A press, or a machine press is a tool used to work metal (typically steel) by changing its shape and internal structure.
A forge press reforms the workpiece into a three dimensional objectâ€”not only changing its visible shape but also the internal structure of the material. A stronger part results from this process than if the object was machined.
Bending is a typical operation performed and occurs by a machine pressing, or applying direct pressure, to the material and forcing it to change shape. A press brake is a typical machine for this operation.
An easy to understand type of machine press is a set of rollers. Metal is fed into the rollers, which are turning to pull the material through. The space between the rollers is smaller than the unfinished metal, and thus the metal is made thinner and/or wider.
Another kind of press is a set of plates with a relief, or depth-based design, in them. The metal is placed between the plates, and the plates are pressed up against each other, deforming the metal in the desired fashion. This may be coining or embossing or forming. A punch press is used for forming holes.
Progressive stamping is a manufacturing method that can encompass punching, coining, bending and several ways of modifying the metal, combined with an automatic feeding system. The feeding system pushes a coil of metal through all of the stations of a progressive stamping die. Each station performs one or more operations until a finished part is made per the requirements on the print. The final operation is a cutoff operation, which separates the finished part from the carrying web. The carrying web, along with metal that is punched away in previous operations, is considered scrap metal.
Machine presses are used extensively around the world for shaping all kinds of metals to a desired shape. A typical toaster (for bread) has a metal case that has been bent and pressed into shape by a machine press.
Machine presses started as a hand-held hammer banging away at a piece of metal to shape it to the desired form. Later, larger hammers were constructed to press more metal at once, or to press thicker materials. Adding wind or steam power allowed for stronger presses. Most modern machine presses use a combination of electric motors and hydraulics to achieve the necessary pressure.