Riveting in Sheet Metal Fabrication(brass worth per pound Walker)

  • Time:
  • Click:7
Rivets are a common and useful fastening method in sheet metal fabrication. They create strong, permanent joints between metal parts while allowing some flexibility. Understanding when and how to use rivets for sheet metal assembly can help produce robust and quality products.
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - the body and mandrel. The body is a specially headed pin that fits through aligned holes in two or more layers of material. The mandrel stems from the head and extends through the hollow body.
During installation, the rivet is placed in position and the mandrel head is upset, or bucked, against the body head. This expands the body, causing it to mushroom against the reverse side material layers. The clamping force locks the rivet in place, creating a solid connection.
Rivet Body Materials
Rivets come in a range of body materials to suit different applications:
- Aluminum - Lightweight and corrosion resistant but lower shear and tensile strength than steel. Used for light duty connections.
- Steel - Stronger and more durable than aluminum but heavier. Provides high load capacity. Common types are Monel, stainless steel and carbon steel.
- Copper - Excellent conductivity and corrosion resistance. Used in electrical connections.
- Plastic - Lightweight with good corrosion resistance. Used for low strength applications.
Rivet Head Styles
Several head styles are available for different design needs:
- Round Head - Conical shape provides a finished look. Countersunk holes allow flush mounting.
- Flat Head - Low profile sits flush against the material surface. Useful in confined spaces.
- Pan Head - Wide dome head improves load distribution and countersinking ability.
- Countersunk Head - Tapered underside nests into a countersink hole for a flat surface.
- Other head types - Oval, truss, brake and large flange heads for specialized applications.
Rivet Sizing
Rivet diameter and length must be matched to material thickness and hole size. Gripping range denotes the minimum and maximum material thicknesses the rivet body can clamp. Length must extend slightly beyond the total thickness to allow mushrooming.
Using Rivets in Sheet Metal Fabrication
Rivets have many advantages that make them a popular fastening choice for sheet metal:
- Permanent - Once installed, rivets cannot loosen or fall out like separate fasteners. Vibration will not affect the joint.
- Adjustability - Rivets can accommodate some variability in material thickness and hole alignment. The clamping action draws layers into alignment.
- Strength - Rivet joints reliably withstand shearing and tensile stresses from loading and vibration. Strength depends on rivet material and size.
- Quick installation - Automated tools allow rapid rivet placement for high volume production. Even manual installation with a bucking bar and hammer is relatively fast.
- Cost - Rivets are an economical fastening method. Automated installation also improves cost-efficiency.
- Appearance - Neat rows of rivet heads provide a uniform industrial look when desired. Countersunk rivets allow flush surfaces.
- Flexibility - The joint has some ability to flex, preventing cracking from vibrations and loads. Not suitable for highly rigid connections.
- Accessibility - Installation only requires access to both sides of a joint. Bolts may require wrench access around complex assemblies.
- Maintenance - Rivets allow repairs by drilling out damaged rivets. New rivets can be installed in the existing holes.
Riveting Methods
The installation process involves inserting the rivet body into aligned holes in the materials, gripping the plates together, then deforming the body with a riveting hammer, mallet or automated tool. Here are some techniques:
- Hand Riveting - A bucking bar holds the body steady while the protruding mandrel head is flattened with hammer blows. The oldest method but still useful for repairs and low volume work. Skill is needed to avoid damaging the materials.
- Pneumatic Riveting - Uses compressed air to draw the mandrel up into the rivet body, flaring it outward. Allows one-sided access but requires costly special tools. Very fast.
- Impact Riveting - Automated tools use strong blows to upset the mandrel head. Highly efficient for production line assembly. Allows access from one side.
- Orbital Riveting - A pneumatic hammer strikes and rotates the rivet at high speed to flare the body. Creates very uniform finished rivets. Requires one-sided access.
Sheet Metal Rivet Joint Design
Properly designing joints is crucial to maximize rivet performance. Follow these guidelines:
- Hole Size - Diameter should match the rivet body with a tight fit. Oversize holes reduce strength. Undersize holes make insertion difficult.
- Hole Spacing - Rivets placed too close together increases risk of material cracking. Minimum spacing is around 3 diameters.
- Edge Distance - Holes should be at least 1.5 diameters from sheet edges. Less risks tear-out under load.
- Row Offset - Staggering rows avoids continuous lines of stress and weakness across the joint.
- Load Direction - Rivets best resist shear loads perpendicular to the rivet axis. Reduce direct tensile loads.
- Number of Rivets - More rivets spread loads over larger joint areas for higher strength. Excessive numbers add cost, time and risk of cracking.
- Joint Design - Lap joints have some flexibility under bending but limited shear strength. Butt joints are rigid and can handle greater shear loads.
Proper rivet selection, joint design and installation technique allows fabricators to produce robust sheet metal assemblies efficiently. Riveting remains a versatile, economical and effective fastening method for both low and high volume productions. CNC Milling