If we look closely at the aircraft, we will find that there are many nails on the skin of the aircraft. We often see such rivet crafts on some large bridge buildings.
It is said that a C919 aircraft uses millions of rivets, and an airliner A380 uses more than five million rivets. ——Then why don't the planes be directly welded, but choose this seemingly troublesome rivet process?
Strive to lose every gram
There is a motto in the aviation industry: "Strive to save every gram." To reduce the weight of the aircraft, the lightest possible materials are used in aircraft manufacturing according to local conditions.
In order to reduce weight, the skin of the aircraft is generally made very thin. With such a thin skin, it is very difficult to weld them together.
Moreover, in some aircraft, the fuselage is made of aluminum material, which has poor heat resistance, and the welding process will generate a lot of heat during welding, which is obviously not suitable for aircraft with an aluminum fuselage.
The most advanced airliners in the world use composite materials in large quantities, and composite materials will also be damaged by welding. The interconnection of different materials must be fixed physically.
Riveting is more stable and reliable
The first time I flew in a plane, I sat near the window of the wing. When the plane encountered the ups and downs of the airflow, the wings also vibrated visibly, and I felt nervous at that time...
I believe that many friends have seen such a scene. If the turbulence is severe, the wings of the plane will swing up and down greatly.
During this repeated oscillation, the skin of the wing is stretched, or squeezed. If the welding process is used, the strength of the weld will decrease significantly under this repeated stress change.
Over time, these welding places are likely to produce some small cracks. If they are not discovered in time, it will be a very big safety hazard.
Civilian aircraft usually have to serve for more than ten years, and the welds are prone to metal fatigue problems, and the connection effect is not ideal. Riveting can reduce the vibration transmission between joints, thereby reducing the risk of cracking. For such repeated stress changes, the firmness is better and more reliable.
Riveting facilitates quantitative production and reduces maintenance costs
Welding quality largely depends on the skill of the operator. Welding is thinner and thicker, and the randomness is relatively large. It is still difficult to formulate a unified standard.
The rivets used in the riveting process have very small parameter errors and are easy to carry out quality control and standardized production.
We all know that when aircraft are manufactured, there are high requirements for standardization.
The most important thing in the aviation industry is quality consistency. An aircraft has millions of rivets, and the first rivet produced must be exactly the same as the tens of millions of rivets after that.
The specific strength of the rivets on the aircraft is required to be as high as 1100 MPa, which is equivalent to the weight of 10 cars on an area of 1 square centimeter. The machining accuracy of the rivets reaches micron-level control.
This principle is similar to the large aircraft itself. It is not too difficult for a large country to manufacture an advanced large aircraft, but it is a great challenge to manufacture tens of thousands of the same product.
Rivets do not increase aerodynamic drag, but decrease it
Some friends may wonder: Will these protruding rivets increase the aerodynamic drag of the aircraft? In fact, the rivets used in the field of aviation manufacturing are mainly convex head and countersunk head rivets.
In the interior of the aircraft, since there is no requirement for aerodynamic shape, low-cost and easy-to-process convex head rivets are mainly used.
The countersunk rivets are mainly used on the smooth parts of the aircraft, which can effectively reduce the resistance of the aircraft. During the processing, there are strict requirements on the tolerance of the nail cap and the surrounding structures. When you touch the surface of the aircraft, you can hardly feel the existence of the rivets.
This application has brought remarkable results. According to relevant data during World War II, after using countersunk rivets, the resistance of the aircraft can be reduced by about 3%.
How to replace a broken rivet?
Generally, frozen rivets are used instead. That is to say, the rivets are quickly frozen after quenching, and must be riveted within 15 minutes when used.
The strength of this frozen rivet will increase under normal temperature conditions, thereby enhancing the stability of the riveted structure.
What happens if the rivets come loose?
A loose nail could cause the aircraft to display a fault message, requiring aircraft maintenance workers to work overtime to find fake nails.
In 2016, in order to eliminate the fault of an A320 aircraft, the maintenance staff worked continuously for three days and three nights. After checking all possible faults one by one, they finally found a loose one among hundreds of data pins with a diameter of less than 1 mm. .
Although it is a lot of work to troubleshoot nails, there is no need to worry. Aviation screws are self-locking, and the chance of loosening is minimal.
Therefore, subject to various restrictions, most of the aircraft seen at present are nailed together.
Scattered aircraft skins are threaded through rivets, and finally they can become aerial battle suits, allowing the flaps to dance flexibly.
Related links: About the riveting process
Pressure riveting is a riveting method, which refers to the use of external pressure to change the plasticity of the material in the riveting project, so as to enter the special prefabricated groove in the riveting screw and nut structure, so as to achieve reliable connection between parts.
Ordinary low carbon steel, aluminum alloy plate, copper plate and other materials are usually used for crimping standoffs. Some materials with excellent materials, such as stainless steel and high-carbon steel plates, generally use special, high-hardness rivet nut studs, so stainless steel is rarely used in general rivet studs and rivet nut sheet metal parts. . Pressure riveting screws and nuts are the same as pressure riveting studs, less stainless steel is used.
Through the analysis of the riveting process and the introduction of the common riveting parts and their process, combined with the quality control method of the riveting process, the riveting process is discussed.
Video material, Wi-Fi is recommended to watch
1. Riveting process
1. The opening size of the riveting bottom hole must be opened according to the standard size table of the hole.
2. Except for special circumstances (such as: after the surface treatment of each process is completed, there is interference with the riveting), the surface treatment of the product must be completed before the riveting process.
3. When selecting the surface color of the riveted parts and the surface treatment color of the product parts, usually when color zinc plating is selected on the product parts, the riveting parts are consistent with the product parts; usually blue zinc, white zinc, When nickel and oxidation, nickel-plated riveting parts are used; special product parts are riveted before surface treatment and need to be welded and strengthened, nickel-plated riveting parts are used, because the chemical substances of the coating affect the quality of welding.
2. Introduction and processing technology requirements of commonly used riveting parts
(1) Pressure riveting nuts and their process requirements
When the aluminum plate of the tooth rivet nut is t≤1.0mm, the processing of the tooth rivet nut code is -0; when the stainless steel material is used for pressure riveting, because the stainless steel material is relatively hard, it is easy to cause the nut to fall off after the pressure riveting, so usually Spot welding is used to strengthen the nut close to the plate; when performing pressure riveting, the pressure riveting of the mold must be in place at one time, and the protruding parts of the nut must all enter the plate without leaving any gaps, so that the nut and the plate can be firmly connected. Good verticality.
(2) Pressure riveting studs and their process requirements
Riveting studs include through-hole threaded riveting studs and blind hole riveting studs; this article mainly introduces two types of full-through studs and blind hole studs. The difference between through-hole full-through studs and blind-hole studs is whether the inner hole is opened and the length of the thread is different, while the rest of the dimensions are basically the same.
The processing technology requirements of the riveting studs are as follows: Generally, the blind hole riveting studs are not riveted before electroplating. The purpose of this is to let the electroplating solution flow out as much as possible and prevent the threads from being corroded.
When performing pressure riveting, the pressure riveting of the mold must be in place at one time, and all corners of the stud must be fully embedded in the plate, and at the same time be consistent with the surface of the part, so that the flatness of the plate and the perpendicularity to the stud are good. When the stud length L≥30mm, according to the structural analysis and process requirements, the stud must be reinforced by spot welding to avoid the inclination of the stud. When using stainless steel plates for pressure riveting, the tolerance between the outer diameter of the stud and the size of the plate opening must be guaranteed to be within ±0.05mm.
(3) Pressure riveting screws and their process requirements
The pressure riveting screws are mainly divided into two types: round head type and hexagon head type: the S part of the round head pressure riveting screw is a round head and a flower tooth, and the pressure riveting method is basically the same as the flower tooth pressure riveting nut introduced earlier; the hexagon head type The S part of the screw is composed of a hexagonal head and a concave-convex, and the riveting method is the same as that of the riveting stud.
The processing technology requirements of the riveting studs are as follows: Usually, the plate with t<1mm is not used for the riveting; the use of the mold must be in place at one time during the riveting, and all corners of the stud must be fully embedded in the plate, and at the same time It is consistent and flush with the surface of the part, so that the flatness of the plate and the perpendicularity to the stud are good. Because the S value of the riveting screw is usually large, it is easy to squeeze the material during the riveting, which will lead to the deformation of the part; when riveting the stainless steel screw on the stainless steel plate, the tolerance of the outer diameter of the screw and the size of the opening should be guaranteed to be within ±0.05mm .
(4) Loose and non-removable pressure riveting screws and their process requirements
Generally, in places where fastening needs to be frequently disassembled and installed, non-removable rivet screws are often used.
The processing technology requirements of the non-loosening pressure riveting screw: the use of the mold must be in place at one time during pressure riveting. The verticality is good.
(5) Locating pins and their technological requirements
The processing technology requirements of the pressure riveting positioning pin: when the length L of the positioning pin is greater than 20mm, according to the structural analysis and process specifications, the positioning pin must be welded (spot welding at the round head) to be reinforced to avoid skewing; the use of molds during pressure riveting It must also be in place at one time, and the boss of the positioning pin must be fully embedded in the plate, and at the same time be flush with the surface of the part, so that the flatness of the plate and the perpendicularity to the positioning pin are good.
3. Quality control of riveting process
1. Processing content of the riveting process: riveting nuts, screws, studs and customized hardware riveting parts (guide pins, positioning support columns, etc.), electrostatic hand bowl seats, riveting wrenches, etc.
2. For the riveting parts that are closer to the edge of the product or the periphery of the hole, the edge of the product or the periphery of the hole will be obviously deformed after being riveted. Take corresponding measures (such as shape correction/or grinding) according to the deformation and expansion of the material to achieve the drawing size and appearance requirements.
3. After riveting, there must be no crooked or deflected phenomenon, and it must be ensured that the thread and the corresponding hole are concentric.
4. The material, specifications and models of the riveting parts must be consistent with the drawings, and the specifications must not be wrong;
5. After the riveting, the surrounding parts of the riveting parts shall not be obviously deformed or convex or concave, and there shall be no obvious embossing or molding that cannot be covered by surface treatment.
6. Do not tilt after riveting. The riveting parts must not loosen or fall off, and their firmness must be tested; their push-pull force and torque values must meet the requirements of the PEM regulations for the riveting parts of their specifications.
7. Before riveting, it is necessary to confirm in time whether the external marks of the riveting parts used in the production line and the actual objects (materials, specifications and models) in the packaging bag meet the requirements of the drawings, and whether there is any mixed material in the packaging bag.
8. After the riveting, the thread of the riveting part must be qualified, the pass rule is pass, and the stop rule is stop.
