Riveting in Sheet Metal Fabrication(3d printing prototype Kimberley)
- source:ZIEG CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - the body and mandrel. The body is a cylindrical shaft that has a head on one end. The mandrel is inserted into the hollow body and fills the hole through the center.
To rivet sheet metal, the rivet body is inserted into aligned holes in the sheets to be joined. The excess length of the body extends beyond the bottom sheet. The mandrel is then pulled, causing the body to flare out and create a second head. This clamps the sheets together between the two rivet heads.
Rivets are commonly made from aluminum, steel, titanium, and other metals. They come in many sizes, shapes, and styles for different applications. Pop rivets, blind rivets, and solid rivets are the most common types used for sheet metal fabrication.
Benefits of Riveting
There are several reasons riveting is a popular joining method for sheet metal:
- Strong and permanent - The flaring of the rivet body creates a wide clamping force that holds the materials tightly together. The joint maintains its strength even when shaken or vibrated.
- Easy to automate - Rivet gun machines allow for quick, consistent rivet placement and setting during mass production. Operators can rapidly follow marked riveting points.
- Allows movement - The joint has slight flexibility that enables the sheets to expand and contract with temperature changes. This prevents cracking from thermal stresses.
- Durable in harsh conditions - Rivets maintain high shear and tensile strength in extreme environments like high heat, cold, or moisture.
- Weight efficient - Rivets add very little weight versus welding or adhesives. This makes them ideal for aircraft and transportation applications.
- Simple installation - Workers can be quickly trained to properly place and set rivets using manual or pneumatic rivet guns. Minimal equipment is required.
- Easy inspection - Installed rivets are easily visually checked to ensure the joint is securely fastened. Failed rivets are obvious and can be replaced.
Applications of Rivets
Riveting is commonly used to assemble sheet metal parts in many industries, including:
Aircraft - Rivets are extensively used to join aluminum fuselage skins, engine housings, wings, and other parts where low weight and high strength are critical.
Automotive - Body panels, frames, doors, hoods, and interior parts are frequently riveted, especially on high-volume production lines.
Appliances - Outer shells and internal components of household appliances like washers, dryers, refrigerators, etc. often utilize riveted joints.
Electronics - Lightweight electronic enclosures and chassis are riveted together to provide sufficient strength and durability.
HVAC Ducting - Galvanized steel HVAC ducts and vents are sealed with rivets because they resist corrosion and fatigue.
Building Facades - Decorative panels, windows, and roofing materials made of metal can be installed on exterior surfaces using rivet fasteners.
Furniture - Riveting sheet metal allows durable and attractive metal office furniture, racks, storage, and displays to be produced.
Key Considerations for Riveting
Here are some important factors to keep in mind when riveting sheet metal:
- Material - Match rivet material and plating to the sheet metal alloys to prevent galvanic corrosion. Use aluminum rivets for aluminum.
- Sheet thickness - Select a rivet length sufficient to fully penetrate both sheet layers plus an additional 1.5x rivet diameter.
- Holes - Holes must be round, match the rivet diameter, and align between sheets to prevent bending or cracking.
- Access - Ensure there is sufficient clearance on the backside for placing the rivet and manipulating the bucking bar.
- Clamping - Use clamps, vises or pressure pads to keep materials pressed flush while riveting.
- Bucking - A bucking bar on the backside is vital for properly upsetting the rivet and spreading the tail.
- Spacing - Follow recommended edge and seam spacing between rivets to distribute load paths.
- Tooling - Invest in quality rivet guns, bits, bucking bars, and other equipment for best results.
- Training - Develop worker skills on proper rivet techniques to achieve tight, uniform joints.
Types of Rivets for Sheet Metal
There are many types of rivets tailored to specific sheet metal joining requirements:
- Blind Rivets - Tubular rivets set by a mandrel inside the body accessed through only one side. No access behind the materials is needed.
- Self-Piercing Rivets - Rounded rivets that pierce and interlock with sheets without drilled holes when set.
- Drive Rivets - Robust, flush rivets with large domed heads set into countersunk holes by hammering rather than pulling.
- Split Rivets - Tubular with radial cuts allowing the rivet to expand outward filling a hole with minimal clamp.
- Structural Rivets - Extra large high-shear rivets for joining thick stacked sheets in structural applications.
- Monel Rivets - Corrosion resistant nickel alloy rivets for use in extreme environments like saltwater.
- Stop Rivets - Shallow domed rivets that do not fully penetrate the lower sheet and act as a fastener stop.
- Screw Rivets - Combine riveting with external threading for bolting additional layers on top.
- Flush Rivets - Countersunk rivet with a flat circular head for a smoother surface profile.
Processes for Rivet Installation
There are several techniques used to install rivets in sheet metal depending on production volume and accessibility:
- Hand Riveting - A rivet gun and bucking bar are manually operated by technicians on low volume fabrication.
- Pneumatic Riveting - Air powered rivet guns increase speed and power for production shops. Hoses provide mobility.
- Impact Riveting - Battery powered rivet guns offer cordless convenience without air hookups. Vibration is lower.
- Robotic Riveting - Programmable robots automate precise, rapid rivet placement for mass production on assembly lines.
- Orbital Riveting - Spindle heads clamp sheets and orbit around the joint setting rivets with programmed pattern and force.
- Self-Piercing Rivets - C-frame presses inject these specialized rivets through stacked sheets without pre-drilling.
- Resistance Riveting - Electrodes apply current and heat/pressure to upset rivets inserted in sheets sandwiched in the machine.
Inspection and Testing Methods
Quality control of riveted sheet metal joints involves several inspection and testing procedures:
- Visual Inspection - Examine for proper rivet fill in holes, full upset head, consistent flushness, and symmetry.
- Ring Testing - Tap rivets with a light hammer to check for loose connections by an audible change in tone.
- Proof Testing - Test sample riveted joints to failure load to verify required performance is achieved.
- Dimensional Checks - Use calipers, gauges, or optical comparators to ensure rivet lengths, diameters, and spacing meet specifications.
- Dye Penetrant - Coat riveted seams with dye then wipe clean to reveal cracks by trapped dye.
- Ultrasonic Testing - Sound waves detect sub-surface voids, cracks, or gaps within the riveted joint.
- X-Ray Radiography - X-ray images show internal inconsistencies in rivets, holes, and clamped sheets.
Properly installed and inspected rivets create durable, permanent sheet metal assemblies ready for their final application - whether its an aircraft, building facade, appliance, or automobile. With the variety of rivet options and installation methods available, riveting remains a versatile, efficient, and robust way to fasten sheet metal. CNC Milling CNC Machining