745 Welding, Cutting, and Brazing Safety

Processes

What is Welding?

Welding joins materials together by melting a metal work piece along with a filler metal to form a strong joint. Welding is classified into two general groups: Fusion Welding and Pressure Welding.

Fusion Welding: This method uses only heat to join materials, typically metals or thermoplastics, by heating the workpieces to their melting point, allowing them to fuse together upon cooling. No additional filler material is always necessary, though it may be used. There are three types of fusion welding: gas, electric arc, and thermit.

• Gas welding, also known as oxy-fuel welding, involves using a flame produced by burning a fuel gas (like acetylene) with oxygen. The heat from the flame is used to melt and join the base metals. A filler rod, typically made of the same material as the workpiece, is added to help form a strong bond when cooled. It is commonly used in automotive and metalworking industries because of its portability and precision.
• Electric arc welding is the most widely used type of fusion welding. It uses a high-temperature electric arc between the electrode and the workpiece to generate heat that melts both the electrode and the base metal. The melting forms a molten pool of metal that solidifies to create a strong bond once it cools. It is widely used in industries such as construction, automotive, aerospace, and manufacturing to build and repair structures, machinery, and pipelines.
• Thermite welding, also called exothermic welding, is a process that uses a chemical reaction between a mixture of metal powders, typically aluminum powder and iron oxide, to generate extremely high heat. The molten metal from the thermite reaction creates a strong, durable bond. It is often used for welding large, heavy sections of metal, especially in railway track maintenance, where it is used to join rails.

Pressure Welding: Pressure welding is a method used to join two metal pieces by applying both heat and pressure without the need for filler materials. The process typically involves applying pressure through resistance, friction, or induction to the metal surfaces while simultaneously heating them, causing the surfaces to soften and bond. There are several different types of pressure welding, including:

• Resistance Welding: In this process, heat is generated by the electrical resistance to current flow as it passes through the metal pieces. The metal is heated and softened at the joint, and then pressure is applied to weld the pieces together. This method is widely used for spot welding, seam welding, and projection welding in various industries.
• Friction Welding: This process uses mechanical friction to generate heat between the two pieces of metal. The workpieces are rotated relative to each other at high speed, and pressure is applied to force them together once they reach the desired temperature. Friction welding is commonly used for joining dissimilar metals, such as steel to aluminum, and is highly effective in applications where other methods might fail.
• Explosive Welding: This is a unique form of pressure welding where high explosives are used to force two pieces of metal together. The explosive force generates intense heat and pressure, causing the metal to fuse without the need for a traditional heat source. Explosive welding is often used to bond dissimilar metals, such as copper to steel, and in applications like heat exchangers or in the aerospace industry.

What is Cutting, Brazing, and Soldering?

Cutting: A process that separates or shapes metal by applying intense heat, mechanical force, or chemical reactions. Oxy-fuel cutting, plasma cutting, and laser cutting are common methods that use different energy sources to remove or shape metal efficiently. Cutting is widely used in manufacturing, construction, and metalworking industries to prepare materials for welding or fabrication.

Brazing: A welding process that joins metals using a filler metal with a melting point above 450°C (840°F) but below the melting point of the base metal. OSHA requires adequate ventilation when brazing to prevent exposure to hazardous fumes.

Soldering: A metal-joining process in which a filler metal, called solder, is melted at a temperature below 450°C (842°F) to bond two or more metal surfaces without melting the base metals. Soldering is commonly used in electronics, plumbing, and jewelry making to create strong but reversible connections.

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