Riveting in Sheet Metal Fabrication(surface roughness scale Newman)
- source:YESCOM CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The rivet shaft is inserted through holes drilled or punched in the materials to be joined. The excess length of the shaft extends out the backside and is mechanically deformed to create a second head. This process is called riveting or bucking.
The two heads mechanically clamp the materials together in a permanent way. Rivets are typically made of steel, aluminum alloys, copper, or Monel. They come in a wide range of diameters and lengths to accommodate different material stackups and strength requirements.
Benefits of Riveting
Compared to threaded fasteners, rivets offer some unique benefits:
- Permanent joining - Once installed, the rivet heads cannot come loose over time from vibration or shock like nuts and bolts can. The materials are joined permanently.
- Smoother surface - Rivet heads add minimal thickness to the overall assembly. This results in a smoother surface that reduces drag, catches less dirt, and is aesthetically cleaner looking.
- Greater strength - The rivet fills the entire hole and clamps close to the edge of the hole. This distributes force over a larger area than a fastener in the center of a clearance hole.
- Faster/easier installation - Rivets can be installed quickly with hand tools or pneumatic riveting guns rather than needing wrenches or other tools to tighten threaded fasteners.
- Material flexibility - Rivets can join dissimilar materials like steel and aluminum. Different rivet materials can be selected to avoid galvanic corrosion.
- No damage during installation - Unlike high-torque threaded fasteners, rivets do not damage soft materials during installation. This makes them ideal for composites and plastics.
There are two main rivet types used in sheet metal fabrication - blind and solid.
Blind rivets are tubular and allow installation from one side when access to both sides is not possible. Blind rivets use a mandrel inside the rivet that is pulled during installation. This expands the rivet body to form the second head.Mandrels can be break-off or non break-off style.
Solid rivets require access to both sides of the material. They typically use a hammer or rivet gun to form the second head after insertion. Solid rivets allow for stronger joints in high-strength materials compared to blind rivets.
Common rivet materials include:
- Aluminum - Lightweight and good corrosion resistance. Used for electronic enclosures and aircraft.
- Steel - Strong and durable. Used in automotive, appliances, and construction. Zinc plating resists corrosion.
- Stainless steel - Highest corrosion resistance. Used in harsh environments.
- Copper - High electrical and thermal conductivity. Used in electrical applications.
- Monel - Resists salt water corrosion. Used in marine and other water exposed applications.
The strength of a riveted joint depends on several factors:
- Rivet material and hardness - Stronger materials allow thinner rivets for weight savings. Hardness resists deformation under load.
- Rivet diameter - Larger diameter rivets spread force over more area for greater shear and tensile strength.
- Material thickness - Thicker stacked material allows bigger grip length for stronger joints.
- Hole size - Smaller clearance between rivet and hole provides greater resistance to forces trying to deform the joint.
- Quality of bucked head - Properly formed heads maximize clamping pressure for greater strength.
Installing rivets in sheet metal requires several steps:
1. Drilling or punching holes - Match the hole size and spacing to the rivet diameter. Pilot and tapered holes help alignment.
2. Deburring holes - Remove any sharp edges or chips that can damage the rivet.
3. Inserting rivets - Rivets are fed through aligned holes in the sheet metal stackup.
4. Bucking the tail - A hammer or rivet gun upsets the protruding tail to form the second head.
5. Inspecting the joint - Check for properly formed heads that secure materials without damage.
Rivets are ubiquitous in sheet metal products across many industries:
- Aircraft - Rivets are the primary fastener joining the aluminum skins to frames and stringers. Riveting allows smooth aerodynamic surfaces.
- Cars - Body panels use thousands of rivets for smooth outer surfaces. Rivets withstand vibration better than threaded fasteners.
- Appliances - Stacked sheet metal enclosures hold electronics and resist moisture. Rivets allow cost-effective manufacturing.
- Furniture - Products like desks and file cabinets use rivets in side panels and drawers for sturdy construction.
- Electronics - Devices use rivets internally to assemble cases and frames that protect sensitive PCBs and components.
- HVAC ducting - Sheet metal ductwork relies on rivets for leakproof and robust joints.
Riveting is an essential process in working with sheet metal across many industries. Properly installed rivets create strong, permanent joints while minimizing added thickness. With the variety of rivet types and materials available, designers can select optimal riveting solutions for their unique applications. Whether used occasionally or in the thousands, rivets will continue to be a trusted method for fastening sheet metal components together. CNC Milling CNC Machining