What is CAD Welding

What is CAD Welding?

As electrical protection systems are installed, it is important that grounded electrical connections remain stable. If these connections break, mechanisms for grounding, locking, and lightning defense may become vulnerable to failures. So, what is Cad welding? Cad welding is a method of joining metals together by using an electrical current. This welding process uses an exothermic thermite contact between aluminum and copper oxide to transfer uncontaminated copper into the weld. We will be discussing everything there is to know about Cad welding. Most of the people confuse this with Tack Welding but it’s different.

How Does it work?

Cadweld employs a precast, clampable mold to secure two metal rods together in a variety of joint configurations. Most often, the rods are flush against each other, but T-joints are also common. After the joint members are inserted into the mold, the mold is clamped together tightly, and a sealing compound is placed around the entry point of the metal pieces to prevent leakage. This weld will not allow any metal to escape during the welding process.

How does it work

Next, the thermite mixture of the chosen filler metal and an oxidizing agent is placed on the top of the precast mold. The mold is then closed from the top. All that is left is to use a heating torch to start the reaction and begin the weld. The hot metal flows from the upper chamber of the mold and down into the weld cavity, forming the weld around the two pieces of metal.

The process can create a lot of smoke and some explosions are known to occur, so it’s important to wear personal protective equipment such as gloves and safety glasses at all times and to keep your distance from the area. Once the weld is done, the mold will be unclamped and there will be slag left over from the weld on the inside. This will all need to be cleared out with a wire brush before setting up the mold again for another weld.

What are the Different Types of CAD Welding?

There are two of the most common kinds of exothermic welding are rail welding and Cadweld

  • Rail Welding This uses the same basic equipment as the Cadweld process we’ve talked about so far. The size of the equipment used for locomotives is much larger than that used for copper cables and rebar. There is typically a mold that is larger and situated on either side of the rails’ joint. However, the reaction that occurs is not contained within the mold.
    Instead, the thermite is deposited into a refractory crucible, which then pours the molten metal into the mold. The still-cooling equipment is removed from the rail so that the excess can be knocked off easily with a sledgehammer. The metal reinforcement that has solidified is then ground off with a grinder so that the surface of the joint is flush. You can see a demonstration of this process here.
  • Cadweld This process was preceded by the messier and more dangerous thermite welding that is used in rail welding. Cadweld is mostly self-contained, with the filler metal and activator often coming prepackaged. This eliminates the need to measure out how much will be needed for each weld.

Where is it Used?

Where is it used
  1. Copper This is one of the best ways to weld copper because it won’t damage the metal or reduce conductivity. The process produces a purity that can’t be matched by other methods. The lower the purity of the metal, the lower its conductivity. Copper is used in power distribution equipment and is also heavily used in transit, such as bus rails and racks.
  2. Electronics Exothermic welding is a process that uses exothermic reactions to bond wires using various alloyed metals and solder filler metals. This is called exothermic brazing. The process is comparable to exothermic welding as it employs a filler metal with a metal oxide to provoke the reaction. This brazing process only requires a short amount of heat input so that there is no damage or distortion to the sensitive electronic materials.
  3. Galvanized Cable The only method for bonding copper to galvanized cable that is acceptable according to the United States National Electrical Code is by using exothermic welding. The conductivity of galvanized material is generally not as great as that of bare metals, due to the zinc coating. If welding is to be done on galvanized material, the galvanization usually has to be ground off. The galvanized coating may also result in porosity and other defects in the weld. However, this can be prevented through exothermic welding. According to the NEC, all welds of this type must be X-ray tested.

Advantages of CAD Welding

  • The conductivity of cables and wires is increased
  • Durable connection
  • Prepackaged thermite is often included
  • It does not take much skill to achieve
Advantages of CAD Welding

Disadvantages of CAD Welding

  • The dangers depend on the application
  • Welding can be adversely affected by certain environmental conditions


What is the temperature of thermite welding?

The temperature of thermite welding is approximately 4,000°F. This is still hot enough to form the strong bond necessary, though it is 7,000°F less than an arc welding process.

Can you CAD weld in the rain?

Even though CAD welding is a self-contained process, it is not recommended to weld in the rain. Water entering the chamber can cause defects.To avoid complications while CAD welding in wet weather, be sure to keep the area around the welding as dry as possible.


We’re accustomed to seeing arc welding, which uses electricity to fuse materials together. Welding in some form or another has been around for thousands of years. The interesting thing about exothermic welding is how it seems so fundamental, yet we still rely on it to secure electrical connections. No matter how old they get, some technologies never go out of style and continue to be useful.

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