Riveting in Sheet Metal Fabrication(molding rubber Walter)
- source:GAENOR CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that connects two or more sheets of material by expanding when deformed. The basic rivet shape consists of a smooth cylindrical shaft with a head on one end. The rivet is inserted into pre-drilled holes in the materials being joined. The tail end is then mechanically deformed, often using a rivet gun. This expansion locks the rivet in place, creating a solid connection.
Rivets come in a variety of styles, materials, and dimensions to accommodate different fabrication needs. Some common types include blind rivets, drive rivets, mandrel rivets, and specialty rivets like tubular or flare rivets. The material is usually steel, aluminum, copper, or monel. Heads can be flat, round, countersunk, or customized.
Benefits of Riveting
There are several key reasons riveting is a popular joining technique in sheet metal fabrication:
- Strength - Rivets form very strong joints, especially important for load-bearing applications. The riveting process work-hardens the rivet material, increasing its strength.
- Durability - Properly installed rivets are resistant to vibration and shock loads, holding up well over years of use. Rivets handle repeated stress better than many alternative fasteners.
- Flexibility - Unlike welding, rivets allow some movement between joined materials. This flexibility prevents cracking under distortion or shifts.
- Cost Effectiveness - Riveting is relatively affordable and simple, especially automated riveting. It requires no glue or finishing work. The tools are inexpensive.
- Material Options - Rivets can join dissimilar or thin materials that may be unsuitable for welding or adhesive bonding. Almost any sheet materials can be riveted.
- Inspection - Installed rivets are easy to visually inspect for proper setting. Failed rivets are also more apparent than hidden weld cracks or debonded glued joints.
- Removability - Rivets can generally be drilled out if disassembly is later required for maintenance or part reuse. This is not the case with permanent joining methods.
When to Use Rivets
Rivets should be considered whenever thin sheets of metal need fastening. Here are some of the most common applications:
- Aircraft and aerospace vehicles - Rivets are the predominant fastener for assembling airplane skins and sections. Their vibration resistance is critical.
- Machinery covers and enclosures - Riveting sheet metal panels together allows removable access while maintaining rigidity and safety.
- Ducts, chutes, and pipes - Rivets can join and seal sheets of galvanized steel, stainless steel, or aluminum used in ductwork.
- Truck and trailer bodies - Rivets withstand road shocks better than other fasteners, important for cargo and equipment transport.
- Modular stages, platforms, and ramps - Rivets allow field assembly and disassembly of temporary structures using metal framing and decking.
- Electronic equipment chassis and racks - Rivets provide excellent electromagnetic interference shielding for sensitive components.
- Signs, safes, and furniture - Rivets offer strength without compromising aesthetics on products with thin metal cladding.
- Storage tanks, bins, and containers - Riveting forms rigid, liquid-tight sheet metal vessels and compartments.
Rivet Joint Design
Proper rivet joint design is important to maximize strength while avoiding common failure points. Here are some key principles:
- Edge Distance - Rivets should be placed at least 1.5 times the rivet diameter from sheet edges. This prevents edge tear-out.
- Spacing - Adjacent rivets should be spaced 3-4 times the rivet diameter apart. Overly dense spacing weakens the material between rivets.
- Rows - Rivets in parallel rows should offset in a staggered zigzag pattern. Aligning rivets doubles local material stress.
- Number - More small rivets are better than fewer large rivets. A joint needs at least 3-4 rivets for redundancy if any one rivet fails.
- Washer - Washers spread load and prevent pull-through of thin sheet at the back rivet head. They also compensate forcountersunk rivets on the front side.
- Materials - Rivet and sheet materials should match in strength. Softer rivets crimp but do not expand enough for tight joints.
Both manual and automated tools and techniques exist for installing rivets. Here is an overview of the standard riveting process:
1. Hole Drilling - Matching holes are pre-drilled into the materials at planned rivet locations. This is done using drill presses or CNC machines.
2. Hole Preparation - The holes are deburred and cleaned using countersinks, reams, and abrasive pads. Proper hole sizing and finish ensures rivet fit.
3. Parts Alignment - The materials are aligned and clamped so that the rivet holes line up accurately across the joint.
4. Rivet Selection - The correct rivet type and size is chosen based on joint design, material thickness, and required shear and tensile strength.
5. Rivet Insertion - The mandrel shank of the rivet is inserted through the prepared holes. An automatic feeder often supplies rivets into the rivet gun tip.
6. Rivet Setting - The gun presses the rivet head tightly against the material while pulling, shearing, or otherwise deforming the tail. This expands the rivet body.
7. Inspection - The shop inspector checks for proper rivet fit, head formation, material distortion, and ring around the rivet from full expansion.
8. Finishing - Any minor inconsistencies are reworked. The joint may be cleaned, sealed, or painted for corrosion resistance and aesthetics.
Automated riveting machines can precisely control force and speed during rivet setting to maximize quality and throughput. However, operators still oversee critical joint locations. Prototype and low volume work relies primarily on manual rivet guns.
Rivet Strength Testing
To ensure optimal rivet performance, physical testing procedures quantify rivet joint capabilities. Common test methods include:
- Shear Testing - A riveted sample is subjected to forces trying to slide the joint sideways. This measures the rivet shear strength perpendicular to the axis.
- Tensile Testing - Opposite forces pull on the ends of a riveted sample to assess the axial tension the rivets can withstand before head pull-off.
- Fatigue Testing - Cyclic stresses are applied to evaluate rivet integrity after thousands of load reversals, as in vibratory environments.
- Peel Testing - Attempting to peel apart the materials checks rivet strength and sheet adhesion. Performance indicates susceptibility to progressive joint unzipping.
- Environmental Testing - Riveted joints undergo temperature extremes, salt spray, fluids, and other exposures to validate performance under service conditions.
Testing determines the safe working load limits for particular riveted structures. Standards often regulate testing procedures for critical aviation, marine, military, and vehicular applications.
In summary, understanding proper rivet selection, joint design, installation methods, and testing procedures allows fabricators to produce robust sheet metal assemblies safely and efficiently using this versatile mechanical fastener. With an expansive range of rivet options available, manufacturers can find the right solution for virtually any thin material joining challenge. CNC Milling CNC Machining