There are many ways to connect the parts together. The most usual are fastening by bolts or rivets, soldering and welding. Welding is a process that creates a continuous joint upon wide materials surfaces. This feature of welding used to make boilers or other enclosed containers.
The original fusion technique is known from the earliest uses of iron. The process of joining small pieces of iron to larger ones was through heating to welding temperature and hammering or pressing together. The most common today’s welding techniques are arc welding, oxyacetylene welding, resistance, electron-beam, friction, laser welding and other. The largest total volume of welding is shielded metal-arc welding. An electric arc is created between materials leading to electrode’s metal melting and transferring it to the joint in this process. Another technique is gas (usually oxyacetylene) welding. The source of heat in this process is acetylene burned in the atmosphere of oxygen. For the resistance welding, the main source of heat is the electrical resistance of the joint. This welding technique is made by using high-current and low-voltage power sources with pressure added to the joint. A dense stream of high-velocity electrons bombarding the joint is a source of heat for electron-beam welding. The friction welding is based on heating joining parts by friction. Laser welding is accomplished when materials are fused together by heat generated from a laser source.
Carbon and low-alloy steels are the most frequently used materials in welded constructions. The amount of carbon or alloying content influences the weldability of steels widely. Another good weldable material is Aluminium and its alloys. Copper and its alloys are also weldable, but the high thermal conductivity makes welding difficult. As a rule, you can easily weld plastic or glass (see also best welding caps). They usually welded by heating to melting range and by simply pressing surfaces together.
Welding is a fabrication that joins materials by causing fusion, which usually melts the base material. In addition, filler materials are typically added to the joint. They form a pool of molten material that creates a joint after cooling. As a rule, a base material is not as strong as a joint. The pressure also can be applied during the welding process.
There are different ways the parts can be geometrically prepared for welding. The basic types of weld joints are the butt joint, V-butt joint, lap joint and T-joint. Other variations exist as well. The particular joint design can be required for many welding techniques. Resistance, laser, and electron-beam welding are most frequently performed on the lap joints.
The quality of weld depends on the base material, filler and flux material, energy and design. The welding method and concentration of energy input, weldability of the base material and type of the filler and flux influence the strength of weld and material. The heat-affected zone has also effect on weld quality. Usually, one of the destructive or nondestructive methods is used to test the quality of the weld. Possible defects of welds are cracks, gas, and non-metallic inclusions, distortions, incomplete penetration, lack of fusion and lamellar tearing.