When buyers select a process and supplier for the production of an important metal part, they face an enormous array of possible alternatives. A great many metalworking processes are now available, each offering a unique set of capabilities, costs and advantages. The forging process is ideally suited to many part applications, however some buyers may be unaware of the exclusive benefits available only from this ancient form of metal forming. In fact, forging is often the optimum process, in terms of both part quality and cost-efficiency-especially for applications that require maximum part strength, special sizes or critical performance specifications.
There are several forging processes available, including impression or closed die, cold forging, and extrusion. However,here we will discuss in detail the methods, application and comparative benefits of the open die and seamless rolled ring forging processes. We invite you to consider this information when selecting the optimum process for the production of your metal parts.
Open Die Forging ::
Open die forging involves the shaping of heated metal parts between a top die attached to a ram and a bottom die attached to a hammer anvil or press bed. Metal parts are worked above their recrystallization temperatures-ranging from 1900°F to 2400°F for steel-and gradually shaped into the desired configuration through the skillful hammering or pressing of the work piece.
While impression or closed die forging confines the metal in dies, open die forging is distinguished by the fact that the metal is never completely confined or restrained in the dies. Most open die forgings are produced on flat dies. However, round swaging dies, V-dies, mandrels, pins and loose tools are also used depending on the desired part configuration and its size.
Although the open die forging process is often associated with larger, simpler-shaped parts such as bars, blanks, rings, hollows or spindles, in fact it can be considered the ultimate option in "custom-designed" metal components. High-strength, long-life parts optimized in terms of both mechanical properties and structural integrity are today produced in sizes that range from a few pounds to hundreds of tons in weight. In addition, advanced forge shops now offer shapes that were never before thought capable of being produced by the open die forging process.
Rolled Ring Forging ::
The production of seamless forged rings is often performed by a process called ring rolling on rolling mills. These mills vary in size to produce rings with outside diameters of just a few inches to over 300" and in weights from a single pound up to over 300,000 pounds.
The process starts with a circular preform of metal that has been previously upset and pierced (using the open die forging process) to form a hollow "donut". This donut is heated above the recrystallization temperature and placed over the idler or mandrel roll. This idler roll then moves under pressure toward a drive roll that continuously rotates to reduce the wall thickness, thereby increasing the diameters (I.D. and O.D.) of the resulting ring.
Seamless rings can be produced in configurations ranging from flat, washer-like parts to tall, cylindrical shapes, with heights ranging from less than an inch to more than 9 feet. Wall thickness to height ratios of rings typically range from 1:16 up to 16:1, although greater proportions can be achieved with special processing. The simplest, and most commonly used shape is a rectangular cross-section ring, but shaped tooling can be used to produce seamless rolled rings in complex, custom shapes with contours on the inside and/or outside diameters.