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Forge welding is an old technique that involves connecting pieces of metal using heat and force. The metal is generally heated with fire and the force is typically applied by hammering, but there are other methods. Forge welding is considered a core technique. It is still taught and used, but it is commonly replaced with more modern welding techniques.
Forge welding is generally not considered difficult but can be dangerous. Some methods are complex and may require good concentration, memory, and safety skills. It is also beneficial to know the characteristics of the metal that is being welded and the heat source that is being used.
Thicker pieces of metal are typically easier to forge. This is because thin pieces may bow when heated, resulting in pockets that appear as bubbles on the surface. Thicker pieces of metal also tend to retain heat longer. Pieces that are chosen should typically be free of oxides and contaminants before welding begins.
A flux is generally applied after the metal has been heated but before it reaches its welding heat. Flux is a substance that melts and creates a coating that prevents oxidation. Borax is a common flux, but may not be suitable for all materials. If the metal oxidizes, the result is generally a poor quality forge.
The source of pressure varies depending on the welder’s preference and technique. Some use hand hammers, while others use power hammers. Still others may use a press. Regardless of which pressure tool is used, forge welders often get burned.
In many cases, knowledge and experience are the only ways to tell when metal is hot enough to be forged. It is also important in preventing metals from getting too hot. Different metals weld at different temperatures. It is estimated that these temperatures range between 50 to 90 percent of a metal’s melting temperature.
This process works because when metal is heated to a certain degree, changes occur in the molecules. When pressure is applied, elements from one piece of metal can cross to the other piece. The result of this exchange is a bond. Forge welding can be done with similar or different metals. When different metals are used, the welded product is generally stronger than either of the metals individually.
When the process is successful, there should be no cracks or spaces between the layers. This is true even when several layers are welded together. The forged materials should appear to be one solid item.
But what is happening that makes it weld?