Riveting in Sheet Metal Fabrication(how to get a broken tap out Bart)
- source:MAJA CNC Machining
What is Riveting?
Riveting involves joining two or more pieces of sheet metal by inserting a metal fastener, called a rivet, through holes in the parts to be joined. The rivet has a head on one end and a tail on the other. During installation, the tail end is upset, or deformed, with a rivet gun or rivet hammer to flare out and clamp the rivet in place. This creates a permanent mechanical fastening.
Types of Rivets for Sheet Metal
There are three main types of rivets used for sheet metal fabrication:
- Solid/Round Head Rivets: As the name suggests, these have a solid, rounded head. They are one of the most common rivets for sheet metal.
- Countersunk Head Rivets: These rivets have a flat, countersunk head that sits flush with the surface of the metal. This gives a smooth finish.
- Blind Rivets: Blind rivets, or pop rivets, can be installed from one side without access to the back. The mandrel stem is pulled to flare the tail.
Steel is the most common material for rivets in sheet metal work. However, other materials are also used, including:
- Aluminum: Lightweight and corrosion resistant. Common for aircraft and marine applications.
- Copper: Used for riveting copper sheets due to compatibility of materials.
- Monel: A nickel alloy known for strength and corrosion resistance. Used in demanding applications.
- Stainless Steel: Added corrosion resistance for harsh environments.
- Titanium: Extremely strong but lightweight. Used in aerospace applications.
Pros of Riveting
There are several advantages that make riveting a popular fastening method in sheet metal fabrication:
- Does not require welding equipment or skills. Riveting only requires simple tools.
- Creates a permanent joint. The rivet cannot come loose over time.
- Evenly distributes stress across the joint. Less likely to fail than other fasteners.
- Quick and relatively simple installation. Automated riveting is also possible.
- Joint integrity can be visually inspected. Loose rivets can be detected.
- Minimal surface preparation needed compared to welding or adhesive bonding.
- Ideal for assembling pre-finished and sensitive materials. Does not damage surface coatings.
- Easily disassembled for repair or modifications by drilling out the rivets.
Cons of Riveting
Some potential downsides of rivets to consider include:
- Holes need to be pre-drilled, adding an extra step.
- Joint strength relies heavily on proper hole alignment.
- Riveting entails higher labor costs than welding.
- Not recommended for gas or liquid-tight assemblies. Rivet holes can lead to leaks.
- Rivets concentrate stress around the holes, which may need to be accounted for in design.
- Hollow or tubular structures cannot be effectively riveted.
Riveting Methods for Sheet Metal
There are several methods used to drive rivets for sheet metal assembly:
The traditional method using a hammer and bucking bar. Requires some skill and practice. Best suited for solid rivets.
Uses compressed air to drive rivet guns and set rivets quickly. Allows one-sided access for blind rivets. Widely used for high production rates.
A rivet gun using hydraulic pressure and pneumatic power. Applied mostly in aerospace applications requiring higher shear and tensile strengths.
A high energy system that hammers rivets in place. Used where access is limited but high pin load capacity is needed.
A specialized machine with an orbital head that spins and presses against the rivet for precision and consistency. Ideal for automated manufacturing.
Manual, pneumatic, and hydro-pneumatic riveting are the most accessible methods for small shops, while impact and orbital riveting require larger capital investments suited to high-volume production.
Riveting Process Steps
While specific techniques may vary, the general process of riveting sheet metal components is as follows:
1. Design parts to be joined and plan rivet pattern, spacing, and orientation. Match rivet type and grip length to material thickness.
2. Cut metal pieces to size and drill rivet holes at precise locations. Deburr holes.
3. Clean and fit parts together, using clamps or temporary fasteners to hold alignment.
4. Insert rivets into holes. The protruding shank fits into the set head of the rivet gun.
5. Use rivet gun or hammer to upset the rivet tail, causing it to flare out and clamp layers together. Avoid damaging the material.
6. Check set rivets for proper seating and reformat any loose connections.
7. File or sand flush any rivet heads extending above the surface (if needed).
8. Apply sealant, corrosion protection, or surface finish as required after riveting.
9. Inspect finished assembly for strength, functionality, and appearance.
Proper rivet installation is key to creating durable sheet metal joints. With an understanding of the riveting process, this simple but effective mechanical fastening technique can be applied in virtually any sheet metal fabrication project. CNC Milling CNC Machining