Welding Methods

One can connect parts together in many ways. The most usual are fastening by bolts or rivets, soldering and welding. Welding is a process that creates a continuous joint upon large materials surfaces. This is the main feature of welding, especially for enclosed cans such as boilers, etc.

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. They usually welded by heating to melting range and by simply pressing surfaces together.

There are different ways the parts can be geometrically prepared for welding. V-butt joint, lap joint butt joint, and T-joint are the basic types of weld joints. Other variations exist as well. Many welding processes require the particular joint design. For example, laser, resistance, and electron-beam welding are performed on the lap joints.

The fusion technique was developed when mankind discovered the iron forging. People heated small pieces of iron to welding temperature and then hammered or pressed them to create larger useful pieces. Oxyacetylene welding, arc welding, friction welding, electron-beam welding, laser welding, resistance and other welding are the most common up-to-date techniques. 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. The resistance welding is a process when the required heat is generated from electrical resistance of the joint. Such welds are made using low-voltage and high current power source with pressure applied. 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. A laser beam is a source of heat when fusing materials in the laser welding.

A proper weld joint can be prevented by dirt, rust, grease, and oxidation. Hot metal requires protection and all weld processes use one of two protection methods: flux or shielding gas. Welding flux is used in solid, paste or liquid form. It creates a small pocket of gas while evaporating. This prevents oxidation. After welding the layer of solid flux must be removed. Shielding gas protects weld directly by surrounding it.

The design of joint, filler, base material and flux influence the quality of the weld. The strength of material and weld depends on the welding method and concentration of energy input, type of the flux and filler, and weldability of the base material. The weld quality also much depends on the heat-affected zone. To test the quality of the weld either destructive or nondestructive methods are used. Gas and non-metallic inclusions, cracks, incomplete penetration, distortions, lack of fusion and lamellar tearing are common defects of welds.