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The forge or smithy is the workplace of a smith or a blacksmith. "Forging" is the term for shaping metal by use of heat and hammer.
A basic smithy contains a forge, sometimes called a hearth (for heating the metals; commonly iron or steel) to a malleable temperature, an anvil (to lay the metal pieces on while hammering), and a slack tub (to rapidly cool, and thus harden, forged metal pieces in). Tools include tongs to hold the hot metal, and hammers to strike the hot metal.
Once the final shape has been forged, iron and steel in particular often get some type of heat treatment. This can result in various degrees of hardening or softening depending on the details of the treatment.
Forging is the working of metal by plastic deformation. It is distinguished from machining, the shaping of metal by removing material (drilling, sawing, milling, turning, grinding, etc.), and from casting, wherein metal in its molten state is poured into a mold, whose form it retains on solidifying. The processes of raising, rolling, swaging, and drawing are essentially forging operations although they are not commonly so called because of the special techniques and tooling they require.
Many metals are typically forged cold but iron and its alloys are almost always forged hot because of their great resistance to deformation.
Forging was done historically by a smith using hammer and anvil, and though the use of water power in the production and working of iron dates to the twelfth century CE the hammer and anvil are by no means obsolete.
In industry forging is commonly done either with machine presses or with hammers powered by steam or compressed air. These hammers are very large, having reciprocating weights in the thousands of pounds. Smaller power hammers (500 pounds or less reciprocating weight) and hydraulic presses are common in art smithies as well.
In industry a distinction is made between open- and closed-die forging. In open-die work the metal is free to move except where contacted by the hammer, anvil, or other (often hand-held) tooling. In closed-die work the material is placed in a die resembling a mold, which it is forced to fill by the application of pressure. A great many common objects (wrenches, crankshafts...) are produced by closed-die forging, which is well suited to mass production. Open-die forging lends itself to very short runs and is appropriate for art smithing and custom work.
Closed-die forging is more expensive for mass production than is casting, but produces a much stronger part, and is thus used for tools, critical machine parts, and the like. One particular variant, drop forging , is often used to mass produce flat wrenches and other household tools.
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