High Quality Rivets Are Essential for CNC Machining(kinds of springs Channing)
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What are Rivets?
A rivet is a mechanical fastener used to join multiple pieces of material by inserting its shank through pre-drilled holes and forming a head on the protruding end. The rivet shank expands when the tail end is hammered or pressed, creating a bulbous shape that holds the materials together. Rivets come in a variety of head shapes, materials, sizes and strengths to accommodate different design needs. Common materials include aluminum, steel, titanium and specialty alloys.
Benefits of Rivets for CNC Machining
Rivets offer several advantages that make them well-suited for CNC machined parts and assemblies:
- Permanent fastening - Unlike screws or bolts, rivets cannot come loose over time due to vibration, temperature changes or material settling. The expanded shank creates a tight, permanent bond.
- Weight savings - Rivets are often lighter than comparable nuts and bolts. This helps reduce component weight in aircraft, vehicles and other applications where lightness is paramount.
- Quick installation - Riveting is generally faster than screwing or bolting, especially with pneumatic tools. This boosts manufacturing efficiency.
- Consistent clamping force - Properly driven rivets provide uniform clamping pressure along the length of the shank. This avoids localized stress concentrations.
- Corrosion resistance - Many rivets feature coatings or alloying additions to improve corrosion resistance. This enhances durability in harsh environments.
- Cost effectiveness - Rivets are inexpensive compared to many other fasteners. And specialized installation tools are not required in most cases, further reducing costs.
These advantages make quality rivets well suited for everything from small precision instruments to large steel structures. But to leverage these benefits, the right rivets must be selected for the application.
Choosing the Optimal Rivets for CNC Machining
Several factors should be considered when selecting rivets for CNC machined components:
- Material - Rivet material must be compatible with the materials being joined and suit the operating environment. Aluminum and steel rivets are most common for manufacturing. Exotic alloys resist heat and corrosion for extreme conditions.
- Size - Shank diameter and length must match the hole size and material thickness. Grip range indicates the minimum and maximum material thickness the rivet can accommodate.
- Head style - Countersunk, round, flat and specialty head shapes are available. Countersunk is preferred for flush surfaces.
- Strength - Shear and tensile strength ratings must exceed the expected service loads. This data should be obtained from the manufacturer.
- Drillability - Some rivets feature drill points to ease hole alignment during assembly. This is advantageous for CNC operations.
- Drivability - Soft or aging materials may require rivets designed to set with lower force. Hard, brittle materials demand rivets that set solidly.
- Surface finish - Smooth, polished rivet shanks facilitate CNC feeding. Coatings like Teflon® further minimize jamming.
Reputable rivet manufacturers provide all necessary specifications to enable proper selection. Consulting application engineers can further aid choosing the optimal product.
Programming Considerations for CNC Riveting
CNC programmers must account for some unique factors when developing riveting sequences compared to drilling, milling and other machining operations:
- Hole alignment - Misaligned rivet holes can prevent shank insertion. CNC drilling operations should include techniques to accurately locate holes, such as depth controls, optical center finding and precision fixturing.
- Shank allowance - Holes must be slightly larger than the rivet shank to permit insertion. The clearance required depends on material and hole precision.
- Countersinks - These chamfers are needed with countersunk rivets to recess the head. Depth must precisely match rivet head geometry.
- Clamping force - Materials must be held tightly together during riveting to prevent joint gaps. Programmers should specify sufficient force based on part thickness, hardness and rivet strength.
- Pecking - Deep rivet holes may require peck drilling and intermittent retracting to clear chips. This prevents binding and poor hole quality.
- Feeding aids - Polymer guide tubes, oriented vibratory bowl feeders and other mechanisms can help properly present and align rivets for robotic or automated loading.
- Setting force - CNC controllers should limit riveting force to avoid crushing or damaging materials. Pressure should be adjusted for different rivet types if using automated equipment.
Proper programming is critical for fast, accurate rivet insertion and quality end results.
Inspection and Testing Considerations
All aircraft, automotive, military and other critical CNC machined assemblies featuring rivets must undergo stringent inspection and testing according to regulatory requirements and internal quality standards. Typical checks include:
- Dimensional - Sample rivet measurements confirm shank diameter, head height, grip length and other dimensions are within specification tolerances.
- Hole examination - Hole size, position and perpendicularity are verified. Countersinks are checked for proper depth and diameter.
- Torque testing - Randomly selected rivets are checked to confirm head torque resistance meets specification.
- Shear testing - Destructive shear tests measure rivet, hole and material integrity. Failed samples are analyzed.
- Process monitoring - Statistical analysis tracks trends in setting force, number of rivets rejected and other process parameters.
- Imaging - X-ray and ultrasonic scans help detect subsurface flaws like cracked or deformed shanks.
- Environmental testing - Assemblies undergo temperature cycling, fluid immersion, vibration and other tests per application needs.
Thorough inspection provides quality assurance while identifying opportunities for continual CNC machining and riveting process refinements.
In summary, properly selected and installed rivets are critical for achieving robust, durable and efficient CNC machined products. By considering material compatibility, design needs, manufacturability, quality control practices and more, manufacturers can leverage rivets to optimize assemblies and avoid costly failures. With attention to detail throughout the design, sourcing, machining, assembly and testing processes, high quality rivets will deliver reliable performance for the application. CNC Milling