Riveting in Sheet Metal Fabrication(metal deburring Valentina)
- source:BAGANZ CNC Machining
What is a Rivet?
A rivet is a mechanical fastener consisting of a cylindrical shaft and head. During installation, the rivet is placed in a hole drilled through the materials being joined. The rivet shaft is then upset, or deformed, to create a second head that sandwiches the materials together. This creates a permanent joint.
Rivets are available in many materials, sizes, and head styles to accommodate different applications. Common materials include steel, aluminum, copper, and monel. Aluminum and steel rivets are popular for joining sheet metal because they are strong, corrosion resistant, and inexpensive.
Proper rivet selection ensures a joint has adequate strength for its application. Factors to consider include:
- Rivet Material: Rivet material should match or be compatible with the materials being joined. Using the same base metal prevents galvanic corrosion.
- Sheet Thickness: Thicker sheets require larger diameter rivets to fill the drilled hole and create sufficient clamping force. Standard rivet diameters range from 1/16” to 1/4".
- Rivet Strength: The rivet alloy and heat treatment determines its shear and tensile strength. Softer rivets are easier to install but may not have adequate strength. Harder rivets are stronger but more difficult to deform during installation.
- Rivet Head Style: Various head styles are available including round, brazier, countersunk, and flush. Select the head needed for proper function and appearance in the application.
- Grip Range: The grip range refers to the maximum and minimum material thickness the rivet can join and should be matched to the application.
Proper Hole Preparation
Drilling accurate, clean holes is critical for rivets to install and function properly. Holes should be round and match the rivet diameter within a tight tolerance. Standard tolerances range from +0.002”/-0.000” for small rivets up to +0.005”/-0.000” for larger 1/4" rivets.
Any burrs or debris present in the drilled holes can prevent the rivet from seating properly. Holes should be deburred and cleaned before riveting.
Through holes are typically used for riveting. Alignment of top and bottom sheets is critical so rivet heads form squarely on both sides. For blind rivets, only one side is accessible for drilling.
With properly prepared holes, rivets can be installed using riveting tools matched to the rivet size and material. Proper installation techniques ensure rivets form strong clinched joints.
Installation steps include:
1. Insert the rivet into the preprared hole. The rivet shaft should completely fill the hole.
2. Use a rivet set to seat the rivet head squarely against the top sheet surface. Apply pressure only to the rivet head.
3. Use a rivet gun or hammer to upset and deform the protruding rivet shaft. This expands the rivet to form a second head and clamp the sheets together.
4. The upset action works hardens and strengthens the rivet material. This is critical for load bearing applications.
5. For closed end rivets, continue upsetting until the rivet shaft breaks at its weak point. This leaves a flat end face.
6. For blind rivets, continue pulling the stem until the pulling head shears off. This provides the clamping force.
Proper installation should produce round, concentric rivet heads on both sides that sit squarely against the material surfaces. The rivet shoulders should be tightly clinched onto the sheets with no gaps, deformation, or cracking.
Inspection and Testing
Thorough inspection ensures properly installed and functioning rivets. All rivet joints should be visually examined for:
- Proper clinching and contact between rivet heads/shoulders and sheet surfaces
- Uniform round head shape without cracks or deformation
- Flush breakage of closed end stems or break-off of blind stem pulls
- Absence of gaps between rivet and hole edge indicating loose installation
Tap testing with a small hammer is also used to detect loose or improperly set rivets. A ringing sound indicates a tight rivet clinch while a dull thud signifies a loose condition.
Destructive testing methods can also evaluate riveted joint strength. These include peel and shear testing per military or industry specifications.
Proper rivet selection, installation, and inspection results in robust, permanent sheet metal joints. Understanding fundamental riveting principles allows fabricators to use this versatile fastening technology effectively across countless applications. With the right processes in place, rivets produce reliable connections able to withstand years of service. CNC Milling