over welding, which appears to be stronger on the surface? This requires an in-depth comparison of the essential differences between the two joining methods.
The first is the strength of the connection.
Welding uses high temperatures to melt and bond materials, which appear to be strong, but aircraft often use high-strength aluminum alloys, which can easily damage the strength of components during the fusion welding process.
For example, the tensile strength of 2024 aluminum alloy welded joints can be reduced by up to 30%, while riveting is cold worked, which does not change the microstructure of the material and has little impact on the strength.
The second is connection stability.
The aircraft works for a long time, and the dynamic loads on the connection points are repeatedly alternately applied.
Under fatigue load, micro-cracks will gradually appear in welded joints, while riveted joints have a low probability of fatigue failure.
Relevant experiments have proved that compared with welding, the service life of riveted joints under high cyclic load can be increased by 1.5~2 times.
Then there is the complex environment in which the aircraft is used.
The temperature difference during the flight is large, and the connection points are subjected to temperature loads, as well as corrosive media.
Both of these accelerate stress corrosion cracking at the weld, while riveted joints are more resilient to temperature and corrosion.
The last advantage is ease of service.
The riveted connections can be replaced simply and quickly, saving maintenance time and costs.
Relevant data show that forging rivet technology can shorten the nail change time by more than 60%.
This reduces the overall operating expenses of commercial airlines.
It can be seen that riveting is a very ideal process choice in the field of aircraft manufacturing.
It provides excellent support for the thin and light modern passenger aircraft, ensuring the safety of hundreds of passengers.
Millions of little heroes
The aircraft industry pursues "every gram counts", so it chooses lightweight aluminum alloy skin and structure.
These components need to be connected with strong and reliable rivets: a Boeing 737 requires about 1.2 million pieces, and large passenger aircraft, such as the Airbus A380, use a staggering amount of 5 million!
These small rivets take on the heavy responsibility of connecting the entire structure of the aircraft.
A Boeing 737 requires about 1.2 million units, and a large passenger aircraft needs up to 5 million units.
Consider the total number of parts in the Eiffel Tower at 2,500,000, which illustrates the structural complexity of building a commercial aircraft.
The quality control of these millions of fragmented parts is not sloppy at all.
Rivets require a dimensional accuracy of 0.01 mm and a thickness error of no more than 2 microns in the surface treatment layer.
Such a demanding degree of craftsmanship is no less than aerospace-grade precision manufacturing.
稍有不慎,就可能让这巨无霸"掉链子"。
What's even more shocking is that not one or two of the millions of rivets are the same!
The specifications and shapes required for each part of the aircraft are different, so the rivets should be customized for the local design.
Engineers need to calculate different load situations and design reasonable riveting patterns and spacing.
On the premise of ensuring the quality of a single chip, suppliers should realize multi-type parallel production.
It can be seen that behind the aircraft is a high degree of synergy between design, manufacturing and assembly.
The engineers "cut and stitched" in the form of insects and butterflies, and finally pieced together huge "wings".
It is the combination of the quality of countless bits and pieces that makes the ultra-long-range airliner an efficient and safe commercial flight.
Zero difficulty in repairing and replacement
Some rivets can become loose or damaged over time, and commercial aircraft must be repaired and replaced quickly in order to operate safely for long periods of time.
At this point, riveted joints shine compared to welding.
Compared to the difficulty of cleaning welding slag, the replacement of broken rivets is very simple.
The commonly used cold expansion rivet technology can be changed with a simple hammer stroke.
The whole process takes about 15 minutes, which greatly saves maintenance time.
These quick-change rivets also have a special storage treatment.
To put it simply, it is quickly placed in a low temperature environment after high-strength riveting, so that the residual stress inside the material is fixed, so as to obtain higher connection strength.
When this "frozen rivet" is re-riveted, its high-strength state can last for about 10-15 minutes, which is fully suitable for quick repair.
But sometimes the problem is not with the rivets, but with a faulty signal that causes the aircraft display to rivet problems.
This happened to an A320 airliner, and the maintenance team worked continuously for 72 hours to troubleshoot the problem, and finally found the real one failure point in tens of thousands of data connectors.
It can be seen that the work behind it is heavy and challenging.
However, it is consoling that the probability of such a "false alarm" is very low.
Aircraft rivets are not only self-locking, but also corrosion-resistant.
It is difficult to loosen in a large area unless there is an anomaly, such as the flight data recorder burning out in the high temperatures after a crash.
A little rivet, a big fearless!
The aircraft industry requires a high degree of precision, which is why mechanical connections are widely used.
These seemingly small rivets carry the long-cherished wishes of the entire industry and even a nation.
It is precisely because of the pursuit of quality that China's rivets and aircraft can write brilliant after the wind and rain.
The simple riveting process has much more than just connecting the fuselage.
It carries the hard work of designers, symbolizes the progress of manufacturing, and also highlights the rise of a country.
There are also those obscure workers, who make these small parts play a huge role, and they create the "China Wing" of the new era.
So, don't underestimate these countless bits and pieces of rivets.
Every time a flight takes off and every waypoint lands, they are infused with incredible strength behind them!
I sincerely hope that on the continent of high-speed rail, there will be more "big birds" that belong to us under the blue sky, and that Chinese-made aircraft will accelerate into the sky, as strong and reliable as steel rivets!
Resources
CCTV.com, "People" Xue Ying: A great craftsman who assembles millions of small rivets for large aircraft2019-04-25
Beijing Association for Science and Technology, why would you rather use millions of rivets to splice the aircraft than weld?2023-10-27