Forging is the process of forming and shaping metals through the use of hammering, pressing or rolling. The process begins with starting stock, usually a cast ingot (or a “cogged” billet which has already been forged from a cast ingot), which is heated to its plastic deformation temperature, then upset or “kneaded” between dies to the desired shape and size.
During this hot forging process, the cast, coarse grain structure is broken up and replaced by finer grains. Low-density areas, microshrinkage and gas porosity inherent in the cast metal are consolidated through the reduction of the ingot, achieving sound centers and structural integrity. Mechanical properties are therefore improved through the elimination of the cast structure, enhanced density, and improved homogeneity. Forging also provides means for aligning the grain flow to best obtain desired directional strengths. Secondary processing, such as heat treating, can also be used to further refine the part.
There are two types of plastics. One is called thermosetting resin which does not soften again once it is formed and hardened, and the other is called thermoplastic resin which becomes soft or hard when its temperature rises or falls. Although thermosetting resin has an older history, the majority of the presently used plastics are made of thermoplastic resins.
There are several types of forging method:
Open die forging
pen 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-shaper 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.
The open die forging process:
-Rough forging a heated billet between flat dies to the maximum diameter dimension.
-A “fuller” tool marks the starting “step” locations on the fully rounded workpiece.
-Forging or “drawing” down the first step to size.
-The second step is drawn down to size. Note how the part elongates with each process step as the material is being displaced.
-“Planishing” the rough forging for a smoother surface finish and to keep stock allowance to a minimum.
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 300000 pounds.
The process starts with a circular perform 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.
The rolled ring forging process:
-Starting stock cut to size by weight is first rounded, then upset to achieve structural integrity and directional grain flow.
-Work piece is punched, then pierced to achieve starting “donut” shape needed for ring rolling process.
-Completed preform ready for placement on ring mill for rolling.
-Ring rolling process begins with the idler roll applying pressure to the preform against the drive roll.
-Ring diameters are increased as the continuous pressure reduces the wall thickness. The axial rolls control the height of the ring as it is being rolled.
-The process continues until the desired size is achieved.