Hot forging metal mold

Abstract

To provide a hot forging metal mold which avoids underfill due to filling of mold lubricant and prevent burrs from occurring when applying the mold lubricant to an inner surface of the metal mold so that a workpiece is easily released from the metal mold after molding.SOLUTION: A hot forging metal mold 2 includes a non-piercing hole 4 which is arranged at an inner surface with which a workpiece contacts and does not penetrate through the metal mold to the outside. Liquid mold lubricant sprayed or coated on the inner surface of the metal mold during hot forging molding of the workpiece is vaporized by heat of the workpiece to be guided into the hole 4 so that the workpiece is inhibited from flowing into the hole because of raised inner pressure of the hole. The hole 4 can be a bag-shaped.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the configuration of a die used in hot forging, and more specifically, to a die having gas vent holes formed therein to prevent a release agent from being trapped between a workpiece and the die when the release agent is applied to the inner surface of the die in order to easily release a workpiece (item to be forged) from the die during the hot forging process. [Background technology]

[0002] In hot forging, burrs and undercuts may occur on the surface of the workpiece after forming, so various techniques have been proposed to prevent such burrs and undercuts on the surface of the workpiece. For example, Patent Document 1 describes that when upsetting a rough workpiece (workpiece) between a lower die and an upper die, a pocket is provided on the edge of the contact surface with the rough workpiece of the upper die to prevent the rough workpiece from flowing into the gap between the lower die and the upper die and generating burrs, and when the rough workpiece enters the pocket, it is cooled and hardened, thereby preventing the rough workpiece from flowing into the gap between the lower die and the upper die. Patent Document 2 discloses that a gas vent passage is provided to discharge gas trapped in the forming hole of the forging die during forming, in order to smoothly release gas trapped in the forming hole even in a complex die shape and suppress the occurrence of undercuts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2014-213364 [Patent Document 2] Patent Publication No. 2012-232347 Summary of the Invention [Problem to be solved by the invention]

[0004] In hot forging, after the workpiece is forged in the die, a release agent is sprayed or applied to the inner surface of the die to facilitate the release of the workpiece from the die. When the release agent is trapped and sealed between the workpiece and the die during forging, it vaporizes and expands, which may result in a portion where the workpiece does not contact the inner surface of the die, and the shape of the die may not be properly transferred to the workpiece, resulting in underfill. As a countermeasure to this, several gas vent holes are provided on the inner surface of the die that penetrate from the inner surface of the die to the outside in order to release the gas of the release agent from the inner surface of the die. In this case, as will be explained later, the material of the workpiece may flow into the gas vent holes, resulting in burrs in those portions.

[0005] The inventor further researched various methods to prevent underfilling of the workpiece after forming while avoiding the occurrence of burrs, and found that by using a die with a closed hole, i.e., a bag-shaped hole, rather than a hole penetrating to the outside of the die, for releasing gas from the inner surface of the die, a workpiece without burrs can be formed in hot forging using a release agent. This finding is utilized in the present invention.

[0006] Thus, a main object of the present invention is to provide a die for hot forging which, when a release agent is used to easily release a workpiece from the die after molding, can avoid underfill caused by the inclusion of a release agent and can also prevent the generation of burrs. [Means for solving the problem]

[0007] According to the present invention, the above object is achieved by providing a die for hot forging, the die having an inner surface in contact with the workpiece that is provided with a hole that does not extend through to the outside of the die.

[0008] In the above configuration, the die may be a die for hot forging of any shape. The hole provided on the inner surface of the die in contact with the workpiece is a gas vent hole for releasing the vaporized release agent from inside the die as described above, but it is a hole that is opened only on the inner surface of the die and does not penetrate to the outside of the die. According to this configuration, as shown in the embodiment column, the shape of the die is sufficiently transferred to the workpiece after forging, and it is possible to suppress the occurrence of burrs in the gas vent hole. This is because the gas generated on the inner surface of the die escapes into the hole, so that no undercut occurs, but because the other side of the hole is closed, the internal pressure of the hole becomes high, and the material of the workpiece does not flow into the hole.

[0009] In the above-mentioned configuration of the present invention, the holes formed on the inner surface of the die may be appropriately provided in a portion where a space to be sealed between the workpiece and the inner surface of the die is formed during forging. The specific positions and number of the holes can be determined experimentally.

[0010] In the above configuration, the hole formed on the inner surface of the mold may be formed in a bag shape having a space therein with a diameter larger than the opening diameter of the inner surface of the mold. With such a configuration, the vaporized release agent can be appropriately accommodated. The volume inside the hole may be determined experimentally. Specifically, when the liquid is vaporized, the volume becomes about 1700 times, so the volume inside the hole may be about 1700 times the volume of the liquid release agent applied to the inner surface of the mold. Effect of the Invention

[0011] According to the above-mentioned configuration of the die of the present invention, when a release agent is used in hot forging to easily release the workpiece from the die after molding, it is possible to prevent undercutting and burrs from occurring in the workpiece. This makes the deburring process of the workpiece unnecessary or simplified, and is expected to improve manufacturing efficiency. The die of the present invention is preferably used in hot forging of shaft-shaped products, but may also be applied to the molding of other flat-shaped articles.

[0012] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief description of the drawings]

[0013] [Figure 1] Figures 1(A) to (C) are schematic side views of a process for forging a workpiece using the hot forging die according to this embodiment. Figure 1(D) is a schematic top view of a die of the hot forging die according to this embodiment. Figure 1(E) is a schematic cross-sectional view of the vicinity of a gas vent hole of the hot forging die according to this embodiment. Figure 1(F) is a photograph of a workpiece formed using the hot forging die according to this embodiment. [Diagram 2] 2(A) to 2(C) are schematic side views of a process for forging a workpiece using a hot forging die without a gas vent hole, and Fig. 2(D) is a schematic cross-sectional view of a state in which a release agent is enclosed between the hot forging die without a gas vent hole and the workpiece. [Diagram 3] 3(A)-(C) are schematic side views of a process for forging a workpiece using a hot forging die provided with a vent hole penetrating to the outside. FIG. 3(D) is a schematic cross-sectional view of the vicinity of a vent hole of a hot forging die provided with a vent hole penetrating to the outside. FIG. 3(E) is a photograph of a workpiece formed using a hot forging die provided with a vent hole penetrating to the outside, and FIG. 3(F) is an enlarged photograph and schematic diagram of a protruding burr generated near the vent hole. [Explanation of symbols]

[0014] 1...Punch (mold), 2...Die (mold), 3...KO punch (mold). 4...Gas vent hole, 4a...Through gas vent hole, W...Work. m...Enclosed space, P...Bur BEST MODE FOR CARRYING OUT THEINVENTION

[0015] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0016] Conventional hot forging dies In hot forging, generally, as shown in Fig. 2(A), a workpiece W heated to a high temperature is placed inside a die 2 of a metal mold, and a KO punch 3 is placed below the workpiece W. As shown in Figs. 2(B)-(C), the workpiece W is pushed into the die 2 from above the die 2 by a punch 1, thereby forming the workpiece W so that the shape of the die 2 is transferred to the workpiece W. At this time, in order to easily release the workpiece W from the die 2 after forming, a liquid release agent is sprayed or applied to the inner surface of the die 2 prior to placing the workpiece W. In this case, the release agent will evaporate due to the heat of the workpiece. If, as shown in the figure, no hole or the like for letting the gas escape is formed on the inner surface of the die 2, and a space m that is sealed from the surroundings is formed between the workpiece W and the die 2 during the deformation process of the workpiece as shown in FIG. 2(D), the vaporized release agent will have no way to escape in that space m. As a result, that part of the workpiece W will not come into contact with the inner surface of the die 2, and when it is molded and hardened, that part may become underfilled.

[0017] As already mentioned, the occurrence of such undercut portions can be avoided by forming a vent hole on the inner surface of the die 2 at a location where a space m sealed from the surroundings is formed between the workpiece W and the die 2, and allowing the vaporized release agent to escape. In the past, therefore, in order to allow the vaporized release agent to escape to the outside of the die 2, a vent hole 4a was provided that penetrated from the inner surface to the outside of the die 2, as shown in Figures 3(A) to (C), and this made it possible to reliably transfer the shape of the die 2 to the workpiece W.

[0018] However, when the die 2 is provided with a gas vent hole 4a penetrating from its inner surface to the outside, as shown in Fig. 3(D), it is known that during the forging process of the workpiece W, a part of the softened workpiece flows into the gas vent hole 4a and hardens in that state to become a burr P. In fact, as shown in Figs. 3(E) and (F), a protruding burr P corresponding to the gas vent hole 4a is formed on the surface of the workpiece W formed using a die having a penetrating gas vent hole 4a. This phenomenon is believed to occur because the release agent vaporized under high temperature between the workpiece and the die and pressurized is pushed out at a high flow rate into the gas vent hole 4a, entraining the material of the surrounding workpiece.

[0019] Hot forging die according to the present embodiment The inventors of the present invention have studied a structure for preventing the formation of burrs in the vent holes for allowing the vaporized release agent to escape as described above, and have found that if the vent holes in the die 2 are not made to penetrate all the way to the outside of the die, but are made to be holes that are closed on the outside, i.e., non-through holes that are open only to the inner surface of the die 2, then the workpiece will not flow into the vent holes and burrs will not be formed.

[0020] Specifically, as shown in Figs. 1(A) to (C), in the die 2 of the mold of this embodiment, a gas vent hole 4 that does not penetrate to the outside is formed at a location where a sealed space is formed between the die 2 and the workpiece W, as shown in the figures. Such gas vent holes 4 may be formed at appropriate intervals along the circumference of the die 2, as shown in Fig. 1(D), and the specific positions may be determined experimentally. The opening diameter of the gas vent hole 4 may be determined experimentally, and for example, if the diameter of the workpiece is about several centimeters, the diameter may be about 1 mm. In addition, the inner shape of the gas vent hole 4 may be a bag shape with a wide opening diameter, as shown in the figures. The volume of the gas vent hole 4 may be large enough to accommodate the vaporized release agent in the die, and may be determined experimentally. For example, the volume of the gas vent hole 4 may be the volume (1700 times the liquid) when all of the applied amount of liquid release agent is vaporized.

[0021] When the gas vent hole 4 is a closed hole that opens only to the inner surface of the die 2 as described above, the vaporized release agent flows into the gas vent hole 4, increasing the internal pressure of the gas vent hole 4, which is considered to prevent the workpiece from flowing into the gas vent hole 4. In fact, when hot forging was performed using a die provided with a closed gas vent hole 4 according to the teachings of this embodiment, as shown in Figures 1(A) to (C), as in the case of Figures 2 to 3, it was confirmed that, as shown in Figure 1(F), no undercuts or protruding burrs were formed in the workpiece after forming, and the die shape could be well transferred to the workpiece.

[0022] The above description has been given in relation to the embodiment of the present invention, but it will be apparent to those skilled in the art that many modifications and changes can be easily made thereto, and that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A die for hot forging, the inner surface of which that comes into contact with the workpiece is provided with holes that do not extend through to the outside of the die.

Images