Riveting in Sheet Metal Fabrication with CNC(annular snap fit Mignon)

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Rivets have been used since ancient times to join pieces of metal together. While welding has become more common, riveting is still an important process, especially for joining thin sheets of metal. Using computer numerical control (CNC) machines has made riveting much more efficient and precise.
What is a Rivet?
A rivet is a cylindrical object that joins materials by passing through holes in the parts to be joined and flaring out on the backside to grip the materials. The flaring is caused by upsetting the tail end of the rivet, which expands when hit by a hammer or squeezed by a rivet gun. This creates a permanent mechanical fastener that holds the materials together.
Rivets come in many sizes and materials like aluminum, steel, titanium and more. They can have round, flat or countersunk heads. The choice depends on the design needs and materials being joined.
Benefits of Riveting
Compared to welding, riveting offers some advantages:
- It avoids concentrated heat which can distort thin sheets. Riveting causes less material distortion.
- It is easier for semi-skilled operators to learn. Welding requires more training and skill.
- Riveting is portable for on-site fabrication and repairs. Welding usually requires a shop environment.
- The joint is not as rigid, allowing for expansion and contraction from temperature changes.
- Disassembly is easier since rivets can be drilled out if needed. Welds are more permanent.
For these reasons, riveting is still frequently used to join metal aircraft skins, bridges, machinery covers, infrastructure and more. It is especially useful for thin sheet metals.
CNC Riveting Machines
Performing riveting completely manually is labor intensive. Modern CNC riveting machines automate the entire process for improved consistency and efficiency.
CNC stands for computer numerical control. In CNC machines, the movements are controlled by software programming rather than manual controls. This allows fast, precise, programmable control of the riveting process.
Here are some of the features of CNC riveting machines:
- Multi-axis drilling heads for flexibility in hole placement. The sheet can be precisely positioned.
- Automated feeding of rivets into the drilling head. Different rivet sizes can be used.
- Programmable clamping force and drill depth for consistency.
- Programmable riveting force, distance and pacing.
- Automated upset of the rivet tail.
- Integration with part fixturing for consistent alignment.
- Robotics for handling parts, tools and quality inspection.
This level of automation improves the consistency and speed compared to manual riveting. Holes can be quickly drilled in the optimal locations, with precision alignment between parts. The riveting force and pace can be programmed for optimal upset and quality.
Other advantages of CNC riveting include:
- Minimal fixture costs. The CNC machine replaces complex jigs.
- Flexibility. Job changes can be programmed rather than physical changeovers.
- Elimination of error-prone manual tasks.
- Ability to program various riveting patterns and layouts.
- Detailed production data monitoring and analytics.
- 24/7 unmanned production.
For medium to high volume fabrication with thin metal sheets, CNC riveting can make the process much more efficient.
CNC Riveting Process
Here is an overview of the automated CNC riveting process:
1. The workpieces are loaded into the machine on a movable table. Fixturing holds the parts in place.
2. Guided by the CNC program, the machine drills holes at the precise marked locations. A drill bit slightly smaller than the rivet is used.
3. Rivets are fed automatically into the drilling head from a vibratory bowl feeder.
4. The drilling head aligns over the next hole and the machine clamps down on the parts.
5. The rivet feeds into the pre-drilled hole. The tail is flush with the bottom sheet.
6. The rivet shaft fills the hole and swages outward, clamping the sheets together.
7. The preset riveting force upsets and flares the tail, securing the rivet.
8. The machine releases, drills the next hole, and repeats the sequence.
9. When the pattern is complete, the finished workpiece is unloaded.
For large production runs, multiple heads can be used simultaneously for high-speed riveting. Automatic tool changers switch drill bits as needed.
This automation provides very consistent hole drilling, rivet placement, clamping force and upset. It produces uniform, quality rivets across the entire production run with minimal operator involvement. Rivet spacing, hole sizes and patterns can be optimized based on the load requirements using FEA software.
Applications of CNC Riveting
CNC riveting machines are commonly used for:
- Aircraft and aerospace fabrication. Rivets are extensively used on wings, fuselages and other components to join aluminum skins.
- Automotive panels and frames. Door skins, hoods, trunks and structural components are riveted.
- Electronics enclosures and chassis. Sheet metal boxes, racks and frames use rivets.
- Signs, kiosks and displays. The sheet metal cores of 3D signs are riveted before finishing.
- Appliances such as washers, dryers and refrigerators. Side panels and internal components are riveted.
- Furniture with sheet metal frames like desks, filing cabinets and shelving.
- Storage containers, trailers and crates which undergo shipping stresses.
- Building and construction panels, siding, ducting and roofing components.
- Infrastructure platforms, railings, walkways and supports.
- Ship hulls and marine components above and below water.
The automated precision of CNC allows riveting to be highly effective and economical for medium to high production volumes. It produces consistent, stong, reliable and visually appealing joints for thin sheet metal components across many industries. CNC Milling CNC Machining