Riveting in Sheet Metal Fabrication(extracting a broken tap Eric)
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Types of Rivets for Sheet Metal
There are several types of rivets that may be used for sheet metal fabrication, each with their own characteristics that make them suitable for different applications.
Solid Rivets
The most common type of rivet used is the solid rivet. Solid rivets are made from a single piece of material, usually steel, aluminum, stainless steel, copper, or brass. When installed, the pre-formed head sits flush on one side of the sheets being joined while the shank passes through the pre-drilled hole. The tail is then deformed and spreads out on the opposite side using a riveting hammer or squeezer tool to create a second head and clamp the materials together.
Blind Rivets
Blind rivets, also known as pop rivets, are tubular and are installed where access is only available from one side of the materials being joined. The rivet is inserted into the hole and as the stem is drawn into the body by a rivet gun, the tail deforms and spreads out to clamp the sheets together. The stem then breaks off flush at the surface. Blind rivets are popular for applications where aesthetics are important since there is no exposed head.
Self-Piercing Rivets
Self-piercing rivets do not require pre-drilled holes. As they are driven into the materials being joined by a rivet gun, the semi-tubular rivet pierces through the top sheet and flares out in the bottom sheet to create a interlocked joint. Self-piercing rivets are ideal for joints where the underside is not accessible. They are commonly used in the automotive industry for body panels.
Split Rivets
Split rivets have a pre-formed head like solid rivets but with a split tail rather than a solid shank. As the rivet is installed, the jaws of the rivet gun spread the split tail outward to clamp the sheets together. The main advantage of split rivets is the ability to pre-insert them from one side without the need for access to both sides of the joint.
Tubular Rivets
Tubular rivets consist of a short hollow tube with a flange at one end. To install, the rivet is placed in the hole with the flange on the accessible side. Then the non-flanged tubular end is upset with a rivet gun to flare out and clamp the sheets together. The flange keeps the rivet centered in the hole for optimal strength.
Rivet Materials
In addition to different types, rivets come in a variety of materials. Using rivet materials that are compatible with the metals being joined is critical for corrosion resistance and joint integrity.
Aluminum rivets are lightweight, corrosion resistant, and typically used with other aluminum alloys. Steel rivets offer high strength and are common for structural steel applications. Stainless steel rivets provide good corrosion resistance when riveting stainless steel or other materials where high strength and corrosion resistance are needed.
Copper and brass rivets are softer and deform more readily so they are ideal for sheet metal materials like copper alloys that require a more ductile rivet. Monel rivets provide strength and corrosion resistance for specialized applications like marine environments.
Rivet Sizes
The shank diameter and grip length are the two key dimensions used to specify rivet size. Shank diameter ranges from 1/16” to 3/8” while grip length can be from 1/8” to several inches depending on the thickness of the materials being joined. Using the correct grip length is critical so the rivet can fully deform to fill the holes and maximize strength.
Rivet Installation Tools
Installing rivets requires exerting substantial pressure to deform the rivet shank and spread the tail. This is accomplished using tools specially designed for riveting. The most common riveting tools include:
Hammer Set - A hammer and combination of bucking bars allows the operator to manually install solid rivets. Force is applied directly with the hammer while the bucking bar supports the opposite side.
Hand Squeezer - A hand squeezer uses compound leverage to generate the force needed to upset rivets. Hand squeezers allow one-handed operation but are limited on hole size and material thickness.
Pneumatic Rivet Guns - Rivet guns attached to an air compressor generate high forces from air pressure to install blind, tubular, and specialty rivets. Guns come in squeezer or impact styles.
Battery Rivet Guns - Cordless battery powered rivet guns offer more mobility and power over longer periods than air tools. Battery rivet guns are ideal for production environments.
Riveting Technique
Proper technique is crucial when riveting to produce a uniform, high-strength joint. The key steps include:
1. Drilling - For solid rivets, holes must be precisely pre-drilled to match the rivet diameter. A drill press is recommended for uniformity and hole perpendicularity.
2. Hole Spacing - Rivets should be spaced 3-4 diameters apart for maximum efficiency. Closer spacing reduces joint strength.
3. Rivet Selection - Make sure rivet length matches material thicknesses and the rivet material and type is suitable for the application.
4. Hole Alignment - Any misalignment between holes will result in an off-center rivet and poor strength. Fixtures help maintain alignment.
5. Insertion - Solid shank rivets are inserted head first with the bucking bar supporting the opposite side. Blind rivets are inserted from the blind side.
6. Set Pressure - Use the riveting tool to apply steady pressure until the rivet deforms and flows to fill the hole. Avoid excessive pressure.
7. Inspection - The set rivet should have a full, round head profile without cracks or underfilling indicating poor technique or damaged rivets.
Riveted Joint Design
Properly designing riveted joints is key to creating robust, reliable structures able to withstand expected loads. Important design considerations include:
- Spacing between rivets and distance to edges based on materials and anticipated stresses
- Rows and columns for multi-rivet joints to distribute load paths efficiently
- Using enough fasteners to meet strength requirements without overdoing it
- Combining rivets of different grip lengths to accommodate multiple material layers
- Allowing for movement between joined parts to reduce shear and fatigue
- Specifying material thicknesses to prevent tear out around holes
- Accounting for how joints may be accessed for maintenance and inspection
By following best practices for design, material selection, hole preparation, and installation technique, high quality riveted joints can be consistently achieved for sheet metal fabrication projects across many industries. With the variety of rivet types and installation tools available, rivets continue to offer an efficient, versatile, and reliable method for permanently joining sheet metal components. CNC Milling CNC Machining