Producing High Quality Rivets with CNC Machines(alloy steel vs stainless steel Erin)
- source:MAJA 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 holes that are drilled or punched into the materials being joined. The rivet is then deformed to create a permanent joint.
The shaft of the rivet fills the hole and the head is flattened against the material surface. This creates a solid riveted connection that can withstand tremendous shear and tensile forces. Rivets are commonly used to assemble aircraft, bridges, ships, railroads, and many other high-stress applications.
Benefits of CNC Machining for Rivet Production
CNC (computer numerical control) machining utilizes programmed computer controls to operate machine tools like lathes, mills, routers, grinders, and drills. For rivet manufacturing, CNC technology offers the following advantages:
- High Degree of Accuracy and Consistency: CNC machines allow for precision control of cutting tools, enabling extremely accurate and consistent rivet fabrication. Tight tolerances of +/- 0.005 inches or better can be held. This level of consistency is difficult to achieve with manual machining.
- Automated Operation: Once programmed, CNC machines can operate unattended for long periods. Automated CNC production boosts output, reduces labor costs, and frees up personnel for other tasks.
- Quick Changeover Between Jobs: CNC programs can be readily altered to switch rivet dimensions or adjust parameters. This allows flexible, economical batch production. Setup and changeover times are minimized.
- Complex Geometries Possible: CNC tools can produce rivets with complex or asymmetric shafts and heads. Special profiles and geometries are programmable.
- Scalable Production: CNC riveting lines can be expanded by adding machines. This cost-efficient scalability enables high volume production to meet demand.
Programming and Operating CNC Riveting
Programming CNC riveting involves using CAD software to design the rivet geometry and CNC code generation software to translate dimensions into machine instructions. Key programming steps include:
- Design the rivet shaft and head profile
- Select tooling like carbide drills, mills, and lathe bits
- Specify feed rates, spindle speeds, depth of cuts, and other parameters
- Optimize tool paths for efficiency
- Input coordinates, commands, and tags to drive the CNC machine
- Simulate program execution to visualize results
- Debug and refine code to eliminate errors
Skilled CNC machinists then take over to physically set up the equipment and oversee the production run. Operators install cutting tools, fixture blank rivet wire or bar stock, set part coordinates, and execute the program. Throughout the run, the CNC system precisely guides the tools to shape each rivet per the programmed specifications. Operators monitor the process and perform any needed adjustments.
CNC Machines for Rivet Production
There are several types of CNC machines well-suited for rivet manufacturing:
- CNC Lathe: Turns rivet blanks from bar stock. Produces the cylindrical rivet shaft.
- CNC Milling Machine: Mills rivet heads using a rotating endmill tool. Allows intricate head profiles.
- CNC Drill Press: Accurately drills the rivet shank hole to accept the rivet shaft.
- CNC Router: Can form specialty groove patterns on rivet shanks for unique installation methods.
- CNC Grinder: Finishes and polishes rivet shafts to a smooth, uniform surface.
- CNC Thread Roller: Rolls threads onto rivet shanks providing strong, precise, rotary fastening.
- CNC Fabrication Center: An integrated, multi-function CNC system that can drill, mill, turn, thread, tap, form - completing all rivet machining in one setup.
These versatile CNC units, aided by robotics and handling systems, can be adapted into automated riveting production lines.
Inspecting CNC Rivet Quality
To ensure high standards, CNC-fabricated rivets should pass several inspections:
- Dimensional Accuracy Inspection: Rivert diameters, head thicknesses, lengths, chamfers, etc. are measured against specifications using optical comparators, CMMs (coordinate measuring machines), or other precision tools.
- Surface Finish Inspection: The rivet surface is examined for flaws like pits, scores, cracks, or uneven tool marks which can weaken the rivet. Visual and tactile methods may be used.
- Hardness Testing: Rockwell and Brinell hardness testers confirm that rivet heads and shanks meet the required hardness. Hardness correlates with rivet strength.
- Proof Testing: Sample rivets are loaded in a tensile test machine to verify that the rivet design withstands expected forces. Proof testing confirms strength.
- Mass Spectrometry: Chemical composition of the rivet materials is analyzed to certify conformance with required alloys like steel, aluminum, titanium, etc.
Automated visual inspection systems can also check for surface defects and dimensional deviations from preset standards. The resulting quality data aids continuous CNC process improvement.
Riveting Technology Continues to Progress
While solid riveting fundamentals endure, CNC and other technologies are advancing fabrication techniques. Some newer trends include:
- In-die riveting presses to replace manual hammering for installed rivets
- Pneumatic, battery powered, and electric rivet tools for portability
- Special aluminum and hybrid rivets combining steel and composites
- Bucking bar stabilizers for handheld rivet guns
- Robotic riveting stations for enhanced automation
- servo-electric presses for precision squeeze riveting
- Computer-controlled direct riveting for aerospace assemblies
- Vision-guided robots that can locate holes and insert rivets
- Specialty fasteners like self-piercing rivets that cut through materials
With CNC machines producing optimized rivet designs, parallel innovations in installation processes, and advanced quality control, the future of riveting looks strong. By leveraging technology, manufacturers will keep improving this venerable fastening method. CNC Milling CNC Machining