Welding and Soldering.

You might have heard of these two terms before. 

But, are they interchangeable? 

While very similar, they do have their differences as both the processes are used to join metals together. 

Welding bonds two pieces of metal by melting them together, whereas Soldering uses a filler bonding material known as Solder to bond two or more pieces of metal together.

But, can you weld with a soldering iron? Using a soldering iron to weld depends on the application. If you do not require a high mechanical bond between the metals then using soldering iron is just fine. 

However, if you require a strong bond between the two metals, using a soldering iron to weld will not be applicable as the soldering iron will not provide a strong enough bond between the metals. 

It all comes down to the application where you will be using the soldering iron to weld. I will discuss these in more detail in this article. 

What is involved when you weld

To understand when soldering can be used to weld and when it cannot, it will help to understand the two processes a bit better. 

Let’s start with Welding.

Welding is the process where two pieces of metal are fused together using high heat and pressure. 

While mostly used with metals, welding can also be used with thermoplastics and wood. 

It can be performed outdoors, indoors (in certain areas), underwater as well as outer space!

How are metals joined together when you weld?

Welding uses high temperatures (up to 3500°C / 6332°F) in order to melt the metals which are then fused together. In some instances, there is a filler material used to help with the bond.

The pieces of metal that are joined together and known as Parent Material. 

The molten pool of the two parent materials when cooled, can be stronger than the individual materials themselves. 

Not all metals can be welded though. 

Weldability defines how easy or difficult it is to weld certain metals. The easier the process is involved in welding, it is said to have high Weldability. 

If the metals require special procedures like preheating, a specified heat input, controlled cooling, and postheating then they have low Weldability. 

Also, there are certain metals that just cannot be welded together. They include;

  • Aluminum and Steel
  • Aluminum and Copper
  • Titanium and Steel

Different types of weld

Welding has been around for many years, and like most things has seen an evolution in its process in the 19th century.

Below are some of the most common welding processes;

  • MIG Welding – Gas Metal Arc Welding (GMAW)
  • TIG Welding – Gas Tungsten Arc Welding (GTAW)
  • Stick Welding – Shielded Metal Arc Welding (SMAW)
  • Flux Welding – Cored Arc Welding (FCAW)
  • Energy Beam Welding (EBW)
  • Atomic Hydrogen Welding (AHW)
  • Gas Tungsten- Arc Welding
  • Plasma Arc Welding (PAW)

Unfortunately there isn’t a single welding machine able to perform each of these processes. Each of these processes requires a certain type of welding machine which can include; 

  • Mig (metal inert gas) welding machines.
  • Thyristor Control Mig welding machines.
  • Tig welding machines.
  • Spot welding machines.
  • Shielded metal arc welding machines.

Common applications where you weld

Welding is a process used in many applications.

It can be used to make a fence in your home or used to build a tall skyscraper. 

The applications are endless. Below are some of the most common.

  • Shipbuilding
  • Automotive
  • Construction
  • Mechanical
  • Sheet metal welding
  • Fabrication
  • Aerospace and Aircraft construction 
  • Railroads

A deeper look at soldering

Now we have seen what is involved when you weld, let’s take a closer look at soldering.

Soldering is the process of joining two pieces of metal using a filler material known as Solder. 

Unlike welding, soldering does not melt the metals that are going to be connected together. It relies on the Solder to create a strong bond between them.

The solder is usually a metal alloy made of Tin(Sn) and Lead(Pb).

Soldering is most commonly used in the Electrical and Electronic industry for joining wires and components to Printed Circuit Boards (PCBs). 

The main purpose being to create an electrical bond so that current can flow freely. 

How metals are connected when soldering

The process of soldering uses a tool known as a Soldering Iron, to melt the filler material (Solder), when connecting two conducting materials.

A soldering iron can be heated to temperatures up to 400°C (752°F). 

The temperature at which the soldering iron is set to, depends on the melting point of the solder and not of the metals being connected together. 

The metals (wires, components etc), are first placed together. The solder is then positioned at the intersection of the metals while simultaneously applying heat using the soldering iron. 

Once the solder cools, it creates a strong electrical and mechanical bond. 

With welding, you have many different types available. However, there is only one type of soldering and almost always uses a soldering iron. 

What metals can be soldered

Just like welding, not all metal types can be soldered. There is a limited range.

Also, the bond between the two pieces of metal depends on the solder being used. So, depending on the parent metals, the right solder alloy composition will have to be chosen. 

The common metals that can used in the soldering process are;

  • Gold
  • Silver
  • Copper
  • Brass
  • Iron

Common applications of soldering

I mentioned earlier that soldering is most commonly associated with the electrical and electronic field. 

But, it is not restricted to just that. It has many applications which include;

  • Jewelry repair
  • Automotive
  • Arts and crafts
  • Plumbing
  • Stained glass work
  • Sheet metal work
  • Computers

When you can weld using a soldering iron

Ok, so we’ve covered what is involved when you weld, and when you solder. 

I briefly mentioned at the start that using a soldering iron to weld really depends on the application. Let’s dive deeper and really understand what that means. 

Since both processes involve joining pieces of metals, you cannot be blamed for thinking they are interchangeable. 

But, of the two processes, welding creates a stronger mechanical bond.

So, if you need to use a soldering iron to weld, you will need to be aware that the bond created will not be as strong.

A note to be made is that if you use a soldering iron to weld, you are not welding, you are soldering.

The end result is going to be a bond that is less stronger.

For structures that are smaller in nature, and have less loads placed on them, soldering would be fine. 

Things like metal sculptures, plumbing, jewelry repair etc. Using welding in these applications would be overkill.

Also, using a soldering iron to weld comes is more advantageous when using non-ferrous metals such as copper and brass are being connected

When you cannot weld using a soldering iron

Imagine you are constructing a building that requires a very strong foundation as it will be subject to forces and stresses from things like weather and humans. 

Using a soldering iron to weld the structure would not be a great idea.

You need links between metals beams that can withstand these high forces and stresses, so welding would be the most suitable process to use. 

Also, if there are high temperatures involved, welding again is the better option as the solder has a lower melting point and the bond will be broken when temperatures exceed the solder’s melting point. 

I have learnt this from experience! 

So, the rule of thumb is to not use a soldering iron to weld when high forces, stresses and temperatures are placed on the bond between two pieces of metal. 

Advantages using a soldering iron to weld

If your application allows for you to use a soldering iron to weld, then it might be more advantageous.

This is because using a soldering iron is cheaper, has a faster learning curve, is smaller (so can be stored easier), can be done indoors (in your bedroom), only needs one kind of soldering iron, and requires less to set up.

But, again this only depends if you can actually substitute soldering for welding which is determined by the application.

Are they any other alternatives other than soldering if you cannot weld?

Brazing is another process that is used to join two pieces of metal (but not limited to just metals as ceramics can be joined as well).

Similar to Soldering, a filler material (known as the braze alloy) is used to join the metals.

The temperatures involved with brazing are above 450°C (842°F), so it sits in the middle of soldering and welding.

Similar to welding, the metals being ‘brazed’ together should be similar in composition to allow for a smoother and stronger bond. 

So, this can be another alternative if you need to weld and do not have the equipment necessary to weld.