EP0560010A1

EP0560010A1 - Plastic working method for a holed member

Info

Publication number: EP0560010A1
Application number: EP93100205A
Authority: EP
Inventors: Kazuto Kobayashi; Toshio Suzuki; Takashi Nakano
Original assignee: Aida Engineering Ltd
Current assignee: Aida Engineering Ltd
Priority date: 1992-03-12
Filing date: 1993-01-08
Publication date: 1993-09-15
Anticipated expiration: 2013-01-08
Also published as: MX9301334A; DE69302040D1; EP0560010B1

Abstract

The present invention relates to a plastic working method for a holed member to obtain a holed member (33) with a through hole at the center by plastic working and its object is to securely prevent any defect such as an underfill from occurring. The present invention comprises a roughing process and a finishing process. In its finishing process, with an intermediate material (57) placed under compressive force caused by a punch (37) and a counter punch (39), a large diameter part or a diameter enlarging part of a mandrel (49) is pulled out of the through hole of the intermediate material (57) with inserting a small diameter part of the mandrel (47) to the same through hole so that the gap between the small diameter part of the mandrel (47) and the through hole is filled with the material.

Description

Background of the Invention

Field of the Invention

This invention relates to a plastic working method for a holed member which can eliminate defects including underfill on the outer circumference when fabricating a holed member with a through hole at the center.

Description of the Prior Art

Fig. 26 shows an example of a known conventional plastic working method for flat end faces of a member having an identical cross section throughout the member or without any change in contour for axial direction such as a column, a prism and a spur gear.
In this method, a die 1 is provided with a die hole 5 shaped corresponding to an identical cross sectional shaped member 3 comprising a spur gear as shown in Fig. 27. After a material 7 smaller than the inscribed circle for the identical cross sectional shaped member 3 is placed into the die hole 5 of the die 1, the material 7 is compressed by a punch 9 and a counter punch 11 respectively mating with each side of the die hole 5 so as to fill the die hole 5 with the material 7 in order to form an identical cross sectional shaped member 3, as shown in Fig. 27.
Such a plastic working method for an identical cross sectional shaped member, however, has a drawback in that the formed identical cross sectional shaped member 3 tends to have an underfill 17 at either end of the outer circumference as shown in Fig. 26. When the material 7 is compressed by the punch 9 and the counterpunch 11, it fills the die hole 5 from the closest point to the furthest point (or from the bottom 13 toward the tip 15 in case of a spur gear in Fig. 27) and the material often fails to fully reach the tip 15.
If a high stress is applied to the material 7 in order to decrease the size of such an underfill 17, there is a fear that the die 1 breaks due to increased stress loaded to the die 1. Besides, when taking out the product from the die, larger partial variations due to spring-back prevent the die accuracy to be properly transferred to the product accuracy.
Another drawback of this conventional method is vertical burr at the mated part 19, for the punch 9 and the die 1 need to be mated.
Further, if a part with twisted grooves at gear teeth such as a helical gear is formed by this method, mating is quite difficult because the punch must be mated with the die while it is rotating.
The above drawback is also found in forming of a hollow holed member 23 with inserting a mandrel 21 at the center of the material 7 as shown in Fig. 28.
Fig. 29 shows another plastic forming method designed for such a holed member 23. In this method, a die 1A and a container 25 are energized toward the punch 9A by an energizing member 27 and the material 7 placed in the die 1A and the container 25 is pushed against the counter punch 29 together with the die 1A using the punch 9A in close contact with the top of the die 1A so as to compress the material 7 by the punch 9A and the counter punch 29.
This method does not require mating of the punch 9A and the die 1A, which results in no vertical burr at the mated part, and enables relatively easy forming of a part with twisted grooves at teeth such as a helical gear.
However, such plastic working method for a holed member still has a drawback of underfill 17 on either end of the formed holed member 23, as shown in Fig. 29.
If a high stress is applied to the material 7 in order to decrease the size of such an underfill 17, it increases the stress against the die 1A, which may result in breakage of the die 1A. Besides, larger partial variations due to spring-back when the product is taken out will make it difficult to properly transfer the die accuracy to the product accuracy.

Summary of the Invention

It is an object of the present invention as a solution to the above drawbacks to provide a plastic working method for a holed member to securely prevent occurrence of defects such as underfills.
According to a first preferred embodiment of the present invention, the plastic working method for a holed member comprises a roughing process where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die, and then a large diameter part of a mandrel is inserted into a through hole formed at the center of the material, and then a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said large diameter part of the mandrel with the material in order to obtain an intermediate material, as well as a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said large diameter part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between said small diameter part of said mandrel and said through hole is filled with the material.
According to a second preferred embodiment of the present invention, the plastic working method for a holed member comprises a roughing process where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die, a small diameter part of a mandrel is inserted into the punch side of a through hole formed at the center of the material and a diameter enlarging part continuing to said small diameter part is press fit to said through hole so as to enlarge the punch side of the through hole, and then a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said mandrel with the material in order to obtain the intermediate material, as well as a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said diameter enlarging part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between the small diameter part of the mandrel and a taper part or the through hole enlarged by the taper part and the large diameter part is filled with the material.
According to a third embodiment of the present invention, the plastic working method for a holed member comprises a roughing process where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die, a small diameter part of the mandrel is inserted into a through hole formed at the center of the material, and then a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said mandrel with the material and then a diameter enlarging part continuing to the small diameter part of said mandrel is press fit to the through hole to enlarge the punch side of the through hole in order to obtain an intermediate material, as well as a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said diameter enlarging part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between the small diameter part of the mandrel and the through hole enlarged by said diameter enlarging part is filled with the material.
According to a preferred embodiment of the present invention, the plastic working method for a holed member is characterized by its finishing process where the large diameter part or the diameter enlarging part of the mandrel is pulled out of the through hole of the intermediate material with placing the intermediate material under the compressive stress caused by the punch and the counter punch, which causes the small diameter part of the mandrel to be gradually inserted into the through hole so that the gap between the small diameter part of the mandrel and the through hole is filled with the material. Here, the entire material makes plastic flow with making other parts susceptible to plastic flow, and the intermediate material plastically flow even to the underfill on the outer circumference so that the underfill of the intermediate material is gradually filled from the bottom.
According to a further preferred embodiment of the present invention, the plastic working method for a holed member is characterized by its finishing method where the large diameter part or the diameter enlarging part of the mandrel is pulled out of the through hole of the intermediate material with placing the intermediate material under the compressive stress caused by the punch and the counter punch, which causes the small diameter part of the mandrel to be gradually inserted into the through hole so that the gap between the small diameter part of the mandrel and the through hole is filled with the material. Here, the intermediate material plastically flow even to the underfill so that the underfill of the intermediate material is gradually filled from the bottom. This realizes secure obtaining of a holed member without any defect such as an underfill.

Description of the Drawings

Fig. 1 is a cross sectional view of a plastic working device used in a first embodiment of the plastic working method for a holed member according to the present invention;
Fig. 2 is a top view to show a holed member formed with the device of Fig. 1;
Fig. 3 is a cross sectional view to show the finishing process with the device of Fig. 1;
Fig. 4 is a cross sectional view to show the knockout process with the device of Fig. 1;
Fig. 5 is a cross sectional view to show a plastic working device used in a second embodiment of the plastic working method for a holed member according to the present invention;
Fig. 6 is a cross sectional view of the knockout process with the device of Fig. 5;
Fig. 7 is a cross sectional view to show a plastic working device used in a third embodiment of the plastic working method for a holed member according to the present invention;
Fig. 8 is a cross sectional view of the finishing process with the device of Fig. 7;
Fig. 9 is a cross sectional view of the knockout process with the device of Fig. 7;
Fig. 10 is a cross sectional view of a plastic working device used in a fourth embodiment of the plastic working method for a holed member according to the present invention;
Fig. 11 is a cross sectional view of a plastic working device used in a fifth embodiment of the plastic working method for a holed member according to the present invention;
Fig. 12 is a cross sectional view to show the finishing method with the device of Fig. 11;
Fig. 13 is a cross sectional view to show a small diameter part where grooves are formed for the device of Fig. 12;
Fig. 14 is a cross sectional view to show a plastic working device used in a sixth embodiment of the plastic working method for a holed member according to the present invention;
Fig. 15 is a cross sectional view to show the finishing process with the device of Fig. 14;
Fig. 16 is a cross sectional view to show the knockout process with the device of Fig. 15;
Fig. 17 is a cross sectional view to show a device to energize the die member upward using an energizing force generating cylinder;
Fig. 18 is a cross sectional view to show a device with separated large diameter part and a small diameter part for a mandrel;
Fig. 19 is a cross sectional view to show the finishing process with the device of Fig. 18;
Fig. 20 is a cross sectional view to show a device comprising a mandrel provided with a taper part and a small diameter part as separate units;
Fig. 21 is a cross sectional view to show a device provided with a die and a container as separated units;
Fig. 22 is a cross sectional view to show a device which forms a holed member with bosses formed on both sides of the teeth;
Fig. 23 is an explanatory view to illustrate the underfill of a helical gear formed according to the first embodiment;
Fig. 24 is a cross sectional view of the helical gear shape of Fig. 23;
Fig. 25 is an explanatory view to illustrate the under fill of a helical gear formed according to the first embodiment with heating the die member;
Fig. 26 is an explanatory view to illustrate a conventional plastic working method for a member without any hole;
Fig. 27 is a top view to show a gear worked by the method in Fig. 26;
Fig. 28 is an explanatory view to show a conventional plastic working method for a holed member; and
Fig. 29 is an explanatory view to show another example of conventional plastic working method for a holed member.

Description of the Preferred Embodiment of the Invention

Referring to the attached figures, preferred embodiments of the present invention will be described in detail below.

(First embodiment)

Fig. 1 shows a plastic working device used in a first embodiment of the plastic working method for a holed member according to the present invention. In the figure, the reference numeral 31 indicates a die member. The die member 31 comprises a die 31a and a container 31b continuing from the die 31a.
The die member 31 is energized upward by a spring 32. The die 31a has a die hole 35 shaped corresponding to a holed member 33 which comprises a helical gear as shown in Fig. 2. The holed member 33 is provided with a through hole 36.
Above the die 31a of the die member 31 is disposed a punch 37 which can make contact with the top face of the die member 31.
A counter punch 39 has its top mated with a container hole 31c at the container 31b of the die member 31. The counter punch 39 has a through hole 41, whose lower part accommodates a driving pin 43 and its upper part accommodates a small diameter part 47 of a mandrel 45.
The mandrel 45 comprises the small diameter part 47 and a large diameter part 49, the latter being inserted to the punch 37. The mandrel 45 is energized toward the driving pin 43 by a spring 51 disposed in the punch 37.
The die member 31 is accommodated in a holder 52 so that it can freely make vertical movement.
In this embodiment, the top end of the punch 37 is further fixed to an upper holder 73 with a punch holder 71.
The punch 37 has at its center a through hole 37a, which accommodates a plug 45a of the mandrel 45.
The spring 51 is disposed between the plug 45a and the upper holder 73, and a mandrel stopper 75 to restrict the uppermost position of the mandrel 45 is disposed near the top of the through hole 37a.
On the other hand, the holder 52 is fixed to a lower holder 77 via a lower plate 79.
The lower plate 79 is provided with a lower through hole 79a, and the lower holder 77 is provided with a hole 77a at its upper part.
The lower holder 77 has, at the bottom of its hole 77a, a pin driving cylinder 81, to which a hydraulic source 83 is connected.
The pin driving cylinder 81 accommodates a piston 85, and to the top of the piston 85, the lower end of the driving pin 43 is fixed.
The hole 77a of the lower holder 77 has a second knockout plate 87 and the through hole 79a of the lower plate 79 has a first knockout plate 89.
On the top of the first knockout plate 89, a thrust bearing 91 is disposed.
The first and the second knockout plates 89 and 87 are connected with a first knockout pin 93, and a second knockout pin 95 has its top fixed to the bottom of the second knockout plate 87. This second knockout pin 95 is designed so that it can move vertically under the effect of a knockout device (not shown) disposed below the second knock out pin 95.
Plastic working for a holed member using the above device according to a first embodiment of the present invention is performed as described below.
Referring first to the left part of Fig. 1, a material 55 with a through hole 53 having a diameter smaller than the inscribed circle for the holed member 33 is loaded into the die hole 35 of the die 31a and the container hole 31c of the container 31b, and the large diameter part 49 of the mandrel 45 is positioned in the through hole 53.
The punch 37 is lowered so that the lower end of the punch 37 makes contact with the upper end face of the die member 31, and then with the top face of the material 55 with further lowering of the punch 37.
Still further lowering of the punch 37 causes the material 55 to be compressed between the punch 37 and the counter punch 39 as shown in the right part of Fig. 1. The material 55 is plastically flown into the die 31a, and at the same time fills the space between the die hole 35 and the large diameter part 49 of the mandrel 45, resulting in an intermediate material 57.
The intermediate material 57 at this stage has an underfill E at the die 31a.
After that, as shown in the left part of Fig. 3, with the intermediate material 57 placed under the compressive stress PP caused by the punch 37 and the counter punch 39, hydraulic pressure is supplied to the pin driving cylinder 81. This raises a piston 85 with subsequently raising the driving pin 43, and the large diameter part 49 of the mandrel 45 is gradually pulled out from the through hole 59 of the intermediate material 57 with gradually positioning the small diameter part 47 of the mandrel 45 in the through hole 59, resulting in a gap S formed between the through hole 59 and the small diameter part 47 of the mandrel 45.
Then, the intermediate material 57 is plastically flown into this gap S and also to the underfill E, which fills the underfill E of the intermediate material 57 from the bottom.
Forming is completed when the small diameter part 47 of the mandrel 45 is positioned all over the through hole 59 of the intermediate material 57 as shown in the right part of Fig. 3, with providing a holed member 33 without any underfill E and having flat end faces at the both ends.
When the punch 37 rises after the finishing process as described above, the knockout device (not shown) is driven in order to raise the second knockout pin 95 as shown in Fig. 4, which raises the first knockout pin 93 via the second knockout plate 87. The thrust bearing 91 supports the counter punch 39, which is now made to be rotatable, makes rotations along the twisting of the holed member 33 so as to knock it out.
Thus, the plastic working method for a holed member as described above is characterized by its finishing process where the punch 37 and the counter punch 39 cause the compressive stress to work on the intermediate material 57. In this process, the large diameter part 49 of the mandrel 45 is gradually pulled out of the through hole 59 of the intermediate material 57 while the small diameter part 47 of the mandrel 45 is inserted into the through hole 59. The intermediate material 57 gradually fills the gap S between the small diameter part 47 of the mandrel 45 and the through hole 59, and at the same time makes plastic flow toward the underfill E with gradually filing it from the bottom. This enables ensured provision of a holed member without any defect such as an underfill.

(Second Embodiment)

Fig. 5 shows a plastic working device used in a second embodiment of the plastic working method for a holed member according to the present invention. This device is provided with a mandrel driving part 43a having the same diameter as the small diameter part 47 of the mandrel 45 at the top of the driving pin 43A, and a knockout 43b having a larger diameter than the mandrel driving part 43a near the bottom.
On the top of the knockout 43b, a thrust bearing 91 is disposed.
The plastic working method using this device is now described. Referring to Fig. 5, a knockout device (not shown) moves the driving pin 43A upward at a first driving speed, which causes the small diameter part 47 of the mandrel 45 to be gradually inserted into the through hole 59 for moving the mandrel 45.
Referring now to Fig. 6, upon completion of forming, the knockout device (not shown) further moves the driving pin 43A upward so that the thrust bearing 91 makes contact with the counter punch 39, making it rotatable. The counter punch 39 now rotatably supported by the thrust bearing 91 rotates along the twisting on the holed member 33 and is knocked out.
In Fig. 5, the alphabet L¹ indicates the distance the driving pin 43A travels for movement of the mandrel 45. In Fig. 6, L² shows the distance the driving pin 43A travels for knocking out the holed member 33.

(Third embodiment)

Fig. 7 shows a plastic working device used in a third embodiment of the plastic working method for a holed member according to the present invention. This device is provided with a taper unit 61 between a large diameter part 49A and a small diameter part 47A of a mandrel 45A for their connection.
The upper holder 73 is provided with a mandrel press fitting cylinder 97, which is connected with the upper end of the mandrel 45A at its piston 99.
The third embodiment of the plastic working method for a holed member according to the present invention using a thus configured device is now described.
Referring to the left part of Fig. 7, a ring-shaped material 55 with a through hole 53 having a diameter smaller than the inscribed circle for the holed member 33 is first loaded into the die hole 35 of the die 31a and the container hole 31c of the container 31b.
The inner diameter of the through hole 53 is almost equal to or slightly larger than the outer diameter of the small diameter part 47A of the mandrel 45A, and is sufficiently smaller than the outer diameter of the large diameter part 49A.
With the mandrel 45A energized toward the container 31b by the piston 99 of the mandrel press fitting cylinder 97, the punch 37 is lowered. This inserts the small diameter part 47A of the mandrel 45A into the through hole 53 of the material 55. Then, the taper part 61 and the large diameter part 49A of the mandrel 45A are continuously press fit into the through hole 53, which enlarges the opening at the material 55 on the side of the punch 37.
When the punch 37 is further lowered, as shown in the left part of Fig. 8, the material 55A is compressed by the punch 37 and the counter punch 39. The material 55A then plastically flows into the die 31a, fills up the die hole 35 so as to obtain the intermediate material 57. The intermediate material 57 has an underfill E near the top of the die 31a.
Next, referring to the right part of Fig. 8, the driving pin 43 is gradually raised up with the pressure PP working on the punch 37 so as to have the punch 37 and the counter punch 39 apply the compressive stress to the intermediate material 57. The large diameter part 49A and the taper part 61 of the mandrel 45A are pulled out of the through hole 59 of the intermediate material 57 and the small diameter part 47A of the mandrel 45A is positioned at the upper part of the through hole 59, with forming a gap S between the through hole 59 and the small diameter part 47A of the mandrel 45A.
The intermediate material 57 makes plastic flow into the gap S and at the same time to the underfill E, which is gradually filled from the bottom.
When the driving pin 43 is gradually rising up, the material 45A moves upward even when the mandrel 45A is under the downward energizing pressure P, if the rising force of the driving pin 43 is higher than such pressure P. However, the upward movement of the mandrel 45A can be made smoother if the downward energizing force on the mandrel 45A is eliminated.
If the downward energizing force on the mandrel 45A is eliminated, the mandrel 45A may rise up without any operation due to downward compressive force of the punch 37 pressing the taper part 61, depending on the shape and friction coefficient. In this case, the driving pin 43 is not always required to raise the mandrel 45A.
As shown in the left part of Fig. 9, forming is completed when the small diameter part 47A of the mandrel 45A is positioned over the entire through hole 59 of the intermediate material 57, with providing a holed member with flat end faces and no underfill E.
After the above finishing process, the punch 37 and the counter punch 39 are raised up so that the holed member 33 shaped to a predetermined shape can be taken out.
Thus, it is now understood that the third embodiment can provide substantially the same result as the first embodiment.
Though the taper part 61 and the large diameter part 49A are inserted into the material 55 in the above embodiment, but it is obvious that the present invention is not limited to such an operation; for example, insertion of the taper part 61 alone may be sufficient. Besides, the taper part 61 may have a curved shape such as an arc.

(Fourth embodiment)

Fig. 10 shows the essential part of a fourth embodiment of the plastic working method for a holed member according to the present invention. In the fourth embodiment, as shown in the left part of Fig. 7, a ring-shaped material 55B having a through hole 53 and an outer diameter smaller than the inscribed circle of the holed member 33 into the die hole 35 of the die 31a and the container hole 31c of the container 31b.
Then, the small diameter part 47A of the mandrel 45A is inserted into the through hole 53A of the material 55B and the punch 37 is lowered. As shown in the left part of Fig. 10, without using the mandrel press fitting cylinder 97, the punch 37 and the counter punch 39 compress the material 55B, which is in turn plastically flown into the die 31a to fill the die hole 35.
Next, the mandrel 45A is energized toward the container 31b by the piston 99 of the mandrel press fitting cylinder 97, causing the taper part 61 and the large diameter part 49A of the mandrel 45A to be subsequently press fit into the through hole 53A. This results in enlarged opening at the material 55B on the side of the punch 37 as shown in the right part of Fig. 10, and an intermediate material 55C is obtained.
Then, the finishing process is performed in the same way as shown in the right part of Fig. 8 and the left part of Fig. 9, and the holed member formed to a desired shape can be obtained.
Thus, this fourth embodiment also realizes substantially the same effect as the other embodiments described above.

(Fifth embodiment)

Fig. 11 shows a plastic working device used in a fifth embodiment of the plastic working method for a holed member according to the present invention. The device is provided with a relief 101 having a smaller diameter than the small diameter part 47 between the large diameter part 49 and the small diameter part 47 of the mandrel 45. In addition, a taper shaped approach 103 is formed under the relief 101.
Plastic working with this device is practically the same as that in the first embodiment, except that the compressive stress working on the material 57 in the mandrel replacement status shown in the left part of Fig. 12 causes the material 57 to flow into the relief 101 first and then to be ironed by the approach 103 and the small diameter part 47.
This realizes highly accurate finishing of the hole 36 in the holed member 33.
If grooves 105 are shaped in axial direction on the outer circumference of the small diameter part 47 under the relief 101 of the mandrel 45 as shown in Fig 13 so as to make an irregular cross sectional shape such as the one for a spline, highly accurate finishing of a spline hole or other irregular shapes can be realized.

(Sixth embodiment)

Fig. 14 shows a plastic working device used in a sixth embodiment of the plastic working method for a holed member according to the present invention. The device is provided with a relief 101 having a smaller diameter than the small diameter part 47A between the taper part 61 and the small diameter part 47A of the mandrel 45A. In addition, a taper shaped approach 103 is formed under the relief 101.
Plastic working with this device is practically the same as that in the third embodiment, except that, as in the fifth embodiment, the compressive stress working on the material 57 in the mandrel replacement status shown in the right part of Fig. 15 causes the material 57 to flow into the relief 101 first and then to be ironed by the small diameter part 47A. This realizes highly accurate finishing of the hole 36 in the holed member 33.
Referring to Fig. 16, the holed member 33 is knocked out in the same way as in the third embodiment.
Though the die member 31 is energized toward the punch 37 by the energizing member 32 comprising a spring in the above embodiments, the present invention is not limited to such a configuration. For example, it is obvious that the die member 31 may be energized upward by a piston rod 111 connected with a piston 109 of an energizing force generating cylinder 107 disposed on the top of a lower holder 105, as shown in Fig. 17.
Further, the large diameter part 49 and the small diameter part 47 of the mandrel 45 are formed as a one-piece unit in the above embodiments, but the present invention is not limited to such a configuration. For example, as shown in Figs. 18 and 19, the large diameter part 49B and the small diameter 47B may be separated at their boundary plane 113.
In addition, though the mandrel 45A has a taper part 61 and a small diameter part 47A formed as a one-piece unit in the above embodiments, the present invention is not limited to such a configuration. It is obvious that, as shown in Fig. 20, the taper part 61 and the large diameter part 45A may be formed by a separated member 115, and the upper end of the small diameter part 47C may be inserted into the separated member 115.
Though the die member 31 has a die 31a and a container 31b formed as a one-piece unit in the above embodiments, the present invention is not limited to such a configuration. For example, it is obvious that a die 117 and a container 119 may be formed as separated units and the die 117 may be disposed at a lower holder 121 and the container 119 at an upper holder 123 as shown in Fig. 21.
Though the above embodiments described forming of a holed member 33 where a boss is formed on only one side of the teeth, the present invention is not limited to such forming. For example, as shown in Fig. 22, a recess 125 may be formed at the end of the punch 37 to form a holed member where bosses 129 and 131 are formed on the both ends of its teeth part 127.
Though the method of the present invention is applied to plastic working of a holed member 33 comprising a helical gear in above embodiments, the present invention is not limited to such an application. It is obvious that the holed member may be a cylinder, a triangle pole, a square pole, a hexagonal pole or a spur gear or a bevel gear.
Further, the cross section of the small diameter part 47 or 47A of the mandrel 45 or 45A is not limited to a circle but also may be a square, a hexagon or spline-shaped.
In addition, in the plastic working method for a holed member according to the present invention, the product dimension accuracy and the service life of the die can be improved by heating the die member 31 for smoother conditions enabling forming under lower stress.
Specifically, Fig. 23 shows an underfill at a tooth edge (A in the figure) when a helical gear 133 having one module and 23 teeth and a pitch cylinder helix angle of 20 degrees as shown in Fig. 24 is formed. The helical gear 133 is placed under the average stress of 120 kg/mm² on teeth 135 with the temperature at the die member 31 kept at the room temperature during forming according to the above first embodiment. An underfill 137 is substantially a triangle having a radial dimension of 5.5 mm and axial dimension of 0.06 mm.
On the other hand, Fig. 25 shows an underfill at a tooth edge (A in the figure) when the die member 31 is heated to 100 °C before forming under the same conditions. This underfill 139 is of an ignorable size with 0.05 mm in radial direction and 0.015 mm in axial direction.
For reference, it is required to apply an average stress of 160 kg/mm₂ to the teeth 135 in order to reduce the size of the underfill 137 in Fig. 23 to that of the underfill 139 in Fig. 25, if the die member 31 is kept at the room temperature.

Claims

Plastic working method for a holed member comprising a roughing process
where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die, and then
a large diameter part of a mandrel is inserted into a through hole formed at the center of the material, and then a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said large diameter part of the mandrel with the material in order to obtain an intermediate material, as well as
a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said large diameter part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between said small diameter part of said mandrel and said through hole is filled with the material.
Plastic working method for a holed member comprising a roughing process
where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die,
a small diameter part of a mandrel is inserted into the punch side of a through hole formed at the center of the material and
a diameter enlarging part continuing to said small diameter part is press fit to said through hole so as to enlarge the punch side of the through hole, and then
a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said mandrel with the material in order to obtain the intermediate material, as well as a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said diameter enlarging part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between the small diameter part of the mandrel and the through hole enlarged by said diameter enlarging part is filled with the material.
Plastic working method for a holed member comprising a roughing process
where the material is loaded into a die member which is energized toward a punch and consists of a die provided with a die hole shaped corresponding to the shape of the desired holed member and a container continuing to said die,
a small diameter part of the mandrel is inserted into a through hole formed at the center of the material, and then a counter punch mating with said container and a punch pressing the die end face of said die member toward the counter punch compress the material so as to fill the space between said die hole and said mandrel with the material and then a diameter enlarging part continuing to the small diameter part of said mandrel is press fit to the through hole to enlarge the punch side of the through hole in order to obtain an intermediate material, as well as
a finishing process subsequent to said roughing process, where, with said intermediate material placed under compressive stress caused by said punch and said counter punch, said diameter enlarging part of said mandrel is pulled out of the through hole of said intermediate material while a small diameter part of said mandrel is inserted into the same through hole, so that the gap between the small diameter part of the mandrel and the through hole enlarged by said diameter enlarging part is filled with the material.
Plastic working method for a holed member of Claim 2 or 3 wherein said mandrel is pulled out by pressure from said intermediate material working on said diameter enlarging part in said finishing process.
Plastic working method for a holed member of any one of Claims 1 to 3 wherein a relief having a diameter smaller than the outer diameter of said small diameter part is formed between the small diameter part and the large diameter part or the diameter enlarging part of said mandrel and, when inserting the small diameter part of the mandrel with pulling out said mandrel, the material is flown into said relief under the effect of the compressive stress and said flown material is ironed by said small diameter part in order to finish the inner side of the holed member.
Plastic working method for a holed member of any one of Claims 1 to 3 or 5 wherein a driving pin is provided with a mandrel driving part and a knockout part so that the pulling of said mandrel and knocking out of the product are performed in two-step operation of the same knockout device.
Plastic working method for a holed member of any one of Claims 1 to 6 wherein said die and said container are formed as separate units.
Plastic working method for a holed member of any one of Claims 1 to 7 wherein forming is performed with said die member heated to a predetermined temperature.