Riveting in Sheet Metal Fabrication(design snap fit Dunn)

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Rivets are a common and reliable fastening method used in sheet metal fabrication. A rivet is a short cylindrical rod with a head on one end. The rivet is inserted through holes in multiple sheets of metal, and the tail end is mechanically deformed to clamp the sheets together. Rivets create a permanent mechanical attachment that can handle vibration and stress better than other joining methods like welding or adhesives.
When riveting sheet metal, it's important to understand the techniques, materials, tools and equipment involved in the process. Properly installing rivets requires some skill, but the results are durable joints that will last the lifetime of the product. Let's take a closer look at how riveting works for sheet metal fabrication.
How Riveting Works
Riveting joins multiple sheets of metal by inserting a rivet through aligned holes in the sheets and mechanically deforming the tail end of the rivet. This flares out the tail, clamping the rivet in place. The flared end is called the shop head or buck-tail, while the pre-formed head on the other end is called the manufactured head or factory head.
When inserting the rivet, the shop head is formed against a bucking bar or dolly, which supports the underside of the sheets being joined. As the rivet is deformed with the rivet gun, the bucking bar counteracts the applied force, flaring the tail uniformly. This creates a flush shop head and securely clamps the sheets together between the two rivet heads.
Rivet Types for Sheet Metal
There are several types of rivets used for sheet metal fabrication:
- Solid/blind rivets - Pre-formed rivets installed with access to only one side using a rivet gun. The mandrel stem fractures after installation. Common for aerospace and appliance fabrication.
- Semi-tubular rivets - Have a partially drilled head so the tail can collapse inward. Require access to both sides during installation. Used for heavy machinery, bridges, and shipbuilding.
- Drive rivets - Similar to semi-tubular but are mechanically driven using hammer blows rather than hydraulic pressure.
- Split rivets - Have a pre-split tail so they can be mechanically expanded using a tool. Allow fast installation but lower strength than solid rivets.
- Self-piercing rivets - Can pierce and join sheets in a single operation without pre-drilled holes. Require access to only one side. Used in auto manufacturing.
Each rivet type has advantages and disadvantages depending on the application requirements. Solid rivets offer the highest strength but require two-sided access. Self-piercing and split rivets are fastest to install but don't match the strength of solid rivets.
Riveting Process
Installing rivets in sheet metal involves several steps:
1. Shear sheets to required size and drill, punch or self-pierce rivet holes at marked locations. Deburr holes.
2. Clean and degrease rivet locations to improve adhesion. Apply sealant if necessary.
3. Insert rivets into holes and position bucking bar on back side.
4. Use rivet gun to upset the rivet tail. Rivet guns use hydraulic or pneumatic force to flare the tail. Repeat for additional rivets.
5. Inspect each rivet to ensure proper flaring and clamping force. Re-strike poorly formed rivets.
6. Evaluate sample rivets through destructive testing to validate joint strength.
Proper edge distances, hole sizes, rivet length, material thickness and rivet placement are critical for a sound joint. Operators must be trained on the appropriate specifications and installation procedures.
Riveting Tools and Equipment
Installing rivets in sheet metal requires a riveting system consisting of:
- Rivet gun - Applies pulling force to deform the rivet tail. Can be pneumatic, hydraulic, battery powered or manual. Popular models are the pneumatic Cleco and hydraulic Cherry rivet guns.
- Bucking bars/dollies - Support the underside of the metal while riveting. Made of steel, high density plastic or wood. Should span several rivet diameters.
- Drill press/CNC punch - Makes holes for rivets. Solid carbide bits and indexed punch tooling ensure accuracy.
- Rivet sets - Shape the rivet head precisely. Use flat, cup, conical and snap sets for different applications.
- Hammers/mallets - May be needed to initially flatten misshapen rivets. Soft face prevents marking metal.
- Micrometers, calipers, gauges - Measure rivet length, material thickness, hole size, etc.
- Deburring tools - Remove burred edges from drilled/punched holes before riveting.
- Personal protective equipment - Safety glasses, gloves, etc. protect operator.
Proper installation also requires a solid, vibration-free worktable to support the fabrication. Fixtures may be needed to hold parts in alignment.
Riveted Joint Design
Proper rivet pattern design is crucial for a strong, long lasting sheet metal joint. Considerations include:
- Rivet diameter - Should be 1.5-2 times sheet thickness depending on application.
- Hole size - Diameter slightly larger (0.05mm) than rivet provides clearance.
- Edge distance - Minimum of 1.5-2 rivet diameters from sheet edge.
- Rivet pitch - Spacing between rivet centerlines, 4-8 diameters apart.
- Rivet rows - Parallel rivet lines spread load across joint.
- Number of rivets - More critical joints require more rivets to distribute load.
- Materials - Rivet material should match or be stronger than the sheets.
The joint design depends on the expected stress, load direction, vibration, potential corrosion and service life. Aircraft and pressure vessel joints require very dense, symmetrical rivet patterns for safety. HVAC ducting may only need intermittent rivets for simple alignment.
Inspection and Testing
All riveted joints must be visually inspected to check for defects like cracks, inadequate flare, scratches, sealant gaps, misalignment, etc. Sample rivets should undergo shear and tensile testing to validate proper installation procedures. Periodic maintenance checks for loose or damaged rivets throughout the service life are also critical.
Pros and Cons of Riveting
Riveting has both advantages and disadvantages compared to other sheet metal joining methods:
- Strong, permanent, full-strength joints
- Vibration and fatigue resistant
- Works with dissimilar metals
- Fast installation with correct tools
- Evenly distributes load across joint
- Long service life, easy inspection
- Requires access to both sides for solid rivets
- Hole drilling/alignment labor intensive
- Installation needs training and skill
- Relatively expensive equipment needed
- Replacing damaged rivets difficult
- Not suitable for certain materials
Despite the drawbacks, riveting remains a preferred choice for fabricating sheet metal in fields from aerospace to architecture due to the reliable, long-lasting joints it produces. With some care taken in design and installation, riveted connections can withstand years ofservice with minimal maintenance. The unmistakable look of neatly lined up of rivet heads has also become an iconic industrial aesthetic.
Riveting is a trusted and versatile fabrication technique that produces robust, permanent sheet metal joints. A variety of rivet types allow joints to be made with access to one or both sides. Pneumatic rivet guns provide the force to deform the rivet tail and clamp the sheets together. Proper joint design, precision hole drilling, controlled riveting force and post-installation inspection are key to ensuring rivets can withstand years of vibration, shock and stress. With the right approach, knowledge and tools, rivets will continue to be a go-to fastening solution for sheet metal applications. CNC Milling CNC Machining