Rivets in Sheet Metal for CNC Applications(working of spring Walker)

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Rivets have long been a popular method of joining sheets of metal together in manufacturing. With the growth of computer numerical control (CNC) machining, riveting continues to play an important role in many sheet metal fabrication processes.
What are Rivets?
A rivet is a mechanical fastener that consists of two main parts - a smooth cylindrical shaft and a head. The shaft is inserted into pre-drilled holes in the materials being joined. The excess length of the shaft extends out the other side. The head comes in a variety of shapes like round, flat, countersunk, and more. As the rivet is driven into place using a riveting hammer, tool, or machine, the excess shaft material mushrooms out and forms another head. This creates a strong clamping force to hold the materials together.
Benefits of Rivets
Rivets offer many benefits that make them a popular choice for joining sheet metal in CNC applications:
- Permanent - Unlike screws or bolts, rivets cannot come loose over time which makes the joint more reliable. The mushrooming effect firmly locks the rivet in place.
- Strength - The mushrooming action creates a strong clamping force and friction. This leads to joints that can handle vibration and shock loads well.
- Quick installation - Rivets provide a fast way to assemble components. Automated riveting systems on CNC machines make the process even faster.
- Variety - With various head shapes and shaft diameters, rivets allow flexibility in design. Flush rivets can provide a smooth surface.
- Cost effective - Rivets are an economical choice compared to welding or using fasteners that require nuts/washers. Minimal tooling is required for installation.
CNC Riveting Methods
CNC machining opens up more possibilities for efficiently and accurately riveting sheet metal. Here are some of the common techniques:
- Robotic riveting - Articulated robots can be programmed to precisely place rivets and upset them. This automates a traditionally manual task for improved speed, quality, and repeatability.
- CNC rivet gun - These specialized tools mount to the CNC machine and can be programmed to automatically insert and upset rivets. Different sized rivets can be used in a sequence.
- Hole punch and rivet - Special CNC heads exist that can punch the hole and insert the rivet in one operation. This improves precision and reduces steps.
- Tool changer - For flexibility, a tool changer can be used to automatically switch between the rivet gun, hole punch, and other required tools.
- Automated feeders - Vibratory bowl feeders or tape feeders can supply rivets to the CNC machine and minimize downtime spent reloading.
Properly Designing Parts for CNC Riveting
To take full advantage of automated CNC riveting processes, parts should be designed with riveting in mind:
- Place rivets where shear and tensile stresses will occur to utilize their strength.
- Use multiple rivets in a pattern to distribute stresses if needed.
- Maintain clearance for rivet upset on the backside of the sheets.
- Include lead-in chamfers if accessible to aid rivet insertion.
- Specify flattened or countersunk rivets for flush surfaces if required.
- Make sure material is not too thick for the rivet length.
- Account for minimum edge distances based on hole diameter.
- Design parts so rivet heads are accessible for automated tools.
Rivet Selection
With many types of rivets available, important factors to consider are:
- Materials - Softer materials like aluminum are easier to rivet than harder materials like steel.
- Hole size - Clearance between the rivet and hole impacts strength.
- Grip range - The combined thickness of materials the rivet must clamp together.
- Shear/tensile strength needed - This determines the rivet diameter.
- Head style - Countersunk, round, flat, etc. based on design needs.
- Alloy - Different alloys provide various levels of strength.
- Plating - Zinc, titanium, colored, etc. coatings are options for corrosion resistance or aesthetics.
Proper selection helps utilize the unique advantages of rivets in CNC fabricated sheet metal assemblies.
In summary, with the precision and automation provided by CNC equipment, rivets continue to be a simple, reliable, and cost-effective choice for permanently joining sheets of metal. When the parts are properly designed and the rivets carefully selected, manufacturers can utilize CNC riveting to improve quality, throughput, and part consistency. CNC Milling