Riveting in Sheet Metal Fabrication(tool lathe Alan)
- source:ZIEG CNC Machining
What is a Rivet?
A rivet is a cylindrical shaft with a head on one end. The rivet is inserted into pre-drilled holes in the materials being joined, and the tail end is flared out with a hammer or specialized tool called a rivet gun. This flaring process is called peening. The flared tail fills the hole and clamps the materials together between the rivet head and tail, creating a solid joint. Rivets come in many head styles like flat heads, round heads and countersunk heads to suit different applications. They are made from various metals including aluminum, steel, copper and more.
Benefits of Riveting Sheet Metal
Riveting offers many benefits for joining sheet metal that make it a popular fabrication technique:
- Strong and permanent - Once installed, the flared tail of the rivet cannot pull back through the hole, resulting in a joint as strong as the parent material. Rivets join sheet metal securely and permanently.
- Vibration resistant - Riveted joints can withstand vibration better than many other mechanical fastening methods. The clamping force of the rivet helps dampen vibration induced failures.
- Lightweight - Rivets add very little weight versus alternatives like welding or bolting. This makes them ideal for weight sensitive applications.
- Quick installation - Hand riveting with a hammer allows rapid installation. Pneumatic rivet guns further speed up the riveting process on production lines.
- No machining needed - The prep work required is simply drilling properly aligned holes. No tapping or threading is required as with screws or bolts.
- Inspectable - Installed rivets are easy to visually inspect for proper installation. Loose or improperly set rivets can be detected through inspection.
These qualities make riveting a cost effective and reliable fabrication technique for many sheet metal assembly applications.
Rivet Types for Sheet Metal
There are several types of rivets designed to suit different sheet metal riveting applications and installation methods:
- Solid rivets - These are one piece rivets made entirely from the rivet shaft material. Common materials are steel, aluminum, copper and monel. Solid rivets require access to both sides of the workpiece for installation.
- Blind rivets - Blind rivets can be installed from one side of the materials being joined, making them ideal for assemblies where the back side is not accessible. Blind rivets have a mandrel that is pulled to flare the rivet tail.
- Self-plugging rivets - These feature a head that completely fills the hole, creating a sealed joint. Widely used in electronics and appliances when a leak-proof joint is needed.
- Drive rivets - These feature oversized rivet heads that are hammered to flare out the tail. Drive rivets allow for some compression of the joined materials during installation.
- Split rivets - These rivets have a pre-cut split tail that folds outward during installation. The split tail facilitates use in tight spaces.
- Specialty rivets - Other types exist like large flange rivets for structural applications and tri-fold rivets which reduce hardware protrusion.
Rivet material, head style, tail design and installation method can be specified based on the particular sheet metal fabrication application.
There are two basic methods used for riveting in sheet metal work - manual riveting and pneumatic riveting.
This traditional technique uses hand tools and elbow grease to insert the rivet and peen the tail. Riveting hammers allow the riveter to hold the bucking bar that counters the force on the back side, while striking the rivet head to flare the tail. Manual riveting takes skill and practice to create quality joints. It allows selective driving of specific rivets in an assembly, but is slower than automated methods.
Pneumatic rivet guns use compressed air to quickly insert the rivet and flare the tail in one action. This greatly speeds up the riveting process, allowing several rivets to be driven per second. Rivet guns have jaws that grip and cut the rivet tail once flared. Guns come in squeezer or impactor styles with varied capacities to handle different rivet sizes and materials. Pneumatic riveting is common in high volume sheet metal production.
Rivet Joint Design Factors
Properly designed riveted joints are critical for sheet metal fabrications that perform reliably. Here are key factors to consider:
- Hole alignment - Rivet holes in each piece must align accurately for the joint to come together correctly. Jigging and fixturing ensures alignment.
- Hole size - Clearance between rivet shaft and hole impacts joint strength. Hole size should match the rivet shank diameter.
- Spacing and pitch - Rivet spacing along the joint as well as distance from sheet edges impacts joint strength. Follow industry guidelines for particular materials and applications.
- Number of rivets - More rivets spread the load over a wider area for stronger joints. Determine the ideal rivet quantity needed.
- Materials - Rivet and sheet metal should have comparable strength. Softer rivets in hard materials may fail.
- Grip range - Specify rivets with an appropriate grip range for the material thickness being joined.
Proper rivet joint design must account for these factors based on the loading, the materials used, and performance requirements.
Riveted Joint Maintenance and Repair
While riveted connections are inherently reliable, maintenance and repair may be needed over time. Reasons for rivet joint repair include:
- Material fatigue or degradation
- Damage from impact or abrasion
- Improper original installation
- Loose rivets from vibration
Loose or damaged rivets should be replaced to maintain joint integrity. This is done by:
1. Drilling out the damaged rivet and removing any remnants
2. Enlarging the hole if needed to accept a larger replacement rivet
3.Installing an oversize or structural rivet in the existing hole
The new rivet should match or exceed the specifications of the original. Proper hole sizing, alignment, and rivet driving technique ensure a solid repair.
In summary, riveting is an essential fastening technology for permanently joining sheet metal components. Understanding rivet styles, installation methods, and joint design principles allows fabricators to produce robust, reliable and long-lasting sheet metal assemblies using this time-tested technique. With the right skills and knowledge, the possibilities of riveted sheet metal fabrication are limitless. CNC Milling CNC Machining