Riveting in Sheet Metal Fabrication with CNC(how to remove a broken tap Evan)

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Rivets have been used since ancient times to join pieces of metal together. While welding has become more popular for many applications, riveting is still commonly used, especially in sheet metal fabrication. The automation of riveting processes using CNC (computer numerical control) has increased precision and efficiency compared to manual riveting.
What is a Rivet?
A rivet is a mechanical fastener that joins materials by expanding when compressed. It is usually made of metal and has a head on one end and a shank on the other. The shank is inserted through aligned holes in the materials being joined and the head is mushroomed using a riveting hammer, press, or other tool. This deforms the shank and creates a second head, clamping the materials together. The rivet head can be various shapes like round, countersunk, or flush depending on functional and aesthetic requirements.
Common rivet types:
- Solid rivets - Made of a single material like steel, copper, aluminum, or titanium. Most common for general applications.
- Blind rivets - Have a built-in pulling mandrel. Allow riveting where only one side is accessible.
- Drive rivets - Have a pre-formed head and are driven by applying force to the shank rather than mushrooming the end. Used where high shear strength is needed.
- Self-piercing rivets - Can pierce through sheet materials without a pre-drilled hole. Used for soft or thin materials.
- Structural rivets - Used for high-stress applications like bridges, towers, and aircraft. Made from specialty alloys.
CNC Riveting Systems
CNC riveting machines provide computerized control of the entire riveting process for optimal quality, precision, and efficiency. Here are some common CNC riveting systems:
- CNC Riveting Cells: Rivet multiple components in a work cell. May include part fixturing equipment, rivet feed system, robotic arm for rivet placement, and rivet gun. Highly flexible and programmable for dynamic production jobs.
- Automatic Riveting Machines: Industrial machines that handle repetitive, high-volume riveting of the same components. Built-in rivet feeder and fast riveting head for rapid cycle times. Used for mass production.
- Multi-Axis Riveting Robots: Robotic arms capable of accessing confined spaces from any angle. Useful for aerospace or auto parts with complex geometry. Offers six degrees of freedom in motion.
- Orbital Riveting Systems: Use orbital riveting heads that rotate rather than reciprocate. Allow high speeds and even pressure distribution. Reduces hardware fatigue and damage.
- Astro Riveting Systems: Automated panel riveting systems for aircraft and aerospace components. Offer precision clamping and positioning of large panels for fuselage, wing, or tail assembly.
- Hot Riveting Systems: Heat rivets just prior to placement to improve fit and fastener strength. Critical for high-stress aircraft structures using specialty rivets.
CNC Riveting Process
The automated CNC riveting sequence generally follows these steps:
1. Material loading: Sheets or components to be riveted are loaded into a fixture that holds the parts in proper alignment. Robotic arms may be used to move materials into place.
2. Hole positioning: Optical systems, machine vision, or probes check existing holes or holes are precisely drilled in the parts by automated machinery.
3. Rivet selection & feeding: The required rivet type, size, and quantity are selected by the CNC program. Rivets are fed to the riveting head from a vibratory bowl feeder or tape reel.
4. Rivet insertion: The rivet is mechanically picked from the feeder and inserted into the hole by the riveting head.
5. Clamping: Parts are clamped together under pressure so that the rivet shank protruding from the bottom sheet is flush.
6. Hammering or upsetting: The rivet shank is upset using an orbital or reciprocating hammer to flare out the bottom, locking the rivet in place.
7. Quality inspection: Cameras, sensors, or testing equipment may verify proper rivet length, grip, strength, flushness, and other critical measures.
8. Part removal: The completed assembly is unloaded from the fixture by an operator or robotic arm. Fixtures are automatically reset for the next cycle.
For large aircraft assemblies, multiple riveting heads may work simultaneously on different areas guided by common toolpaths. The CNC program can be modified to adapt to new parts or riveting patterns simply by updating the input data.
Benefits of CNC Riveting
Transitioning from manual to CNC riveting offers manufacturers many benefits including:
- Increased throughput and production volume due to automated speed and continuous operation.
- Improved consistency and quality since machines rivet precisely the same way each time.
- Reduced dependency on specialized labor since machines perform the riveting tasks.
- Ability to rivet complex or difficult geometries by adding axes of motion.
- Flexibility to accommodate design changes by altering the CNC program.
- Lower per-part riveting costs and reduced waste.
- Better ergonomics and workplace safety with less heavy lifting or repetitive tasks required.
- Detailed production data for analytics, optimization, and maintenance.
While CNC riveting requires upfront investment and programming, it offers outstanding advantages for manufacturers doing sheet metal fabrication or any high-volume riveting applications. The automated precision and configurability of CNC provides both productivity and agility. As rivets remain integral to countless products, CNC allows leveraging their strengths in new ways. CNC Milling