Forge welding

Forge welding (FOW) is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process. Forge welding (FOW) is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process. Forge welding is a process of joining metals by heating them beyond a certain threshold and forcing them together with enough pressure to cause deformation of the weld surfaces, creating a metallic bond between the atoms of the metals. The pressure required varies, depending on the temperature, strength, and hardness of the alloy. Forge welding is the oldest welding technique, and has been used since ancient times. Welding processes can generally be grouped into two categories: fusion and diffusion welding. Fusion welding involves localized melting of the metals at the weld interfaces, and is common in electric or gas welding techniques. This requires temperatures much higher than the melting point of the metal in order to cause localized melting before the heat can thermally conduct away from the weld, and often a filler metal is used to keep the weld from segregating due to the high surface tension. Diffusion welding consists of joining the metals without melting them, welding the surfaces together while in the solid state. In diffusion welding, the heat source is often lower than the melting point of the metal, allowing more even heat-distribution thus reducing thermal stresses at the weld. In this method a filler metal is typically not used, but the weld occurs directly between the metals at the weld interface. This includes methods such as cold welding, explosion welding, and forge welding. Unlike other diffusion methods, in forge welding the metals are heated to a high temperature before forcing them together, usually resulting in greater plasticity at the weld surfaces. This generally makes forge welding more versatile than cold-diffusion techniques, which are usually performed on soft metals like copper or aluminum. In forge welding, the entire welding areas are heated evenly. Forge welding can be used for a much wider range of harder metals and alloys, like steel and titanium. The history of joining metals goes back to the Bronze age, where bronzes of different hardness were often joined by casting-in. This method consisted of placing a solid part into a molten metal contained in a mold and allowing it to solidify without actually melting both metals, such as the blade of a sword into a handle or the tang of an arrowhead into the tip. Brazing and soldering were also common during the Bronze age. The act of welding (joining two solid parts through diffusion) began with iron. The first welding process was forge welding, which started when humans learned to smelt iron from iron ore; most likely in Anatolia (Turkey) around 1800 BC. Ancient people could not create temperatures high enough to melt iron fully, so the bloomery process that was used for smelting iron produced a lump (bloom) of iron grains sintered together with small amounts of slag and other impurities, referred to as sponge iron because of its porosity. After smelting the sponge iron needed to be heated above the welding temperature and hammered, or 'wrought.' This squeezed out air pockets and melted slag, bringing the iron grains into close contact to form a solid block (billet). Many items made of wrought iron have been found by archeologists, that show evidence of forge welding, which date from before 1000 BC. Because iron was typically made in small amounts, any large object, such as the Delhi Pillar, needed to be forge welded out of smaller billets. Forge welding grew from a trial-and-error method, becoming more refined over the centuries. Due to the poor quality of ancient metals, it was commonly employed in making composite steels, by joining high-carbon steels, that would resist deformation but break easily, with low-carbon steels, which resist fracture but bend too easily, creating an object with greater toughness and strength than could be produced with a single alloy. This method of pattern welding first appeared around 700 BC, and was primarily used for making weapons such as swords; the most widely known examples being Damascene, Japanese and Merovingian. This process was also common in the manufacture of tools, from wrought-iron plows with steel edges to iron chisels with steel cutting surfaces. Many metals can be forge welded, with the most common being both high and low-carbon steels. Iron and even some hypoeutectic cast-irons can be forge welded. Some aluminum alloys can also be forge welded. Metals such as copper, bronze and brass do not forge weld readily. Although it is possible to forge weld copper-based alloys, it is often with great difficulty due to copper's tendency to absorb oxygen during the heating. Copper and its alloys are usually better joined with cold welding, explosion welding, or other pressure-welding techniques. With iron or steel, the presence of even small amounts of copper severely reduces the alloy's ability to forge weld. Titanium alloys are commonly forge welded. Because of titanium's tendency to absorb oxygen when molten, the solid-state, diffusion bond of a forge weld is often stronger than a fusion weld in which the metal is liquefied. Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that consists of only the welded materials without any fillers or bridging materials. Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.