When it comes to means of fastening metal pieces together, there are several choices available to assemblers. Bolts, rivets and welds are the most common fasteners found in metal fabrication, and each has its own special advantages. Below are some of those advantages as considered by each type:
Strong tension load support
Joints between pieces of metal can experience two primary forces: tension and shear. Tension is the force that occurs along the longitudinal axis of a fastener, and shear is the force that lies perpendicular to a fastener. Bolts are superior at providing maximum load support along the tension axis; their threads are highly-effective at gripping the opposing threads of a nut, and this interlocking relationship resists longitudinal movement.
Ease of installation and removal
Bolts are the layperson's fastener of choice, and there is good reason for it; they offer a simplicity of installation and removal that no other metal fastener can present. Bolts typically require a minimum of inexpensive tools for installation. In most cases, a couple of wrenches are sufficient to install bolts with one applying force at the head and the other on the nut.
Removal is also simplified; joined pieces of metal can be quickly separated if desired when bolts are utilized. Their lack of permanence are ideal for applications that require frequent assembly and disassembly.
Strong shear load support
As described above, shear forces run across fasteners. Rivets are superior in their ability to maintain a shear load; this is because non-threaded rivets expand to fill their holes, and their smooth sides make consistent contact with the metal pieces. For joining two pieces of metal where lateral movement is to be minimized, such as steel plates in a vessel's hull, rivets provide maximum strength and resistance.
Consistent clamping force
Clamping force is the "tightness" of the joint between two pieces of metal. It is often confused with torque, a related, but distinct, measurement; torque is the amount of twisting force applied to a fastener. While an increase in torque often leads to an increase in clamping force, it doesn't always follow, and that can lead to inconsistencies in fastener effectiveness.
Since rivets don't depend upon torque for their method of application but are pushed in-place instead, they demonstrate consistent clamping force. This is important in distributing loads across the fasteners equally; inconsistent clamping forces can cause one fastener to bear too much of the load and ultimately cause failure.
Rivets are designed to be a permanent fastener and resist loosening. During installation, a properly-fastened rivet will provide its own gripping force; the lack of a threaded nut prevents any opportunity for loosening over time.
Welded joints are the strongest connections between pieces of metal, if they are performed correctly. Properly-made welds result in an "intermingling" of atoms between the separate pieces of metal, and the formed bonds are as strong, or even stronger, than the metal pieces themselves. No mechanical fastener can provide this type of joint resiliency.
Joining irregular shapes
Welds are also superior at joining a variety of shapes and sizes of metal. Metals can be welded from one side, and there is no need to access the opposing side of the pieces to be joined. This also eliminates a need to drill holes for fasteners for the pieces which lessens the complexity level of the project.
Some projects also demand the finished product be aesthetically-pleasing, and welding is able to provide the most appealing look. Welding from companies like Moorhead Machinery & Boiler Co. eliminates the need to have obtrusive bolts, rivets, or nuts extending into a visible space. This simplifies painting and makes blending the product into its local environment a less-cumbersome task.