Difference between Welding, Soldering and Brazing?
Welding, soldering, and brazing are joining methods to join materials. There are physical and technological differences between these terms although the main difference between welding, soldering, and brazing is melting temperature. In soldering, and brazing metals are heated to a high temperature but they are melted. While in welding, base materials are melted to produce a welding joint.
Soldering actually includes applications similar to both braze welding and brazing. The main difference is in the melting temperature of the filler metal between soldering, brazing, and braze welding. Soldering occurs at temperatures below 449 °C (840 °F). Traditionally, soldering uses several compositions of tin-lead alloys with melting points from 185 °C (361 °F) to slightly above 315 °C (600 °F). The mechanical strengths of soldered joints, particularly built-up joints of the braze-weld type, are low, and the greatest use for soldering is for providing fluid-tightness, for electrical connections, and for sheet metal joint filling in automotive assembly work.
Soldering is similar to brazing as both work on the principle of capillary action to flow the molten filler metal to fill the joint and produce a permanent weld.
The fundamental difference between fusion welding and soldering is that, when soldering, the joining surfaces are wetted, the solder is molten, but the base material is not melted. Technically correct in terms of materials, one would say that the liquidus temperature * (usually not even the solidus temperature *) of the base materials is not reached. Typical fusion welding is characterized by the fact that the liquidus temperature of the base and filler metals is exceeded. In addition, it can be said that in the case of welding, the base and filler materials are quite similar and therefore the melting temperatures are almost identical. The connection mechanism also differs: When soldering, a diffusion zone forms in the area of the phase boundary, whereas melting takes place during welding.
The aim of welding is to create a very strong bond between two materials that can take weld loads, such as sheet metal joining or structural welding. During welding?
- Metallurgically suitability of metals to be joined: To weld two metals together, they must be similar or having metallurgical suitability for joining. For example, you can’t weld aluminum to steel although various dissimilar metal can be joined easily such as steel to copper, stainless steel to carbon steel etc.
- High temperature: The temperature needed to weld two metals together must be quite high so they can melt and join. Welding low melting metals is not possible for example welding of Lead.
- Filler materials: Welding can be carried out with filler or without filler. When welding without filler, its known as autogeneous welding.
- Strength: If the welding job was properly done, the weld should be as strong as the surrounding, “unwelded” metal. Too much heat, for instance, can change the metal’s characteristics and weaken the weld.
- Different welding techniques: There are various welding techniques, depending on what metal you work on. In a welding program, you can learn which technique to use with what kind of metal. Different welding techniques have different heat sources, like oxyacetylene gas, electrodes, lasers, or ultrasonic.
Soldering visually appears similar to welding, although it is having different purposes. Soldering filler wire are soft compare to weld and melt at low temperature. The main application of soldering is for electronic circuits joining the electronic parts. As solder material is an electric conductor, it’s easy to join parts on the circuit board. In soldering, we shall have:
Low temperature for soldering: Soldering is done at low temperature where the part to be solder is not melted.
Filler materials: Soldering filler wires melt at below 840 °F (450°C).
Dissimilar material can be soldered: Dissimilar materials such as copper, silver, aluminum, gold or iron can be easily soldered to each other.
Weaker joint compare to welding or brazing. Soldered joints are having weak strength because of low strength filler. Joints are not strong like welding or brazing but they fulfill their purpose by proving a good joining of different materials.
Flux needs to be applied: Soldering flux is mandatory to clean the material surface, allow the melted filler to flow, and providing and better bonding.
(Minimum) overlap on soldered joints
When creating overlapped joints, basic requirements exist, which were originally developed for soldering but which were later also applied to brazed joints. In principle one dimension, depending on the minimum sheet thickness, applies for the minimum overlap length. The type of base metal also exerts an influence.
Base metals that can be soldered
In general, practically all metallic materials and their alloys can be soldered. The frequent, common main groups are:
Steels: Practically all steels are suitable for soldering, compared to welding, particularly while maintaining material-specific properties. The soldering temperature can be selected such that heat treatment can be integrated into the soldering process, (e.g. tempering, annealing, precipitation hardening etc.)
Aluminium: Nowadays, aluminium and aluminium alloys are brazed and (soft) soldered. Mixed joints are possible, thus, e.g., aluminium is very frequently mixed with corrosion-resistant, high-alloy steel
Copper: Unalloyed copper, as well as low and high-alloy copper alloys, can be brazed and (soft) soldered. Mixed joints with steel do not pose a problem either. Copper brazing is often restricted because of the issue of undesired softening of cold-formed or precipitation-hardened copper. The oxygen content in the copper determines whether it is suitable
for soldering or even whether it can be soldered at all.
Soldering is done most often by two methods:
1. Dipping the component in the solder pot to cover the leads with solder and placing them on the solder patches deposited on the printed wire boards. The leads and patches are cleaned using fluxes. The connections are then heated to reflow the solder and form the joint.
2. Using a solder-wave machine: In this procedure, a revolving impeller, immersed in a pot of molten solder, produces a vertical wave of solder between two parallel surfaces, so that the height of the wave, depending upon the impeller speed, is above the normal level of solder. Components that have to be soldered are inserted into through-plated holes on the printed circuit boards, and flux is applied to the surfaces where contacts have to be established. The assembled and fluxed board then passes over a relatively clean wave of solder, which is in slight motion at its surface.
Brazing is similar to soldering in that it also uses filler wire for joining two metals and base metals are not melted like welding. Brazing is done at temperatures above 449 °C (840 °F). Brazing uses several varieties of filler material, which is chosen based on its application. The word brazing, when used alone, designates the use of filler materials similar
to those used in braze welding but applied to a close-fitting joint by preplacement or by capillary action. The filler material may be rod, wire, foil, slug, or powder, and fluxes similar to those used in braze welding is necessary.
The melting temperature of the brazing wire is higher than the soldering. Alike to welding, brazing produces a permanent joint between two materials. In brazing we shall have:
- Filler wire melt and fill the joint: Brazing process involves heating and melting of brazing filler wire. which after solidification join the two materials
- Filler materials with low melting temperature: In brazing, filler wire melt at low temperature but higher than soldering.
- Dissimilar materials: Dissimilar materials such as copper, silver, aluminum, gold or iron can be easily brazed to each other.
- Flux needs to be applied: Brazing flux is mandatory to clean the material surface, allow the melted filler to flow, and providing and better bonding.
- Weld joint Strength: A good braze weld can have weld strength slightly less to fusion welding. But they are quite strong in case of emergncy repairs of cast iron, for example.