Riveting in Sheet Metal Fabrication(ra surface finish Sebastian)
- source:ESKRIDGE CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that connects two or more pieces of material. It consists of a smooth cylindrical shaft with a head on one end. The rivet is inserted through holes in the materials being joined, and the protruding end is then hammered and forged to create a second head. This process is called riveting.
The forging of the rivet heads causes the shaft to expand, creating tight contact with the sides of the holes. The rivet acts like a bolt to clamp the materials together. However, unlike standard threaded fasteners, rivets form a permanent connection that cannot be removed or unfastened without destroying the rivet.
Types of Rivets
There are several types of rivets used in sheet metal work:
- Solid/blind rivets - These have a pre-formed head on one end and are driven using a rivet gun or hammer to form the second head. Because access is only needed from one side, these are ideal for blind joints.
- Semi-tubular rivets - These have a partial hole through the center of the shaft. They require access to both sides of the material during installation.
- Tubular rivets - Fully hollow rivets that are commonly used in aviation and other high-strength applications. They provide excellent shear strength.
- Split rivets - These feature a shaft that is split down the center. As the tail is compressed during installation, the legs splay outward to grip the inside of the hole.
- Drive rivets - Also known as screw and mandrel rivets. These are inserted with an attached mandrel, which is removed after forming the second head.
- Self-piercing rivets - Designed to pierce through stacked materials without pre-drilled holes. Often used to join light gauge metals.
- Structural rivets - Large heavy-duty rivets designed for structural fabrication. Require pneumatic hammering tools for installation.
Materials include aluminum, steel, stainless steel, copper, and monel. The choice of material depends on the application requirements.
Benefits of Riveting
Riveting provides numerous advantages that make it a popular fastening method in sheet metalwork:
- Permanent - Unlike threaded fasteners, rivets form a permanent joint that cannot loosen over time. This makes them ideal for critical structural connections.
- Strength - Properly installed rivets provide excellent shear and tensile strength to joints. The strength comes from the friction and mechanical interlock of the deformed rivet shank.
- Vibration resistant - Riveted joints can withstand high vibration environments better than many other fastener types. The interlocking shank helps prevent loosening.
- Corrosion resistant - Many rivets are made from aluminum, stainless steel, or other materials that resist corrosion. This gives riveted products excellent durability in harsh conditions.
- Quick installation - Riveting tools allow for fast mass installation of multiple rivets compared to other techniques like welding or bolting. This improves manufacturing efficiency.
- No damage to materials - The riveting process does not require high heat like welding. This prevents any potential damage to sensitive materials being joined.
- Appearance - The smooth finished heads of rivets can provide a neat and appealing look to finished products. Countersunk rivets allow flush mounting.
Riveting Tools and Equipment
Installing rivets properly requires having the right tools:
- Rivet hammer - A hammer specifically designed for flattening rivet tails to form the second head. Often has an offset head.
- Bucking bar - A handheld block that is placed behind the rivet to absorb hammer impacts and form the second head.
- Rivet guns - Pneumatic, electric, or battery powered tools that quickly pull the rivet tail and upset it to form the second head. Make installation much faster.
- Rivet sets - Exchangeable tip sets for rivet guns to accommodate different rivet head styles and materials. Include flush, oval, round, and countersunk sets.
- Hole punches - Circular cutters mounted in presses to punch rivet hole patterns in sheet materials prior to installation. Ensure consistent and properly aligned holes.
- Drill press - For drilling holes in thicker stacked materials before riveting. Jigs and fixtures are used to locate holes accurately.
- Sheet metal tools - Snips, bending brakes, shears, and other metalworking tools to fabricate shapes being riveted.
Proper Planning for Rivet Joints
Careful planning of riveted joints is crucial for achieving maximum strength and durability:
- Hole alignment - Any misalignment between stacked holes can compromise the joint. Fixtures should be used to drill mating parts together.
- Hole size - Clearance between rivet and hole must be carefully controlled. Too tight makes installation difficult, too loose reduces strength.
- Spacing and pitch - Rivets must be spaced appropriately for the materials and stress levels. Follow established engineering guidelines for your application.
- Rows and patterns - Staggering rows or using diagonal pitch patterns evenly distributes load across the joint. Prevents a single weak point forming.
- Edge distance - Rivets should be placed a minimum distance from joint edges based on the material thickness. Prevents edge tear-out under load.
- Materials and platings - Consider any coatings or platings that could interfere with rivet installation or strength. Some platings require oversized holes.
By following best practices and industry standards, high quality and dependable riveted connections can be produced.
Proper technique is critical for a secure joint:
- Drill holes to precise size using sharp bits. Deburr any holes before riveting.
- Select the rivet material, size, length, and head style appropriate for the joint design.
- Insert rivets into holes with the manufactured heads on the accessible side.
- Position bucking bar against the blind side head. Strike rivet head with steady, medium force blows from rivet hammer.
- Continue hammering until the tail buckles, spreads, and forms a second rounded head that clamps materials securely.
- Inspect rivets to ensure both heads are properly formed and material is visibly compressed.
- For large or long rivets, use pneumatic rivet guns or squeezers to upset the tails. This prevents hammer marks on materials.
- Countersink flush rivets so heads sit slightly below the surface. Fill sunken heads with sealant if exposed to moisture.
- Confirm final joint meets required tolerances for hole alignment, material draw, and rivet head protrusion.
With practice and quality tools, strong and professional looking riveted joints can be consistently achieved.
Here are some of the many uses for riveted connections in sheet metal fabrication and beyond:
- Aircraft and aerospace vehicles - Rivets are extensively used to assemble aluminum airframes and other components that demand safety.
- Machinery guards and covers - Perforated sheet metal panels are often riveted to frames to create protective guards around industrial machinery.
- Electronic enclosures - Sheet metal electronics housings and racks use rivets for simple assembly and serviceability.
- Ducting and pipe fittings - Round and rectangular duct sections are easily joined with rivets to create air handling systems.
- Signs and displays - Plastic and metal faced signs depend on rivets to join parts like panels, brackets, and trim.
- Cartss and shelving - Sturdy retail shelving, kitchen carts, and workshop units rely on rivets to assemble sheet metal members.
- Automotive panels - Rivets secure non-structural body panels like inner fenders on cars and trucks. Quick installation aids mass production.
Riveting remains a trusted fabrication technique after over a century of proven performance across countless applications. With the right planning and tools, rivets produce durable leakproof joints quickly and efficiently. For assembling sheet metal or other rigid materials, rivets should be considered as a first choice over temporary fasteners. CNC Milling CNC Machining