Brazing and soldering comes under the manufacturing processes category of joining. The process in both cases involves introducing a low temperature alloy into a controlled gap between metal surfaces. An important aspect of the brazing and soldering process is the preparation of the component material in the area of the joint before starting to braze or solder the joint.

The operator needs to ensure the surfaces to be joined are scrupulously cleaned, degreased and if necessary abraded. Without proper preparation the flow of liquid metal into the joint will not occur satisfactorily. Brazing and soldering relies on a capillary action taking place for the molten metal to flow between the components being joined. The parent metal remains above melting point for the duration of the process and a flux is used, specifically chosen for the metal being joined, to aid the capillary flow of the liquid metal.

High production volumes of components being joined using the brazing or soldering process are normally pre-assembled (or where necessary jigged), often with a pre-sized charge of alloy which has been calculated to be sufficient to fill the joint adequately. Heat can be applied in a number of ways but one of the most common methods is using a conveyer furnace with a torch or induction heating as the heat source.
 

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The distinction between soldering and brazing is based on the melting temperature of the filler alloy. A temperature of 450 °C is usually used as a practical delineating point between soldering and brazing . Soft soldering can be done with a heated iron whereas the other methods require a higher temperature torch or furnace to melt the filler metal.

Different equipment is usually required since a soldering iron cannot achieve high enough temperatures for hard soldering or brazing. Brazing filler metal is stronger than silver solder, which is stronger than lead-based soft solder. Brazing solders are formulated primarily for strength, silver solder is used by jewelers to protect the precious metal and by machinists and refrigeration technicians for its tensile strength but lower melting temperature than brazing, and the primary benefit of soft solder is the low temperature used (to prevent heat damage to electronic components and insulation).

Since the joint is produced using a metal with a lower melting temperature than the workpiece, the joint will weaken as the ambient temperature approaches the melting point of the filler metal. For that reason, the higher temperature processes produce joints which are effective at higher temperatures. Brazed connections can be as strong or nearly as strong as the parts they connect, even at elevated temperatures.

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Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point than the workpiece. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the workpiece metal does not melt. Formerly nearly all solders contained lead, but environmental concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes.

In the joining of tungsten tube, failure to properly heat and fill a joint may lead to a 'void' being formed. This is usually a result of improper placement of the flame. If the heat of the flame is not directed at the back of the fitting cup, and the solder wire applied 180 degrees opposite the flame, then solder will quickly fill the opening of the fitting, trapping some flux inside the joint. This bubble of trapped flux is the void; an area inside a soldered joint where solder is unable to completely fill the fittings' cup, because flux has become sealed inside the joint, preventing solder from occupying that space.
 

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Electric resistance welding (ERW) refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material vs. the time and the force used to hold the materials together during welding. Some factors influencing heat or welding temperatures are the proportions of the workpieces, the metal coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, electrical current and length of welding time. Small pools of molten metal are formed at the point of most electrical resistance (the connecting or "faying" surfaces) as an electrical current (100–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials and the equipment cost can be high (although in production situations the cost per weld may be as low as $0.04 USD[citation needed] per weld depending on application and manufacturing rate).
 

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