Riveting in Sheet Metal Fabrication(instant cnc quote Enid)
- source:ESKRIDGE CNC Machining
What are Rivets?
A rivet is a mechanical fastener that joins two or more sheets of material by insertion in holes through the stacked sheets. The rivet shank is inserted through the aligned holes in the sheets to be joined and a second component called a mandrel is inserted into the hollow end of the rivet. The rivet body is then mechanically deformed with a riveting hammer, squeezing and expanding the rivet to form a permanent head on the solid end. This pulls the rivet tight against the sheet materials to clamp them together. The excess shank is then sheared or snapped off, leaving the rivet firmly in place.
Advantages of Rivets
Rivets offer certain advantages over other fastening methods like welding, screws or adhesives:
- Strong and permanent - Once properly set, the mechanically deformed rivet head cannot detach or loosen over time. Riveted joints can be as strong or stronger than welded joints.
- Vibration resistant - Rivets maintain clamping force securely even when subjected to vibration and shock loads.
- Quick installation - Automated riveting machines allow very rapid installation compared to welding or screwing components together.
-joints maintain flexibility - While keeping sheets securely fastened, riveted joints allow some movement and flexibility which can be beneficial in certain applications.
- Electrical conductivity - Rivets allow metal-to-metal contact which provides electrical continuity across a joint. Insulated rivets are available when conductivity is not desired.
- Easy visual inspection - It is quick and simple to visually check for properly set and locked rivets.
- No post-work required - Unlike welds, no need to clean up or finish a riveted joint after fastening.
- Variety of materials - Rivets are available in a wide range of metals, polymers and composites to suit the assembly.
Types of Rivets for Sheet Metal
There are several types of rivets commonly used in sheet metal fabrication, each suited for different applications and assembly requirements:
These are the simplest and most commonly used rivets. A blind rivet is inserted into pre-drilled matching holes in the materials being joined. Blind rivets have a pre-formed head on one end and a mandrel stem protruding from the opposite end. As the rivet is set with a rivet gun or hammer, the mandrel is pulled into the rivet shank, flaring out the rivet body to form a second head and clamp the materials. The stem breaks off when the riveting is complete. Blind rivets are ideal for quick simple assembly where accessibility to only one side is possible.
Bulbed Tubular Rivets
These have a hollow tubular body and are flared outward on one end to form a pre-formed head. The opposite end contains a stem which is drawn into the rivet body to flare out the tubular end during setting. The flared end bulbs out to approximately twice the original shank diameter, providing a wide bearing surface and high strength. Common in aircraft assembly.
These contain a pre-formed head on one end and split legs on the opposite end which splay outward during installation to form the second head. The legs fold inward for insertion in the joint holes before spreading back out when set. Split rivets allow tight clinching of materials and no shank remains. However, split rivets have less strength than solid rivets.
No preformed head - both ends are cylindrical with one end slotted or cross-cut. A drive pin tool is used to flare out one end during installation. Drive rivets can be challenging to install correctly.
Have countersunk heads that sit entirely flush with the surface of the materials being joined. The smooth low profile is useful for aerodynamics and aesthetics. But flush rivets have less clamping force than protruding head designs.
Other specialty rivet types like large head, high shear and tri-fold rivets are available for specific applications. Usage depends on factors like materials, service loads, assembly access and cost.
Rivets used for sheet metal fabrication are most commonly aluminum, steel, stainless steel, copper or titanium. Exotic alloys are utilized in high-strength aerospace applications. The rivet material should match the sheets being joined to avoid galvanic corrosion. Plastic and composite rivets are also produced, but have much lower strength than metal.
Sheet Metal Riveting Process
Properly riveting sheet components together involves following a systematic process:
1. Prepare and align materials - Sheets must be orientated and fixtured if necessary to align holes precisely. Proper edge distances and spacing between rivets is critical.
2. Select rivets - Material, grip length, diameter and head style should be specified. Allowance for sheet thickness variations should be made.
3. Insert rivets - Rivets are manually or automatically fed and inserted through the aligned holes with the headed end on the accessible side for setting.
4. Set the rivet - Using a rivet gun, hammer or other tool, the rivet is compressed to flare out and clamp the sheets tightly together.
5. Inspect the joint - Check for poorly formed or cracked rivet heads indicating improper setting. Also check for appropriate clamping and hole fill.
6. Finish the joint - Any mandrel stems are sheared or ground off and rough edges smoothed if needed.
Avoiding problems like undersetting, cracking, or distorting the materials when riveting requires proper tool selection and operation, skill, and testing on non-critical samples first.
Riveting Tool Options
Setting rivets properly and efficiently requires specialized tools:
- Manual rivet guns - Versatile hand-operated pliers-like tools for light duty use. Limited strength and operator fatigue can be issues.
- Pneumatic rivet guns - Air-powered tools provide the force needed for most applications while minimizing operator effort. Widely used for aviation and industrial assembly.
- Battery riveters - Offer cordless convenience with sufficient power for common tasks. Quicker than manual tools but heavier.
- Hydraulic riveters - Develop very high squeezing force for large or high strength rivets. Used on bridges, heavy machinery, etc.
- Automated riveting - Robotic auto-feed tools increase production rates substantially. Programmable for custom applications. Requires considerable setup time and cost.
Proper tool maintenance and matched set up pressure for the specific rivets are crucial for quality and efficiency. Operators must be skilled in proper tool use.
Riveting Best Practices
Following best practices helps ensure properly riveted sheet metal joints:
- Use the recommended drill size for hole diameter - Undersized holes can damage the rivet and joint while oversized holes reduce strength.
- Account for sheet thickness variations when specifying rivet length
- Apply pressure gradually and uniformly when bucking the rivet
- Set rivets starting from the center and moving outwards to minimize distortion
- Use flush head rivets when possible for airflow-critical surfaces
- Be mindful of pinch points and snagging hazards from protruding rivets
- Inspect set rivets visually and with test samples before production
- Consider future disassembly needs when locating and specifying rivets
Rivets will continue to be a trusted method for fast precision joining of sheet metal assemblies for countless applications. Understanding proper rivet selection, preparation and installation technique helps optimize the strength, durability and appearance of riveted joints. With an array of rivet options and specialty tools now available, this tried and true fastening technology will carry on as an essential component of modern sheet metal fabrication. CNC Milling CNC Machining