Riveting in Sheet Metal Fabrication(what is a fastener Franklin)
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In this article, we’ll explore what rivets are, the types commonly used in metal fabrication, and best practices for riveting sheet metal by hand or with automated Computer Numerical Control (CNC) machines.
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - the rivet body and mandrel. The body is a head on one end, and a shank on the other. The mandrel fills the hollow shank portion of the rivet body.
To join materials together, the rivet shank is inserted through pre-drilled holes in the materials being fastened. The protruding end of the shank is then flared outward with a riveting hammer, upsetting tool, or rivet gun. This causes the rivet body to expand, clamping the materials together between the rivet head and the upset shank end. The tightly clamped joint is held together by the compressive force of the deformed rivet.
Rivet Types for Sheet Metal Fabrication
There are several types of rivets suitable for joining sheet metal depending on the project requirements:
- Solid/Round Head Rivets: As the name suggests, these have a solid, round head. They are one of the most common rivets for sheet metal because they can be easily flush riveted for a smooth surface.
- Countersunk Head Rivets: These have a conical shaped head that sits flush within a countersunk hole in the top sheet metal piece for a smooth surface. The rivet head is then flush with the material.
- Large Flange/Universal Head Rivets: These have a built-in washer face under the head that provides a wide bearing surface. This distributes force over a larger area for applications where high shear strength is needed.
- Structural Rivets: Structural rivets have large domed heads combined with a large shank for joining thick materials or where vibration resistance is important.
- Drive Rivets: Designed to be installed in blind locations where only one side is accessible. Drive rivets have no central mandrel. They are driven in place using a rivet gun and acquire their holding power through displacement of the rivet body.
- Self-Piercing Rivets: These unique rivets do not require pre-drilled holes. They have an chamfered pierce point that cuts through stacked layers of sheet metal and spreads outward to interlock behind the lower layer on installation.
- Blind Rivets: Like drive rivets, blind rivets can be installed where only one side of a workpiece is accessible. But blind rivets have an internal mandrel. On installation, the mandrel is pulled into the rivet body, flaring the rivet and clamping the workpieces together.
Hand Riveting Sheet Metal
Hand riveting sheet metal is a simple, low cost process suitable for lower volume fabrication and repair work. It only requires basic riveting tools that are relatively inexpensive. Let's go over the essential steps involved:
1. Cut sheet metal to required sizes and layout any hole locations needed.
2. Drill properly sized holes for the rivets being installed. Hole diameter should match the rivet shank diameter closely for a tight fit.
3. Deburr holes thoroughly to ensure proper rivet seating.
4. Place rivets in holes with the manufactured head against one sheet metal piece, and the shank end protruding through the mating sheet metal piece.
5. Place the tip of the appropriately sized rivet set against the rivet shank end.
6. Use a riveting hammer to drive the rivet set, upsetting and flaring out the rivet shank. This clamps the sheet metal layers together under pressure.
7. Strike until the rivet shank end is flush with the surrounding material. Take care not to overstrike the rivet and damage the sheet metal.
8. Inspect each set rivet for proper seating and clamping before moving to the next rivet.
9. Repeat steps 4-8 to install all required rivets in the fabrication.
CNC Riveting
For higher volume production runs, CNC automated riveting machines are vastly more efficient than hand riveting. CNC machines use programmable technology to precisely control rivet placement and installation. Here are some of the benefits of CNC riveting:
- Highly repeatable results with minimal human input required during the riveting process. Rivet locations, hole sizes, and installation force is computer controlled.
- Much faster process time than manual riveting. A CNC machine can install hundreds of rivets per hour.
- More consistent quality since rivet placement and setting force is consistent.
- Integration with other automated fabrication processes like punching, shearing, forming, etc.
- Flexible changeovers between rivet sizes and patterns through software programming rather than mechanical changeovers.
- Increased worker safety by reducing direct handling of materials during riveting.
CNC riveting systems use advanced technologies like robotic arms, pneumatic or hydraulic force, and specialized tooling that allow high speed, precision riveting accuracy within 0.1mm. Systems can be designed to handle everything from small electronics components to large aerospace assemblies.
While CNC riveting requires higher capital equipment investment, the long term gains in efficiency, consistency, and volume production capability make it invaluable for medium to high production scale manufacturing.
Best Practices for Quality Riveted Joints
Whether riveting by hand or with automated equipment, following some basic best practices will ensure properly formed, high strength riveted joints:
- Use the recommended drill size for the rivet diameter to achieve a tight fit in holes. Loose fit in the drilled hole can lead to joint failure.
- Rivets should completely fill the hole thickness with minimal gap between materials. Proper rivet length selection is key.
- Upset both ends of structural rivets to maximize strength. Rivet ends should be flush with the surrounding material surface.
- Inspect each rivet after installation for proper setting and flushness to material surface. Re-strike improperly set rivets.
- Orient the manufactured rivet head where it will best resist applied loads in the assembly.
- Stagger adjacent rows of rivets where possible to prevent a straight shear plane through fastener rows.
- Follow any material and rivet manufacturer specific recommendations for hole spacing, edge distance, etc.
- Deburr, clean, and prepare mating surfaces properly before riveting to achieve maximum strength.
Riveting is an efficient, economical fastening method for permanently joining sheet metal while allowing some flexibility and vibration dampening that rigid welds do not permit. By selecting the proper rivet type and following recommended riveting procedures, high quality sheet metal fabrications can be consistently achieved. CNC Milling CNC Machining