Quality Rivets: A Key Component in CNC Manufacturing(what is a casting Mamie)
- source:ESKRIDGE CNC Machining
What are Rivets?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. Rivets are inserted into pre-drilled holes through the materials being joined, and the protruding end is then upset, or flattened to form the second head. This creates a permanent mechanical joint by clamping the materials together. Rivets come in a variety of sizes, materials, and head styles to accommodate different design needs and installation methods.
Common types of rivets include:
- Solid rivets - made entirely from a single material like steel, aluminum, or titanium. Used for high strength applications.
- Blind rivets - tubular rivets designed to be installed from one side without access to the back. Common in aircraft and appliance manufacturing.
- Drive rivets - designed to be installed using powerful hydraulic or pneumatic tools for very high clamping forces.
- Self-piercing rivets - creat their own hole during installation so pre-drilling is not required. Popular for cars, trucks, and buses.
- Structural rivets - large heavy-duty rivets for critical load-bearing joints like bridges, cranes, or transmission towers.
Benefits of Rivets in Manufacturing
Rivets provide a number of benefits that make them a favored fastening method in high-volume manufacturing:
- They can be installed very quickly by automated equipment for high productivity. Hundreds of rivets per minute can be driven by CNC-controlled machinery.
- The joint clamping force can be tightly controlled through precision drill diameters and rivet length selection. This ensures consistent quality.
- Heads are formed uniformly for an attractive appearance on visible surfaces.
- Disassembly for repair or modifications is straightforward by drilling out the rivets if required.
- Riveting applies compressive force to join materials, unlike screws or bolts which produce shear or tension stress. This makes riveted joints highly resistant to shock, vibration, and fatigue loads.
- Installation only requires access to one side of a joint for most rivet types like blind rivets. This facilitates assembly of complex or enclosed structures.
- Riveting tools are relatively inexpensive and versatile for low start-up costs.
CNC Riveting Processes
Computer numerical control allows riveting operations to be precisely automated for mass production. Here are some typical CNC riveting methods:
Drilling - CNC machining centers use high-speed drills to produce holes optimized for each unique rivet diameter and material stack-up. This ensures consistent quality and strength.
Driving - Pneumatic rivet guns or hydraulic squeezers on the CNC machine insert rivets into the pre-drilled holes and upset the tail to form the second head. Multi-axis capabilities allow access at various angles.
Inspection - Machine vision systems can check hole quality and rivet head geometry to validate proper installation after driving.
Feeding - Vibratory bowl feeders orient and deliver rivets to the driving tooling for hands-off operation. Robotic pick-and-place systems are also used.
These automated processes enable thousands of rivets to be installed per hour with minimal operator intervention for productivity and consistency. Programming flexibility also allows for different rivet patterns, locations, and sequences tailored to each part number.
Factors in Rivet Quality and Selection
To achieve maximum performance in CNC riveting, quality rivets designed for automated installation should be used. Here are key factors to consider:
Size Consistency - Precise rivet diameters allow consistently snug holes fits for optimum clamp force. Variations will result in loose or overly tight rivets.
Material - Aircraft grade aluminum is ideal for strength, corrosion resistance, and formability. Steel, titanium, nickel alloys, or specialty materials may be required depending on application needs.
Head Styles - Button, round, flat, countersunk, or custom head shapes may be needed. Machine heads should be precise and free of defects that could mark finished products.
Grip Range - Various rivet lengths must be on hand to accommodate different material stack ups. Minimum and maximum grips should be confirmed.
Lot Traceability - Detailed manufacturing records for each lot provides traceability in the event of defects and assists with quality control.
Special coatings and post-treatments like anodizing are also available for unique requirements like conductivity, lubricity, or color-coding. Consulting with rivet suppliers during design can ensure optimal rivet selection and sourcing for each application.
Inspecting Rivet Quality
To confirm incoming rivets meet specifications, several inspections should be performed:
1. Dimensional checks - Sample rivets should be measured to validate head, shank, and grip lengths are within tolerance. This can be done using digital calipers, optical comparators, or CMMs.
2. Material verification - Certificates of compliance from the manufacturer are necessary to confirm proper material composition. Additional testing like chemical analysis or hardness checks may be warranted.
3. Surface defects - Visually inspect for dents, cracks, scratches, discoloration, or other flaws on a sample of rivets. Check head markings for legibility.
4. Crimp grip tests - Manually crimp sample rivets at minimum, middle, and maximum grip lengths specified to validate hole fit and crimp quality across the grip range.
5. Installation trials - Test run production riveting processes with samples to confirm quality before full production. Check for head defects, improper upset, loose fits, etc.
Proper documentation and record keeping of these quality inspections provides oversight to ensure each rivet shipment conforms to requirements. This helps prevent production issues or rework down the line.
Optimizing Rivet Quality for CNC
Close coordination between the end user and rivet supplier is key to optimizing rivet selection and performance in CNC machinery. Here are some best practices:
- Share detailed product designs and specs like materials, stack-ups, and quality needs with prospective rivet suppliers during the quoting process. This allows them to recommend the best rivet type and geometry for your specific application.
- Request samples during prototyping to test the recommended rivets using your actual machines, tools, and processes. Provide feedback to the supplier on any quality or performance issues observed.
- Define inspection criteria and quality documentation requirements upfront so the supplier can implement appropriate checks before shipment. Statistically sampling larger lot sizes is preferred.
- Start with a small pilot order to confirm the production riveting process works smoothly before committing to a full production run.
- Audit supplier operations periodically to ensure quality standards are maintained over time. Review manufacturing records and measure key rivet dimensions on sample shipments.
- Provide ongoing feedback to suppliers on any quality deviations observed in production to drive continuous improvement. Share suggestions on potential root causes.
- Consider long term agreements or blanket orders with suppliers to better forecast demand, enable JIT delivery, and reduce per-unit costs.
With close communication and collaboration between end users and quality rivet suppliers, CNC machinery can achieve maximum uptime, quality, and productivity. Investing in optimized, purpose-made rivets tailored for automated processes is a wise choice to minimize manufacturing defects and rework. CNC Milling CNC Machining