Riveting in Sheet Metal Fabrication(tact weld Robin)
- source:ZIEG CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - the rivet body and mandrel. The rivet body is a head on one end and a shank on the other. The mandrel is inserted into the hollow end of the rivet shank and is used to flare out the tail of the rivet body against the reverse side of the workpieces being joined. This creates a widened shape that holds the rivet in place.
The head of the rivet is kept on the accessible side of the joint, while the flared tail is created on the backside. This keeps things together without requiring access to both sides of the assembly. There are a few different types of rivets that work in slightly different ways, but the general concept is the same.
When to Use Rivets
Rivets create a permanent mechanical attachment. Unlike screws or bolts, they cannot be removed without destroying the rivet. For this reason, they are best suited for applications where you do not need to take things back apart later.
Rivets are commonly used in sheet metal fabrication of:
- Vehicles - cars, trucks, trailers, etc.
- Aircraft and aerospace applications
- Ducting, venting, and HVAC systems
- Electronic enclosures and chassis
- Decorative metal fabrications
- Pipe brackets and hangers
- Signs and displays
Nearly any application where two or more pieces of thin sheet metal need to be securely fastened together permanently is a candidate for riveting. The joint created has a finished look and does not require any separate fasteners like washers or nuts.
Benefits of Rivets
There are several advantages that make riveting a popular choice for joining sheet metal:
- Permanent - Once installed properly, the rivets become a permanent part of the assembly. Vibration or other forces will not cause them to come loose over time.
- Consistent strength - The mechanical design of the rivet shank flare creates a very consistent clamping force and strength. Proper rivet selection ensures this.
- No accessories - Rivets provide their own flange and fastening method. No extra washers, nuts, etc. are required.
- Flush finish - With most rivets, the flared tail is hidden behind the joint while the head provides a smooth, finished look.
- Quick installation - Rivet guns allow for quick installation compared to drilling and bolting.
- No electricity - Rivet guns use pneumatic power or simple hand squeeze power rather than electricity. This makes them very portable.
- Sheet metal only - Rivets are designed to join thinner sheet metals rather than thicker materials or larger hardware.
For these reasons, rivets will often be the first choice for permanently joining sheet metal components together. The joint needs to be properly designed, however, to take full advantage of rivet strengths.
Rivet Joint Design
For optimal results, the riveted joint should be designed with the following considerations:
- Rivet diameter - This needs to match the thickness and strength needs of the sheet metal involved. Using too small or too large of a rivet diameter can compromise strength.
- Rivet length - Allowance needs to be made for the flared tail. Grip length should be 1.5-2 times the combined thickness of the materials.
- Hole size - Clearance between the rivet and the hole is important to allow flexing as the tail flares. Generally 120-150% of rivet diameter.
- Material strength - Softer materials like aluminum may require more rivet diameter than harder steel. The material type impacts strength.
- Spacing - Rivets should be spaced 3-4 times the rivet diameter apart for even load distribution. Closer spacing can split the metal.
- Edge distance - Holes should be at least 1.5 times the rivet diameter from sheet edges. Closer can cause edge tearing.
- Alignment - Rivet holes should align precisely between both sheets to prevent distortion. Misalignment stresses the rivet unevenly.
Proper rivet joint design distributes load across multiple rivets and avoids localized stress that could cause joint failure or metal tearing. Consulting rivet manufacturers' specifications and load/spacing guidelines helps maximize this.
There are several types of rivets to choose from for sheet metal fabrication. Common options include:
- Blind rivets - Form a flared tail from one side only using a rivet gun. No backside access needed.
- Solid rivets - Require access to both sides of the workpieces. Mandrel is removed after forming.
- Self-plugging rivets - Similar to blind rivets but with a softer mandrel that folds into the rivet body.
- Split rivets - Have a pre-formed split mandrel that folds up into the rivet body cleanly.
- Structural rivets - Used for high-strength aerospace and structural applications.
Within these types are various head styles - round, countersunk, flat, etc. Material is commonly aluminum but sometimes specialty metals for strength or corrosion resistance.
Selecting the right rivet type and specifications allows you to achieve both functional and aesthetic goals for any sheet metal fabrication project.
There are three main ways to install rivets to join sheet metal:
The traditional method using simple hand tools. Holes are drilled or punched in the metal. The threaded mandrel of the rivet is inserted through the holes and a bucking bar is used on the backside while the operator hammers the head to flare the tail. Hand riveting takes practice to master.
This uses compressed air powered tools to quickly insert and "shoot" the rivets in place. The rivet set is placed in the hole and the gun bucks the mandrel to flare the rivet body. Pneumatic rivet guns allow faster production riveting.
Battery Powered Riveting
Cordless battery rivet tools provide an alternate method without need for compressors. Jaw sets grab and buck the mandrel to set the rivet. Battery riveters offer more flexibility in terms of workspace than pneumatic tools.
Any of these methods can produce excellent riveted joints in sheet metal when done properly. The right approach depends on production environment, mobility needs, available equipment, and operator skill.
Inspecting Riveted Joints
Once rivets are installed, the joints should be inspected to ensure proper function and appearance:
- Check rivet flushness - The heads should seat cleanly without damage to the surrounding surface.
- Confirm mandrel release - Split tail mandrels should break cleanly. Solid shank mandrels need removing.
- Verify flare size - Flared tails should be 1.5 times rivet diameter to achieve sufficient clamping.
- Rivet spacing - Even gap spacing should be seen around each rivet.
- Feel for looseness - Joint should not shift when rivets are laterally tapped.
- Look for cracks - No radial cracking in the metal surrounding the rivet.
- Check alignment - Rivet holes should align cleanly through both sheets with no offsets.
well formed and seated rivets that pass inspection will provide maximum longevity and strength. Any issues found can be remedied by removing and replacing suspect rivets.
Rivets have been used for decades to securely fasten sheet metal while allowing efficient fabrication. Understanding when and how to properly apply rivets helps create strong, professional results. With some practice and the right joint design, riveting in sheet metal can produce astounding results. CNC Milling CNC Machining