Riveting in Aviation: The Engineering Principle Behind Aircraft's 'Metal Stitching' Process in aircraft
The riveting process in aircraft manufacturing is a critical technology. Why do aircraft utilize the riveting process instead of welding? Primarily, it is closely tied to the manufacturing materials—composite materials such as aluminum alloys, which are not easily welded. Aircraft soar through the sky, bearing the responsibility for passengers' safety and trust. Any flaw in the manufacturing materials could lead to immeasurable consequences and potentially compromise the aircraft's safe operation at any time.
I. Basic Principles and Classification of Riveting Processes
1. Basic Principles
Riveting is a mechanical fastening method that joins multiple workpieces using rivets. Rivets create permanent connections through plastic deformation and transfer loads via the interference fit between the rivet shank and the hole wall. The riveting process typically involves positioning, stamping, piercing, forming, and release. The rivet undergoes deformation within the rivet hole to form both a rivet head and an expanded section, thereby establishing a secure connection between the workpieces.
Aircraft riveting processes are primarily classified according to the following three dimensions:
1. According to temperature control:
- Cold riveting: Riveting is performed at room temperature and is suitable for steel rivets with diameters less than 10 mm, as well as non-ferrous metals, light metals, and alloys with good plasticity.
- Hot riveting: Riveting is conducted after heating the rivets to a specific temperature. Typically, steel rivets with diameters exceeding 10 mm are heated to 1000–1100°C for hot riveting, with a hammer force per unit area on the rivet rod ranging from 650 to 800 MPa. Hot riveting provides superior tightness, though a gap remains between the rivet rod and the rivet hole, preventing it from participating in force transmission.
2. According to the riveting method:
- Initially, manual riveting, primarily performed using rivet guns, was the dominant method. While labor-intensive, it offered high flexibility.
- With industrial advancements, mechanical riveting became the primary approach, utilizing specialized riveting equipment to enhance efficiency and consistency.
3. According to rivet type:
- Solid rivets: Composed of solid metal, these rivets exhibit excellent strength and durability, making them the most widely used type in aircraft structures.
- Hollow rivets: Featuring a hollow center or being entirely hollow, these rivets are lighter in weight but offer lower strength, making them suitable for lightly loaded connections.
- Blind rivets: Installed from one side, these rivets are ideal for joining surfaces that are not easily accessible, such as the internal structure of a wing.
II. Specific Applications of Riveting Technology in Aircraft Manufacturing
1. Application Scenarios and Rivet Selection
Riveting is utilized extensively in aircraft manufacturing and is primarily applied to the following structures:
• Fuselage Structure: The fuselage of an aircraft consists mainly of the front fuselage, mid-fuselage, and tail section. Skins and fuselage structures of varying sizes are securely joined together through the riveting process. A medium-sized passenger aircraft contains millions of rivets across its body, while an Airbus A380 typically employs approximately 5 million rivets.
• Wing Structure: The wing serves as the primary source of lift for the aircraft and is a critical component for riveting. The rivets at the wing's leading edge are movable parts and must be countersunk, meaning the surface must remain flush with the skin after installation. Failure to achieve this may cause turbulence during airflow, leading to increased fuel consumption.
• Tail Structure: The tail comprises a horizontal stabilizer and vertical fin, which control the aircraft's pitch and yaw. The stabilizer and movable control surfaces of the tail are also connected via riveting.
• Composite Material Connection: As composite materials constitute an increasing proportion of aircraft structures (accounting for 40–60% in modern fighter jets), riveting technology is especially vital for composite material connections. Composite materials exhibit minimal plasticity and are susceptible to impact damage during riveting, necessitating advanced riveting techniques and processes.
2. Rivet Materials and Specifications
The material selection and specification standards for aircraft rivets are exceptionally stringent. How stringent are the material requirements? Even more rigorous than those for aerospace components!
The following factors are primarily considered:
Material Type:
- Aluminum alloy rivets: The preferred choice for lightweight applications, primarily used to connect aircraft skins.
- Titanium alloy rivets: Offer higher strength (1100–1250 MPa) and superior corrosion resistance, typically employed for critical components such as aircraft frame structures and landing gear.
- Stainless steel rivets: Provide excellent corrosion resistance and are suitable for areas exposed to prolonged humidity or corrosive environments.
Dimensional Tolerance:
- Diameter tolerance: Aircraft rivets demand exceptionally high dimensional consistency. For example, the diameter tolerance requirement for domestic rivets used on the C919 domestic large aircraft is 0 to 0.05 mm, which is equivalent to one eightieth of the diameter of a hair.
- Hole diameter tolerance: For cold riveting, the hole diameter should closely match the rivet shank diameter, whereas for hot riveting, a slightly larger difference between the hole and shank diameters is permissible.
- Strength Requirements: The specific strength requirement for aircraft rivets is as high as 1100 MPa, equivalent to supporting the weight of 10 cars on a 1-square-centimeter area. Rivets made from different materials correspond to varying strength levels. For example, titanium alloy rivets typically exhibit shear strengths exceeding 2500N.
3. Process Parameters and Quality Control
Process parameters and quality control are critical and must be meticulously considered. A 1mm difference may cause the aircraft to disintegrate. The aircraft riveting process requires strict control of the following parameters: riveting pressure, riveting speed, and riveting force.
Aircraft riveting quality requirements are exceptionally stringent, with a rivet diameter tolerance of 0 to 0.05mm. The first rivet must be identical to the millionth rivet. National and international standards impose strict regulations on rivet materials, dimensions, strength, and other specifications.