Riveting in Sheet Metal Fabrication with CNC(friction fit Oswald)

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Rivets have been used since ancient times to join pieces of metal together. While welding has become more common for joining metals, riveting is still an important process, especially for joining thin sheets of metal where welding may cause warping. Modern CNC (computer numerical control) machines have made riveting sheet metal faster and more efficient.
What is a Rivet?
A rivet is a mechanical fastener that joins two or more pieces of material by passing a metal shaft through aligned holes in the pieces and forming a head on one or both ends. The rivet holds the materials together through clamping force and friction.
Rivets come in various head styles, shapes, materials and lengths depending on the application. Some common types include blind rivets, drive rivets, pop rivets and specialty rivets. Blind rivets can be installed from one side, pop rivets require access to both sides, and drive rivets use a hammering process to form the second head.
Benefits of Riveting
Compared to welding or adhesives, riveting offers several advantages:
- It is quick and easy for assembling products.
- It works well on thin sheets that may warp if welded.
- The joints allow for some flexibility and movement.
- Disassembly is easier than with welding or adhesives.
- Minimal edge finishing is required.
- It can join dissimilar metals.
- Installation requires access to only one side for many rivet types.
For these reasons, riveting is commonly used in aircraft and automobile manufacturing, ducting, appliances, electronics, signage, and other sheet metal fabrication industries.
CNC Machines for Riveting
Computer numerical control (CNC) machines are able to automate repetitive riveting tasks with precision and efficiency. Here are some of the CNC machines used for riveting:
CNC Riveting Machines: These are fully programmable riveting machines designed specifically for high-volume rivet installation. They use automated fastener feeders and can install multiple rows of rivets. The riveting heads apply consistent pressure and can swivel for optimum placement.
CNC machining centers: Machining centers with riveting attachments can drill holes, countersink, and install rivets in one setup. This saves time and improves accuracy over separate operations.
CNC routers: For large sheet metal parts, CNC routers cut the required shapes and holes, then routing attachments install the rivets in the same program.
Robotic riveting cells: Robotic arms team up with special riveting end effectors to handle parts and install rivets. The robots can access confined spaces and rivet at multiple angles.
Flexible manufacturing systems: FMS integrate CNC machines, automated material handling, and part storage and retrieval systems. Different stations carry out drilling, riveting, welding, inspection and other functions.
Benefits of Automated Riveting
Here are some of the benefits CNC automated riveting offers over manual riveting:
- Higher production rates and reduced labor costs. CNC machines rivet much faster than humans.
- Improved consistency and quality. CNC applies optimal force and positioning every time.
- Ability to rivet complex or curved parts. Robotic arms can access confined spaces.
- Flexible production. CNC programs can be changed to accommodate new parts.
- Integration with other processes. Machining centers combine drilling and riveting in one setup.
- Reduced chance of operator injury. Operators are moved to a safe distance from machinery.
- Ability to work 24/7. CNC automation eliminates breaks, fatigue and human error.
- Data collection and analysis. Modern CNC machines log production rates, faults and provide data to improve quality.
The Rapid Prototyping Process
One of the key advantages of CNC riveting is the ability to rapidly prototype or produce low volume parts. Here is an overview of the rapid prototyping and production process:
1. Design: CAD software is used to design the part and specify rivet locations. For low volume parts, rapid prototyping methods like 3D printing can create prototype pieces faster.
2. CNC programming: The riveting sequence is programmed offline based on the CAD design. Software converts CAD into CNC code.
3. Fixture fabrication: Custom fixtures hold the parts in position during riveting. These are made in-house or outsourced.
4. Material preparation: Sheet stock is sheared, formed or machined to spec. Holes may be punched or CNC drilled. Parts are deburred.
5. Setup: The fixtures and sheet metal parts are loaded onto the CNC machine. Rivet feeders are loaded with the appropriate rivets.
6. Cycle start: The operator starts the CNC program and the machine begins riveting automatically per the sequence.
7. Inspection: Finished parts are taken to quality control where they are inspected to meet specifications.
8. Process refinement: During production, the CNC program can be tweaked to improve cycle times or quality.
For high volume production, dedicated automation and extensive fixture design is implemented after initial prototyping. But CNC flexibility allows riveting procedures to be tested and refined before large investments in hard tooling are made.
CNC Riveting Techniques
Modern CNC machines allow for innovative riveting techniques that maximize strength while minimizing weight and material use. Here are some popular techniques made possible by CNC automation:
- High speed riveting. CNC machines can quickly install many rivets for fast assembly times.
- Multi-angle riveting. Robotic arms maneuver to install rivets at compound angles and clear obstructions.
- Blind rivets. Rivets can be installed from one side for assemblies where backside access is constrained.
- Self-piercing rivets. CNC controls the force of self-piercing rivets that punch through both sheets to eliminate hole drilling.
- Hemming. CNC forms tight folded seams reinforced with linear rows of rivets. Great for enclosures.
- Stitch riveting. CNC applicators insert rows of rivets along panels using masking tape or chains to prevent buckling.
- Rivnut installation. Rivnuts combine a rivet shaft and threaded nut for bolted connections without welded nuts.
- Auto-indexing. Programmable indexers rotate large parts in sequence for riveting at multiple positions.
- Bucking automation. Some machines include mechanical or pneumatic bucking bars that back up the rivet tail for solid clinching without an operator.
Proper Selection of Rivets
Choosing the optimal rivet design and material is critical for high quality riveted joints. Here are some factors to consider:
- Materials being joined - Rivet material should match or be compatible with the materials being joined.
- Sheet thickness - Longer rivets are needed for thicker stacks of material.
- Grip length – The unformed shank needs to be longer than the total thickness of sheets.
- Strength required – Larger diameter rivets offer greater shear and tensile strength.
- Accessibility – Blind rivets can be installed from one side. Drive rivets require two sided access.
- Head profile – Pan head, countersunk flush head, and other profiles suit different aesthetics.
- Environmental factors – Certain platings and materials resist corrosion or chemicals.
- Codes and standards – Structural applications may require specific sized or positioned rivets.
Proper rivet sizing, material selection, and placement is critical for achieving rivet joint integrity. CNC automation helps ensure every rivet meets the required specifications.
CNC Riveting Safety
Working with powerful machinery requires proper safety precautions and procedures. Here are some tips for safe CNC riveting:
- Enclose the work area with light curtains, screens or barriers to prevent contact with moving parts.
- Ensure the machine and work area is clear of loose objects, tools, and extra rivets that could become projectiles.
- Use chip guards and shields to contain debris from drilling and rivet setting.
- Require eye protection to be worn in production areas at all times.
- Include emergency stop buttons within easy reach of operators. Test them regularly.
- Inspect machine components for wear and immediately replace worn drill bits, rivet setters, grippers or other items.
- Follow manufacturer procedures for safe programming, setup, operation and maintenance.
- Keep software up to date and implement cybersecurity measures.
- Only let properly trained staff operate CNC machinery. Provide ongoing training.
With proper safety protocols, CNC riveting improves production while protecting workers.
Riveting remains a practical and efficient method for fastening thin sheets of metal in manufacturing. CNC automation makes the riveting process faster and more flexible compared to manual methods. Programmable CNC machines allow for high speed production, precision placement, integration with other processes like drilling and machining, and innovative techniques difficult to perform manually. When paired with CAD design tools and rapid prototyping techniques, CNC riveting enables fast production from concept to finished product. With continued advances in robotics and software, CNC promises to further improve the productivity and quality of industrial riveting. CNC Milling