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Welding, soldering, and brazing are techniques for joining two or more metal pieces and, in some cases, other materials. They are also methods to fill gaps in metal parts. So, how do you determine which technique to use? This decision depends on the material, the desired strength, and the application.

The main difference between welding and soldering is fusion. In soldering, the metals to be joined are heated but never melted. In welding, the base metals are melted to form a joint.

Welding

The purpose of welding is to melt the base metals, with temperatures above the melting point of the material, generally over 1,000°C. The goal is to create a very strong bond between two metal pieces that can withstand various types of stress and pressure, such as in an automobile frame or aircraft fuselage.

What does welding involve?

Similar metals required: To weld two metals, they need to be similar. For example, copper cannot be welded to steel.

High temperature: The temperature needed for welding two metals must be very high to melt and bond them.

Common examples of melting temperatures for metals in welding processes:

• Carbon steel: around 1,500°C
• Aluminum: between 600 and 660°C
• Copper: approximately 1,085°C
• Titanium: between 1,660 and 1,670°C

Filler materials: Often, a filler material is used in welding, which is an additional piece of metal that seals any gaps.

Strength: If welding is done correctly, the joint should be as strong as the surrounding “unwelded” metal. Excessive heat, for example, can alter the metal’s characteristics and weaken the weld.

Different welding techniques: There are various welding techniques depending on the metal being worked on. Different welding methods have different heat sources, such as oxyacetylene gas, electrodes, lasers, or ultrasonic waves. Aluminium welding presents more challenges than welding steel or other metals.

Brazing

The brazing process is a capillary welding technique, working at temperatures between 450°C and 1,000°C (depending on the filler material), without melting the base metals. It is like soldering in that it uses a filler material to join two metals, though at a higher temperature. Like welding, brazing creates a mechanical bond between two metal pieces.

What does brazing involve?

• Joining metals by melting filler material: Brazing involves heating and melting a filler alloy. Once the filler material solidifies, the metal pieces are joined.
• Filler materials: The filler alloy should have a lower melting temperature than the metal pieces to be joined.

In the case of copper, brazing is performed at temperatures around 600-700 °C, depending on the type of filler material, such as copper-phosphorus or silver alloy, which are very common for joining copper and other metals in applications like plumbing, HVAC, and the refrigeration industry.

• Dissimilar metals: Brazing allows for joining different metals like aluminum, silver, copper, gold, and nickel.
• Flux is often used: Flux material promotes wetting and cleaning of the metal parts to be joined, allowing the filler material to flow over them and bond more easily.
• Mechanical strength: Brazed joints are generally stronger than soft soldering joints but less strong than welded joints. They can withstand considerable loads and are suitable for structural applications, especially in environments with moderate temperatures or where the base materials should not be melted.

Soldering

Soldering is like brazing, but it operates at lower temperatures, typically below 450°C. It uses a filler material known as “solder” to bond metals, usually for electrical or plumbing applications. The process relies on capillary action to draw the solder into the joint, creating a secure connection as it cools and hardens.

What does soldering involve?

Lower Temperature: Soldering requires a lower temperature compared to brazing and welding, making it suitable for delicate or heat-sensitive components.

Filler materials (Solders): The solder must have a melting point lower than the components being joined. Solders are often made from alloys of tin and lead, although lead-free solders are now more common for environmental and health reasons.

Applications: Soldering is widely used in electronics for creating electrical connections, as well as in plumbing for joining pipes.

Key differences between welding, brazing, and soldering

1. Temperature: Welding operates at the highest temperatures, melting the base metals. Brazing uses moderate temperatures, melting only the filler metal. Soldering uses the lowest temperatures, suitable for fragile joints.
2. Material fusion: Welding fuses the base metals, while brazing and soldering rely on filler materials to join the components without melting the base materials.
3. Applications: Welding is used for high-strength structural applications, brazing for moderate-strength joints, and soldering for low-strength or delicate components.

In summary, choosing between welding, brazing, and soldering depends on the required strength, temperature limitations, and the types of materials involved in the application.