Riveting in Sheet Metal Fabrication(cnc g and m codes Sara)
- source:GAENOR CNC Machining
To install rivets, holes are drilled or punched into the sheets being joined. The rivet body is inserted into the holes and the mandrel stem protruding through the rivet body is gripped by a rivet gun and pulled, upsetting the unformed head into a second head and clamping the sheets together.
There are several types of rivets used in sheet metal fabrication:
These are one of the most common types of rivets. They are made of malleable steel and have the mandrel stem attached to the rivet body. As the mandrel is pulled by the rivet gun, it breaks off at the breakpoint, leaving the deformed rivet body behind to fasten the sheets. Drive rivets produce a very tight fit but can only be used where the rear of the rivet is accessible.
As the name suggests, these rivets can be installed where only one side of the work is accessible. Blind rivets have the mandrel stem threaded into the body rather than attached. As the mandrel is drawn into the rivet body, it folds the body material outward to form the second head. The mandrel threads fracture when the rivet fully sets, leaving only the body in place. Blind rivets are also used with access to both sides when a flush finish on both surfaces is desired.
This specialized rivet combines piercing and riveting in one operation. The rivet has a semi-tubular head that pierces the top sheet and interlocks into the bottom sheet as the head flares outward. Installed using a rivet gun, self-piercing rivets don't require pre-drilled holes, eliminating many steps in assembly. They produce a fast joint with good shear strength. Self-piercing rivets are ideal for joining dissimilar or multi-layer materials.
Pop rivets consist of a rivet body and mandrel stem that is connected with small rings rather than being threaded. The mandrel has a spherical head that pops off at the breakpoint after installation. Pop rivets are commonly used in light duty consumer products and assemblies where occasional rivet replacement may be necessary.
Engineers should consider several factors when selecting the right type of rivet for an application:
- Material - Rivet material should match or be compatible with the base materials. Steel, aluminum, copper, and monel rivets are common.
- Strength - The rivet should be strong enough to withstand expected forces without failing. Mechanical properties are critical.
- Head style - Rivet heads come in many styles like round, flat, countersunk, large flange, etc. Choose a shape suitable for the design.
- Access - Is blind or through rivet installation required?
- Process factors - Consider assembly methods, automation, and quality control.
- Cost - Weigh rivet cost versus alternatives like welding, adhesive bonding, or screws.
Riveted Joint Design
Properly designing riveted joints is crucial for strength and durability. Guidelines include:
- Spacing - Rivets should be spaced 3-4 diameters apart in rows and columns. Closer spacing is required around plate edges.
- Edge distance - Rivets should be 1.5-2 diameters from plate edges. More distance reduces edge tearing.
- Staggering - Offset adjacent rows to equalize stress distribution in the joint.
- Number - Adding more rivets spreads force over a wider area. But too many rivets can also weaken the assembly.
- Hole fit - Hole diameter should match the rivet body size. Tight holes provide precision while loose holes allow minor adjustment.
The main steps in riveting sheet metal components are:
1. Planning - Designers plan the rivet pattern, hole locations, sizes, and types. Drawings and specs are created.
2. Fabrication - Sheets are cut to size and holes created by punching, drilling, laser/waterjet cutting.
3. Deburring - Holes are deburred to ensure flush fit-up of mating surfaces.
4. Assembly - Components are assembled and temporarily clamped.
5. Rivet installation - Rivets are inserted into holes and upset using manual or auto rivet guns.
6. Inspection - The quality team verifies rivet length, grip, tail height, and any cracks.
7. Rework - Any defective rivets are drilled out and replaced to meet standards.
Stringent quality control ensures optimal riveted joint integrity:
- Rivet hardness and mandrel integrity are checked to prevent premature failure.
- Rivet tails are examined for acceptable protrusion and symmetry.
- Joints are visually inspected for cracks starting from holes.
- Parts are matched drilled for hole alignment.
- Operators are trained on proper rivet gun use and maintenance.
- Downward pressure is applied to sheets when riveting to minimize curling.
- Fixtures are used to hold parts in alignment if needed.
Troubleshooting Riveting Issues
Common challenges when riveting sheet metal and solutions include:
- Loose rivets from inaccurate gun pressure - Adjust pressure settings and inspect worn parts.
- Offset or uneven rivet sets - Ensure gun is perpendicular to work, proper ventilation, and nose pieces are in spec.
- Rivet snaps/breaks - Increase rivet hardness or diameter. Check for burrs interfering with insertion.
- Hole misalignment - Use precision drilling, proper fixturing, or match drilling.
- Rivet bending/rotation - Increase rivet-to-hole tolerance. Center punch holes before drilling.
- Hole elongation - Increase distance from hole edges. Reduce the number of rivets.
- Top sheet cracks - Use softer/more malleable top sheet material or add washers under rivet heads.
Riveting remains a trusted method for assembling sheet metal components across countless industries. With sound joint design principles and proper control of fabrication and installation processes, engineers can rely on riveted connections to provide robust mechanical fastening in their products. CNC Milling CNC Machining