In order to reduce the cost of forged products, the forging must be performed in a closed cavity to obtain near-net or net shape parts. Additionally, the preform must be simple enough to be mass-produced. In both studies the use of process simulations has been helpful in the performance of several iterations without requiring the construction of expensive tooling. All rights reserved. Keywords: Die design; Flashless forging; Tool design 1.
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It is also used as a thermal barrier to restrict heat transfer from the workpiece to the die. Finally, the lubricant acts as a parting compound to prevent the part from sticking in the dies. The amount of time the dies are in contact with the workpiece is measured in seconds as compared to the milliseconds of drop-hammer forges. The press forging operation can be done either cold or hot. Drop-hammer forging usually only deforms the surfaces of the work piece in contact with the hammer and anvil; the interior of the workpiece will stay relatively undeformed.
By controlling the compression rate of the press forging operation, the internal strain can be controlled. There are a few disadvantages to this process, most stemming from the workpiece being in contact with the dies for such an extended period of time. The operation is a time-consuming process due to the amount and length of steps.
The workpiece will cool faster because the dies are in contact with workpiece; the dies facilitate drastically more heat transfer than the surrounding atmosphere. As the workpiece cools it becomes stronger and less ductile, which may induce cracking if deformation continues. Therefore, heated dies are usually used to reduce heat loss, promote surface flow, and enable the production of finer details and closer tolerances. The workpiece may also need to be reheated.
When done in high productivity, press forging is more economical than hammer forging. The operation also creates closer tolerances. In hammer forging a lot of the work is absorbed by the machinery; when in press forging, the greater percentage of work is used in the work piece.
Another advantage is that the operation can be used to create any size part because there is no limit to the size of the press forging machine. New press forging techniques have been able to create a higher degree of mechanical and orientation integrity.
By the constraint of oxidation to the outer layers of the part, reduced levels of microcracking occur in the finished part. Impression-die press forging usually requires less draft than drop forging and has better dimensional accuracy. Also, press forgings can often be done in one closing of the dies, allowing for easy automation. For other uses, see upset disambiguation. Upset forging increases the diameter of the workpiece by compressing its length. Upset forging is usually done in special high-speed machines called crank presses.
The machines are usually set up to work in the horizontal plane, to facilitate the quick exchange of workpieces from one station to the next, but upsetting can also be done in a vertical crank press or a hydraulic press. The standard upsetting machine employs split dies that contain multiple cavities. The dies open enough to allow the workpiece to move from one cavity to the next; the dies then close and the heading tool, or ram, then moves longitudinally against the bar, upsetting it into the cavity.
If all of the cavities are utilized on every cycle, then a finished part will be produced with every cycle, which makes this process advantageous for mass production. Lengths of stock greater than three times the diameter may be upset successfully, provided that the diameter of the upset is not more than 1.
In an upset requiring stock length greater than three times the diameter of the stock, and where the diameter of the cavity is not more than 1. This all occurs rapidly; small parts can be made at a rate of parts per minute ppm and larger can be made at a rate of 90 ppm. The main advantages to this process are its high output rate and ability to accept low-cost materials.
Little labor is required to operate the machinery. Tool life is nearly double that of conventional forging because contact times are on the order of 0. It is then descaled with rollers, sheared into blanks, and transferred through several successive forming stages, during which it is upset, preformed, final forged, and pierced if necessary. This process can also be coupled with high-speed cold-forming operations. Generally, the cold forming operation will do the finishing stage so that the advantages of cold-working can be obtained, while maintaining the high speed of automatic hot forging.
Roll forging is performed using two cylindrical or semi-cylindrical rolls, each containing one or more shaped grooves.
A heated bar is inserted into the rolls and when it hits a spot the rolls rotate and the bar is progressively shaped as it is rolled through the machine. The piece is then transferred to the next set of grooves or turned around and reinserted into the same grooves. This continues until the desired shape and size is achieved.
The advantage of this process is there is no flash and it imparts a favorable grain structure into the workpiece. Net-shape and near-net-shape forging[ edit ] See also: Near-net-shape This process is also known as precision forging. It was developed to minimize cost and waste associated with post-forging operations. Therefore, the final product from a precision forging needs little or no final machining. Cost savings are gained from the use of less material, and thus less scrap, the overall decrease in energy used, and the reduction or elimination of machining.
The downside of this process is its cost, therefore it is only implemented if significant cost reduction can be achieved. Aluminum is a common material that can be cold forged depending on final shape. Lubrication of the parts being formed is critical to increase the life of the mating dies. Main article: Induction forging Unlike the above processes, induction forging is based on the type of heating style used.
Many of the above processes can be used in conjunction with this heating method. Multidirectional forging[ edit ] Multidirectional Forging is forming of a work piece in a single step in several directions. The multidirectional forming takes place through constructive measures of the tool. The vertical movement of the press ram is redirected using wedges which distributes and redirects the force of the forging press in horizontal directions.
Adiabatic heating is used to assist in the deformation of the material, meaning the strain rates are highly controlled. Commonly used for forging aluminium, which has a lower forging temperature than steels.
The process is used to produce a near-net or net shape forging. The dies make no provision for flash because the process does not depend on the formation of flash to achieve complete filling. Actually, a thin fin or ring of flash may form in the clearance between the upper punch and die, but it is easily removed by blasting or tumbling operations, and does not require a trim die. The process is therefore called "flashless forging", and is sometimes called "enclosed die forging". Enclosed dies are illustrated in Figure In some cases the lower die may be split, allowing as-forged undercuts. Split die arrangements are illustrated in Figure