Riveting in Sheet Metal Fabrication(conventional milling Sandy)

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Rivets are a fundamental fastening method in sheet metal fabrication. They create strong, permanent joints between multiple sheets of metal or other materials. Compared to welding, riveting is quicker and more accessible for small workshops and hobbyists. However, understanding the riveting process and techniques is key to creating robust and professional results. This article will explore everything you need to know about riveting sheet metal.
What is a Rivet?
A rivet is a short cylindrical rod with a head on one end. The rivet is inserted through pre-drilled holes in the materials being joined. The tail end is then flattened and spreads out (known as bucking or peening) to form the second head, clamping the materials together. The rivet heads on both sides hold the joint securely together through tension and friction.
Rivets were traditionally made from steel, aluminum, copper, or brass. However, specialist rivets are now available in exotic alloys for high strength and temperature applications. The head shapes can also vary, with common options being round, brazier, countersunk, and flush. The choice depends on the joint requirements and materials.
Traditional solid rivets are still popular. However, blind rivets have become widely used where access is only available from one side. Blind rivets have collapsible mandrels that are pulled to form the second head. Pop rivets are a type of blind rivet designed for quick manual installation without tools.
Benefits of Riveting
Compared to other joining techniques, riveting in sheet metal fabrication offers:
- Speed and simplicity - hand tools allow quick installation without complex equipment.
- Strength - rivets form highly reliable permanent joints. The tension between the rivet heads provides excellent resistance to shocks and vibration.
- Disassembly and rework - drilled-out or ground off rivets can be replaced if access is available. This allows repairs and modifications.
- Material versatility - rivets can join dissimilar sheet metals and other materials like plastics. Minimal heat also avoids warping or damaging sensitive materials.
- Appearance - countersunk or flush rivets allow smooth unbroken surfaces for aerodynamics and aesthetics.
- Cost effectiveness - rivets are inexpensive components available in bulk. Installation only requires basic hand tools for small jobs.
Riveted Joint Design Considerations
Properly designing joints is crucial for rivets to perform as expected. Key factors include:
- Materials - the strength and ductility of the base materials must suit the joint stresses. Rivet material should match or exceed the sheets.
- Sheet thickness - thicker materials require longer rivets and smaller drill holes to develop sufficient clamping force. The rivet diameter should be 3 times the sheet thickness.
- Hole size - clearance between the rivet and hole allows the deformation needed to form heads. Holes should be 1/16" larger than the rivet shank diameter.
- Rivet spacing - adequate edge margins and pitch between rivets prevents tear-out. As a rule of thumb, space rivets at 2-3 times the rivet diameter.
- Rivet strength - static and fatigue strength ratings must exceed the expected loads. This depends on rivet diameter, material, and head style.
- Access - joints must allow bucking tool access or use blind/pop rivets. Closed sections may need prototype assembly to check access.
Proper design prevents joint failure modes like rivet shear, rivet pullout, and material tearing. Detailed analyses and testing are used for critical aviation and structural applications. However, empirical guidelines are suitable for most general fabrication.
Riveting Process Overview
The main steps in riveting are:
1. Material preparation - cut and shape sheet metal components to final dimensions. Deburr holes and surfaces.
2. Drilling holes - align materials and clamp together. Punch/drill holes using matched drill bits. Check hole size and alignment.
3. Degreasing - clean joint surfaces with solvent to improve adhesion.
4. Insert rivets - place rivet in holes with head against one sheet. Rivet length should match total material thickness.
5. Bucking - hold rivet head stationary with a bucking bar. Strike tail end to flatten into a second head.
6. Inspection - confirm properly formed heads and tight joint. Check for cracks or inadequate deformation.
7. Finishing - remove any burrs and smooth surfaces. Seal joints if needed against corrosion.
Proper technique and quality control ensures optimal rivet strength and appearance. Riveting is generally done manually, but pneumatic rivet guns automate high volume production.
Riveting Tools & Equipment
Riveting only requires a few essential tools:
- Drill bits - matched to pilot hole size in the rivet's specifications. Cobalt or titanium coated for longevity.
- Rivet set - precisely sized tip that presses against the rivet head during bucking. Various tip shapes are available.
- Bucking bar - rigid block that holds the rivet steady against the rivet set blows. Rubber or plastic tips prevent marring.
- Hammers/mallets - ball peen hammers or dead blow mallets transfer impact energy to form the rivet.
- Rivet gun - pneumatic tool with an impact tip for rapid installation. Often with vacuum pickup for rivets.
- Hole template - sheet metal template for consistent hole alignment when drilling stacks.
- Clamps - used to compress and align sheet layers when drilling holes.
- Deburring tools - files, deburring blades, and abrasive brushes clean up drilled holes.
- Inspection tools - magnifying glass,calipers, etc. to check rivet heads and joint tightness.
Proper riveting also requires adequate workshop equipment like drills, belt sanders, sheet metal brakes, and shears. Investing in quality tools ensures precision and reliability in riveting work.
Types of Rivets
With an overview of the basic riveting process, we can look closer at the various rivet types and their installation methods:
Solid Shank Rivets
- Traditional two-piece rivets with a plain shank. Require access to both sides of the workpiece.
- Heads are formed using a bucking bar and hammer. Rivet set has a concave tip that fits the rivet head profile.
- Common head styles include round (universal), countersunk, and brazier (high shear strength).
- Available in aluminum, steel, stainless steel, copper, and specialty alloys.
Blind Rivets
- Single piece tubular rivets with an internal mandrel stem.
- The mandrel is pulled with pliers or a rivet gun to form the second head. No rear access needed.
- Often have small shallow dome heads. The head shape is less critical since not bucked.
- Used for repairs, internal joints, or where back side access isn't feasible. Not quite as strong as solid rivets.
Pop Rivets
- Blind rivets designed for quick, tool-free hand installation.
- To set, the mandrel stem is simply pulled until it snaps off after forming the rear head.
- Flush break-mandrel types leave a smooth surface with no stem remnant.
- Available with round, countersunk, or large flange heads in various materials and strengths.
Self-Plugging Rivets
- Blind rivets that seal the remaining mandrel hole after installation.
- Increased watertightness and improved aesthetics versus ordinary blind rivets.
- The mandrel has a tapered or stepped tip that swages hole closed when pulled into rivet body.
- More specialized and expensive than standard blind rivets.
Rivnut Rivets
- Nut-style blind rivet with internal screw thread in the rivet body.
- Provides threaded hole in sheet material that accepts standard fasteners.
- Mandrel stem has a threaded tip which forms matching thread in the rivet body.
- Allow removable bolted joints while only requiring rivet-gun access.
Typical Applications of Riveting
Now that we've covered the riveting process and hardware, we can look at some typical current uses:
Aircraft Construction - rivets are the primary fastener in airframes. High static loads combined with fatigue require consistent quality. Solid and blind rivets used extensively.
Automotive - riveting sees limited use in high volume auto manufacturing today. Still used for truck frames, seat tracks, and attaching interior trim pieces.
Appliances - versatile pop rivets ideal for assembling sheet metal enclosures and parts like control panels, vents, ducts etc. Allow leak-free joints.
Furniture - provides invisible fastening for sheet metal legs, frames, and supports. Quick attachment of decorative trim parts.
Ducting & HVAC - fast and reliable sealing of exhausts, vents, duct segments. Withstands vibration and thermal cycling over decades of use.
Electronics Enclosure - joins thin aluminum or steel chassis and covers. Tamper resistant and electrically conductive. Allows custom mods.
Jewelry Craft - miniature pop rivets ideal for assembling delicate jewelry components. Quick setting and custom head styles.
Sheet Metal Art - rivets are perfect for assembling abstract and sculptural creations. Gives industrial appearance.
The simplicity and reliability of rivets ensures their ongoing usage across many fields. With attention to detail and proper techniques, high quality riveted assemblies can be achieved even in small workshops. Riveting remains a foundational metalworking skill with many applications.
Riveting is a straightforward yet versatile sheet metal joining method. It produces permanent joints using tension between headed pins (rivets) inserted in holes. Benefits include strength, speed, and accessibility.
However, proper design and installation practice are needed to utilize rivets safely and effectively. Factors like materials, hole fit, and access must be considered. Minimal tools are required - drills, hammers, and bucking bars. But precision and quality are critical, especially in structural applications.
The variations in rivet styles and materials allow rivets to be adapted to nearly any situation. From intricate aircraft wings to rugged pressure vessels to delicate jewelry, rivets deliver reliable performance. Taking the time to learn riveting principles and techniques helps fabricators fully exploit this simple but immensely useful mechanical fastener. CNC Milling