What is a Rivet?
A rivet is a permanent mechanical fastener consisting of a head at one end and a cylindrical stem at the other end (called the tail) which has the appearance of a metal pin. Rivets are used to join large structural members, small electronic assemblies, and just about any manner of part falling between these extremes.
On installation, the rivet is placed in a punched or drilled hole, and the tail is upset or bucked (i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, the pounding or pulling creates a new “head” on the tail end by smashing the “tail” material flatter, resulting in a rivet that is roughly a dumbbell shape.
To distinguish between the two ends of the rivet, the original head is called the factory head and the deformed end is called the shop head or buck-tail.
Because there is effectively a head on each end of an installed rivet, it can support tension loads. However, it is much more capable of supporting shear loads (loads perpendicular to the axis of the shaft).
Fastenings used in traditional wooden boat building, such as copper nails and clinch bolts, work on the same principle as the rivet but were in use long before the term rivet was introduced and, where they are remembered, are usually classified among nails and bolts respectively.
How do Rivets Work?
A rivet is a mechanical fastener with a plane unthreaded shaft that’s inserted through holes to join two or more parts together. A permanently formed head at each end prevents the rivet from being removed from the hole. The shaft prevents any radial movements of the components.
Depending on the type of rivet, and its ability to support shear load, it can resist considerable forces. The heads prevent axial movements of the parts, although less force is supported in this way.
The function of a rivet is similar to that of a nut and bolt. However, while nuts can readily unscrew for disassembly and reassembly, typically rivets are broken or damaged before removal. They are, therefore, designed for permanent or semi-permanent joints, fulfilling the same role as structural adhesives or welding. The benefits are their ability to resist vibration and can secure joints with short clamp lengths.
A rivet has a pre-formed head at one head, called the factory head. Another head is formed after insertion and it’s referred to as the shop head. The factory head is similar to the head at one end of a bolt while the shop head is like a nut, which forms a temporary head at the other end of a bolt.
The end of a rivet’s shaft, which is formed into the shop head is called the tail. The process of forming the tail into the head is known as upsetting or bucking, which means it is deformed. By doing so, the tail expands, allowing it to securely hold the rivet in place.
The two heads on each end of an installed rivet let it support tension loads (two forces pulling in opposite directions) and shear loads (the force is parallel to the surface or axis of the shaft).
What is the Riveting Process?
Riveting is a forging process that may be used to join parts together by way of a metal part called a rivet. The rivet acts to join the parts through adjacent surfaces. A straight metal piece is connected through the parts. Then both ends are formed over the connection, joining the parts securely.
The metal workpiece used to form the connection may be hollow or it may be solid. Rivets have many uses, such as in the construction and sheet metal industries.
Riveting is a forging process that may be used power to fix the parts together by engrossing and fascinating by use of a metal part called a rivet.
Material use in Rivets
The material of the rivets must be tough and ductile. They are usually made of steel (low carbon steel or nickel steel), brass, aluminum, or copper, but when strength and a fluid-tight joint are the main consideration, then steel rivets are used.
Types of Rivet
There are Different Types of rivets:
- Blind rivets.
- Solid/round head rivets.
- Semi-tubular rivets.
- Oscar rivets.
- Drive rivets.
- Flush rivets.
- Friction-lock rivets.
- Split rivets
- Threaded rivets
- Self-Piercing Rivet
1. Blind Rivet
Blind rivets or break stem rivets are tubular fasteners with a mandrel through the center. Blind rivets are inserted into drilled holes in the parts to be joined, and a special tool is used to draw the mandrel through the body of the rivet. The blind end expands, and the mandrel is snapped off.
Unlike solid rivets, blind rivets can be installed in joints from only one side of the part—making them “blind” to the opposite side.
Blind rivets get their name from the fact that they can be completely installed from one side. Ideal for projects where access to the joint is limited to only one side. Blind rivets are available in standard, structural, closed-end, and various other styles for a wide range of applications.
2. Solid Rivet
Solid rivets are among the simplest, most reliable, and oldest types of fasteners. These simple devices consist of a solid shaft with a head on one end; once installed, the headless end of a solid rivet is deformed with a hammer or rivet gun to hold it in place.
Solid rivets are perhaps the most widely used type of rivets and are used in applications where reliability and safety are important.
It has been found in archaeological findings dating back to the Bronze Age. Solid rivets consist simply of a shaft and head which are deformed with a hammer or rivet gun. Such rivets come with rounded (universal) or 100° countersunk heads.
3. Drive Rivet
A drive rivet is a type of blind rivet with a short mandrel that protrudes from the head. Once the drive rivet is inserted into a hole, the mandrel is driven in with a hammer or other implement to flare out the end of the rivet that is inside the hole.
This is commonly used to rivet wood panels into place since the hole does not need to be drilled all the way through the panel, producing an aesthetically pleasing appearance.
They can also be used with plastic, metal, and other materials and require no special setting tool other than a hammer and possibly a backing block placed behind the location of the rivet while hammering it into place.
Drive rivets have less clamping force than most other rivets. Drive screws, possibly another name for drive rivets, are commonly used to hold nameplates into blind holes.
4. Semi Tubular rivets
Semi-tubular rivets are similar to solid rivets but contain a hole at the end of the rivet opposite the head. This hole causes the tubular portion of the rivet (around the hole) to roll outward when force is applied. Semi-tubular rivets also require less force needed for application and assembly.
The force needed to apply a semi-tubular rivet is about 1/4 of the amount needed to apply a solid rivet. Tubular rivets are sometimes preferred for pivot points since the swelling of the rivet is only at the tail.
The type of equipment used to apply semi-tubular rivets ranges from prototyping tools to fully automated systems. Typical installation tools are a handset, manual squeezer, pneumatic squeezer, kick press, impact riveter, and, finally, PLC-controlled robotics.
The most common machine is the impact riveter, and the most common use of semi-tubular rivets is in lighting, brakes, ladders, binders, HVAC ductwork, mechanical products, and electronics.
5. Split rivets
Split rivets are ideal for piercing through softer materials such as most woods, leather, and plastic. These are the standard “home repair” rivets. They have sawed or split bodies with sharp ends to make their own holes through leather, fiber, plastic, or soft metals. They are not used in critical applications.
6. Threaded rivets
Threaded inserts and rivet nuts provide a uniquely strong permanent thread through sheet materials and other materials where installation is only possible from one side.
Threaded Rivets have a threaded internal mandrel (stem) with the external portion machined flat on two sides for the tool to grip and rotate. The head is normally hexagonal to prevent rotation of the tubular body while the mandrel is torqued and broken off.
7. Oscar Rivet
Oscar rivets are similar to blind rivets in appearance and installation but have split along the hollow shaft. These splits cause the shaft to fold and flare out as the mandrel is drawn into the rivet.
This flare provides a wide bearing surface that reduces the chance of rivet pull-out. This design is ideal for high-vibration applications where the back surface is inaccessible.
A version of the Oscar rivet is the Olympic rivet which uses an aluminum mandrel that is drawn into the rivet head. After installation, the head and mandrel are shaved off flush resulting in an appearance closely resembling a brazier head-driven rivet.
8. Flush Rivet
A flush rivet is used primarily on external metal surfaces where good appearance and the elimination of unnecessary aerodynamic drag are important. A flush rivet takes advantage of a countersink hole; they are also commonly referred to as countersunk rivets.
Countersunk or flush rivets are used extensively on the exterior of aircraft for aerodynamic reasons such as reduced drag and turbulence. Additional post-installation machining may be performed to perfect the airflow.
9. Friction-lock Rivet
These resemble an expanding bolt except the shaft snaps below the surface when the tension is sufficient. The blind end may be either countersunk (‘flush’) or dome-shaped.
One early form of the blind rivets that was the first to be widely used for aircraft construction and repair was the Cherry friction-lock rivets. Originally, Cherry friction locks were available in two styles, hollow shank pull-through, and self-plugging types.
The pull-through type is no longer common; however, the self-plugging Cherry friction-lock rivet is still used for repairing light aircraft.
Friction-lock rivets cannot replace solid shank rivets, size for size. When a friction lock is used to replace a solid shank rivet, it must be at least one size larger in diameter because the friction-lock rivet loses considerable strength if its center stem falls out due to vibrations or damage.
10. Self-Piercing Rivet
Self-pierce riveting (SPR) is a process of joining two or more materials using an engineered rivet. Unlike solid, blind, and semi-tubular rivets, self-pierce rivets do not require a drilled or punched hole.
SPRs are cold-forged to a semi-tubular shape and contain a partial hole to the opposite end of the head. The end geometry of the rivets has a chamfered poke that helps the rivet pierce the materials being joined.
A hydraulic or electric servo rivet setter drives the rivet into the material, and an upsetting die provides a cavity for the displaced bottom sheet material to flow.
The self-pierce rivet fully pierces the top sheet material(s) but only partially pierces the bottom sheet. As the tail end of the rivets does not break through the bottom sheet it provides a water or gas-tight joint.
With the influence of the upsetting die, the tail end of the rivet flares and interlocks into the bottom sheet forming a low-profile button.
What is Rivet Joint?
A riveted joint is a permanent joint with mainly two components (parts to be joined) that are held together by a rivet with the head at the top and the tail at the bottom.
Riveted joints are very similar to bolted joints though rivets pierce through CFRPs and partly to aluminum alloys in the bottom and flare inside aluminum alloys with the help of a die to generate the bonding.
Types of Riveted Joint
Following are the two types of riveted joints: lap joints and butt joints depending upon the way in which the plates are connected.
In lap joints the components to be joined overlap each other. Lap joints can be used to join wood, plastic, or metal. A lap joint can be used in woodworking for joining wood together. A lap joint may be a full lap or half lap.
In butt joints, an additional piece of material is used to bridge the two components to be joined which are butted up against each other. The name ‘butt joint’ comes from the way the material is joined together.
A butt joint is one in which the main plates are kept in alignment butting (i.e. touching) each other and a cover plate (i.e. strap) is placed either on one side or on both sides of the main plates. The cover plate is then riveted together with the main plates.
Butt joints are classified into the following types:
- Single strap butt joint, the edges of the main plates butt against each other and only one cover plate is placed on one side of the main plates and then riveted together.
- In a Double strap butt joint, the edges of the main plates butt against each other, and two cover plates are placed on both sides of the main plates and then riveted together. And In addition to the above, the following are the types of riveted joints depending upon the number of rows of rivets.
- Chain riveted joint In this type accommodated rows of rivets may lie exactly opposite to each other over straight lines.
- Zig Zag Riveted Joint, Unlike the above type, here the rows may appear staggered and not complement each other.
- Diamond Riveted Joint You will find this type of joint typically in butt joints. here the rivets are arranged in rows which are broader at the butt ends and taper out at the opposite edges forming quite the shape of a diamond.
Application of riveted joints
These are some applications of Riveted joints:
- Rivet joints are permanent joints used mainly for fastening sheets and shaped rolled metal.
- Used for aircraft structures where Aluminum is used.
- It’s used in the manufacturing of bus and trolleybus bodies to create a heavily loaded joint
- Used for metals that have poor weldability.
- Used for heterogeneous materials like asbestos friction lining and steel.
- It is used where we have to avoid after-thermal effects, as in the case of welding.
- Welded joints have poor vibration damping capabilities so where required rivets are used in place of it.
- They are used in lap, abutment, and double-cover plate joints.
- It has lightweight, much cheaper, and has high strength.
- They can still be used for constructing a metal bridge, hoisting cranes, boilers, and pressure tanks. But some other joining processes may serve better.
- In essence, rivets are widely used to join components in aircraft, boilers, ships, and boxes as well as other enclosures.
Advantages and Disadvantages of Riveting
Benefits of Riveting
- Relatively inexpensive method. The production of the rivet is cheap.
- The rivet can be used in the joining of ferrous as well as nonferrous metals like aluminum and copper alloys.
- The rivet can be used in the joining of nonmetallic materials like wood, plastic, asbestos sheet, etc.
- One of the main advantages of the rivet is that it can use to join dissimilar materials. ( joining aluminum plate and copper plate).
- Ability to make joints regardless of location. (Vertical, overhead, etc.)
- No fumes and gases are produced as in the welding; the production is environmentally as well as user-friendly.
- Riveted joints are more reliable than other methods in applications where the joint is subjected to excessive vibration and impact forces.
- High shear strength, and good fatigue resistance.
- Aluminum rivets are lighter than bolts and screws. They also possess high resistance to atmospheric and chemical corrosion.
- Since there is no melting of metal and uneven heating and cooling involved while the joining process, thermal effects on the riveted joints are minimum. So, it causes little or no damage to the protective coatings of the material.
- The quality inspection of the riveted joint is easier than the welding inspection.
- Dismantling of the riveted joint causes less damage when compared to the welded joint.
Limitations of riveting
- Riveting take more labor time than welding. Additional operations like the layout and drilling holes are necessary. The labor cost of rivet joints is high.
- Stress concentration at the rivet holes of metal plates.
- The holes may weaken the working cross-section of the plate. Then the additional thickness is required to compensate for this problem. This additional thickness and overlapping of plates for riveting increase metal consumption.
- It has more weight than welded joints due to the strap plates and rivets.
- The riveted joints are bulkier than welding and brazing. The projection of the rivet also affects aesthetic appearance.
- They typically do not make a tight or leak-proof joint unless using a hot rivet or sealant along with the rivets.
- The riveting process is noisier than welding due to hammer blows.
Types of Failures in Riveted Joints
- Shear failure
- Tensile failure of plates
- Crushing failure of plates
- Shear failure of plates in the margin area
- Tearing of plate in the margin area