What are the 8 joints?

Covalent bonding takes place when one of the constituent atoms loses one or more electrons, with the other atom gaining the electrons, resulting in an electron cloud that is shared by the molecule as a whole. In both ionic and covalent bonding the location of the ions and electrons are constrained relative to each other, thereby resulting in the bond being characteristically brittle. Metallic bonding can be classified as a type of covalent bonding for which the constituent atoms are of the same type and do not combine with one another to form a chemical bond. Atoms will lose an electron(s) forming an array of positive ions. These electrons are shared by the lattice which makes the electron cluster mobile, as the electrons are free to move as well as the ions. For this, it gives metals their relatively high thermal and electrical conductivity as well as being characteristically ductile.

Forge welding was still the only form of welding that existed until the end of 19th century. It was used by blacksmiths for millennia to join steel and iron by heating and pressing. Arc welding was one of the first technologies to emerge late in the century. Oxy-fuel welding and electric resistance were soon followed. As the world wars pushed for more reliable and economical joining methods, welding technology advanced rapidly in the early 20th Century. There were many new welding methods developed following the wars. In the second half century, the inventions of laser beam, electron beam, magnetic pulse welding and friction stir welding furthered the progress. Robot welding has become a common practice in industrial settings. As the science of welding advances, researchers continue to create new welding methods and better understand weld quality.

The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C (5600 °F). The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct current (DC) or alternating current (AC), and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.

Other solid-state welding methods include friction welding (including friction stirring welding and friction spot welding), magnetic impulse welding, co-extrusion welding, cold welding and diffusion bonding. There are many ways to prepare welds geometrically. There are five main types of weld joints: the butt, lap, corner, edge, and T-joint. A variant of the last is the Cruciform joint. There are other variations. Double-V preparation joints, for example, have two pieces of material that taper to a single point at one-half of their height. Double-U and single-U preparation joints are very common. Instead of straight edges as the double-V and single-V preparation joints, their edges are curved and form the shape of an U. A lap joint is often more than two pieces thick. Depending on the process and the material thickness, multiple pieces can be welded together to create a lap joint geometry.

Submerged arc weld (SAW), is a high productivity welding method that strikes the arc beneath a layer of flux. Because the flux blocks any contaminants from the atmosphere, this improves the quality of the arc. The flux can remove the slag from the weld by itself. This is combined with a continuous wire feeder, which increases the weld deposit rate. Because the flux hides any arc and produces almost no smoke, working conditions are significantly better than other arc welding processes. It is often used in industry for large items and to make welded pressure vessels. Others arc welding methods include atomic hydrogen weld, electroslag welding(ESW), electrogas weld, and studarc welding. ESW is a single pass welding process that produces high-quality thicker materials. It works well for thicker materials with thicknesses between 1 inch (25mm) and 12 in (300mm) in a vertical, or close to vertical, position.