Riveting in Sheet Metal Fabrication(defects in welds Stacey)
- source:ZIEG CNC Machining
How Rivets Work
A rivet is a mechanical fastener with a head on one end, a shank, and a second head formed on the opposite end during installation. The shank is inserted through aligned holes in the materials being joined. The tail end is then flattened into a second head using a hammer, squeezing the rivet tight. This pulls the rivet heads toward each other, clamping the materials together.
There are three main categories of rivets:
- Solid/Hard rivets: Made from steel, aluminum, copper, or other metals. Require access to both sides of the assembly.
- Semi-tubular/Soft rivets: Have a partial hole through the center of the shank. Use softer metals like copper, aluminum, or monel. Allow tighter clamping force.
- Blind rivets: Hollow and open on one end. Can be installed from one side when there is only access to one surface. Often used for field repairs.
Solid rivets create the strongest and most permanent joints. Semi-tubular and blind types are quicker and easier for assembly situations where backside access is limited.
Rivet Joint Design
Proper rivet spacing is crucial for joint strength. As a rule of thumb, rivets should be at least 2 times the material thickness apart, and 4-5 times the rivet diameter. Rows should be staggered brickwork style to distribute force. The edge distance should be at least 1.5 times the rivet diameter. Holes must be accurately punched or drilled to match the rivet shank size.
Here is an overview of the standard riveting process:
1. Shear the proper length and diameter solid rivet for the materials and joint design.
2. Lubricate the rivet shank if needed for smooth driving.
3. Insert the rivet through the aligned holes in the materials to be joined.
4. Place a bucking bar against the rivet tail.
5. Use a rivet hammer or rivet gun to form the second head, flattening the tail onto the backside surface.
6. Check that both heads are tightly formed without cracking or deforming the surrounding material.
Proper technique is key for quality results. Rivet heads should be 1.5 times the shank diameter. Heads formed too small can pull through the holes. Oversize heads weaken the material. Consistent hammer force and perpendicular alignment are essential.
Many manufacturing operations use pneumatic rivet guns or hydraulic squeezers to automate riveting. This increases speed and joint consistency. CNC machines can also install rivets programmatically for high-volume production.
However, manual hand riveting still plays an important role in lower-volume fabrication, field repair work, and custom aircraft building. Skillful technicians can precisely control location, alignment, and hammer force. Automated systems lack this level of finesse and versatility.
Riveted Joint Strength
When properly designed and installed, rivets create very strong permanent joints. Friction and mechanical interlock between the rivet heads and underlying materials resist shear forces trying to slide the layers. Tension strength comes from the clamping action drawing the rivet heads together.
Rivet strength depends on metals used, diameters, head design, and adequate edge distance. Shear and tensile strengths can exceed that of bolts. Fatigue life is excellent with minimal loosening over time. This makes rivets well suited for structures undergoing vibration.
Best Uses for Rivets
Rivets have key advantages that make them the preferred mechanical fastener for many applications:
- Permanent assembly of sheet metal parts
- Joining dissimilar or thin materials prone to cracking
- Quick installation with basic tools
- Vibration and fatigue resistance
- Weight savings versus bolts
- No threads to strip out
- No collateral damage from heat (vs. welding)
- Repairability in the field
Riveting sees heavy use in aircraft assembly for these reasons. Appliances, electronics, HVAC ducting, off-road vehicles, furniture, storage containers, and more also rely extensively on rivets for durable construction.
While advanced adhesives now compete with rivets in some applications, traditional riveting remains a trusted and proven method for assembling sheet metal components and fabrications. The process continues evolving through new techniques like friction-stir blind riveting for aerospace. This mechanically joins layers from one side without heat or compressed air.
In summary, rivets provide versatile, lightweight, and reliable permanent joints for all types of sheet metal fabrication. When properly incorporated into joint design and installed using skilled technique, rivets outperform most other mechanical fasteners. Riveting will continue playing a key role in metal manufacturing and repair across industries. CNC Milling CNC Machining