Types of Rivets for Sheet Metal
There are several types of rivets suitable for joining thin sheets of metal:
- Solid rivets - These are one-piece rivets made of steel, aluminum, copper, or other metals. They are inserted through pre-drilled holes and deformed with a riveting hammer or rivet gun to flare out the bottom shank, securing the rivet in place.
- Blind rivets - These rivets can be installed from one side of a joint, making them ideal for assemblies where you only have access to one side. Blind rivets are inserted into a pre-drilled hole and then a rivet gun pulls a stem, flaring out the rivet body on the blind side.
- Self-piercing rivets - As the name suggests, these rivets pierce through stacked sheets of metal as they are set. There is no need to pre-drill holes. A rivet gun compresses and flares out the rivet in one action.
- Drive rivets - They have a pre-formed head on one end and are driven into place using a hammer rather than a rivet gun. Drive rivets allow for easy removal and are common for temporary repairs.
Steel rivets are very strong but can corrode over time when exposed to moisture. Stainless steel resists corrosion but is more expensive. Aluminum and copper rivets are lightweight and corrosion resistant but not as strong as steel. Monel rivets offer strength and corrosion resistance for demanding applications but are costly.
Proper rivet choice depends on the service environment, joint strength needed, and riveting equipment available. Soft malleable rivets are preferred for hand riveting with a hammer while high strength rivets work better with automated riveting systems.
Rivet diameter should match the thickness of the sheets being joined. As a rule of thumb, rivet diameter should be 1.5 to 2 times the thickness of the top sheet. Grip length, the unflared length of the rivet shank, must span the total thickness of all sheets with enough extra length for the forming of the shop head.
For structural joints, the center-to-center spacing between rivets should be about 4 times the rivet diameter. For less critical applications, up to 6-pitch spacing may be acceptable. Rows of rivets should be offset rather than aligned to distribute load more evenly.
Matching the rivet shank and hole diameter is critical for a tight joint. Hole diameter should be equivalent to the rivet shank diameter. Allowing slop by oversizing the holes results in a loose joint.
Holes can be punched or drilled depending on sheet thickness. Punching is quicker but causes slight deformation around the hole. For thin sheets under 1/8” thick, punching is usually acceptable. Thicker material should have holes drilled for dimensional accuracy and quality.
Deburring holes after punching or drilling removes sharp edges that can damage the rivet surface during installation. A quick pass with a file, deburring tool, or Scotch-Brite pad cleans up the holes.
The basic riveting process involves four steps:
1. Holes are punched or drilled through the sheets to be joined. Proper alignment is critical before drilling or punching.
2. Rivets are inserted into the holes with the flared shop head against the accessible side of the joint and the shank through the hole.
3. The protruding shank is flared outward with a hammer, rivet squeezer, or rivet gun to create the shop head. This expands and clamps the rivet in the hole.
4. The excess shank material is trimmed off with a nipper, shear, or saw flush with the shop head profile.
For multi-layer stacks, temporary fasteners like Clecos may be needed to clamp layers before riveting. Set rivets starting from the middle and working outwards to draw the sheets together evenly. Apply moderate pressure when forming shop heads - excessive force can pull holes out-of-round.
Here are some tips for quality riveted joints:
- Use rivets with a grip range suitable for your application. Underfilled or overfilled grip reduces strength.
- Make sure rivet length provides enough exposed shank for shop head formation. At least 1.5 x rivet diameter should protrude.
- Hold the riveting hammer perpendicular to the shank to flare the rivet smoothly. Off-angle hammering deforms the shop head unevenly.
- Use rivet sets matched to the rivet head profile for uniform shop head shape.
- Set rivets in a consistent pattern to draw sheets together evenly without distortion.
- Avoid hammering directly on the rivet head as this work-hardens the material and causes cracks. Use the appropriate rivet set.
- Trim excess shank flush with rivet heads for smooth joints. Avoid leaving sharp edges.
With the right techniques and quality rivets, riveting is an economical, reliable method of fastening sheet metal components in a wide range of fabrication projects. CNC Milling