Riveting in Sheet Metal Fabrication(melting point cast iron Kerr)
- source:MAJA 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. The shaft is inserted into holes that have been pre-drilled in the materials to be joined. The excess length of the shaft extends out the opposite side. The head comes in a variety of shapes that are forged onto one end of the shaft. As the rivet is driven using a riveting hammer or squeezed using a rivet gun, the excess shaft material mushrooms out to form a second head, permanently joining the rivet within the holes. This process is called riveting.
Types of Rivets
There are several types of rivets used in sheet metal fabrication:
- Solid/Round Head Rivets: As the name suggests, these have a solid, rounded head. They are one of the most common types used for sheet metal.
- Countersunk Head Rivets: These have a flat, tapered head that sits flush with the surface of the metal. This gives a smooth finished look.
- Brazier Head Rivets: These have a shallow cone-shaped head that is slightly rounded. They are designed to be streamlined.
- Universal Head Rivets: These have a variable head shape that can be round, brazier, or countersunk. This makes them versatile.
- Blind Rivets: These are tubular and allow for riveting in situations where only one side is accessible. The mandrel stem folds up inside the rivet body.
- Structural Rivets: These extra strong rivets are used for high-stress situations like in aircraft. They are heat treated and have large head designs.
- Drive Screw Rivets: These function like a screw and can be removed. They have a pin through the center that shears off during installation.
The most common materials used to make rivets include:
- Aluminum: Lightweight yet strong, these are suitable for aircraft and other applications where weight savings matter.
- Steel: Strong and durable for high stress situations. Can be heat treated to various levels of hardness.
- Copper: Used for riveting copper materials since they avoid galvanic corrosion. Also used decoratively.
- Monel: This nickel alloy resists corrosion and heat, making it ideal for marine and chemical plant applications.
- Titanium: Extremely strong but lightweight, these are used in aerospace applications. Also medically implanted since it is biocompatible.
- Plastics: Useful as non-structural fasteners, nylon and polyethylene plastic rivets have good corrosion resistance.
The shaft diameter and length needed depends on the thickness and number of sheets being joined. Some common sizes include:
- 1/16 inch rivets: For very thin sheets less than 1/16 inch thick.
- 3/32 inch rivets: Light duty use in 20 to 22 gauge sheets.
- 1/8 inch rivets: Most common size for general sheet metalwork with 18 to 22 gauge sheets.
- 5/32 inch rivets: Used for medium applications with 16 to 18 gauge sheets.
- 3/16 inch rivets: Heavy duty use with 10 to 14 gauge thicker sheets.
- 1/4 inch rivets: Only used for joining thicker plates.
Grip range must also be considered. This refers to the combined thickness of all the layers being riveted.
Benefits of Riveting
There are several advantages to riveting over other fastening methods in sheet metal fabrication:
- Excellent shear strength: Rivets have powerful resistance to forces trying to slide the sheets apart sideways.
- Permanent fastening: Once installed, the rivets are not meant to be removed. This creates durable joints.
- Allows movement: The rivet holds the sheets together while allowing some movement which helps with vibration absorption.
- Improved appearance: The smooth finished look provides a more appealing aesthetic than spot welds.
- Variety of materials and finishes: Rivets come in different colors and coatings to match the base materials.
- Quick installation: Automated riveting is simple and fast on an assembly line. Hand riveting also goes quickly with practice.
- Low cost: Rivets are an economical choice compared to screws or welding. The tools are also affordable.
Rivet Joint Design
Properly designing joints is crucial when riveting sheet metal to ensure the rivets carry the load stresses safely. Here are some best practices:
- Use at least 2 rows of rivets spaced closely in the direction of the force. More rows/rivets increase strength.
- Space rivets in staggered rows rather than directly aligned.
- Put more rivets near the edges and ends of the joint where shear forces concentrate.
- Add washers under the rivet head and nut where needed to spread the load.
- Make sure the drilled holes align perfectly between both sheets before inserting rivets.
- Do not fill all holes initially in case re-drilling is needed for alignment.
- Rivet sheets only when they are fully supported underneath to avoid distortion.
While automated machines are commonly used, smaller-scale riveting can also be done by hand using simple tools. The basic process involves:
1. Shearing or laser/water jet cutting metal sheets to size. Deburring edges.
2. Marking and center punching hole locations.
3. Drilling holes using a drill press with the joined sheets clamped tightly.
4. Inserting rivets in matching holes of top and bottom layers.
5. Supporting sheets with a heavy bucking bar underneath.
6. Holding the rivet head steady with a rivet set aligned on top.
7. Hitting the rivet set head with the hammer until the rivet shank spreads and clinches tightly.
8. Inspecting visually and with a feeler gauge to check for abnormalities.
9. Touching up protective coatings and refinishing the materials as needed.
Proper rivet installation should pull the materials tightly together without cracking or distorting the metal around the rivet. The resulting joint will be strong, reliable, and have an attractive uniform appearance. CNC Milling CNC Machining