The Importance of Using Quality Rivets in CNC Machining(galvanized vs galvanneal Molly)

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Rivets are an essential fastening component in many manufacturing and fabrication projects, especially those done with computer numerical control (CNC) machines. While rivets may seem insignificant, using quality rivets that meet required specifications is critical for the safety, durability, and performance of the finished product. Here is a look at why quality rivets matter in CNC machining and how to select the right rivet type and material for your application.
What are Rivets?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The rivet is inserted into pre-drilled holes in the materials being joined, and the tail end is upset, flattened, or bucked to form the second head. This creates permanent mechanical fastening.
Rivets come in different materials, types, head shapes, and sizes to meet strength, appearance, and installation requirements. Common materials include aluminum, steel, stainless steel, copper, and Monel. Popular types are blind rivets, solid rivets, and drive rivets.
Importance of Proper Rivet Selection
Using the right rivets is important for several reasons:
Strength and Durability: The rivet must be strong enough to withstand expected forces and loads on the assembly without failing or fatigue over time. This depends on the rivet material properties, diameter, and design.
Fit: The rivet shaft and head dimensions must match the hole size specifications in the base materials. A properly fitting rivet maximizes strength. Loose or too tight rivets can compromise the joint.
Appearance: For exposed rivets, head shape and finish may matter for the visual aesthetics of the final product. Using rivets with matched finishes gives a consistent look.
Ease of Installation: The rivet must be easy to install correctly either manually or with automated tools. Rivet driving forces, accessibility, and technique needs to be considered.
Corrosion Resistance: If riveted materials will be exposed to weather, water, chemicals, or high temperatures, the rivet material needs to resist corrosion and environmental degradation.
Using inferior or incorrect rivets can lead to mechanical joint failure, leaks, misalignment, increased wear and tear, and poor product performance or life.
Quality Rivets for CNC Machining
CNC machined parts are commonly joined together with rivets because they can be accurately located and fast installation is possible. Here are tips on selecting quality rivets for CNC projects:
- Choose reputable branded rivets that meet established standards like AN, NAS, or MS. These have certified material and dimensional properties.
- Match the rivet head type, hole size, material strength, and grip range to the application requirements and assembled materials. Consider factors like sheet thickness, joint stresses, corrosion risks, and precision needs.
- For structural joints, aerospace-grade and other high-strength rivets are recommended to withstand vibration, shock, and fatigue.
- Select rivet finishes like anodizing or passivation that prevent galling and minimize friction during installation.
- Consult rivet manufacturer technical guides for proper hole sizing, grip range, and driving recommendation to get optimal performance.
- Carefully check rivet certification sheets to verify all specifications are met, including head style, material, heat treatment, hardness, and dimensions.
Quality rivet selection, handling, and storage helps prevent problems like jamming in automated rivet feed systems or issues during installation.
Automated Riveting With CNC Machines
One of the key advantages of using CNC machining for riveted assemblies versus manual fabrication is the ability to automate fastener insertion for quality and efficiency benefits.
Pre-drilling holes and precisely driving rivets with CNC tools ensures consistency in hole size, placement, and rivet seating. This gets optimal clamping force. Robotic arms equipped with special rivet guns can access hard to reach or dangerous installation sites.
Programmed riveting parameters control variables like insertion speed, force, and hammer impact that determine joint strength. Automated vision systems can inspect every rivet after installation for defects.
CNC machines can handle many different rivet types and sizes used across aerospace, automotive, electronics, appliances, and other fabrication industries.
Common automated riveting techniques include:
- Impact Riveting: A hammering rivet gun forces the rivet into the hole and uses impacts to flare the tail. Best for solid rivets in softer materials.
- Orbital Riveting: Uses a hydraulically-powered orbital head to buck the rivet precisely and powerfully for strong consistent joints. Ideal for aerospace grade rivets.
- Radial Riveting: Exerts riveting force from the sides along the rivet shaft with rollers. Allows better access in confined spaces.
- Specialized systems for blind rivets, lockbolts, and other fastener types.
With CNC-controlled automation, riveting can be done much faster, more reliably, and with higher total quality control compared to manual processes.
Inspection and Testing of Riveted Joints
To ensure riveted CNC-machined products meet the design intent, finished assemblies must be inspected, tested, and validated. Some practices include:
- Dimensional Inspection: Confirm rivet head and shank dimensions are within tolerance using optical comparators, coordinate measuring machines, or automated vision systems. Verify hole locations and spacings.
- Joint Sectioning: Destructive cross-sectioning and microscopy of riveted joints reveals internal defects like cracks or poor rivet flaring.
- Tensile Testing: Measures the failure force of riveted samples when subjected to tension loading. Indicates if joint strength meets requirements.
- Vibration Testing: Assesses rivet and joint integrity when exposed to vibrations expected during product use. Loosening or fractures mean the joint does not withstand dynamic loads.
- Pressure and Leak Checks: Validates riveted seams or enclosures can contain internal pressures without leakage, seepage, or rivet popping. Critical for pipes, tanks, and vessels.
- Non-destructive Testing: Methods like radiographic, ultrasonic, and thermographic inspection locate voids, gaps, or subsurface flaws in riveted joints.
The quality control validation data collected ensure optimal rivet selection and CNC riveting processes deliver repeatable and robust joints that function safely over the product lifetime.
From aircraft fuselages to appliances and machinery, quality rivets are a small but vital component in CNC machined assemblies. Choosing the optimal rivet design along with automated precision riveting enables manufacturers to produce strong, reliable, and durable riveted products efficiently. Careful rivet planning, process control, inspection, and testing creates robust permanent joints that withstand wear, pressure, impacts, and years of use. Investing in quality rivets ensures the integrity and performance of the end product. CNC Milling CNC Machining