1.Substrate remains solid throughout, therefore less heat energy is required
2.Less of the substrate is affected metallurgically by the application of heat
3.The process is less expensive because it requires less energy

Soldering can be differentiated from brazing because of the lower melting temperature of the filler material. Typically solder constitutes primarily of a tin/lead* alloy with alternative alloy components or percentage changes being introduced and varied to increase/decrease the melting temperature. The cut off between soldering and brazing is generally recognized as being above or below 450C.

A melting point below 450C is typically considered to be soldering and above 450C it is typically considered to be brazing, although silver soldering or hard soldering is normally above 450C and consequently should be considered to be the first level of brazing even though it is never really referred to as brazing and nearly always as soldering.
 

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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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Cycle times are dependent on heating and cooling times and the quality of the joint is dependent on the care taken preparing the surfaces. Inadequate surface preparation will cause defects due to incomplete wetting of the joints.

Equipment costs are low so consequently the process of brazing and soldering is a low cost option. Costs will increase where automated systems are employed dependent on the level of sophistication required. There is also virtually no waste of the soldering or brazing alloy, particularly where pre-sized charges are use, but the flux used for the process is consumed.

Brazing and soldering, when you consider that you are introducing a layer of material between two surfaces and rely on the chemical and physical bonding of the materials to hold the joint together, can be considered a gluing process for metals.

Abrasion of the surfaces can provide the mechanism for allowing the molten liquid to penetrate into the resulting surface crevices which when solidified effectively anchors the filler material to the surface and holds the parts together mechanically.

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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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