Riveting in Sheet Metal Fabrication with CNC(overmold Baldwin)
- source:GAENOR CNC Machining
What is a Rivet?
A rivet is a mechanical fastener that joins two or more pieces of material by passing a shaft through aligned holes in the members to be joined. The rivet shaft has a head on one end that is larger than the hole, while the other end is tail that is deformed after insertion to secure the rivet in place. When the tail is flattened against the material, it creates a second head that holds the rivet tight.
The most common types of rivets used in sheet metal fabrication are:
- Solid rivets - made entirely from a single material like steel, aluminum, copper, or titanium. The rivet shaft and head are one solid piece.
- Blind rivets - have a hollow tubular shaft that is inserted into a pre-drilled hole. A stem inside the shaft is then pulled to flare out the tail into a second head.
- Self-piercing rivets - can pierce through stacked sheets of material without the need for pre-drilled holes. Often used for joining dissimilar metals.
- Drive rivets - have undersized pre-drilled holes, and the force of driving the rivet expands the hole to fit the rivet snugly.
Benefits of Riveting vs. Welding
While welding permanently fuses two pieces of metal together, riveting creates a mechanical fastening that can allow more movement or vibration between parts. Riveting also has benefits over welding that make it ideal for many sheet metal applications:
- Does not melt or weaken the base material like high heat welding
- Allows dissimilar metals to be joined
- Lower skill level required compared to precision welding
- Portable riveting tools allow repairs in the field
- Rivets can be removed if needed for repairs or modifications
- Creates smooth surface without burred edges or welding spatter
For these reasons, riveting is commonly used in aircraft and automobile manufacturing, HVAC ductwork, building facades, furniture, and other sheet metal fabrication.
CNC Riveting Process
Historically, riveting in manufacturing has been a manual process requiring workers to mark hole locations, drill holes, insert rivets, and buck each rivet tail one at a time using hand tools. This was a labor intensive and low productivity process.
With CNC riveting machines, the process is automated for higher quality and volume riveted assemblies. The basic CNC riveting process involves:
Sheets or parts to be riveted are loaded into a jig or fixture that holds the components in the proper alignment. Vacuum pads may hold sheets in place during riveting.
The CNC machine will use a drill bit to create the rivet holes at the coordinates programmed into the control software. This ensures fast, accurate, and repetitive hole placement.
An automated feeder supplies rivets directly to the nose assembly where they are inserted into the pre-drilled holes. Feed rates of up to 5 rivets per second are possible.
As the rivet is held in place by the nose, a rivet set directly behind it presses against the rivet tail, flattening and spreading it to form the second retaining head. This may be done with spinning roller sets or reciprocal hammering sets.
Vision systems, sensors, and CNC program logic can be used to inspect each rivet for head profile, material deformation, and final height after setting. Any defects can be flagged to the operator.
Benefits of Automated CNC Riveting
Transitioning from manual to CNC riveting provides many benefits for manufacturers when riveting sheet metal and components:
- Dramatically increased productivity and output volumes
- Improved consistency and quality compared to manual process
- Ability to control and finely adjust rivet feed rates, hole sizes, and setting force
- Integration of drilling, riveting, and inspection into one automated cell
- Flexible enough for low or high production volumes
- Reduced rework and scrap rates
- Safer working conditions by removing workers from repetitive tasks
- Programming allows rapid set up changes for new riveting patterns
- Digital documentation of the entire fabrication process
With CNC controlled automation, riveting remains a practical and versatile fastening method for modern sheet metal manufacturers. The efficiency and precision of automated riveting machines make it an appealing modern alternative to manual fabrication processes. By understanding the workings and benefits of the automated riveting cell, manufacturers can improve productivity and quality. CNC Milling CNC Machining