Riveting in Sheet Metal Fabrication(machine shop tools Betty)
- source:BAGANZ CNC Machining
What is a Rivet?
A rivet is a cylindrical shaft with a head on one end. The shaft is inserted through holes drilled or punched in the materials being joined. The unused end of the shaft is then deformed with force creating a second head to clamp the materials together. The rivet fills the hole and its deformed heads grip the materials on both sides preventing movement.
Rivets are made from various materials including aluminum, steel, copper, stainless steel, and specialty alloys like Monel or silicon bronze. Aluminum and steel are most common. The material and hardness is selected based on the application and strength requirements.
There are several types of rivets used in sheet metalwork:
- Solid/Semi-Tubular - Most common type with a solid shank. Used for normal strength applications.
- Blind - Has a built-in head on one end and does not require access to the backside for installation. Used when backside access is limited.
- Tubular - Hollow and lightweight while still strong. Used in aviation for strength-to-weight ratio.
- Drive - Has pre-cut drive pin in the shank to facilitate installation. Used in high production environments.
- Large Flush - Countersunk head for a flush surface. Used in aircraft skins for aerodynamics.
- Split - Rivet splits into a rivet body and mandrel during installation. Quick and easy.
- Self-plugging - Seals itself. Used in watertight applications.
- Multi-grip - Single rivet size fits multiple material stack ups. Very versatile.
Rivets are available in different shear and tensile strengths for different applications. Shear strength refers to the parallel-to-shaft load a rivet can withstand before shearing off. Tensile strength is the perpendicular-to-shaft load a rivet can handle before pulling out and deforming. Standard aluminum rivets have typical shear strengths around 60-70ksi and tensile strengths of 30-50ksi.
Rivet strength depends on the material, hardness, shank diameter, grip length, and head size. Increasing any of these factors leads to higher strength. Harder materials like steel provide stronger rivets than soft aluminum. Larger diameter shanks, shorter grips, and bigger heads all increase strength as well.
Rivet Installation Process
Installing rivets in sheet metal is a simple three step process:
1. Holes are first drilled or punched through the materials to be joined. Hole size equals the rivet diameter. Accurate alignment is critical.
2. The rivet shank is inserted through the holes so the head rests against one material surface.
3. Using a rivet gun, the tail end of the rivet is upset/deformed to create a second retaining head. This clamps the materials together.
Proper upsetting of the rivet tail is the key to a strong joint. Rivet guns can be manual, pneumatic, or hydraulic. Heat and vibration resistant rivets may require specialty installation methods.
Riveted Joint Design
For optimal strength, riveted joints should be properly designed. Here are some best practices:
- Space rivets evenly to distribute load. Rule of thumb is 3-4 x rivet diameter.
- Use enough rivets to meet strength needs. More rivets = stronger joint.
- Place rivets staggered instead of in-line to reduce chance of splitting.
- Position rivets perpendicular to applied load/stress.
- Use flush rivets on exterior surfaces for aerodynamics.
- Seal joints with sealant if needed for liquid/gas leakage prevention.
Riveted joints can be designed to fail safely. Rows of rivets are oriented so outer rows take load first and fail first indicating overload.
Compared to other joining methods, riveting offers many advantages:
- Permanent assembly. Rivets do not loosen over time.
- Excellent vibration resistance. Rivets withstand shock and cyclic loads.
- No consumables. Installation requires only the rivet itself.
- Works on all metals. Rivets can join dissimilar metals.
- Easy visual inspection. Missing or deformed rivets are easy to identify.
- Predictable failure. Joints fail progressively depending on rivet pattern and design.
- Requires access to only one side for most installs. Blind rivets require no backside access.
Riveting is a trusted and proven technology that continues to be the go-to joining method for sheet metal assemblies and components. Correct design and installation results in an extremely robust mechanical connection. The versatility and reliability of rivets makes them ideal for everything from HVAC ducting to offshore oil platforms to spacecraft. Whether your project involves steel, aluminum, or exotic alloys, consider the advantages of riveting. CNC Milling