Making High Quality Rivets with CNC Machines(how to rivet sheet metal Kevin)
- source:GAENOR CNC Machining
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 excess shaft is then upset, or deformed, to form the second head. This creates a solid rivet tightly clamping the materials together.
Rivets come in many sizes, shapes and materials to accommodate different applications and material thickness. Common rivet materials include aluminum, steel, copper, stainless steel, titanium and monel. The most popular head styles are round, countersunk and brazier.
Benefits of Rivets
Rivets offer unique benefits over other fasteners:
- Permanent - Once installed, rivets cannot come loose over time. This makes them ideal for critical structural joints.
- Vibration resistant - Riveted joints can withstand vibration better than threaded or bolted joints.
- Strength - Well-designed riveted joints are very strong and can handle shear and tensile loads.
- Lightweight - Rivets add little weight versus other fastening methods. This makes them perfect for aircraft and transportation applications.
- Quick installation - Riveting is generally faster than welding or bolting. Automated riveting is extremely quick.
These qualities make quality rivets highly desirable across many industries, including aerospace, shipbuilding, construction, automotive, electronics and more.
CNC Machines for High Quality Rivet Manufacturing
Producing flawless rivets requires precision machining and consistency across thousands of parts. This is where CNC machines provide major advantages over manual fabrication techniques.
CNC machining uses computer-controlled tools to automate the machining process. Programmers can write G-code to instruct the CNC machine exactly how to manufacture each rivet perfectly and identically. The basic CNC rivet making process involves:
- Starting with rivet blank material - usually rods or wires of the desired rivet material. Common sizes range from 1/16 to 3/4 inches in diameter.
- Facing off the end of the blank in a CNC lathe to square it up.
- Drilling the precise hole size through the center of the blank with a CNC drill or lathe.
- Using a CNC lathe to turn down the blank and form the rivet head profile and shank.
- Utilizing CNC milling to cut the rivet head shape, such as domed, countersunk or flat.
- Tapping or upsetting the drilled shank to form the second head and finish the rivet. Multi-spindle CNC machines allow high volume heading.
- Automated feeding and collection of rivet blanks and finished rivets with the use of tubes, hoppers, tracks and robots.
Programmable CNC instructions control every step to micron-level accuracies. This removes variance and ensures each rivet comes out identical. Diameters, head dimensions, chamfers, undercuts and more are created perfectly across production runs.
Automated production enables manufacturers to make thousands of rivets per hour compared to far slower manual methods. Together, this precision and speed ensure the highest quality and efficiency.
Optimizing Rivet CNC Programs
To get the best results, CNC programmers must optimize rivet machining programs. Key factors include:
- Utilizing the best tooling - Carbide and PCD cutters stay sharp longer for clean, consistent cutting.
- Proper toolpaths - Optimal feeds, speeds and stepovers avoid tool deflection and chatter.
- Efficient order of operations - Program the sequence of turning, milling and drilling to maximize cycle times.
- Minimizing air cuts - Position multiple operations in one setup to reduce rapid movements.
- Rigid setups - Clamp blanks firmly to avoid vibration and runout. Use short, rigid tooling.
- Fixture automation - Quick-change collet blocks, pallet shuttles and gantry loaders streamline changeovers.
- In-process inspection - Probe finished dimensions and track tool life real-time to nip any issues.
- Post-process automation - Automate rivet unloading, inspection and packaging for a hands-off process.
With attention to these parameters, manufacturers can optimize CNC cycle times while maintaining quality standards.
Rivet Production Materials
Choosing the best blank material is crucial for performance and manufacturability. Common materials include:
- Aluminum - Lightweight, strong and corrosion resistant. Easy to machine and form heads. Popular for aircraft and hardware. 6061 alloy is very common.
- Steel - The strongest and most durable option. Usually low carbon 1018/1020 or alloy steel. Used for high strength applications. Prone to corrosion if not plated.
- Stainless steel - Offers good strength without corrosion issues. More difficult to machine and upset than other steels due to work hardening. 304 and 316 are standard grades.
- Copper and brass - Decorative appearance and excellent conductivity. Can cold flow over time, limiting use for structural joints.
- Monel - Superalloy nickel-copper blend with strength, toughness and corrosion resistance. Biocompatible. Costly but ideal for marine and chemical.
- Titanium - Extremely strong yet lightweight. Excellent corrosion resistance. Challenging to machine and used primarily in aircraft or critical joints.
Manufacturers select materials to meet strength, appearance, conductivity, cost and environmental needs. Hardness also impacts machining - annealed temper is easiest to work for most metals.
Inspection and Testing
To verify rivet quality, manufacturers at minimum test dimensions, hardness, tensile strength and head integrity according to applicable specs such as ASME, MIL-SPEC or ISO. Typical inspection and tests include:
- Dimensional inspection - Confirm diameters, lengths, head styles and other dimensions are within tolerance using optical comparators, CMMs or other metrology tools.
- Rockwell hardness testing - Ensure hardness falls within specified range. Important for machinability and final strength.
- Tensile testing - Pull test rivets in tension to validate shearing and tensile strength meet requirements.
- Microstructure analysis - Check for proper grain structure and absence of flaws using imaging techniques.
- Head tests - Confirm proper head formation by measuring upset and conducting destructive shear tests.
- Salt spray testing - Evaluate corrosion resistance by exposing samples to salt fog for a set duration.
- Sample lot testing - Audit random samples from production runs to confirm continued quality.
By thoroughly inspecting and testing, manufacturers can guarantee the strength, longevity and reliability of their rivets for customers.
Quality rivets are crucial for binding materials securely across countless critical applications. CNC machining delivers unparalleled precision and consistency in high volume rivet production. With optimized programs and rigorous inspection, manufacturers can deliver perfectly-formed rivets to safely join products for years to come. CNC Milling CNC Machining