What is a Rivet?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. To install a rivet, the shaft is inserted into pre-drilled holes in the materials being joined. The rivet is then deformed on the opposite side, forming a second head that compresses the materials together. This creates a permanent, solid riveted joint.
Rivets come in a variety of styles, sizes, and materials. Common types include solid rivets, semi-tubular rivets, blind rivets, and drive rivets. The type of rivet selected depends on factors like joint strength needs, materials being joined, installation access, and cost.
Key Properties of Quality Rivets
So what makes for a quality rivet suitable for CNC machining applications? Here are some of the most important properties to look for:
Consistent Dimensions: Quality rivets have highly consistent shaft diameters and head dimensions. This allows for precision installation and uniform clamping force. Variations in rivet sizes can lead to poor fit, altered joint stresses, and reduced strength.
High Shear and Tensile Strength: The rivet must be strong enough to withstand shearing and tensile stresses without failing. Higher strength alloys and heat treatments are used to maximize rivet strength. Strength will be matched to the design loads of the joint.
Ductility: Ductile rivet materials like aluminum and mild steel can deform during installation. This allows the rivet to fill holes completely and form a tight joint. Brittle materials may crack or fracture instead of deforming.
Corrosion Resistance: Rivets should resist corrosion and environmental degradation. Coatings, platings, weather-resistant alloys, and passivation can improve corrosion resistance for harsh operating conditions.
Fatigue Resistance: Fluctuating loads over time can fatigue and fracture rivets. Quality rivets made from materials like stainless steel have high fatigue strength and resistance.
Manufacturing Quality Control: Reputable rivet manufacturers have tight quality control over production processes, raw materials, heat treating, finishing, and dimensional tolerances. This results in consistent quality batch-to-batch.
Rivet Material Options
Rivets are available in a wide selection of materials to suit different performance needs and operating environments:
Aluminum: Lightweight, readily available, and highly corrosion resistant, aluminum is a common rivet material. Grades like 2117 and 7075 offer high strength.
Steel: Strong, durable, and inexpensive, carbon steels like 12L14 and 11L17 are popular rivet choices. They can be heat treated for added strength. Stainless steel offers the highest strength and corrosion resistance.
Copper: Due to its ductility and fatigue resistance, copper is an excellent choice for rivets in vibration-prone environments. It also has good corrosion resistance.
Titanium: Extremely strong yet lightweight, titanium rivets provide the ultimate in high strength-to-weight ratio performance. The aerospace industry frequently uses titanium rivets.
Nickel Alloys: Nickel-based superalloys like Monel and Inconel are very strong and withstand high temperatures and corrosion. Mainly used in extreme environments.
Plastics: Light duty plastic rivets have good corrosion resistance and electrical/thermal insulation properties. Not suitable for structural joints.
The finish applied to the rivet also matters for both appearance and function:
Unfinished: No coating applied, resulting in a natural metal appearance and lower cost. Provides no corrosion protection.
Zinc Plating: Thin zinc coating applied electrochemically for corrosion protection and lubricity during driving. Silver or yellow color.
Cadmium Plating: Now phased out due to toxicity, but provided excellent corrosion protection. Often replaced with zinc-nickel.
Anodizing: Anodized aluminum resists corrosion, galling, and has color tinting ability. Hard anodizing further increases abrasion protection.
Painting: Organic paint coatings in various colors provide good corrosion resistance plus ability to color code. May chip over time.
Passivation: Chemical treatments produce a thin, transparent protective oxide layer on stainless steel. Improves corrosion resistance.
Choosing Quality Rivets for CNC
Here are some key steps to select the optimal rivet type, size, material, and finish for your CNC machined components:
1. Evaluate joint strength needs - shear, tensile, vibration/fatigue loading. Also desired service life and safety factors.
2. Determine the materials being joined - thicknesses, strengths, potential galvanic corrosion if dissimilar.
3. Consider the service environment - temperature, humidity, salt spray, chemicals, UV exposure, etc.
4. Choose candidate rivet materials capable of meeting structural, environmental, and assembly needs. Lean on rivet manufacturer expertise.
5. Select rivet type and size to suit joint geometries, grip lengths, and installation access. Consider processing impacts.
6. Specify rivet finishes that provide needed corrosion protection and color coding/identification ability.
7. Review rivet manufacturer data sheets and test reports to validate specs match your requirements. Ask for samples to test further if needed.
8. Perform test assemblies and qualification testing to confirm selected rivets produce a robust joint. Refine as needed.
The combination of advanced high-performance materials and computer-controlled precision make today’s CNC machined parts better than ever. But realizing the full quality and durability potential of your designs requires choosing the right rivets for the job. Investing in quality rivets matched to your specific needs will pay dividends with parts that last. CNC Milling