CAD Welding – All You Need to Know

Among all other welding procedures, CAD welding has become quite popular over time. If you’re not new to the welding business, you probably have heard of thermite welding or exothermic bonding. CAD welding is a brand name for exactly that.

This method is mostly applied when it comes to joining cables. We’ll talk about all that in complete detail in this one. So, if you’re interested in knowing about CAD welding and how the procedure works, you’ve come to the right place.

Enough with the introductions; let’s get into the good stuff.

Defining CAD Welding

Defining CAD welding

Before we get into CAD welding or Exothermic welding, let’s talk about where the term comes from. The word Exothermic has a Greek origin. Here, Exo stands for outside, and thermic stands for heat. This whole procedure is based on a chemical reaction that produces heat.

You should know that all types of combustions are exothermic. These include fire and explosions alike.

When we come to CAD welding in specific, it involves a large-sized wall pipe-like sleeve that acts as a vortex. It’s meant to be positioned between the connection while keeping some space between the edges. Then thermite powder is pumped through a hole that acts as a point of combustion.

The thermite is then ignited via an oxyacetylene torch that burns at a very rapid rate. This, in turn binds the bars together.

The same procedure is applied when joining cables. This is applicable when it comes to underground grids on a smaller scale. It creates a permanent joint where mechanical contraction joints have the possibility of failing over time.

The Procedure

The procedure of CAD welding

Now that I’ve given you the general idea of what CAD welding is let’s jump to the procedure or how the process actually works. Let’s discuss step by step.

  • Cadweld basically uses a precast, clampable mold that’s used to hold together two rods of metal in various joint configurations.
  • So, after the joint members are put inside the mold, the mold is clamped together.
  • Then the sealing compound is placed around all the entry points of both metal pieces. This really helps to prevent the weld metal from getting out during the process.
  • The combination of oxidization agent and selected filler metals, otherwise known as thermite, is put into the top of the precast mold.
  • The molten metal then gets spilled from the upper chamber into the mold and down to the weld cavity. This is what causes the weld around the two pieces of metal.
  • The mold is unclamped once the weld is complete.
  • Then the slag leftover from the weld on the inside must be cleaned up. A wire brush can be used for this purpose.

Caution: There’s a possibility of a lot of smoky build-ups during the process. It’s wise to use personal protective gear like gloves and safety glasses at all times. Keeping a fair distance while the process takes place is advised as well.

Cad Welding Types

Cad welding types

The most common types of CAD welding or exothermic welding are known as Rail welding and Cadweld. Let’s talk a bit about both variants elaborately.

Rail Welding

In rail welding, the equipment used is pretty much the same as CAD welding that we’ve discussed before. However, you should know that rails used for locomotives are way larger than basic copper cables and rebar. It’s pretty much common sense that the equipment has to be much larger as well.

Usually, there’s a larger mold that’s placed from either side around the rail joints. The difference here is that the reaction that’s caused isn’t contained within the mold. In this case, the thermite is stored in a refractory crucible. Then it’s poured into the molten metal into the mold.

After this is done, the equipment is removed from the rails while the cooldown process is going on. This helps to knock off the excess easily with a sledgehammer. Then a grinder is used to ground off the solidified metal reinforcement. This ensures the joint surface is flush.


There’s really not much new to say about this, as we’ve discussed the procedure in detail before. However, I should tell you that, unlike rail welding, Cadweld is pretty much self-contained.

The activator and the filler metal generally come pre-packaged. So, you don’t need to worry about the measurements before each weld.

The Application

You might be wondering in which cases CAD welding might be applied. Have no worries; we’re gonna give you a general idea on that right now.


Much similar to the exothermic welding procedure is known as the exothermic brazing process. It uses exothermic reactions to create bonds between wires. Various types of metals and solder filler metals are used in this procedure.

This also uses a filler metal along with metal oxide to cause the reaction (Much like exothermic welding). This particular brazing process uses heat input only for a brief moment. This ensures no damage or distortion is created when dealing with sensitive electronic materials.


When it comes to welding copper, there’s hardly any alternative to CAD welding. The process neither damages nor lessens the conductivity of the material at hand. However, the conductivity can get weak if the metal isn’t as pure.

In power distributive equipment, we often see the use of copper wires. It’s also seen in bus rails, racks, and other transits.

Galvanized Cable

There’s really no alternative when it comes to copper to galvanized cable other than exothermic welding. I should tell you beforehand that galvanized material doesn’t have as good conductivity as bare metals. This is due to the zinc coating.

To do any kind of welding on galvanized metal, it has to be ground off first. Galvanized coating also introduces porosity, including other kinds of defects, into the weld. This can be avoided with exothermic welding with ease.

The Advantages and Disadvantages

Now that we’ve gone through all the basic stuff let’s take a short look at the advantages and disadvantages of CAD welding.

The GoodsThe Bads
It's really great for establishing long-lasting connections.Depending on the application, this procedure might prove to be dangerous.
This type of welding often comes with pre-packaged thermite.It can't be executed in certain environmental conditions.
It really doesn't require high-level skills to execute properly.
It offers increased conductivity when it comes to cables and wires.

The Temp Talk

Before parting ways, let’s give you some additional information that should help you out in your future ventures. An interesting question regarding this topic is, how hot can exothermic welding get?

Well, the welding material generally responds to temperatures reaching up to 1400 ° C or 2500 ° F. There’s also a focused discharge of smoke in this case to form hot molten steel. These materials aren’t really dangerous. However, the ignition temps of the welding material can reach up to 1650 ° F.

If we generally stick to CAD welding protocols, the possibility of accidents can be minimized. By accidents, I mean to say, burns and spillage caused by hot molten materials.

The application of water or CO2 in case of fire hazards can really help out. However, the application of water should be performed from a certain distance. Also, keep in mind the suggestions below.

  1. Ensure that the mold fit is appropriate. All the equipment should be properly assembled as well.
  2. Moisture and chemicals should be avoided in welded mold and materials. Hot materials can eject if a connection between hot molten metal and moisture or pollutants is made.
  3. The thickness of the base metal must be kept in mind. It has to be just right for the volume form of the connection. It has to be ensured to avoid melting and leakage of molten metal.

No matter how hot things get with CAD welding, just follow the precautions I stated above, and you should be just fine.

Final Words

In order to establish a molecular connection between two metal parts, an exothermic reaction is needed. After going through all the details above, we can safely say that the procedure has been well explained.

Things can get a bit ugly if you don’t know how to pull things off the right way. That’s exactly where the precautions come in. So, I believe I’ve given you all the information you could possibly need regarding CAD welding. With that said, let’s close things off for now. Farewell!

Hi! My name is Josh Mathews and I’m a professional welder residing in the state of Texas. As I’m a writer by heart, I believe it would be wonderful to share the knowledge I’ve gained over the years working in the welding industry, which worked as my initial motivation. I want others who read through our blogs to get inspired and enter the welding scene one day.

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