Riveting in Sheet Metal Fabrication(snap fitting Ophelia)
- source:GAENOR CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a cylindrical body called the shank and a head. During installation, the shank is inserted into pre-drilled holes in the materials being joined. The tail end of the shank is then deformed to create a second head which spreads out and secures the rivet in place. This creates a permanent mechanical bond between the rivet and the materials.
Rivets come in a variety of styles and materials for different applications:
- Solid/blind rivets - These are the simplest and most commonly used rivets. The deformation occurs on the blind side of the joint using a rivet gun or other tool.
- Bulbed/tubular rivets - These have a hollow shank that is expanded on both sides of the joint for extra strength. Used in high vibration/load areas.
- Drive rivets - These have pre-formed heads on both ends and are driven into place by hammering rather than deformation. Used where access is limited.
- Monobolts - A type of semi-tubular drive rivet that creates a flush surface on both sides.
- Structural rivets - Extra-large rivets used for load-bearing structural joints. Usually aluminium or steel.
- Self-piercing rivets - Can pierce and joint sheets without pre-drilling. Used in auto manufacturing.
Rivet material is chosen based on strength, corrosion resistance and cost requirements. Common options are aluminium, steel, copper, stainless steel, and Monel (nickel-copper alloy).
Benefits of Riveting
There are several key advantages that make riveting a popular choice for joining sheet metal:
- Permanent - Once installed, the deformed rivet shank locks components together preventing detachment. This can help products withstand vibrations and loads during use.
- Fast installation - Riveting is generally quick compared to techniques like welding or screwing. Multiple rivets can be set rapidly to assemble products efficiently.
- Low profile - Rivet heads have a relatively small footprint which minimizes added bulk and weight.
- No adhesives/sealants - Rivets form a direct mechanical bond so no consumables are required during installation.
- Easy visual inspection - It's quick to check rivets visually for defects compared to hidden fasteners like clinching.
- Material versatility - A wide range of metals and even some plastics can be riveted together in an assembly.
When to Rivet Sheet Metal
Rivets work well when an permanent, non-detachable joint is needed between thin sheet metal sections. The rivet shoulders spread force over a large area reducing risk of the sheets tearing. Riveting is commonly used when:
- Joining panels and enclosures for electronic devices, appliances, furniture etc. Rivets allow periodic access for repair while preventing everyday loosening.
- Assembly of aircraft and automobile outer 'skins' and panels. The flush rivet heads minimize air drag.
- Connecting ducting and tubing. Rivets provide reliable leakage-free joints at seams and connections.
- Joining sheets for cargo beds, trailers and containers. Rivets withstand vibration while allowing some flexing between sheets.
- Installation of hinges, brackets, trim and other components to sheet metal. Rivets provide permanent, reliable attachments.
Riveting is less suitable for highly loaded structural joints in heavy machinery or load bearing building components. The rivet would need to be significantly oversized which adds weight. Welding, bolting or adhesives are better choices in these instances.
Best Practices for Riveting Sheet Metal
Proper technique is important when riveting sheet metal to maximize joint strength and quality. Here are some top tips:
- Drilling - Holes must be round, clean and match the rivet diameter closely. 1/16" greater than rivet diameter is ideal. Deburr holes thoroughly after drilling.
- Hole spacing - Space rivets no less than 2 times the sheet thickness. More spacing may be required for vibration resistance.
- Hole alignment - Use clamps or jigs to align pieces being joined before riveting. Misaligned holes strain the joint and rivets.
- Rivet length - Choose rivet shank length to match the combined thickness of the materials being joined. The shank should extend at least 1/2" beyond the bottom sheet.
- Bucking - Use a steel bucking bar behind the joint when setting blind rivets. This absorbs deformation force for a tight joint.
- Riveting order - Start riveting from the center of a joint and work outwards to draw sheets tight together.
- Corner rivets - Add rivets as close to joint corners as possible to resist sheet peeling.
- Clamping - Keep materials firmly clamped until rivets are fully set to prevent movement or offset.
- Inspection - Check set rivets have full heads formed without cracks or defects. Tap each rivet to ensure tightness.
By following these guidelines, manufacturers can achieve consistently strong, reliable riveted joints in sheet metal assemblies. Checking joint quality on a sample basis is also advised for quality control.
Riveting Tools for Sheet Metal
Several tool options exist for setting rivets in sheet metal depending on production needs:
- Manual rivet guns - Affordable and versatile for small run products. Require some operator skill.
- Pneumatic rivet guns - Increased speed and power for medium to large production runs. Require air compressor.
- Battery rivet guns - Cordless electric power for mobility. Limited run time between charges.
- Hydraulic rivet squeezers - Heavy duty for structural steel rivets. Expensive but high productivity.
- Impact riveters - Deliver sharp hammering force to set drive rivets. Require limited access space.
- Automated riveting - Used in high volume manufacturing like auto plants. Robotic arms precisely install hundreds of rivets per minute.
The choice comes down to tradeoffs between cost, quality, speed, operator effort, and joint access requirements. Even higher volume shops may still use manual or pneumatic guns for specialty joints in products.
Riveting is an essential fastening technique that brings speed, strength and reliability to sheet metal fabrication. Understanding proper joint design, rivet sizing, hole drilling/prep and installation technique allows fabricators to produce professional quality results. While other methods like welding, screwing and bonding have their place, the simplicity and permanence of rivets will continue making them foundational to modern manufacturing. CNC Milling CNC Machining