Riveting in Sheet Metal Fabrication with CNC(precision cnc Uriah)
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How Rivets Work
A rivet is a mechanical fastener that connects two or more sheets of material by expanding and pressing against the hole margins. Rivets come in two main types: solid and blind. Solid rivets are inserted into a hole drilled through the stacked materials to be joined. The rivet shank is flared on one or both ends, clamping the materials together between the rivet head and flared end(s). Blind rivets are installed from one side when there is only access to one surface. The rivet is inserted into a pre-drilled hole and a puller tool or rivet gun flares the blind end on the backside.
Riveting Pros and Cons
Compared to welding, screwing or gluing, riveting offers many advantages:
- Rivets distribute load stresses over a wider area, reducing risk of fatigue and failure.
- Riveted joints allow some flexibility, preventing crack formation.
- Riveting is easy to inspect visually.
- Installation requires access to only one side (for blind rivets).
- Riveting can be automated more easily than welding or screwing.
Potential downsides include:
- Drilling rivet holes weakens the base material slightly.
- Riveted joints are permanent and difficult to dismantle.
- Rivets are more expensive than screws.
- Rivet strength relies heavily on proper hole size and installation.
Despite these limitations, riveting remains a highly popular and versatile mechanical fastening method, especially for sheet metal parts.
CNC Drilling of Rivet Holes
The first step in riveting is drilling holes to accept the rivet shank. Modern CNC machining centers can drill rivet holes with extreme precision and repeatability. Operators program the CNC with the rivet hole size and locations. The CNC machine then uses automated drill heads to bore the holes to the exact specifications.
CNC drilling provides advantages over manual drilling:
- Higher consistency: CNC ensures each hole is identical in diameter and position.
- Faster speeds: CNC drilling is much quicker than manual methods.
- Reduced errors: CNC eliminates human measurement variances.
- Less skill needed: CNC drilling has a gentle learning curve vs manual methods.
- Higher strength: Precise CNC holes optimize rivet clamping strength.
- Better finishes: CNC produces clean, uniform hole edges.
- Simpler fixturing: CNC drill heads move in 3D so parts can be fixed flat.
- Automated production: CNC drilling enables mass-scale riveting.
For riveting sheet metal parts like aircraft skins, electronic enclosures, or building panels, CNC drilling is far superior to manual hole punching or drilling. The precision of CNC results in optimized rivet joint integrity.
CNC Riveting Solutions
While early riveting relied on manual hammering or hydraulically squeezed rivet guns, CNC now enables automated installation. Two main methods are used:
Pneumatic Riveting
Pneumatic rivet guns use compressed air to quickly insert rivets. CNC machines can mount pneumatic rivet guns on heads to automate the process. Operators load rivets into feed tubes that orient and deliver each rivet to the gun nosepiece precisely. The CNC program positions the material layers under the rivet gun, drills each hole, then actuates the gun to drive rivets through the holes and flare the tails. This creates an assembly line-like process for fast mass production of riveted components.
Robotic Riveting
For more flexibility, articulated robots can be programmed to handle riveting. Robotic arms emulate human arm movement with more precision. Grippers allow robots to grab rivet guns and position them at any orientation to install rivets in hard-to-reach spots. Offline programming software uses CAD models to generate optimal motion paths for the robot. Sensors provide feedback to ensure correct rivet placement. While slower than dedicated CNC machinery, robot riveting enables high flexibility and reduces re-fixturing time.
Riveting System Selection
To select the optimal automated riveting system, consider:
- Production volume - Dedicated CNC is better for high volumes
- Part size - Small parts suit tabletop CNC machines
- Complexity - Robots can reach difficult geometries
- Strength - Pneumatic hitting provides stronger deformation
- Speed - Pneumatic is fastest, robot is slowest
- Fixturing - Robot may allow simpler jig design
- Changeovers - Robot requires just reprogramming
While initial investment is higher, automated CNC riveting quickly pays for itself in reduced labor and increased throughput. For high strength and reliable riveted joints in sheet metal, CNC is the clear choice over error-prone manual methods. CNC Milling CNC Machining