Metal deforming – With stopping upon completion of prescribed operation
Reexamination Certificate
1999-04-30
2002-02-26
Larson, Lowell A. (Department: 3725)
Metal deforming
With stopping upon completion of prescribed operation
C072S355600
Reexamination Certificate
active
06349582
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to a die system for full enclosed die forging and more particularly to a forging die system for particular use in a stock diversion (diffluence) full enclosed die forging process in which a workpiece stock is allowed to divert in a full enclosed die cavity formed with and by means of a pair of dies.
BACKGROUND ART
Machine components such as gears have customarily be manufactured by a forging or extrusion process as known in the art. Conventional techniques that fall in this genre are described, for example, in Japanese patent literature No. JP H5-154598 A and No. JP 2534899 B2.
Patent literature No. JP H5-154598 A describes a forging method of manufacturing a spur gear that includes a first working step of upsetting a workpiece in a single die and forming it into a primarily worked gear that is smaller in gear contour geometry than the spur gear to be obtained. The method includes a second working step of compression molding the primarily worked gear in a single die while permitting the workpiece stock to freely flow (divert) in the area of it other than its gear forming area in the die to provide a fabricated gear. In the third working step of the method, the fabricated gear is drawn with a single die and formed into the end gear product. The first, second and third working steps are advantageously performed each by cold forging to permit an appropriate drawing allowance for the third working process step to be provided with constancy and maintained, which is described to allow products spur gears to be obtained consistently with an increased accuracy.
Patent literature No. JP 2534899 B2 describes a method for forming by extrusion a mechanical component in which a workpiece in a single die is extruded by means of a punch in the form of a hollow or bored cylinder to produce a raised portion of the mechanical component with the central bore of the punch. The workpiece is further extruded in the die while an open end region of the raised portion is held under a given pressure and the pressure is then reduced or released prior to completion of the extrusion process. This method is described to have an effect of providing the ability to largely reduce the maximum load acting on the die in a region of the lower dead point of the extrusion stroke.
These conventional techniques are found to be unsatisfactory, however, as having certain disadvantages.
Thus, the forging method described in JP H5-154598 A in which a workpiece stock must be preliminarily formed into a gear contour geometry that is smaller than that of a spur gear to be obtained, makes several process steps indispensable to perform including one or two sub-steps for preparing a primarily molded gear, and three successive steps forging. Disadvantageously enough, therefore, the method makes the process time-consuming and is thus poor in productivity.
Also, the need to replaceably use a number of different combinations of dies and punches for the different forging steps necessitates their troublesome or otherwise complicated exchanging procedures and requires preparation not only of these dies and punches in combination but also their individual mandrels, thus making the method costly with respect to the die system expenditure as well.
On the other hand, in the extrusion method described JP 2534899 B2, use is made of a pressure member associated with an upper punch to apply a pressure to the workpiece to cause it to be extruded rearwards with the workpiece stock flowing as in part constricted (diverting). The pressure member described is designed to apply to the workpiece stock a pressure that remains high until the extrusion process is almost complete and then it is reduced or removed, which may adversely act on a die to the extent that the die can inconveniently seize or become quickly unusable.
Also, the construction in which such a pressure member is only associated with the upper punch tends to cause an imbalance in pressure between the upper and lower punches. Then, causing a stock material to divert or flow only in one direction, this system may give rise to an unevenness of fiber flows in an end product, thus inconveniently reducing its strength and tending to develop a defect such as a crack or a surface sink in it.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to overcome these inconveniences in the prior art by providing a die apparatus for full enclosed die forging process in which a pressure means produces an intense force of enclosure and whereby mechanical components that are free of defect and excellent in quality can readily be obtained.
This and other objects are attained in accordance with the present invention by a die system for full enclosed or closed die forging in which an enclosed cavity is formed between an upper die attached to the side of a slide and a lower die mounted to the side of a bolster, and a workpiece stock disposed in the cavity is pressurized to be diverted with an upper counter-punch in the upper die and a lower counter-punch in the lower die and is thereby forged within the confines of the cavity, which system comprises: a pressure means disposed in at least one of a first region above the said upper die and a second region below the said lower die for applying pressure to at least one of the said upper and lower dies from at least one of their upper and lower sides to act to enclose or close the said cavity at least unilaterally; a back or backing pressure imparting means disposed in at least one of a third region above the said upper counter-punch and a fourth region below the said lower counter-punch for applying back pressure to at least one of the said upper and lower counter-punches to force the said workpiece stock being formed to be diverted at least unilaterally in the said cavity; and a back pressure removal means associated with the said back pressure imparting means for removing the said back pressure upon the said workpiece stock filling said cavity.
In performing the process of forging a workpiece stock using the arrangement described, the upper die may be lowered with the slide to bring the upper and lower dies into close and firm contact. An enclosed cavity that accommodates the workpiece stock in it is formed thereby. A pressure applied to at least one of the upper and lower dies tends to enclose or close the cavity at least unilaterally. Under a back pressure then exerted to at least one of the upper and lower counter-punches, the workpiece stock is forced to be diverted at least unilaterally and flow out within the cavity. Upon the workpiece stock as the result of diversion filling the cavity, the back pressure on the at least one of the upper and lower counter-punches is removed. An abnormal rise of pressure in the cavity is thereby prevented. The ability by the pressure means under an elevated pressure to readily achieve an intense force of enclosure or closing makes the system particularly advantageous in producing a large machine part by forging. As any adverse build-up of high pressure after the cavity is filled up with the workpiece stock is avoided by the back pressure removal means, any consequential adverse effects such as a damage to a die or disadvantage of the die becoming quickly useless are effectively prevented.
Also, the ability of the system to maintain a large and sufficient force of enclosure or closing until the slide reaches its lower dead point ensures yielding a forged or formed product that is free of void and is excellent in quality. Also, since a product yielded is free of burr, any work required to perform burr removal that is typical in a conventionally forged product is dispensed with.
Further, hydraulic or fluid pressure only needs to be produced during each forging operation alone. This allows die mounting components to be smaller in size, thus rendering the entire die system less costly.
Preferably in the system described, the said pressure means comprises a first pressure means disposed above the said upper die for applying pressure to the said
Matumoto Isamu
Tanaka Kunihiko
Kananen, Esq. Ronald P.
Komatsu Ltd.
Larson Lowell A.
Rager, Fishman & Grauer PLLC
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