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Also known as short-stroke honing or micromachining, superfinishing is a technique using in metalworking to enhance the look and feel of a metal surface. First developed in the United States by the Chrysler Corporation during the 1930s, this process is used to gently remove the thin layer left behind after smoothing the surface with some type of abrasive, but before the process of polishing the metal to a sheen takes place.
In order to manage the superfinishing process, some type of abrasive that carries an extremely fine grit is rotated along the surface while the metal is being rotated in the opposite direction. The action helps to remove the final layer that was left behind by the initial finishing action. The end result is a fine crosshatch pattern on the surface of the metal that is ideal for the final polishing or the application of some type of sealant or paint to the metal. Depending on the nature of the metalworking, some type of liquid or lubricant may be used to control the level of heating that takes place during the process.
While there are various approaches to superfinishing, three main types prevail. The method known as the plunge is considered most effective with surfaces that are irregular in shape. The through-feed method is considered ideal for working with cylindrical metal pieces, and involves rotating the pieces between two drive rollers. A third method known as "wheels," makes use of abrasive wheels or cups to enhance the finish on metal objects that are flat or spherical.
The actual process of superfinishing provides some benefits as well as the potential for a couple of disadvantages to emerge. This process can prolong the usable life of the metal object, typically by decreasing the level of wear and tear that is sustained during normal usage. The metal is likely to remain sealed for longer periods of time as well. An example of how this strategy can make a difference in the life of a metal component is best illustrated with the common gear. Assuming that the teeth on the gear have been superfinished, the component is likely to last anywhere from three to four times as long as a gear that has not undergone the process.
In terms of possible liabilities, superfinishing is an added expense that requires the use of special abrasives and equipment, which in turn may drive up the unit cost of the finished product. The complexity of working with different shapes of metal pieces may also result in the need to take additional time with the overall finishing process, which in turn can also add to the total cost of producing each unit. For this reason, the process may not be employed when the goal is to produce goods quickly and cheaply, without any focus on prolonging the life of the goods.