Welding, brazing and soldering are all methods for joining two or more pieces of material – primarily metals. The key difference among these processes is the temperature used to create the joint.
Welding – for the majority of processes - involves melting of the base materials to create a consolidated joint. Welding may or may not involve the use of filler metals or shielding gases.
Brazing and soldering, in essence, are the same in that they both melt the filler metal (braze or solder) only, not the base materials. The liquid filler metal wets the base materials through capillary action. When the liquid filler metal solidifies, it is bonded to the base materials, creating a joint. What differentiates soldering and brazing is the melting temperature of the filler metal; brazing is hotter.
Each process has its advantages and disadvantages, from a processing and application perspective.
Welding
There are numerous types of welding processes, including:
Welding has been used to join most metals known to humankind, but the process is extensively used for common manufacturing materials, such as aluminium, steel and titanium. Welded components are in use all around us in everyday life, such as in aeroplanes, bridges, buildings, cars and ships.
Advantages of Welding Include:
- Produces stronger joints than brazing or soldering
- Produces welded joints that are better suited for high-temperature applications
- Being able to join thin and thick sections of metal (depending on process type)
Disadvantages of Welding Include:
- Producing greater thermal distortion and residual stresses in the joint compared to soldering and brazing
- Requiring a post-processing heat treatment to relieve joint residual stress (depending on application and process)
- Only being able to join similar base materials (for most processes, but not all)
Soldering
Solders are melted using heat from a temperature-controlled soldering iron. The solder melts at a temperature below 450°C. A flux is used in soldering to clean the metal surfaces, allowing easier flow of the liquid filler metal over the base material.
Base materials suitable for joining by soldering include brass, copper, iron, gold and silver. Filler metals used in soldering were once lead based, however, owing to regulations, lead-based solders are increasingly replaced with non-lead versions, which may consist of antimony, bismuth, copper, indium, tin or silver.
Soldering is widely used in the electronics industry for making electrical connections, such joining copper to printed circuit boards (PCB). Plumbers also use the process to join copper pipes. One high-value application of soldering is for the assembly of jewellery.
Advantages of Soldering Include:
- Having a lower power input and processing temperature compared to welding and brazing
- Being able to join dissimilar base materials
- Being able to join thin walled parts
- Having minimal thermal distortion and residual stresses in the joints
- Not needing a post-processing heat treatment
Disadvantages of Soldering Include:
- Producing lower strength of joints compared to welding and brazing, making them undesirable for load-bearing applications
- Not being able to join large sections
- Producing joints that are unsuitable for high-temperature applications
- Fluxes may contain toxic components
Brazing
Brazing is considered as a high-temperature version of soldering. There are several brazing variants, including torch brazing, vacuum brazing, furnace brazing and induction brazing. Regardless of the type, the braze filler metal melts at a temperature above 450°C, but always below that of the base materials to be joined. The filler metal, while heated slightly above melting point, is protected by a suitable atmosphere, which is often supplied by a flux. The flux, as with soldering, also helps to clean the metal surfaces.
Base materials suitable for brazing include aluminium, copper, gold, nickel, silver and steel. Primary filler metals used in brazing include aluminium, cobalt, copper, gold, nickel or silver. These primary filler metals are often alloyed with other elements to obtain desirable properties and performance.
Brazing is a commercially accepted process used in a wide range of industries due to its flexibility and the high integrity to which joints may be produced. This makes it reliable in critical and non-critical applications, and it is one of the most widely used joining methods.
Advantages of Brazing Include:
- Having a lower power input and processing temperature than welding
- Producing joints with minimal thermal distortion and residual stresses when compared to welding
- Not needing a post-processing heat treatment
- Being able to join dissimilar base materials
- Producing stronger joints than soldering
Disadvantages of Brazing Include:
- Producing lower strength joints compared to welding
- Producing joints that are not as well suited to high-temperature applications as welds
- Fluxes may contain toxic components
Contact TWI
Please contact TWI to learn more about how we can help you with your welding, brazing and soldering needs.
contactus@twi.co.uk