Riveting in Sheet Metal Fabrication(g codes Ryan)
- Time:
- Click:10
- source:ZIEG CNC Machining
How Rivets Work
A rivet is essentially a cylindrical shaft with a head on one end. To rivet two or more pieces of sheet metal together, holes are drilled through the sheets at the point of contact. The rivet is inserted into the aligned holes and the tail end is upset, or sm smithing the tail against an anvil or bucking bar. This smithing causes the tail to flare out and clamp the sheets together. The flared tail is called the shop head, while the pre-formed head is called the buck-tail.
Different rivet types have variations on this basic concept, but the general principle is the same. When installed correctly, the rivet clamps the materials together with tremendous force, creating a solid connection.
Common Rivet Types
There are many different types of rivets used for sheet metal fabrication. Some of the most common include:
- Solid/blind rivets - These are the simplest type. They are solid all the way through and can be used for single-sided applications where access is only available to one side of the materials.
- Semi-tubular rivets - These have a partial hole through the center of the shaft. They are also used for single-sided applications.
- Tubular rivets - These have a hole through the entire shaft. They require access to both sides of the materials so the tail can be flared by smithing.
- Self-piercing rivets - As the name implies, these pierce through the top layer of material and flare out on the back side. No drilling is required.
- Drive rivets - These are installed using a rivet gun that contains an exerts force to flare the tail. Used for high-strength applications.
- Pop rivets - These have a mandrel through the center that is pulled to flare the tail. The mandrel snaps off after installation. Quick and easy for low-strength uses.
- Structural rivets - Used for critical structural fabrication. Require drilling and come in high-strength alloys.
- Specialty rivets - There are many other varieties designed for specific uses, such as large-flange rivets and high shear rivets.
Proper Rivet Selection
Choosing the right type of rivet for an application depends on a number of factors:
- Materials – Rivet material must be compatible with the base materials to prevent corrosion.
- Sheet thickness – Larger rivets are required for thicker stacks of sheet metal.
- Strength needs – Structural joints require high strength rivets. Decorative joints can use lower strength options.
- Access – Solid rivets for single-sided access. Tubular rivets when both sides are accessible.
- Assembly method – Self-piercing, pop, or drive rivets for rapid assembly. Structural rivets for critical joints.
- Appearance needs – Some projects require rivets to be countersunk for a flush surface.
Proper rivet selection ensures a joint has adequate strength for its intended purpose without using excess materials or processing. Consult engineering specifications for particular rivet requirements.
Rivet Joint Design
Properly designing riveted joints is crucial for strength and durability. Here are some key riveting joint design considerations:
- Spacing – Rivets must be spaced appropriately to distribute load across the joint. Too few rivets concentrates stress while too many adds unnecessary weight.
- Edge distance – Rivets should be placed a minimum distance from joint edges based on material thickness. This prevents edges from tearing.
- Pitch – Rivets in a row should be evenly spaced. Staggering rows also distributes stress.
- Number – More rivets spread force better but add weight. Determine minimum required.
- Pattern – Layout rivet placement in a pattern optimized for load path. Common patterns include zigzag and chain.
- Materials – Joint designs must account for material properties like hardness and ductility.
- Load – Design for the required service load on the joint plus a safety factor.
Following established engineering guidelines for rivet joint design ensures proper riveting practice.
Drilling Holes for Rivets
The first step in riveting is drilling holes for the rivets to be inserted through. Holes must be precisely positioned and sized. Here are key drilling guidelines:
- Use sharp drill bits designed for metal to avoid tearing the edges of holes.
- Holes should be round and perpendicular to the surface.
- Diameter should match the rivet shank with a tolerance of +/- 0.1 mm. Too large and the rivet won't grip tightly. Too small and the hole can crack.
- Depth should allow rivet head to seat flush with material surface.
- Apply masking tape over holes when drilling through multiple layers to prevent tear out.
- Drill guides and jigs ensure accuracy for production runs.
- Deburr holes thoroughly after drilling to remove sharp edges.
Proper hole drilling is critical to rivet joint integrity. Take measures to achieve clean, accurate, and appropriately sized holes.
Rivet Insertion
Once holes are drilled, rivets can be inserted to join materials. Use these tips for proper rivet insertion:
- Inspect holes and rivets for defects before inserting.
- Lubricate rivets and holes with oil if needed to ease insertion.
- Insert rivet head first through the holes using gentle pressure. Do not pound.
- Rivet head should seat flush against top material layer.
- Clamp materials together to keep everything aligned if needed.
- Tail end should protrude enough to allow flaring against the anvil/bucking bar.
Care during insertion helps set up the rivet to be flared properly. Avoid damaging the materials or rivets during this stage.
Flaring the Rivet
The key step that completes the riveted joint is flaring the tail to form the shop head. This expands the rivet and clamps the sheets tightly together. Use these guidelines when flaring rivets:
- Place an anvil or bucking bar under the protruding tail.
- Use a rivet set aligned above the rivet head.
- Strike the set with a hammer until the tail flattens out against the anvil to form a shop head.
- Rivet should flare out to about 1.5 times the shank diameter.
- Do not strike so far as to crack the rivet or sheets.
- Set force and number of hammer blows depends on rivet size and materials.
- Self-piercing, drive, and pop rivets use tools for controlled flaring.
- Inspect final joint to ensure head and shop head are formed properly.
Proper flaring technique ensures maximum joint strength. Take care not to damage materials or overly work harden the rivet when flaring.
Inspection and Testing
Once riveted, joints should be inspected to verify sound construction. Check for:
- Rivet flushness – Heads and shop heads should sit tight against materials.
- Flaring size – Shop heads should be about 1.5 times shank diameter.
- Cracks – In rivets or sheet metal around holes.
- Chips/tears – Around holes from drilling or insertion.
- Misalignments – Off-center rivets or mismatched holes.
Testing can also check riveted joint integrity:
- Hammer taps – Ringing sound indicates solid connection. Thud indicates problems.
- Shear testing – Apply test load to joint to verify strength.
- Disassembly – Remove random rivets for analysis.
- Non-destructive testing – Use methods like ultrasound or x-ray to view internal joint condition.
Proper inspection validates quality riveting workmanship and joint strength. Testing provides quantitative confirmation.
Riveting is an efficient, reliable, and cost-effective method for mechanically fastening sheet metal. With an understanding of the various rivet types, design considerations, and proper installation procedures, this staple fabrication technique can continue producing robust and durable sheet metal assemblies. The basics covered here provide a good overview of how to effectively use riveting for a wide range of sheet metal construction needs. CNC Milling CNC Machining