Riveting in Sheet Metal Fabrication(brass versus bronze Borg)
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What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The shaft is inserted through holes in the materials being joined. The rivet head is then smashed against the shaft using a tool called a rivet gun or riveting hammer. This causes the shaft to flare out and clamp the materials together. The flared end is called the shop head or bucktail.
Rivets work using both friction and mechanical interference to hold materials together. The flaring of the rivet shaft against the rivet hole creates tension, friction, and pressure that prevents the rivet from working loose over time. This makes rivets ideal for uses where vibration could cause threaded fasteners like screws and bolts to fail.
Types of Rivets
There are several types of rivets commonly used in sheet metal work:
Solid/blind rivets - These are the simplest and most common type. They are inserted into a pre-drilled hole and hammered into place. The rivet cannot be removed once installed.
Tubular rivets - These have a hollow shaft rather than a solid shank. Often used in aviation applications.Requires access to both sides during installation.
Split rivets - These have a pre-cut split along the shaft. As the head is hammered, the rivet shaft splits along this pre-cut line. Allows for installation where only one side is accessible.
Self-piercing rivets - Cut their own hole rather than requiring pre-drilled holes. Often used to join dissimilar or multi-layer materials.
Pop rivets - Installed using a specialized rivet gun. Allows very quick installation for high volume production.
Rivet Materials
Steel - The most common rivet material. Low cost but prone to corrosion. Often zinc plated for corrosion resistance.
Aluminum - Lightweight and corrosion resistant. Common for aircraft and marine applications.
Monel - A nickel-copper alloy. Very corrosion resistant but expensive. Used in demanding applications.
Copper - Used for its appearance. Offers good conductivity and weather resistance.
Plastics - Lightweight option but not as strong. Usually a nylon or polycarbonate.
Titanium - Extremely strong but expensive. Used in critical aerospace applications.
Riveting Process
The basic process for riveting sheet metal is:
1. Prep materials - Deburr edges, clean surfaces. Match drill holes.
2. Insert rivets - Place rivet into holes with rivet head against one material.
3. Compress rivet - Use rivet gun, hammer, or squeezer to flare rivet shaft.
4. Inspect joint - Confirm properly flared shaft and tight joint.
Proper riveting relies on quality prep work. Drilled holes must match precisely between materials and be deburred to allow smooth rivet insertion. Surfaces must be free of dirt, oil, paint, or other contaminants.
Using a riveting hammer takes practice - an experienced operator can quickly make thousands of high-quality rivets daily. Pneumatic rivet guns allow one-handed use for faster riveting. Mechanical squeezers automate the process for production environments.
Rivet Strength
Rivet strength depends on the rivet material, shaft diameter, grip (material thickness), and joint design. Typical shear strengths range from 1,000 psi for soft aluminum rivets up to 200,000 psi for steel structural rivets.
Proper grip is important - too little and the rivet can tear out of the hole, too much and it may not flare properly. Minimum grip is usually 1.5 times the rivet diameter.
Rivet spacing also affects joint strength. A spacing of 4-6 diameters between rivet centers is recommended for most applications. For maximum strength, an offset or staggered pattern can be used.
Riveted Joint Design
Well-designed riveted joints properly transfer load while minimizing stress concentrations. Here are some best practices:
- Use multiple rows of rivets to distribute load rather than single row.
- Place rivets in shear rather than pulling directly on them.
- Use washers under rivet heads and countersunk rivets to reduce stress risers.
- Avoid placing rivets at corners, instead spacing them inwards at least 1 diameter.
- Use round holes rather than slotted holes to maximize bearing area.
Inspection & Testing
All riveted joints should be visually inspected during installation and after completion. Check for:
- Consistent flaring of the shop head without splitting.
- Sufficient clamping of material with no gaps.
- Flushness of the shop head relative to material surface.
- Any cracks radiating from rivet holes.
For critical applications, riveted samples can also be destructively tested to confirm shear and tensile strength.
Riveting vs. Other Fasteners
Compared to other fastening methods, rivets offer:
- Ease of installation with no threading or torque requirements.
- Vibration resistance - less prone to loosening than threaded fasteners.
- Strength in shear loading.
- Permanent joint - cannot loosen over time.
- Smoother surface finish without fastener heads protruding.
The main downsides are lack of disassembly and lower strength compared to hi-lock fasteners and structural bolts. Rivets also require access to both sides of a joint for installation.
Despite the rise of welding and adhesive bonding, riveting remains a tried-and-true fastening method for sheet metal fabrication across countless industries and applications. With a long history and proven performance, the rivet will continue playing a key role in metalworking for the foreseeable future. CNC Milling CNC Machining