Quality Rivets are Crucial for CNC Machined Parts(alloy steel Victoria)
- source:GAENOR CNC Machining
What are Rivets?
Rivets are mechanical fasteners used to join multiple pieces of material. They consist of a smooth cylindrical shaft and a head on one or both ends. The rivet is inserted into pre-drilled holes through the materials being joined. The tail end of the rivet is then deformed, usually by hammering or pressing, to flare out and clamp the materials together tightly. The flared end acts like a bolt head to securely hold the rivet in place.
Rivets have been used since ancient times to construct armor, buildings, ships, and machinery. Today, rivets remain a popular fastening method in many manufacturing industries, including aerospace, transportation, electronics, and more. Unlike screws or bolts, rivets form a permanent connection and do not loosen over time. Installation is also relatively quick and requires access from only one side of a joint. These qualities make rivets well-suited for automated installation by CNC machines.
Choosing Quality Rivets for CNC Machining
While rivets may seem like simple off-the-shelf hardware, not all rivets are created equal. For CNC machined parts and assemblies, it is important to select high-quality rivets matched to the design requirements. Here are key factors to consider:
Aircraft-grade aluminum is the most common rivet material for aircraft and aerospace applications due to its high strength-to-weight ratio. However, stainless steel, copper alloys like brass, and specialized materials like Monel or titanium may be used for enhanced corrosion resistance or to withstand high temperatures. The rivet material should be compatible with the underlying materials being joined to avoid galvanic corrosion.
Aluminum Alloy Grade
Aluminum rivets come in a range of different alloy grades numbered 1xxx to 7xxx, with varying properties. Higher grade aluminum alloys like 2117, 5056, 6061 offer improved strength for critical structural joints. Lower grades may be suitable for non-structural applications. Matching the alloy grade to the base materials ensures the rivet has adequate shear and tensile strength for the joint.
Rivets come in a range standard diameters, lengths, head shapes, and head heights to accommodate different material thicknesses. Precision aircraft rivets have tighter dimensional tolerances on shaft diameter, head height, and other parameters. Confirming rivet dimensions match the design drawings is critical so they seat properly in rivet holes. Using undersized or oversized rivets can compromise joint integrity.
Rivet heads are available in several standard styles, including round, brazier/universal, countersunk, and specialized aircraft heads. Selecting the head shape appropriate for the part design ensures a flush surface and avoids clearance issues. Countersunk heads are commonly used with CNC machined parts so rivet heads are flush with the surface.
Heat treating processes like solution heat treatment and artificial aging harden and strengthen certain aluminum rivets. Heat treated rivets have higher shear strength and bearing loads than non heat-treated rivets in the same alloy. Aerospace-grade rivets typically undergo proprietary heat treatments to optimize their mechanical properties.
The surface condition of the rivet shaft and head affects performance. Anodizing aluminum rivets provides corrosion resistance for long service life. Shot-peening induces beneficial residual stresses and removes defects from machining. Smooth, uniform finishes allow rivets to be inserted and set with minimal friction or galling.
Reputable rivet suppliers provide certification documentation confirming military or aerospace specifications, test reports, lot traceability, and quality systems audit results. Common standards include NASM, AN, MS, AS, BAC, and ISO 9001. Proper certification provides assurance of the rivet’s pedigree and reliability.
By selecting quality rivets designed specifically for the application, CNC machined parts will have optimal fastening strength and endurance. This attention to detail is well worth the effort for critical assemblies and mission-critical systems.
CNC Machining Processes for Installing Rivets
Modern CNC machining centers can be programmed to automatically insert and set rivets to assemble components. This saves enormous manual labor compared to hand riveting. Here is an overview of how rivets can be incorporated into CNC machined parts:
Drilling Rivet Holes
CNC machines use specialty drill bits to produce the holes that rivets are driven into. The holes must have a precise diameter slightly larger than the rivet shaft to allow it to pass through but tight enough to grip. Drilling orthogonal holes is ideal to maximize rivet strength, but angled holes are also possible. G-code controls hole location, depth, and diameter.
For flush rivets with countersunk heads, CNC counterboring using a machining center produces a conical recess around holes. This allows the rivet head to sit flush with the part surface. Countersinks give riveted assemblies a smooth exterior surface free of protruding fastener heads.
CNC machines can be loaded with rivet feeders or hoppers to supply rivets directly to the machine spindle for installation. Vibratory bowls, tubes, and robotic feeders are available. They orient and deliver rivets to the tool at high speeds so the machine does not have to stop between rivets.
The CNC machine inserts each rivet sequentially into the matching hole in the parts being joined by pushing it through with the machine spindle or rivet gun tool. Part fixtures hold the components being riveted in the correct alignment so holes line up accurately.
A riveting head on the CNC machine upsets the protruding rivet tail to clamp the rivet in place permanently. The pressure flares the tail and compresses the rivet, creating a strong joint. Rotary riveting heads allow any orientation. CNC riveting pressure, diameter, and duration must be dialed in perfectly.
Automated inspection checks for any missing or malformed rivets. Dimensional metrology and leak testing verifies rivet integrity and joint strength meet stringent tolerances for aircraft, medical, and other quality-critical applications.
By integrating riveting into the CNC machining program, all fastening steps can be completed in one automated setup with no need for secondary manual riveting. This improves quality, reduces labor cost, and boosts manufacturing productivity. However, the machine tool must have the appropriate capabilities and be carefully programmed for riveting to work seamlessly.
Applications of CNC Riveting
Riveting with CNC machines enables mass production of high-quality riveted products across many industries, including:
Aerospace: Aircraft fuselages, wings, tail sections and almost every major assembly are joined with thousands of rivets. CNC machining with automated riveting is vastly more efficient than manual riveting. It also improves quality for flight safety.
Transportation: Cars, trucks, buses, railcars, ships and recreational vehicles rely on rivets for body panels and internal structures. CNC riveting robots transform sheet metal into smooth-sided assemblies rapidly.
Construction: Steel I-beams, rebar, HVAC ducts, and exterior panels are commonly joined with rivets. CNC factory riveting of panels and trusses is faster and more consistent than hand riveting.
Electronics: Rivets assemble enclosures and chassis for computers, appliances, and instruments due to quick installation and electrical/thermal conductivity. CNC provides precision and efficiency.
Medical Devices: Surgical instruments, implants, tables, carts and medical hardware use CNC riveting for strong, sanitary bonding. Automation ensures high quality and reliability for patient health.
Automation: Robots, CNC machines, conveyors, and other industrial machinery rely on CNC riveted frames and links. Automated build processes improve production rates and endurance.
In all these cases, CNC machining with integrated riveting vastly outpaces manual processes in speed, quality, consistency, and cost-effectiveness. As riveting technology continues improving, CNC will take on an even greater role assembling mechanical components and products.
Quality Control for CNC Riveting
While CNC automation provides tremendous advantages, manufacturers must implement rigorous quality control practices for riveting processes:
- Inspect rivets upon receipt to ensure they meet specifications for dimensions, certification, surface condition, and defects. Reject any suspect rivet batches.
- Perform first article inspection to dial-in and validate CNC riveting programs on a pilot run before production. Verify joint quality.
- Include rivet parameters like hole depth, hole size, countersink dimensions, and upset force in statistical process control tracking.
- Monitor and maintain machinery regularly, replacing worn rivet tooling and inspecting for any mechanical issues.
- Conduct failure mode and effects analysis to identify possible riveting defects and their impacts on product safety/function.
- Implement procedures like leak tests, shear tests, torque checks, and dimensional inspection to confirm rivet joint integrity.
- Perform visual inspection of CNC-riveted products at multiple stages from in-process to final audit.
With vigilant quality control and the optimal choice of rivets, CNC machining can deliver exceptional riveted assemblies cost-effectively.
Rivets join materials in countless products across every industry. While deceptively simple, the quality and performance of rivets are critical to manufacturing success. By selecting premium rivets engineered for the application and automating installation using CNC machining, manufacturers can improve quality, reduce rework, and gain a competitive advantage. With continued advancement in riveting technology and CNC equipment, manufacturers can push the boundaries of efficiency and innovation. CNC Milling CNC Machining