Riveting in Sheet Metal Fabrication(sheet metal welding Larry)

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Rivets are a common mechanical fastener used in sheet metal fabrication to join pieces of metal together. They create a permanent joint by inserting a metal pin through holes in the sheets and mechanically deforming the protruding ends. Riveting offers several benefits that make it a popular choice for assembling sheet metal components and structures.
How Rivets Work
A rivet consists of a smooth cylindrical shaft and a head on one end. To install a rivet, holes are drilled or punched through the materials being joined. The rivet is inserted into the holes and the protruding end is mechanically deformed, usually using a tool called a rivet gun. This expands the rivet shaft, pressing it tightly against the hole edges and clamping the materials together. The deformed end is called the shop head or buck-tail, while the pre-formed head on the opposite end is called the factory head.
There are two main types of rivets:
- Blind rivets (aka pop rivets) - These have the factory head on one end and just a mandrel stem protruding from the other end. They are inserted into pre-drilled holes from one side only, without access to the opposite side. A rivet gun pulls on the stem, expanding the rivet and forming the shop head. The stem then snaps off.
- Solid rivets - These traditional rivets have heads on both ends and are installed with access to both sides of the material. The protruding end is hammered or pressed to flare it into a shop head.
The flaring of the rivet fills the hole and creates a tight clamping force to hold the materials together. The rivet shank expands slightly in diameter, resulting in a strong, permanent and vibration-resistant fastening.
Benefits of Riveting Sheet Metal
There are several reasons riveting is a popular joining technique for sheet metal fabrication:
- Permanent fastening - Unlike screws or bolts, rivets cannot come loose over time from vibration. The flaring process deforms the rivet to grip the materials securely together. This prevents loosening of the joint.
- Strength - The direct contact of the rivet shank with the hole edges creates strong resistance to shearing and tension loads. Pound for pound, rivets have higher strength than many other types of fasteners.
- Vibration resistance - Riveted joints are resistant to loosening under vibrations. This makes them well suited for assemblies that will undergo shaking, rotations or frequent movements.
- Lightweight - Rivets add very little weight, which is advantageous for applications where added mass must be minimized. They are lighter than most mechanical fasteners.
- Material versatility - Rivets can join dissimilar metals since there is no electrical connectivity between the joined pieces. This allows more flexible material choices.
- Quick installation - Rivet guns allow for fast installation compared to other techniques like welding or screwing. Automated riveting is also possible for high volume production.
- No damage to materials - The riveting process does not degrade the joined materials by applying heat or torque. It does not damage coatings or change material properties beyond the immediate area around the rivet hole.
- No bolt heads/threads - Rivets provide a smooth surface without bulky bolt heads or external threads that can cause issues in assembly and operation.
Riveting techniques are highly suited for sheet metal components like brackets, supports, enclosures, aircraft fuselages, automobile panels and many other fabrication applications.
Rivet Materials
Rivets are available in a wide range of metals, providing flexibility for designers to match the rivet material to the application:
- Aluminum - Lightweight and corrosion resistant, ideal for aircraft and transportation applications. Easy to drill and deform.
- Steel - Very strong but heavier. Provides high shear strength and durability, good for structural applications.
- Stainless steel - Corrosion and heat resistant. Used in harsh environments and appliances.
- Copper - Good electrical and thermal conductivity. Used to also create an electrical link across a joint.
- Monel - Corrosion resistant nickel alloy used in marine components and chemical/process equipment.
- Titanium - Extremely strong but light. Used in aircraft and high-performance applications.
The choice of rivet material depends on strength needs, environmental conditions, weight restrictions, electrical conductivity requirements and compatibility with the materials being joined.
Rivet Sizing
Rivets are available in a wide range of diameters and lengths to accommodate different material stackups and strength requirements. The rivet diameter must closely match the hole size for proper fastening. Typical diameters range from 1/16 inch up to 1/4 inch or more.
Length depends on the combined thickness of the materials being joined. The rivet must be long enough to fully fill the hole and flare properly when installed, with some allowance for the deformed shop head. Standard lengths are commonly available in 1/16 inch increments.
For structural joints, the rivet diameter and length are carefully matched to the materials and design loads. Critical aircraft components may use special flush head rivets and close tolerances. Other general applications may allow looser sizing standards.
Rivet Hole Preparation
Proper hole sizing and preparation are critical for achieving secure riveted joints in sheet metal:
- Drilling - Holes are usually drilled through the stacked materials at each rivet location using standard twist drills. Drill presses allow perpendicular holes.
- Hole diameter - Drill bit size should closely match the rivet diameter, typically within a few thousandths of an inch larger than the rivet. Tight tolerance gives optimal filling of the hole.
- Deburring - Any burrs or rough edges around the hole must be removed to allow proper seating of the rivet. Deburring can be done with countersinks, files or abrasive spinning tools.
- Alignment - Holes must align across both sheets so the rivet can pass through without binding. Fixturing or templates may be used for consistent hole alignment.
- Spacing - Codes or specs often dictate minimum spacing between rivets and distance from sheet edges. This prevents distortion or tearing of the metal around holes.
Proper hole preparation is key to achieving strong, reliable riveted joints in sheet metal assemblies.
Riveting Methods
There are several techniques for mechanically upsetting the rivets to flare the shop head and fasten components together:
- Hand riveting - A hammer and bucking bar are used to manually flare the rivet by hammering the protruding shank. Access to both sides of the assembly is needed.
- Pneumatic rivet guns - Air-powered squeeze or impact tools upset the rivet using pneumatic force. Makes one-sided installation possible.
- Hydraulic riveting - Hydraulic power provides the flaring force. Allows high strength and uniform shop head formation.
- Orbital riveting - Spinning orbital heads are pressed against the rivet tip to flare it outward. Provides fast, consistent flaring.
- Automated riveting - Robotic auto-drilling and riveting machines are used for high-volume production. Maximizes speed and consistency.
The riveting method depends on factors like production volume, joint accessibility, quality control needed, and equipment availability.
Inspection of Riveted Joints
To ensure proper fastening, riveted sheet metal connections must be checked for:
- Shop head shape - The flared end should form a full hemispherical shape, without cracks or deformation irregularities.
- Grip length - The shop head's diameter must be at least 1.5 times the rivet diameter to demonstrate adequate flaring and hole filling.
- Fastener tightness - Attempts to spin the rivet should not produce any movement, indicating it has fully locked into the hole.
- Material compression - Joined materials should be pressed tightly together without gaps, cracks or scratches around the rivet.
Visual inspection and simple checks with standard gages can verify if riveted sheet metal joints meet specifications. More advanced techniques like ultrasonic testing are occasionally used.
In summary, riveting is an efficient, reliable method of permanently fastening sheet metal components that will continue being a go-to joining technique for fabrication projects across many industries. Proper hole preparation, rivet sizing, installation, and inspection practices allow rivets to create robust, long-lasting sheet metal assemblies and structures. CNC Milling