Metal deforming – By use of closed-die and coacting work-forcer – Forcing work into or within closed die; e.g. – forging
Reexamination Certificate
1999-10-13
2001-06-26
Tolan, Ed (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Forcing work into or within closed die; e.g., forging
C072S020200, C072S344000, C072S355200, C072S376000, C072S453010
Reexamination Certificate
active
06250128
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a forging die device used in cold and hot forging operations and to an upset forging method using the forging die device for forging parts such as a gear or the like.
BACKGROUND ART
Conventionally, machinery parts such as a gear or the like are worked by utilizing metal cutting machines such as gear cutting machine or the like because it is required for the parts to have a high accuracy. However, according to this method, much time is required to work the parts, so that productivity is disadvantageously lowered.
To improve such disadvantages, there has been proposed and actually used a method of manufacturing a small-sized gear by utilizing a forging method. However, in a case where the gear is manufactured by the forging method, many processes such as extruding, upsetting of raw material, ironing of a tooth surface of the gear, or the like are required, so that a surface pressure to be applied to the tooth surface is increased thereby to cause burning or the like. As a result, there is inevitably posed the disadvantage that molding with high accuracy cannot be performed.
In order to improve such disadvantages, for example, an official gazette of Japanese Patent Laid-open Publication No. HEI 5-154598 has proposed a forging method in which a raw material is forged to form a spur gear without increasing the surface pressure of the tooth portion of the gear.
The method of forging the spur gear disclosed in the official gazette is characterized by comprising: a first working process in which a raw material is upset-molded into a primary worked gear having a gear-shape whose tooth profile is set to be smaller than that of a spur gear to be obtained; a second working process in which the material is freely flowed at portions other than tooth portion of the primary worked gear while the gear is compressively molded into a secondary worked gear; and a third working process in which the secondary worked gear is ironically molded into a final product, and wherein the respective processes are performed in accordance with a cold forging working method.
According to the above method, an ironing allowance for the ironical-molding operation is stably formed, so that there can be provided an effect of obtaining a product having a high accuracy by a low molding load.
Further, as a conventional extrusion working method, there is a method in which the material is extrusion-molded using a punch having a hole portion thereby to form a convex portion from the hole portion of the punch, a free end portion of the convex portion is extrusion-worked under a state of being pressed with a predetermined pressure, and the pressure is reduced or removed before the extrusion-work is completed. This method provides an effect of greatly reducing a maximum load to be applied to the molding die in the vicinity of a bottom dead point of the molding die.
However, in the forging method described in the above mentioned official gazette, since the raw material is molded in advance so as to have a gear-shape whose tooth profile is set to be smaller than that of a spur gear to be obtained, one or two processes are required for molding the raw material to form a gear-shape. In addition, three processes are required for forging the raw material, and the number of processes is increased, so that the forging operation requires much time, providing a disadvantage of lowering the productivity.
In addition, changing the punch for every process, the forging operation is performed, the changing work of the punch becomes to be complicated, and a plurality of punches and mandrels are required to be prepared in advance, so that there is posed a disadvantage of increasing the cost of the molding dies.
On the other hand, in the conventional extrusion working method, the material is subjected to a back-extrusion while a flow of the material is partially suppressed by a pressing member provided to an upper punch, and the pressing force of the pressing member is reduced or removed before the extrusion-work is completed, so that a high surface pressure is applied to the molding die from a time when the molding operation is started. As a result, there may be caused various disadvantages such that the molding die causes burning and a life of the molding die decreases in a short period of time.
In addition, in the conventional extrusion working method described above, since the device for effecting the method has a structure in which the pressing member is provided only to the upper punch side, the pressing forces of the upper and lower punches are not uniform with each other and the material flows in only one direction, so that there may also be posed disadvantages such that a strength of the product is lowered, and defects such as cracks and shrinkage cavity are liable to be caused in the product.
Therefore, the present invention has been achieved for improving such disadvantages, and an object of the present invention is to provide a forging die device and upset-forging method capable of forging parts such as a gear having a high accuracy without requiring the pre-working of the raw material and the change of dies during the forging, thereby to improve the productivity and to decrease the cost of the molding dies.
DISCLOSURE OF THE INVENTION
In order to achieve the aforementioned object, in a first aspect of this invention, there is provided a forging die device for upset-forging a raw material filling in a cavity of a lower molding die at a portion between an upper punch of an upper molding die provided to a slide and an lower punch of the lower molding die provided onto a bolster,
wherein the upper and lower punches are provided with an upper pin and a lower pin respectively so that one end of each pin is protruded and withdrawn from each of end surfaces of the upper and lower punches and the pins are vertically movable in the upper and lower punches respectively, while the other end sides of the upper and lower pins are provided with back-pressure imparting means for imparting a back-pressure to each of the upper and lower pins at a time of molding operation and for removing the respective back-pressures immediately before the cavity has been completely filled up with the raw material.
According to this structure, at an initial stage of the molding, the raw material can be flowed to the tooth molding portions with a high pressing force, so that there can be obtained a gear having no lacking portion in tooth portion and having a good quality. At the same time, before the molding load is rapidly increased because the cavity is filled up with the raw material to be completely closed, the back-pressures of the upper and lower pins are removed immediately to allow the upper and lower pins to move in a direction reverse to the pressing direction of the upper and lower punches, so that the raw material can flow into the concave waste hole portion formed by the initial back-pressure and flow into an unfilled portion (a portion which has not been injected) at the outer peripheral portion, and the raw material can be injected so as to have a thickness of the final shape of the product, so that it becomes possible to mold a gear without requiring a large molding load.
Due to this operation, the surface pressure to be applied to the molding die becomes small, the life of the molding die is improved. In addition to this, a pressing capacity can be reduced, so that it becomes possible to upset-forge a gear by using a small-sized pressing machine.
In addition, each of the upper and lower punches is provided with the upper and lower pins respectively and the raw material is pressed by the upper and lower pins in the vertical direction, so that the raw material is uniformly pressured in a vertical direction. Due to this operation, the flow of the raw material becomes to be uniform, so that there can be provided a product in which the fiber flow is uniformly arranged and a product having a high strength and accuracy. Further, since defectives such as crack or shrinkage cavity do not occur, a rate of oc
Ando Hiroyuki
Ishihara Yoshihiro
Matsumoto Isamu
Yamamoto Akira
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Komatsu Industries Corporation
Tolan Ed
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