Riveting in Sheet Metal Fabrication(aerospace machining Lou)
- source:YESCOM CNC Machining
What is a Rivet?
A rivet is a short cylindrical rod with a head on one end. The head is typically flat or dome-shaped. The rod, known as the shank or body, is inserted through pre-drilled holes in the materials being joined. The empty end of the rivet shank is then deformed, or "bucked," to create a second head that locks the rivet in place.
Rivets are commonly made from steel, aluminum, copper or brass. The material and hardness of the rivet should match the strength of the materials being joined. Rivets come in a range of diameters and lengths to suit different applications and material thicknesses.
Benefits of Riveting
Compared to other joining methods like welding or adhesive bonding, riveting offers several advantages:
- Permanent joint - Once installed, rivets create a permanent, non-reversible joint that will not come loose over time. The deformed rivet head locks the joint securely in place.
- Vibration resistance - Riveted joints can withstand significant vibration and shock without failing. This makes them well-suited for applications like aircraft and machinery.
- No heat or chemicals - Riveting is a cold fabrication process that does not require heat, solvents or adhesives. This avoids any fire hazards, fumes or chemical contamination.
- Adjustments possible - Mistakes in hole alignment can often be corrected by slightly elongating the rivet holes. This level of adjustment is not possible with welding.
- Only access to one side needed - Rivets can be installed where there is only access to one side of the materials being joined. The rivet just needs somewhere to form the second head.
- Quick and portable - Riveting tools are generally small, portable and able to make joints rapidly. This makes riveting suitable for field repairs and on-site fabrication work.
- Wide material suitability - Rivets can join dissimilar materials like steel and aluminum. The materials do not need to be fusible like they would for welding.
There are several types of rivets used in sheet metal fabrication, each suited to different applications:
- Solid/Round Head Rivets: As the name suggests, these feature a solid shank and round head. They are versatile general-purpose rivets.
- Countersunk Head Rivets: The head is conical and designed to sit flush with the material surface for a smooth finish.
- Large Flange Rivets: These have a wide dome-shaped head that distributes load over a bigger area. They are often used in soft or brittle materials like plastics.
- Split Rivets: These have a pre-formed notch in the shank so it splits as the tail is bucked. This allows blind riveting where access is only available from one side.
- Structural Rivets: Larger and stronger rivets designed for load-bearing structures. The heads are usually countersunk.
- Tubular Rivets: Hollow and lightweight while still strong. Often used in aircraft fabrication.
- Drive Rivets: Also known as blind rivets. They are set using a specialized power tool from one side. Common in mass production.
Rivet Joint Design
For optimal strength, rivets in sheet metal fabrication should be applied using proper joint design principles:
- Rivet diameter should be 1.5 times the thickness of the thinner sheet for aluminum and 2 times for steel. This provides sufficient shank deformation.
- Rivet length should span the total thickness of all sheets with 1/8 inch grip length minimum.
- Edge margins from rivet holes to sheet edges should be at least 1.5 times rivet diameter to avoid edge tear-out.
- Rivets along a row should be evenly spaced at 3-4 times rivet diameter. Staggered rows should offset by 1.5 times rivet diameter.
- For multi-row joints, rivets should align diagonally to distribute stress evenly across overlapping rows.
- Avoid drilling holes near bends or curved areas which can act as stress concentrators.
Hand Rivet Tools
The simplest riveting tool is a hand-held squeezer tool with interchangeable nosepieces to fit various rivet sizes. Using the squeezer and a bucking bar on the opposite side, the riveter can manually set solid rivets. Though slow, this allows riveting without power, suitable for small jobs.
Pneumatic Rivet Guns
These popular professional tools use compressed air power to quickly and forcefully set rivets for mass production. The hammer action and jaw design allows one-handed use, freeing the other hand to position rivets. Rivet guns can set 300-600 rivets per hour.
Battery-Powered Rivet Tools
Cordless battery rivet tools offer the portability of air tools without needing a compressor. Models made by Milwaukee, DeWalt and other brands allow fast riveting almost anywhere with less noise than air tools. Runtime can be limited by battery life.
Blind Rivet Tools
To install blind or pop rivets from one side, specialized power tools are needed. Handheld blind rivet tools use hydraulic power to pull the rivet mandrel and set the rivet head. They are suitable for occasional on-site blind riveting needs.
For mass production in factories, automated machines can install hundreds of rivets per hour without human intervention. Computer-controlled drilling, feeding and riveting technology is programmed to the required rivet patterns. This automation ensures fast, repetitive high-quality riveting.
Inspection and Testing
Once installed, rivets should be inspected to ensure proper formation. Hammering down any loose or misformed heads can correct minor issues. For critical applications, riveted joints may need proof testing by applying sample loads to verify design strength. Failed rivets can be drilled out and replaced.
Proper rivet joint design, tool selection and fabrication technique allows riveting to be a versatile, high-strength sheet metal joining solution. With advantages like speed, permanence and adjustability, rivets will continue playing a key role in metal products and structures across many industries. CNC Milling CNC Machining