Riveting in Sheet Metal Fabrication(aluminum 6061 vs 7075 Atwood)

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Rivets are a crucial fastening method in sheet metal fabrication. They create strong, permanent joints between metal sheets and other components. Compared to welding, riveting has some key advantages that make it an indispensable technique for many applications.
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a cylindrical shaft and a head. The shaft is inserted through pre-drilled holes in the materials being joined. The tail end of the shaft is then flattened into another head with a riveting hammer or specialized tools, clamping the materials together. The rivet holds the materials together through deformation, rather than threads like a screw or bolt.
Rivets come in a variety of styles, sizes and materials to suit different purposes. Common types include:
- Solid/blind rivets - tubular rivets where access is only needed to one side for installation. The tail is mechanically deformed.
- Structural rivets - solid rivets with large head sizes for structural connections. Require access to both sides.
- Drive rivets - tubular rivets with pre-formed heads. Only need to flare the tail. Quick to install.
- Self-piercing rivets - can pierce through the top sheet without pre-drilling. Often used for joining dissimilar metals.
- Pop rivets - tubular rivets set using a specialized plier tool. Widely used in aerospace and other lightweight designs.
Rivet materials include steel, aluminum, copper, stainless steel, and more. The material is chosen based on strength, corrosion resistance and appearance needs.
Benefits of Riveting
There are several key advantages that make riveting a preferred choice for many sheet metal fabricating applications:
- Permanent but removable - Rivets form a strong, fixed joint between parts. However, drilled-out rivets can be removed later if needed for repairs or modifications. This gives rivets an advantage over welding or adhesive bonding.
- No heat or fumes - Rivet installation is a cold process, unlike welding or brazing. This prevents any risk of heat damage, distortion or fumes. Riveting can often be done directly on the fabrication floor.
- Consistency - Automated riveting processes provide extremely uniform, repeatable connections. This leads to higher quality and reliability.
- Material versatility - Rivets can join dissimilar or multi-layered materials that may be unsuitable for welding, such as plastics or composites. Different rivet materials and coatings expand options.
- Accessibility - Rivets only require access to both sides of a joint for some types. Others, like blind rivets, can be installed from one side where space is limited. This flexibility suits many fabrication needs.
- Strength-to-weight ratio - Rivets produce very strong joints relative to their light weight and size. This makes them ideal for aircraft and transportation applications where weight savings matter.
- Appearance - The smooth, finished look of flush rivet heads blends nicely into the overall aesthetic of many products. Rivet rows can also create decorative designs.
- Cost effectiveness - Both manual and automated riveting offer a relatively low-cost, high speed fabrication method. This makes riveting economical for high volume production.
Riveting Methods for Sheet Metal
There are several techniques available for installing rivets to join sheet metal or attach components:
Manual Riveting
The traditional approach uses manual tools to insert and head rivets by hand. It requires access to both sides of the work:
- A pneumatic rivet gun bucks the rivet by upsetting the tail to form the second head. Different nosepieces suit various rivet diameters.
- Set hammers/dollies are struck with a heavy hammer to flare the rivet tail. The rounded set shapes the rivet head profile.
- Hand squeezers buck the rivet by lever action. Lower force is needed but speed is slower.
Manual riveting allows flexibility in head shape and location. However, it is relatively slow and labor intensive.
Self-Piercing Rivets
These special rivets do not need pre-drilled holes. A punch presses the rivet through stacked sheets, flaring the tail. This saves time by combining hole forming and riveting in one process. No access to the bottom side is required. Often used for aluminum alloys and dissimilar metals.
Pneumatic Riveting
Pneumatic (air powered) rivet guns provide faster, higher volume rivet installation. Pop rivets fed into the nosepiece are quickly set with uniform force and head profile. This automated process is commonly used for aircraft skin fabrication.
Impact Riveting
Large structural rivets can be installed using hydraulic riveting equipment. A hydraulic ram impacts a heavysetHeader toolthat upsets the rivet tail in place. This generates sufficient force to install large diameter or high strength rivets.
Robotic Riveting
For mass production environments like automotive plants, robotically automated riveting systems offer the highest throughput and consistency. Programmable robots handle part positioning and rivet installation with precision at a high rate. Sophisticated vision systems and tooling further increase speed, quality and flexibility.
Rivet Joint Design Considerations
Proper design is key to creating strong, lasting riveted connections in sheet metal assemblies:
- Rivet diameter should match material thickness. Grip length must span the combined thickness of all sheets.
- Edge margins need to provide sufficient material for joint strength. Two times the rivet diameter is a typical minimum distance from sheet edges.
- Rivet spacing along a seam should not exceed 4-5 times the rivet diameter for aluminum or 3 times for steel. Closer spacing increases joint strength.
- Rows of staggered rivets distribute load more evenly than lined up rows. Overlap rows by 50-75% of the rivet pitch.
- Countersunk or flush rivet heads provide a smooth surface but reduce strength slightly. Button head rivets are stronger but more noticeable.
- Avoid drilling holes right at bends. Place rivets slightly offset from bends.
Proper hole size, alignment and deburring also prevent problems like rivet failure or material cracking. Test installations on scrap pieces help fine-tune any fabrication process.
Riveting Tips
Some helpful techniques will produce quality riveted joints:
- Use quality sharp drill bits for clean, accurate holes. Ream holes for an optimal fit if needed.
- Clamp layers securely together while drilling to prevent misalignment.
- Deburr thoroughly around each hole before riveting to prevent cutting rivet shafts.
- Use a bucking bar behind the joint when hand setting rivets. This prevents deformation of the Rear surface.
- Set rivets starting from the middle and working out towards edges. This avoids distortion.
- Peel, don’t shear rivets. Shearing leaves sharp edges that require additional deburring.
- Set structural rivets in several progressive passes to prevent cracking from overstressing.
- Visually inspect each rivet head profile and check for cracks or oozing filler/coating.
- Ensure rivet gun pressures match rivet size - higher air pressure for larger diameters.
Riveting is an essential fabrication skill that produces sturdy, reliable and attractive joints in sheet metal components and assemblies. Both manual and automated riveting processes continue to be workhorses in many manufacturing industries. With an understanding of the fundamentals, riveting can be applied effectively across diverse materials, components and production environments. CNC Milling