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What is Fusion Welding, and How Does it Work?

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Fusion welding

Have you come across the term fusion welding and wondered what it means? Like any other welding process, fusion welding is used to join two or more objects using heat. However, this welding process is unique since you can either use filler materials or not, and it does not require the application of external pressure. Assuming the two materials to be welded are made of similar materials, heat from the welding rig melts their surfaces, allowing the objects to fuse.

How Fusion Welding Works

From the definition, fusion welding joins edges of different materials by heating them to a melting point. Sometimes, a filler material is necessary if there are gaps in the joint you are making. The materials will undergo many phase transitions because the heating process creates a heat-affected zone (HAZ) on the material(s).

Fusion welding takes place when the molten base materials join with molten fillers. The heat that melts the materials can be applied to the joining zone or developed externally at the intended weld point. For instance, you can pass current via an electrical contact resistance between the edges of the materials you are welding together to develop the heat you need.

The Difference between Fusion Welding and Non-Fusion Welding

Whereas fusion welding must include heat to the melting point, non-fusion welding can occur under low heat intensity since it does not involve the melting of the parent materials. Additionally, no filler materials are needed in non-fusion welding. Examples of non-fusion welding include soldering, brazing, and pressure welding.

What are the Basic Types of Fusion Welds

Understanding different types of fusion welding processes are critical when discussing fusion welding. Based on the heat source, fusion welding processes can be categorized as follows:

1. The Arc Welding Process

Arc welding is among the preferable ways of a fusion welding process. True to the hype, arc welding connects two parts (or more) using an electric arc. The reason is that electric arcs generate heat levels that reach up to 6,000 degrees Fahrenheit, making them ideal for fusing hard metals and materials. Additionally, arc welding is also suitable for offshore applications where you can perform underwater fusion welding. Commonly, arc welding processes include:

  • Shielded Metal Arc Welding (SMAW): Commonly used for welding non-ferrous and ferrous materials in nearly all positions.
  • Metal Gas Arc Welding: An electric arc is forming between the material and consumable wire electrode, allowing them to melt and fuse. Shielding gas is used to avoid airborne contaminants and oxidation for MIG welding.
  • Tungsten Inert Gas Welding: Non-consumable tungsten is used in creating an arc between the basal plate and electrode. To avoid oxidation and atmospheric contaminations, an inert shielding gas is used.
  • Plasma Arc Welding (PAW): In this arc, an electric arc is formed between the torch nozzle and electrode. The argon gas (plasma), usually in the chamber, is ionized by the electric arc.
  • Submerged Arc Welding (SAW): It uses a continuously fed consumable electrode together with a flux. The flux prevents spatter and sparks and becomes conductive in a molten state, hence providing the current electrode and material path.
  • Flux Cored Arc Welding (FCAW): The process is also continuously fed consumable electrodes with flux; hence it serves as an alternative to SMAW.
Gas metal arc welding or GMAW
Image Credit: Matee Nuserm, Shutterstock

2. Laser Beam Welding (LBW)

As the name suggests, this is a fusion welding process that uses a focused laser beam as its energy heat source. The high heat levels have precision rates useful for joining metals and polymers. It is a fast and automated process that uses light to generate heat.

You can perform an LBW in the air instead of a vacuum, unlike the electron beam fusion welding processes.

3. High-Energy Welding Processes

It is a fusion welding process that produces heat through light radiation. To fuse the different materials, you blast the radiation light to the materials’ surface, making them become hot and start to melt. The workpiece will later merge as they gradually cool down.

 These are typical examples of high-energy fusion welding processes.

4. Electronic Beam Welding (EBW)

The electronic beam welding process involves high-velocity electrons to join workpieces together. The electrons produce intense heat that enters the materials changing their solid-state to molten. EBW welds are deep and thin and can only be achieved under specific atmospheric conditions.

electronic beam welding
Image Credit: Nordroden, Shutterstock

5. Friction Welding

When applying the friction welding technique, the different materials are joined together using mechanical friction. There are various ways to perform mechanical friction on aluminum, steel, and sometimes wood materials.

The process of mechanical friction is arduous. However, the heat you generate will soften both materials, creating a bond after mixing and cooling afterward.

There are various ways to perform friction welding, which determines the kind of joints you will have. These processes include:

  • Friction stir welding
  • Rotary friction welding
  • Friction stir spot welding
  • Linear friction welding

When applying friction welding, there is no need for shielding gas, flux, or filler metals. The process is ideal for applications that are considered lightweight and for non-weldable materials like some forms of aluminum alloys.

6. Resistance Welding Processes

It is among the fastest fusion welding options you can apply, making it a preferable choice for the automotive industry. Today, there is two resistance welding process. These are:

Resistance spot welding

It works by producing heat on two electrodes. However, the bonding process depends on the properties and thickness of the materials. The process confines the welding voltage to a single spot when fusing the different workpieces.

Resistance seam welding

It is a form of spot welding that includes a sequence of joint-alternating nuggets. It uses shifting disks to replace the spot welding electrodes to join the materials together.

resistance Spot welding
Image Credit: Dmitry Kalinovsky, Shutterstock

Where is Fusion Welding Used?

Today, there are many uses for fusion welding, including the manufacture of megastructures like ships, airplanes, welded pipes, bridges, automobiles, and pressure vessels. Fusion welding is also inherently used for sealing explosives besides other functions.

Because fusion welding uses a good heat source, you can fuse a thick section of a workpiece with relative ease. Primary uses of fusion welding include:

Fusing Metals

The primary difference between fusion welding and soldering or brazing is the high heat process involved. Brazing and soldering do not melt the base metal, while fusion welding must sometimes include a filler material.  

When different parent metals are subjected to high heat intensities, the increased temperatures create a molten state where they join and form a weld bead when it cools. The result can be a stronger joint than the parent materials.

In some instances, you can use pressure to make welds either on their own or together with a heat source. When fusing metals, you can use a shielding gas to prevent the filler metals or the molten joint from getting oxidized or contaminated.

Joining Polymers (plastics)

Heat is an essential requirement when joining to or more plastic materials. However, it does not apply to solvent welding because the use of adhesives is applied. The process takes place in three vital stages.

  1. Preparation of the surfaces. It includes cleaning and drying.
  2. Application of heat and pressure. It marks the bonding process that forms total coalescence.
  3. Cooling the materials to create the fusion. There can be particular room for cooling, depending on the parent materials. However, because cooling is also fast, this process is merely applicable.

When joining plastics together, you can use either internal or external heating methods. Polymers are generally weaker than metals. Therefore, less heat is required.

Fusion Welding for Joining Wood Materials

Wood welding also uses heat that is generated from mechanical friction to join different materials. The materials are subjected to immense pressure followed by a linear friction movement to create the heat that bonds the workpieces firmly.

The process is fast and allows the joining of wood materials without using nails or adhesives within seconds. It is also a better way to preserve the wood design while strengthening the final workpiece.

Advantages of Fusion Welding

  • Easy use of filler material when filling a large gap when joining different workpieces.
  • The initial shape of the materials does not matter. Hence there is no need for external pressure.
  • No need for edge preparation or design as they will affect the heat penetration.
  • Fusion welding allows more than two-parent materials to be joined firmly together.
  • The fusion welding process is fast and straightforward, making it the best solution for industrial use.

Disadvantages of Fusion Welding

  • It is difficult to join metals with different melting points.
  • Profound heat-affected zones (HAZ) are evident on welded components. HAZ is the weakest part of a welded workpiece.
  • There are cases where the mechanical properties of the workpiece materials get compromised due to intensive heating. Such instances occur when using filler materials and different metals.
fusion welding process
Image Credit: Kimtaro, Shutterstock

FAQs: What Is Fusion Welding?

How is fusion welding different from solid-state welding?

Solid-state welding requires close contact of two clean metal surfaces to form a metallic bond. The advantage of solid-phase welding over fusion welding is that you can achieve it in temperatures as low as room temperature.

The bonding process takes place either by deformation or limited deformation by diffusion. The diffusion (atomic movements) will make new bonds between the atoms of the two-parent materials.

What is electric arc welding?

Electric arc welding involves joining two or more different metals. The process can be achieved with or without filler material and external pressure application. 

What are the basic principles of fusion welding?

Fusion welding primarily uses a heat source to generate sufficient heat necessary to maintain a molten pool. You can find various heat sources, including a gas flame or electricity. However, not all forms of fusion welding require heat. For instance, pressure welding can create permanent bonds at lower or room temperature. 

What is a fusion welding zone?

A fusion zone is a section of the parent material that is left after the welding. A fusion zone is marked by the beginning and ends of the coalesced workpiece. All fusion zones possess a chemical composition of the mixed substrates you are welding together. In instances where you use a filler material or gas shielding, the fusion zone will have all these elements in its composition, making it different from the parent materials.

Final Thoughts

Having all the information about what fusion welding is will make one understand when to apply the ideal processes for the kind of welding you have. Fusion welding is fast and suited for fusing two or more dissimilar materials of any weight. The various fusion welding techniques can be applied underwater, air, and in a vacuum. It is diverse and adjusted to accommodate commercial use across many industries.

Fusion welding leads to stronger bonds because the different materials join to form a homogenous workpiece. In some cases, the bonding section results in a stronger bond than other areas of the parent materials. It is inherent that fusion welding is suitable for creating permanent bonds, thereby making firm and reliable megastructures.

Featured Image Credit: Mohamed Adel, Shutterstock

Cameron Dekker

Cameron grew up in Allentown, Pennsylvania, a once-proud steel town on the Lehigh River, where he got a taste of TIG welding in his high school shop class. He holds certificates for Certified WeldingEducator (CWE) and Certified Resistance Welding Technician (CRWT) from the American Welding Institute. His interests include scuba diving, sculpture, and kayaking.