Pressure controlled fluid pressure extrusion method

Abstract

The lower part of a material to be molded forms a lower seal with a die. A punch applying a molding force to the material forms an upper seal with the perimeter of the die. The space between the upper and lower seals forms a pressure chamber that is filled with a fluid. As the punch descends into the die, the fluid is pressurized. The lower seal is a complete seal to prevent leakage of fluid into the die. The upper seal is given a clearance with the die that permits controlled leakage of fluid therepast at a rate that limits the maximum pressure in the pressure chamber while permitting the development of an adequate pressure on the material being molded.

Description

BACKGROUND TO THE PRESENT INVENTION

[0001] The present invention relates to a pressure controlled fluid pressure extrusion method. The term “fluid pressure extrusion method” defines a method in which extrusion is conducted under the action of fluid pressure. Pressure control describes the adjustment of this fluid pressure in order to conduct proper extrusion. These extrusions can be used to make parts for automobiles such as helical gears and the like.

[0002] Examples of the prior art include forward extrusion methods as shown in FIG. 1 of Japanese Laid-Open Patent Publication Number 11-254082 and FIG. 3 of Japanese Laid Open Patent Publication Number 7-308729.

[0003] Referring to FIGS. 3(A)-3(D), the essentials of these prior art methods are schematically shown in order to compare these methods of the prior art with the present invention. A material 11 progresses through the steps of 3(A), 3(B), 3(C), and 3(D) to produce a manufactured product 15. Because the example of product 15 is perforated, material 11 is also perforated and a mandrel present in the metal mold.

[0004] Referring to FIG. 3(A), the outer diameter of material 11 is approximately the same size as the inner diameter of a container 12b. Referring to FIG. 3(C), when material 11 is extruded into a die 12 and molded by a punch 13, a large frictional force is generated between the material outer diameter and the container. Furthermore, when molding helical gear part 15a of manufactured product 15 with a helical gear part 12a of die 12, product 15 rotates as it advances along a lead. This rotation adds a large additional frictional force in the direction of rotation as well as the frictional force in the axial direction as described above. As a result, the load needed for working is increased, and there are negative effects on the product precision and on the die life. With this method, the outer diameter part of the material must be straight. If the outer diameter is tiered, the smaller diameter part could become deformed and expand during molding, and the specified molding cannot be conducted.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

[0005] The first object of the present invention is to lengthen the life of the die.

[0006] The second object is to improve product precision.

[0007] In the present invention, a fluid pressure is disposed between the die and the material. When molding the material, a suitable fluid pressure acts upon the material.

[0008] Briefly stated, the present invention provides a fluid pressure molding method in which the lower part of a material to be molded forms a lower seal with a die. A punch applying a molding force to the material forms an upper seal with the perimeter of the die. The space between the upper and lower seals forms a pressure chamber that is filed with a fluid. As the punch descends into the die, the fluid is pressurized. The lower seal is a complete seal to prevent leakage of fluid into the die. The upper seal is given a clearance with the die that permits controlled leakage of fluid therepast at a rate that limits the maximum pressure in the pressure chamber while permitting the development of an adequate pressure on the material being molded.

[0009] Described in more detail, according to an embodiment of the invention, a suitable fluid pressure acts on the outer perimeter surface of a material, the material is pushed directly by a punch into a die for molding, whereby the material is molded into a desired shape.

[0010] According to a feature of the invention, the fluid is suitably sealed by the material, the die, and the punch. The action of the die and the punch compresses and pressurizes the fluid. The fluid pressure acts on the material to form the product.

[0011] According to an additional feature of the invention, the fluid pressure is adjusted by a clearance of the die and the punch.

[0012] The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIGS. 1(A) through 1(D) are drawings of the steps in the process according to an embodiment of the invention.

[0014] FIG. 2 is an expanded view of the principal part of FIG. 1(B).

[0015] FIGS. 3(A) through 3(D) are drawings illustrating the method of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] Referring to FIGS. 1(A)-1(D), the process of molding material 1 into molded product 5 is shown. A metal mold 100 is constructed from a die 2, a punch 3, and a mandrel 4. The metal mold 100 is set into a conventional press (not shown). The metal mold 100 is actuated by the ascending and descending motion of a slide of the press.

[0017] Referring to FIG. 1(A), die 2 includes a cavity 10 having the shape of the desired molded product. In the illustrated embodiment, the molded product is a helical gear. Teeth 2a are formed on the lower part of cavity 10. Teeth 5a of molded product 5 are formed by teeth 2a.

[0018] Referring to FIGS. 1(B) and 2, material 1 is supplied to die 2. Material 1 is transported to die 2 by a transport device and is inserted into cavity 10 of die 2. After inserting material 1 into cavity 10, mandrel 4 is inserted into the hole of material 1. A fluid is supplied to cavity 10. In the present embodiment, oil is used as the fluid.

[0019] Next, punch 3 is lowered into cavity 10. The lower end surface of punch 3 contacts the upper surface of material 1. As punch 3 descends further, a fluid pressure chamber 6 is sealed between the punch 3 and the lower portion of the material 1. With further descent of punch 3 the fluid inside cavity 10 is compressed. In other words, the fluid is sealed by a first seal 7 at the contact surface between material 1 and punch 3, a second seal 8 at the insertion surface between die 2 and punch 3, and a third seal 9 at the insertion surface between die 2 and the lower end of material 1.

[0020] Seal 9 must completely seal to prevent leakage of fluid from fluid pressure chamber 6 to the portion of the die 2 containing the teeth 2a. If the pressurized fluid from fluid pressure chamber 6 penetrates into teeth 2a, the presence of the material 1 may produce partial depressions in teeth 5a of molded product 5. This would prevent achieving the desired shape.

[0021] Seal 7 may have some leakage without producing any problems. In the present embodiment, because teeth 2a are a helical gear, while molding, material 1 rotates with respect to punch 3. As punch 3 advances, a film of fluid penetrates between the teeth 2a and the teeth 5a being formed. The resulting lubrication reduces the frictional force that accompanies this rotation.

[0022] With seal 8, the pressurized fluid must be actively released. If the fluid pressure in fluid pressure chamber 6 rises without limit, there can be problems such as the rupture of members such as die 2 and the like. However, if a large amount of fluid in fluid pressure chamber 6 leaks from seal 8, material 1 expands radially. This can cause problems such as incomplete molding action of material 1. Taking these points into account, it is necessary to determine the clearance for the restriction of seal 8. Seal 8 acts as a relief valve.

[0023] As described above, the clearance of seal 8 is determined so that an optimal fluid pressure of fluid pressure chamber 6 is achieved.

[0024] Referring to FIG. 1(C), while fluid pressure from fluid pressure chamber 6 is applied to material 1, material 1 is pushed by punch 3 to become molded into molded product 5. In this situation, because the fluid in fluid pressure chamber 6 is disposed between die 2 and material 1, frictional forces are not generated between the two. Therefore, material 1 is molded with only the pushing pressure that is needed for molding. In the present embodiment, because teeth 2a of die 2 form a helical gear, material 1 is rotated while being pushed into die 2. However, due to the action of the above fluid, the frictional resistance associated with the rotation is not generated.

[0025] Referring to FIG. 1(D), molded product 5 inside die 2 is impelled from below by a knockout device (not shown) and is removed from above die 2. In other words, the molded product is lifted to the top of die 2 by a rotatable lifting member.

[0026] In the present embodiment, a tiered material is used, but the present invention can be used for a straight material as well. Although there is a hole in the center of the molded product, the present invention does not require a hole. In the present embodiment, the molded product is a helical gear, but the present invention can be used for molded parts with super gears or with no gears as well.

[0027] According to the present invention, because there is no associated frictional force, the load needed for molding is reduced. As a result, the stress on the die is reduced, and product precision is improved. There are advantages such as having a die with a long life and conserving energy. Furthermore, even if there is a space between the die and the material, there is no deformation of the material. As a result, extrusion of tiered materials becomes possible. As a result, the cross-section reduction rate for the extrusion is small, and the molding load is further reduced.

[0028] The fluid pressure in fluid pressure chamber 6 is controlled by the clearance of seal 8. As a result, control is easy and stable. The present invention permits molding of parts that have heretofore been considered difficult to process.

[0029] Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

1. A pressure controlled fluid pressure extrusion method comprising: placing a material to be molded in a die; applying a fluid pressure to an outer perimeter surface of a material; and pushing said material directly by a punch into said die for molding, whereby said material is molded into a desired shape.

2. A pressure controlled fluid pressure extrusion method according to claim 1, wherein: sealing said fluid by seals formed of contact between said material, said die, and said punch; and the step of applying includes compressing and pressurizing said fluid by an action of said die and said punch.

3. A pressure controlled fluid pressure extrusion method according to claim 2, wherein the step of applying includes adjusting a clearance between said die and said punch, said clearance controlling said fluid pressure.

4. A pressure controlled fluid pressure extrusion method according to claim 2, wherein the step of sealing includes completely sealing between said material and said die, whereby leakage of said fluid therepast is completely prevented.

5. A pressure controlled fluid pressure extrusion method according to claim 4, wherein the step of sealing includes providing a clearance between said punch and said die effective to permit leakage of said fluid therepast at a rate which produces the desired fluid pressure.

6. A pressure controlled fluid pressure extrusion method comprising: placing a material to be molded in a die; completely sealing a lower portion of said material to said die; adding a fluid to a space above said lower seal between a perimeter of said material an said die; urging a punch into said die; said punch forming an upper seal with said die; a space between said lower portion and said upper seal being a pressure chamber; advancing said punch into said die to mold said material into a product; the step of advancing being effective to pressurize said fluid; and providing a fit between said punch and said die at said upper seal that is effective to permit an amount of leakage that produces a desired level of fluid pressurization in said pressure chamber.