Quality Rivets - The Key to Strong and Durable CNC Machined Parts(first cnc machine Yvonne)
- source:GAENOR CNC Machining
What are Rivets?
A rivet is a mechanical fastener used to join two or more materials together. Rivets consist of a cylindrical shaft and a head. During installation, the rivet is placed in a pre-drilled hole through the materials being joined. The rivet shaft is then upset, or deformed, creating the rivet head which grasps the materials tightly together. The upsetting process work-hardens and expands the rivet, creating a strong clamping force.
Rivets vs. Screws and Bolts
Unlike screws and bolts which rely on tension to hold materials together, rivets create joints through compression and deformation. This makes rivets ideal for applications where vibration may loosen screw threads over time. Rivets also distribute load over a wider area compared to screws or bolts. And installation is often faster compared to screwing components together.
However, rivets form a permanent joint - the materials cannot be easily disassembled like with bolted connections. So rivets are best for one-time assembly of permanent structures.
Common Rivet Materials
Several materials are commonly used to manufacture rivets:
- Aluminum - Offers high strength-to-weight ratio. Resists corrosion. Used extensively in aircraft and other transportation applications.
- Steel - Very high strength. Withstands high shear and tensile loads. Used in heavy machinery, bridges, and structural applications. Can be heat-treated to increase hardness.
- Copper - Ductile material. Used for electrical conductivity in electronics. Resists corrosion.
- Monel - Nickel-copper alloy. Very corrosion resistant. Used in marine and other harsh environments.
- Titanium - Extremely strong yet lightweight. Excellent corrosion resistance. Used in aircraft, medical implants, and other demanding applications.
- Plastics - Lightweight. Electrically insulating. Used in electronic equipment casings and consumer products.
Key Properties of Quality Rivets
So what makes for a quality rivet suitable for CNC machined components and structures? Here are some of the most important properties to look for:
- Shear and Tensile Strength - Rivets must withstand shear forces perpendicular to the axis of the shaft as well as tensile forces along the axis. Rivet strength ratings are typically expressed in psi or MPa.
- Ductility - Quality rivets exhibit good ductility to deform and fill the drilled hole during installation. Ductile materials like aluminum and copper make excellent rivets.
- Hardness - The rivet must be harder than the materials being joined to resist wear and deformation when clamping them together. Heat treating and alloying can increase rivet hardness.
- Fatigue Strength - Rivets undergo cyclic stresses in vibrating machinery. Good fatigue strength resistance prevents cracks and failure over time.
- Temperature Resistance - Rivets must maintain strength and corrosion resistance at temperature extremes seen in applications like automotive exhaust systems, aircraft, and process equipment.
- Corrosion Resistance - Rivets exposed to weathering, chemicals, salt spray and more must resist corrosion to avoid joint deterioration. Stainless steel, aluminum, and monel rivets offer excellent corrosion protection.
- Head Style - Various rivet head shapes like round, countersunk, and specialty heads are available for different application requirements.
Best Practices for Quality Rivet Selection
Keep these tips in mind when selecting rivets for your CNC machining applications:
- Choose rivet material compatible with the base materials being joined. Consider temperature resistance, galvanic corrosion, and CTE mismatches.
- Match or exceed the base material hardness to avoid rivet wear and deformation under clamping pressure.
- Select rivets with sufficient shear and tensile capacity for the expected loads and safety factor. Consider dynamic, shock, and peak loads.
- Use rivets with suitable ductility to fill holes during installation and ensure a tight fit.
- Specify thread type – coarse or fine – for threaded rivets used in tapped holes.
- Include head style, drive type, grip range, and length specifications.
- Obtain rivets from reputable manufacturers like Cherry Aerospace, LISI Aerospace, or Alcoa Fastening Systems to ensure reliable quality.
Rivet Installation Best Practices
Proper installation is also critical for a durable riveted joint:
- Holes must be properly aligned between both workpieces. Jigs and fixtures help maintain alignment.
- Joint surfaces should be clean and free of burrs, rust, and contaminants.
- Use a riveting hammer or pneumatic squeezer with sufficient force to completely set the rivet.
- Avoid underdriving or overdriving rivets during installation.
- Set multiple rivets progressively starting from the center outward to draw materials together evenly.
- Inspect set rivets for proper head shape, good clamping, and no cracks.
Quality rivets are indispensable fasteners for creating robust, permanent joints in CNC machined parts and assemblies. With attention to material properties, strength values, and proper installation, rivets will provide reliable service over the lifetime of the component. Consult engineering resources and experienced rivet manufacturers to select the optimal rivet type and specifications for your specific application needs. CNC Milling CNC Machining