Metal deforming – By use of closed-die and coacting work-forcer – Forcing work into or within closed die; e.g. – forging
Reexamination Certificate
2000-04-03
2001-06-05
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Forcing work into or within closed die; e.g., forging
C072S352000
Reexamination Certificate
active
06240765
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the benefit of U.S. Provisional Application Ser. No. 60/033,250, filed Dec. 6, 1996, and U.S. Provisional Application Ser. No. 60/038,493, filed Feb. 24, 1997, the disclosures of which are hereby incorporated herein by reference.
This invention relates to a forging method for generally axisymmetric articles and to a forging press wherein generally axisymmetric articles are forged in an incremental fashion.
In forging, a workpiece is compressed between two or more forging dies by a machine termed a forging press. The workpiece plastically deforms to a new shape determined by the shapes of the forging dies and the amount of compression. The forging may be accomplished in a single press stroke, or there may be multiple press strokes to gradually deform the workpiece to the required final shape of the article.
The forging operation thins the workpiece in the direction of force application and causes it to enlarge in the perpendicular plane. The workpiece is thereby deformed to the final forged shape. The final forged shape must be distinguished from the final article shape, because in general it is not possible or desirable to forge the workpiece to precisely the final desired article shape. The degree to which the final forged shape approximates that of the final desired article determines the difficulty of the forging operation to some degree. It is relatively easy to uniformly forge the workpiece over its entire plan view area, termed pancake forging. However, in a typical situation involving a complexly shaped final desired article, pancake forging leaves large amounts of material to be machined away to reach the details of the shape of the final desired article. In a more-advanced approach to forging, the workpiece is forged to a near-net-shape (NNS) configuration that closely approximates the shape of the final article but is intentionally slightly oversize to permit ultrasonic inspection, removal of sufficient material to account for distortion experienced during heat treatment, and final machining of the details. In this NNS forging approach, the amount of metal machined away is relatively small. NNS forging requires considerably more ingenuity in designing the forging process than does pancake forging.
Forging is used in a wide variety of operations to produce both small and large articles. To deform the workpiece, a forging press must apply the required force. The production of large articles is particularly challenging because the larger the article, the larger is the required forging force. Consequently, a larger and more expensive forging press is needed to accomplish the forging. As noted, NNS forging usually requires greater forging forces, and thence a larger forging press, than pancake forging.
In some cases, it is desired to produce an article whose size and material of construction are such that the force capacity of the available forging press is exceeded. To forge such articles, it is known to incrementally forge the workpiece using an open-die forging operation. In incremental open-die forging, the design of the forging dies and the operation of the forging press are such that only a portion of the workpiece is forged at any one time. The workpiece is moved incrementally relative to the forging dies after each region is forged, eventually leading to complete forging of the entire workpiece. Unfortunately, open-die forging and incremental open-die forging cannot achieve near-net-shape configurations for most articles, because the unconstrained portion of the workpiece is allowed to expand to whatever size and configuration results, rather than to a near net shape.
In one application, a workpiece is forged into an axisymmetric turbine disk for use in a large land-based gas turbine. Such turbine disks are as much as 70-96 inches in diameter or larger. They are made of nickel-base or iron-base superalloys and cannot be forged to a desired near-net-shape geometry even on a press having a capacity of 50,000 tons. The axisymmetric near-net-shape, dimensional, and mechanical property requirements of the final turbine disks are quite stringent. The existing incremental forging techniques for such disks cannot meet these requirements.
Accordingly, there is a need for an improved approach to the forging of large axisymmetric articles. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides an incremental forging press and technique for producing large, axisymmetric, near-net-shape (NNS) forgings. The shapes, dimensions, and mechanical properties of the forgings are acceptable for precision applications such as final machining to large land-based turbine disks. In the final forging operation, only a portion of the workpiece is contacted by the forging dies in each forging stroke, so that the size of the workpiece may be larger than otherwise possible for an available forging press capacity. The required amount of final machining of the article is significantly reduced as compared with prior approaches, resulting in greatly reduced material waste. The latter is important, because a significant part of the cost of the forging is the material cost of the workpiece, which is a nickel-base superalloy. Reducing the amount of material which must be machined away reduces the manufacturing cost of the article.
In accordance with the invention, a method of forging a workpiece is operable with a generally axisymmetric, disk-shaped starting workpiece having a plan view area. The method includes first forging the starting workpiece over substantially its entire plan view area, and thereafter incrementally forging the first-forged workpiece to a final forged configuration. In the first forging operation, the starting workpiece is forged with a (non-incremental) forging die that extends over substantially the entire plan view area. Preferably, a radially inner portion of the workpiece is forged to about its final forged configuration, but a radially outer portion of the workpiece is not forged to its final forged configuration. In the following step of incremental forging, the radially outer portion of the workpiece is preferably incrementally forged to its final forged configuration without substantially altering the radially inner portion of the workpiece, although there may be some relatively minor deformation of the radially inner portion of the workpiece in the incremental forging step.
The approach of the invention allows the forging of radially larger, substantially axisymmetric articles by closed-die forging than is possible with conventional, non-incremental closed-die forging techniques. A maximum forging capacity of a forging press is defined by the largest size article that may be forged by the forging press using closed-die, non-incremental forging. The use of incremental closed-die forging allows the forging of a larger (but otherwise identical) article using the same press and forging conditions. In accordance with this aspect of the invention, a method of forging an oversize workpiece comprises the steps of furnishing a forging press having a forging press maximum force capacity sufficient to forge an axisymmetric article of a non-incrementally forged maximum final size by closed-die, non-incremental forging, under a set of forging conditions. The method further includes furnishing an axisymmetric workpiece, and incrementally forging the workpiece by closed die forging in the forging press under the set of forging conditions, to form an incrementally forged article having an incrementally forged final size greater than the non-incrementally forged maximum final size. In order to make a fair comparison, all other forging conditions such as material, temperature, forging rate, and geometric similarity are the same, and only the dimensions of the workpiece and the dies are scaled. “Size” refers to the radial dimension measured outwardly from the axis of symmetry.
The incremental forging is preferably closed die incremental forging leading
Antaya Paul D.
Delgado Hugo E.
Doherty Thomas F.
Gargolinski Paul J.
Howson Timothy E.
Larson Lowell A.
Wyman Gordon Corporation
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