Introduction(types of casting Archibald)
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In recent years, computer numerical control (CNC) machines have been adapted for automated riveting applications. CNC riveting provides consistency, speed, and accuracy compared to manual riveting. This article will discuss CNC riveting of sheet metal, including machine setup, tooling, programming, and process considerations.
CNC Riveting Machines
CNC riveting machines are programmable power tools that automatically drive rivets to join sheet metal or other materials. They use servo motors and precision ball screws to accurately position and manipulate riveting tools.
Different machine configurations are available:
- Single spindle riveters install one rivet at a time. They are ideal for lower volume production.
- Multi-spindle riveting machines have multiple spindles to simultaneously drive multiple rivets for higher throughput. Some have as many as 18 spindles.
- CNC punch-riveting machines integrate a punching station to punch rivet holes and then install rivets in the same machine. This improves accuracy and reduces handling.
- Specialized CNC riveting robots provide maximum flexibility to access confined spaces.
Tooling for CNC Riveting
CNC riveting machines use tooling specific to the rivet style and application:
- Nose assemblies or anvils support the rivet tail and flatten the tail during rivet setting. Different anvil sizes match various rivet diameters.
- Riveting heads or sets are attached to the spindle and apply pressure to deform the rivet shank. Sets are matched to the head profile and diameter of the rivets.
- Die buttons fit into the riveting head and contact the rivet head during setting. Various die button geometries are used for specialty head profiles.
- Pressure feet hold the sheets firmly together and absorb reaction forces from the rivet setting. Pressure feet sizes correspond to rivet diameters.
- Backing anvils support the back side of the rivet setting and provide a smooth set finish.
Tooling must be maintained in good condition and replaced promptly when worn to achieve quality rivet setting. Most CNC riveting machines use quick change tooling for fast changeovers between rivet sizes.
CNC Programming for Riveting
CNC riveting programs provide instructions for the machine to automatically drive rivets in the correct locations. Programs are generated using CAD models and computer aided manufacturing (CAM) software.
Riveting programs specify positioning coordinates, rivet locations, order of operation, spindle selection, riveting force, and other parameters. Programs compensate for tooling dimensions and perform multiple hits for large or hard rivets.
Engineers optimize the riveting sequence to minimize repositioning time. Multi-spindle machines allow simultaneous riveting at adjacent locations to maximize throughput.
Rivet files from CAD/CAM systems are post processed into machine-specific G-code that operates the CNC controls. Most machines also allow manual programming via teach pendant for flexibility in production.
Production Riveting with CNC Machines
CNC automation provides both productivity and quality benefits for production riveting:
- Consistent quality: CNC machines apply optimized forces and precisely control set position for uniform results. Rivet setting defects are minimized.
- High speed: Multi-spindle units install hundreds of rivets per hour. Automated operation enables lights out production.
- Reduced labor: CNC riveting slashes labor time compared to difficult manual riveting in hard-to-reach locations.
- Flexible production: Quick change tooling allows frequent rivet and material changes. Modified programs can easily accommodate design revisions.
- Improved ergonomics: Automated riveting removes workers from physically strenuous tasks and repetitive motion that causes injuries.
- Diverse applications: CNC can rivet virtually any size or material, from micro fasteners to large structural joints. Robotic riveting provides access to tight spaces.
- Data feedback: Modern CNC controllers record sensor data on cycle times, forces, and errors for process monitoring to pinpoint improvements.
While CNC riveting requires an initial machine investment, the long-term benefits often provide a rapid return on investment in high volume production through reduced labor, improved quality, and increased output.
Process Considerations for Quality Rivets
Achieving consistent, high quality CNC riveted assemblies requires attention to multiple process factors:
- Rivet type selection: Structural and mechanical properties must match design loads. Use standard rivets where possible.
- Joint design: Joints must adequately support riveted loads and allow tool and rivet clearance.
- Sheet stackup: Materials must be cleanly aligned without gaps. Clamps may be required for difficult geometries.
- Hole alignment: Misaligned holes load rivets eccentrically in shear and reduce strength. Use CNC hole punching.
- Hole size: Diameter relative to rivet size affects rivet tolerances and setting force. Test for optimal fit.
- Clamping: Pressure feet must fully clamp joint during riveting to prevent separation gaps.
- Tool condition: Worn or damaged tooling leads to poor quality rivet setting and reduced life. Inspect frequently.
- Machine setup: Rigidity, spindle angles, lubrication, and clearances are critical for quality output.
- Program Verification: Thoroughly test programmed rivet sequences on scrap material to validate machine motions.
- Quality control: Inspect sample rivets’ set position, head height, grip, and substitutions. Monitor for defects and tool wear.
Detailed process control is key to gaining the maximum performance of CNC automated riveting. However, the efficiency gains allow manufacturers to achieve higher throughput with improved reliability compared to historical manual methods.
Conclusion
Riveting sheet metal components with CNC automation provides accuracy and repeatability difficult to achieve with manual processes. Multi-spindle CNC riveting machines can install hundreds of rivets per hour and operate lights out for continuous production.
Programming coordinates, spindle control, specialized tooling, and optimized operation lead to robust joining. Properly applied, automated CNC riveting improves quality, reduces labor costs, and increases manufacturing productivity. Continued advancement will further improve flexibility, capabilities, and data-driven optimization in coming years. CNC Milling CNC Machining