What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - the rivet body and mandrel. The rivet body is a head on one end and a shank on the other. The mandrel fills the hollow shank portion during installation and is discarded afterwards.
Rivets are installed by placing them in pre-drilled holes through the materials being joined. The rivet body is inserted through the hole and the mandrel head is upset, or smashed against the rivet body. This smashing force deforms the rivet body, causing it to flare out and clamp the materials together. The flared portion is called the shop head.
Benefits of Riveting
There are several key reasons riveting is a popular joining technique:
- Strong and Durable - The flaring process work-hardens the rivet material, creating a very strong joint. Riveted connections have excellent fatigue and vibrational resistance.
- Low Part Count - Rivets provide fastening with only a two-part system. Other techniques like bolting require a bolt, nut, and sometimes washers.
- Alignment Not Critical - Precise hole alignment is not necessary for rivets. The flaring process can draw materials together and compensate for small mismatches.
- Quick Installation - Riveting is very fast compared to welding or screwing many fasteners. Automated equipment can install thousands of rivets per hour.
- No Heat Affected Zone - The cold installation process avoids altering the microstructure surrounding the joint, unlike welding. This reduces the risk of distortion or weakness near the connection.
- Can Pre-assemble - Riveting allows parts to be joined into assemblies before final installation. Other methods like welding must be done in final position.
- Vibration Resistant - The flared rivet shank firmly clamps materials, while allowing pivot movement. This makes rivets ideal for high vibration applications.
The most common rivet materials are:
- Aluminum - Lightweight and easy to flare. Used for aircraft and other weight-sensitive applications.
- Steel - Very strong but more difficult to flare than aluminum. Used in high strength applications.
- Copper - Excellent fatigue and vibration resistance. Used in dynamic applications like motors.
- Monel - Corrosion resistant. Used for marine and other wet environments.
- Titanium - Highest strength-to-weight ratio. Used in critical aerospace applications.
Riveting Sheet Metal
Sheet metal presents unique challenges for riveting. The thin material is more prone to buckling or deformation around the rivet. Proper techniques must be followed to create high quality sheet metal rivet joints.
Hole Size - Sheet metal holes must be sized correctly relative to rivet diameter to prevent tearing or enlargement during installation. Typically the hole is 1.5 times the rivet shank diameter.
Rivet Spacing - Rivets must be spaced adequately apart, with larger rivets requiring more edge margin. This prevents sheet distortion between rivets. Common spacing is 3-4 times rivet diameter.
Joint Strength - Multiple rows of rivets may be required to achieve necessary joint strength, compared to thicker materials. Staggering rows prevents following the same load path.
Clamping - Pressure pads, anvils, or bucking bars should be used to support the joint when riveting thin sheet. This prevents sheet deformation on the non-shop side.
Flush Setting - For aerodynamic purposes, rivets in sheet metal may be flush set by driving the shop head completely flat. This requires specialized riveting equipment.
There are various techniques used to install rivets based on equipment availability and joint requirements:
- Hand Riveting - A bucking bar is held against the rivet tail while the shop head is set with hammer blows. Still commonly used for repair and small-scale work.
- Pneumatic Riveting - Uses compressed air to quickly drive a riveting hammer and bucking bar. Allows high riveting rates with moderate operator skill.
- Hydraulic Riveting - Powerful hydraulic jaws squeeze the rivet to deform it. Allows very high force installation for large or high-strength rivets.
- Automated Riveting - Pre-programmed robots install rivets with precision and excellent consistency. Used for mass production aerospace and automotive fabrication.
- Self-Piercing Rivets - Special rivets that pierce and flare out sheet metal in a single step. Eliminates the need for pre-drilled holes.
Proper rivet installation requires the right techniques and equipment to maximize joint quality and production efficiency.
Rivet Joint Design
Successfully employing rivets in sheet metal depends on sound joint design principles:
- Edge Distance - Rivets should be placed at least 2x the rivet diameter from sheet edges. This prevents edge tear-out.
- Pitch Distance - Spacing between rivet centerlines should be 3-4x rivet diameter to prevent buckling between rivets.
- Rows - For long joints, use multiple rows of rivets staggered so rows do not align. This distributes load across the joint.
- Materials - If riveting dissimilar metals, choose rivets made from the less noble material to minimize galvanic corrosion.
- Interference - For slip-critical joints, chamfer holes and use oversize rivets to create tighter fitup. This enhances static friction between parts.
- Inspection - Quality checks of rivet length, grip, and flaring should be conducted to identify bad rivets that must be replaced.
Proper joint design is crucial for rivets to withstand the expected loads without coming loose or damaging the materials being joined.
Riveting has long been a staple joining method in key metal fabrication industries:
Aerospace: Rivets are the fastener of choice for airplane assembly. Their vibration resistance combined with low weight make them ideal for wings, fuselages, and other flight components.
Construction: Sheet metal roofs, siding, ducting, and stud framing often rely on rivets for weather-resistant mechanical fastening.
Appliances: The outer shells of appliances like washers, dryers, and refrigerators depend on rivets to clamp and hold sheet metal panels.
Automotive: While welding is prominent, rivets are still used extensively for non-structural auto body panels, interiors, and accessories.
Electronics: Rivets assemble sheet metal enclosures for computers, appliances, and other electronic devices where welding would damage components.
The popularity of rivets stems from their simple but robust and versatile nature for joining sheet metal across a vast array of industries and applications. CNC Milling