What Are Rivets?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. To install rivets, the shaft is inserted into pre-drilled holes in the materials being joined. The rivet head is then deformed or "bucked" so that it spreads out and locks the rivet in place. This creates a permanent mechanical connection.
Rivets come in a variety of types, shapes, sizes and materials to suit different applications. Common types include blind, solid and semi-tubular rivets. Each has advantages and tradeoffs. Blind rivets can be installed from one side which is useful for confined spaces. Solid rivets tend to be stronger as they fill the entire hole. Semi-tubular rivets offer a compromise between strength and weight.
Key Properties for CNC Rivets
For quality rivets suitable for CNC work, there are several important properties to consider:
- Consistent Dimensions: Rivets must conform precisely to their specified diameter, head height, shaft length, etc. Any deviations can prevent proper fitting and installation.
- High Shear Strength: The rivet needs strong cross-sectional area to resist shearing forces between joined materials without failing.
- Good Ductility: The rivet material should be ductile enough to deform and buck when setting the head without cracking or fracturing.
- Corrosion Resistance: Rivets need to withstand humidity, temperature changes and potential chemicals without excessive corrosion.
- Fatigue Resistance: They must endure repetitive stresses and load cycles without cracking or premature failure.
Recommended Materials and Finishes
The optimal rivet material depends on the CNC application, operating conditions and materials being joined. Here are some top choices:
- Aluminum: Lightweight yet strong. Offers good corrosion resistance and ductility when anodized. Ideal for aircraft and low-medium strength applications.
- Steel: Very high strength and robustness. Carbon or stainless steel provide excellent performance but may rust over time. Often nickel or zinc plated for added corrosion protection.
- Copper: Great conductivity and ductility. Used for electronics and as softer compliant rivets to account for thermal motions. Requires plating/coating to prevent oxidation.
- Titanium: Extremely strong but lightweight. Excellent corrosion resistance and biocompatibility. Costly but ideal for high-performance aerospace and motorsports uses.
- Plastics: Low cost and weight. Easy to color match aesthetic applications. Not as strong but usable for light duty consumer products, electronics, etc.
In addition to material selection, surface treatments like anodizing, plating, painting or powder coating can enhance corrosion and wear resistance. This helps rivets retain optimal clamping force for the life of the product.
For CNC work, look for rivets that meet or exceed the following specifications:
- Diameter tolerance: +/- 0.001”
- Shaft straightness: 0.003” TIR per inch
- Head concentricity: 0.002” TIR or better
- Shear strength: At least 60% of tensile strength
- Hardness: H35 minimum for aluminum, H40 for mild steel
- Plating thickness: 0.0002” - 0.0004” for nickel, zinc, tin & copper
Reputable manufacturers will provide documentation confirming their rivets meet these benchmarks. Always review technical data sheets before purchasing.
Installation Best Practices
Properly installing CNC rivets requires care and the right techniques:
- Use the recommended drill size to produce holes with correct clearance
- Deburr holes thoroughly to ensure proper rivet seating
- Use a rivet gun with aligned jaws to prevent bending shafts
- Set force/impact energy should deform head adequately without damaging join
- Use rivet set with correct concavity to evenly form heads
- Set from the correct side for blind rivets to expand properly
- Ensure set rivets fill holes fully and heads are symmetrically formed
With quality rivets and proper installation, CNC machines can produce durable, long-lasting products. The right rivets maximize joint integrity and clamping strength while withstanding intense operating environments. Carefully selecting and sourcing rivets, confirming specifications, and following best practices will lead to success with your CNC riveting applications. CNC Milling