What is Soldering?

What is soldering? In basic terms, the soldering process involves joining two or more pieces of metal together using a filler metal (the solder). In this process, the base metals are not melted, only the filler. Instead of fusing the metals together, the solder melts and flows into the joint, which creates a strong bond once cooled.

Soldering is similar to welding in a lot of respects but with some key differences. Welding is just one of the many sheet metal fabrication services we offer here at Salamander Fabrications, so we have plenty of knowledge and expertise around the subject.

So we’ve come up with this complete guide on what soldering is and the soldering process. Continue reading for more!

How the soldering process works

Generally speaking, and in the most basic terms, here is a rundown of how the soldering process works. There are a number of different techniques, applications, and variables that may affect or add to this baseline process, as we will cover later on in this article. 

1. Prepare the surface: To ensure proper adhesion, clean the base metals to remove oxidation, dirt, and grease.
2. Apply the flux: A chemical cleaning agent (flux) prevents oxidation when you apply heat and improves the solder flow.
3. Apply heat: A number of tools or techniques can be used to apply heat to the joint, including a soldering iron, torch, or hot air gun.
4. Melt the solder: Apply the filler metal (solder). Capillary action will draw it into the joint.
5. Cool and solidify: A strong mechanical bond is formed once the solder cools.

What is soldering used for?

Soldering has a wide range of uses and applications, but some of the most common are listed here.

• Electronics: To connect wires, circuit boards, and electrical components. Provides good electrical conductivity and secure connections.
• Plumbing: To seal copper pipes and more. Requires an acid-based flux to remove oxidation.
• Jewellery making: Attaching delicate metal pieces and creating strong bonds.
• Automotive and aerospace: To manufacture or repair electrical systems and metal components.
• Musical instruments: Brass instruments use silver soldering for precise assembly.
• HVAC: Used for gas pipelines, refrigeration coils, and heat exchangers.

Benefits of soldering

• Low heat required (compared to welding)
• Can be used to join dissimilar metals (for example, copper to aluminium)
• Provides good electrical conductivity
• Simple and cost-effective process
• Works well with precious metals (for example, gold, silver, and platinum)
• It can be resistant to heat and corrosion

Types of soldering

Soft soldering (low-temperature soldering process)

Soft soldering is the most common soldering process method. It involves using a solder with a low melting point. This creates a weaker bond compared to hard soldering or brazing, which we detail next. It also cannot withstand high temperatures, which limits its use in high heat applications.

• Temperature range: Below 450°C
• Solder material: Tin-based alloys (for example, tin-lead or lead-free alternatives)
• Flux used: Rosin-based or acid-based flux
• Common tools: Soldering iron, soldering gun, hot air gun

Hard soldering (silver soldering process)

Hard soldering uses a solder with a higher melting point, often containing silver, to create a stronger joint. It requires more heat than soft soldering, which is typically provided by a blowtorch. This usually makes it more expensive. Oxidation can also occur if flux is not used properly.

• Temperature range: 450°C to 900°C
• Solder material: Silver-based or brass-based alloys
• Flux used: Borax-based flux
• Common tools: Blowtorch, propane torch, oxy-acetylene torch

Brazing (high temperature soldering process)

Brazing operates at an even higher temperature. The filler metal (often brass or copper-based alloys) creates an extremely strong and heat resistant bond. This requires high temperatures, specialised tools, and skilled labour – which, of course, makes it more expensive than soft or hard soldering. It’s also not suitable for delicate electronics due to extreme heat.

• Temperature range: Above 900°C
• Solder material: Brass, copper, or aluminium-based alloys
• Flux used: Borax-based flux
• Common tools: Oxy-acetylene torch, induction heating, furnace brazing

What is soldering vs welding?

A metallic bond occurs in all welding services, brazing, and soldering processes. However, with brazing and soldering, the base metals being joined together are not melted. Whereas, when it comes to welding, they are. With both brazing and soldering, the filler metal has a melting point lower than the metal parts being joined together. 

Many welding processes do not even require a filler metal. They rely solely on melting and fusing the base materials together, while others use a filler metal to strengthen the joint.

Soldering process variables

Here, you’ll find a set of process variables that need to be managed to ensure the quality and strength of the final solder joint.

Time and temperature

Together, these factors control how much dissolution occurs, which refers to the process where the base metal gradually dissolves into the molten solder. It also controls how thick the intermetallic compound layer becomes. Temperature primarily controls the speed at which the solder occurs and the type of compounds that form.

Amount and type of flux

The flux cleans the surfaces of all components and keeps them from oxidizing when soldering. The type you use affects how it reacts with the metals and the range of temperature. The amount you use affects whether or not the solder joint forms before oxidation. In some cases, a shielding gas may also be used to help prevent oxidation.

Joint geometry

This affects the strength of the final solder. If optimum, the joint will pull filler metal in and hold it in place. If the joint gap is too big, the strength of the joint is dictated by the properties of the solder. If it’s too tight, the strength of the joint begins to weaken, and solder flow can be nipped off. 

Specialised soldering techniques

Soldering Method	Temperature	Heat source	Best used for	Advantages	Disadvantages
Hot Dip Soldering	Low	Molten solder bath	Coating wires, corrosion protection	Fast, uniform coating	Not suitable for complex shapes and excess solder build-up is possible
Wave Soldering	Medium	Molten solder wave	PCB assembly	Ideal for high-volume production, ensures strong connections	Not suitable for heat-sensitive components, requires precise temperature control
Torch Soldering	High	Gas flame	Plumbing, metalwork	Strong joints, portable, good for large components	Can overheat materials, not precise enough for small electronics
Furnace Soldering	High	Furnace	Aerospace, automotive	Precise, batch processing allows multiple parts to be soldered at once	Expensive, requires specialised equipment, not flexible for small-scale jobs
Induction Soldering	High	Electromagnetic field	Automotive, delicate components	Fast, precise, energy-efficient, no flame	Requires conductive materials, expensive setup
Iron Soldering	Low	Soldering iron	Electronics, DIY repairs	Simple, low-cost, good for small workpieces	Slow for large-scale soldering, requires manual skill
Infrared Soldering	Medium	Infrared light	Surface-mount electronics	Precise heating, no contact needed	Expensive, reflective surfaces don’t absorb heat well
Resistance Soldering	High	Electrical resistance	Miniature components, precision work	Fast, localised heat prevents damage to surroundings	Requires specialised tools, not suitable for large joints

The benefits and applications of welding

Welding services offer a range of benefits over soldering and brazing, and they are more commonly used for mass production and more industrial applications.

The benefits of welding services include:

• creating permanent, high strength connections
• versatility with the ability to weld various metals, alloys, and even thermoplastics
• being cost-effective and efficient for mass production and repairs
• precision and customisation with advanced methods allowing detailed and complex fabrications
• the ability to integrate robotic systems for automation compatibility

Here at Salamander Fabrications we use a number of different types of welding techniques, such as MIG, TIG, and spot welding. Our team consists of qualified, well-trained welders who have meticulously built up their expertise and use cutting-edge tools on every job. Our welding capabilities are also coded in line with numerous standards and specifications.

Would you like some more information on welding services? You can take a read of our blog – ‘5 Types of Welding Joints Explained’

Our welding specifications

• EN 15614-1: Specification and qualification of welding procedures for metallic materials. Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys.
• EN 15614-2: Specification and qualification of welding procedures for metallic materials. Part 2: Arc welding of aluminium and its alloys.
• EN 9606-1: Qualification testing of welders. Fusion welding – steels.
• EN 9606-2: Qualification test of welders. Fusion welding – aluminium and aluminium alloys.

Other metal forming techniques

Let’s take a look at some other metal forming techniques:

Cutting and shaping

Metals can be cut and shaped using methods like shearing, sawing, laser cutting, and plasma cutting. Here at Salamander Fabrications we use a fibre laser as it is a more efficient choice that requires fewer external gases when compared to a CO2 laser. Fibre lasers allow for smooth cutting, fast speeds, more flexibility, and less wastage. This can be used to create components for structural frames, machinery parts, and other custom products.

We have two Bystronic lasers, one 3kw and one 6kw. The bed size for our laser cutter is 3000mm x 1500mm, which allows us to take on a range of different projects.

Machining

Turning, milling, and drilling can be used to achieve precise dimensions and finishes. Metals such as high-carbon steels are commonly machined for parts that require high strength and precision.

Sheet metal folding

Sheets of ferrous metal are bent into shape using a CNC press brake or folding machine. Sheet metal folding allows for accurate bends and angles, and maintains strength and structural integrity.

We use laminating techniques that allow us to make our own bespoke tooling. This allows us to provide more bespoke solutions. We offer both Amada and Bystronic press brakes, which improve our programming quality and speed.

Heat treatment

Heat treatment can be used to change the mechanical properties of metals to improve hardness, strength, and ductility. These processes can include annealing, quenching, and tempering.

Coating and finishing

Commonly, a lot of metals will undergo a final coating or finishing process, like painting or powder coating services. This is done to improve aesthetic appearance and provide resistance to corrosion, especially in outdoor environments.

Casting

Investment casting and sand casting can be used to create complex shapes from molten metals, like cast iron. The resulting cast can be used for engine blocks, pump housings, and decorative items.

Sheet metal fabrication services from design to delivery

Here at Salamander Fabrications, we have over 50 years’ experience providing end-to-end machining and fabrication services throughout the UK.

Our company provides a complete range of CNC machining services. We are extremely proud of our ability to offer both full service sheet metal fabrication and sub-contracting services.

If you would like some more information or advice, please feel free to contact us. Give us a call on 01484 843599 or send an email to sales@salamanderfabs.com. Our friendly sales team will be more than happy to help.