JP3415033B2 - Mold for thickening drawing and method of manufacturing yoke - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to the increasing thickness drawing mold and applied to the diaphragm thickening molded while preventing a decrease in the thickness of the outer peripheral portion of the cylindrical workpiece in the drawing of the metal
For manufacturing motor yokes by thickening drawing
The present invention relates to a yoke manufacturing method .

[0002]

2. Description of the Related Art A metal flat plate is drawn as a housing for accommodating a member constituting a motor such as an armature and a permanent magnet, and for constituting a yoke as a passage of a magnetic flux generated by a permanent magnet disposed inside. There is one formed by forming into a bottomed tubular shape.

When the housing is formed by general drawing, tensile stress is applied to the cylindrical portion of the housing during the processing, and the thickness of the cylindrical portion of the housing after processing is greater than the thickness of the metal plate before processing. The thickness becomes thin. As mentioned above,
Since the housing is used not only for accommodating the components that form the motor but also as a yoke through which magnetic flux passes, the actual magnetic flux amount becomes smaller than the preset magnetic flux amount due to the thin wall thickness of the tubular portion. Therefore, it is conceivable to use a thick metal plate in advance, considering that the thickness will be thin, but in this case, the thickness of the housing increases unnecessarily because the wall thickness becomes unnecessarily large at the bottom of the housing. Moreover, the cost increases due to the use of a thick metal plate. Therefore, the wall thickness of the cylindrical portion of the predetermined housing is set to a predetermined thickness by a drawing process called thickening drawing.

[0004] Here, Japanese Utility Model Laid-Open No. 4-43415 discloses a die (referred to as "compression drawing die" in the publication) in which the wall thickness of the tubular portion can be set to a predetermined wall thickness. In this mold, the lower mold is formed with a concave portion that opens upward. Set the work piece in the shape of a cylinder with a bottom and the opening end extending outward in the radial direction, with the opening end engaged with the recess, lower the die of the upper die, and press the work into the hole of the die. Then, the work is squeezed and compressed by the inner peripheral portion of the hole. Further, at this time, the outer periphery of the opening end is supported by the inner periphery of the recess, and the work resists the drawing force due to being pressed by the inner periphery of the hole.

Further, the lower die is provided with a deformation preventing member which can be moved up and down with respect to the lower die, and when the work is set in the lower die, the deformation preventing member is fitted onto the work and the deformation of the work is prevented. The upper end portion of the deformation prevention member abuts on the inner bottom portion to limit the deformation of the work inward in the radial direction. Since the work formed by this mold is compressed without applying a tensile force to the cylindrical portion of the work during molding, the wall thickness of the cylindrical portion of the work can be increased.

[0006]

However, in such a mold, since the outer periphery of the opening end of the work is supported by the inner periphery of the recess of the lower die, the opening end of the work is placed in the inner periphery of the recess after the molding is completed. There is a drawback in that it becomes difficult to bite the workpiece and take out the work, which deteriorates workability.

In consideration of the above facts, the present invention provides a thickening die for thickening without reducing workability and a thickening die without lowering workability.
It is an object of the present invention to obtain a yoke manufacturing method capable of manufacturing a motor yoke .

[0008]

According to a first aspect of the present invention, there is provided a die for thickening and drawing, wherein a bottomed cylindrical work having a flange portion extending from an opening end is placed from the opening end side. Flat plate
And the mounting part corresponding to the open end of the work.
The through hole formed in the work piece through the placing portion.
Punch and, diameter smaller than the inner diameter the outer diameter of the workpiece to be inserted through from the opposite side to the inside of the workpiece and
And a die for press-fitting the work into the hole by moving the hole of the hole coaxially with the punch and moving relatively close to the placing part along the axial direction of the through hole. , And the inner diameter of the hole and the punch.
The difference between the outer diameter of the
The above-mentioned wafer after processing is made 2.1 times or more and 2.8 times or less.
Characterized in that the increase rate of the wall thickness of the ark is more than 1 time.
I am trying.

When performing the drawing work with the thickening drawing die having the above-mentioned structure, first, the flange portion and the mounting portion formed at the open end of the cylindrical work having a bottom are placed in a state of facing each other. The work is placed on the placing part coaxially with the through hole formed in the placing part, and then the punch is passed through the through hole of the placing part in this state, and further, along the axial direction of the through hole. The work is pressed into the hole of the die by moving the die relatively close to the mounting portion. When the die moves closer to a predetermined position with respect to the placing portion, the flange portion of the work is sandwiched and held by the die and the placing portion.

Since the inner diameter of the hole of the die is smaller than the outer diameter of the work, the work is drawn by pressing the work into the hole of the die. However, since the projecting size of the punch from the through hole is equal to or smaller than the size from the open end of the work to the inner bottom, tensile stress in the direction along the axial direction of the work is not generated in the work. Moreover, the outer diameter and the die hole portion difference outer peripheral portion of 2.1 times or more 2.8 more than double of a thickness of the previous work to be press-fitted into the hole of the die with the inner diameter of the punch Therefore, the wall thickness dimension of the cylindrical portion of the work is increased while maintaining the dimensional accuracy of the inner diameter of the work and the roundness.

As described above, in the die for thickening and drawing,
Even if the mounting part is flat, the wall thickness of the cylindrical part of the work can be increased while maintaining the inner diameter accuracy and roundness of the work. The work can be easily taken out and transported, and the work efficiency is improved. The die for thickening drawing according to claim 2 is the die according to claim 1.
Inner diameter of the hole in the thickened die for mounting
The outer diameter of the punch and the outer diameter of the punch
That the thickness is 2.4 times or more and 2.5 times or less
It has a feature. In the thickening die having the above structure,
If the difference between the inner diameter of the hole and the outer diameter of the punch is outside the work
Should be 2.4 times or more and 2.5 times or less of the wall thickness at the circumference
There is. In this way, the inner diameter of the hole and the outer diameter of the punch
By setting the difference between
When thickening is performed by
The rate of increase in thickness is at its peak, or maximum.

A thickening and drawing die according to a third aspect is the thickening and drawing die according to the first or second aspect , wherein the punch is set to the placing portion with respect to the placing portion. It is characterized in that it is relatively slidable along the through hole.

According to the die for thickening and drawing having the above structure,
The punch is slidable along the through hole of the mounting portion. Therefore, when the processing is completed, the die is relatively separated from the mounting portion along the axial direction of the through hole of the mounting portion, and the punch is slid in the direction of pulling out from the inside of the work. The work fitted in the punch in the finished state can be easily taken out. Claim
In the present invention described in 4, the flange portion is extended from the open end.
Place a cylindrical work with a bottom on a substantially flat plate-shaped mounting
The work from the side opposite to the work through the placement unit
Corresponding to the above, the punch is inserted into the through hole formed in the placement section.
A hole smaller than the outer diameter of the workpiece.
Insert the die formed coaxially with the punch into the
Part relative to the hole to move the hole into the hole.
The work is thickened and drawn by pressing
A method for manufacturing a yoke, comprising:
The difference between the inner diameter of the hole and the outer diameter of the punch is calculated as
2.1 times or more and 2.8 times or less of the wall thickness at the outer peripheral portion of the ark
The increase rate of the wall thickness of the workpiece after processing
It is characterized by making it more than 1 time. With the above configuration
The yoke is manufactured by so-called thickening drawing
Is built. That is, first, the opening of the bottomed cylindrical work
The flange portion and the mounting portion formed at the end faced each other
In the state, the work is placed on the placing section and the through-hole formed in the placing section.
Place it coaxially, and then in this state, place it in the through hole
The punch penetrates, and then the punch is mounted along the axial direction.
Move the dice relatively close to the table
Press work into the hole. Predetermined die for mounting part
When approaching to the position of
Hold the flange part of. Where the hole in the die
Since the inner diameter of the part is smaller than the outer diameter of the workpiece,
The work is squeezed by pressing the work into the hole of the chair.
Is processed. However, the protrusion from the punch through hole
The dimension is less than the dimension from the open end of the work to the inner bottom.
The tensile stress along the axial direction of the workpiece.
It doesn't cause it. Moreover, the outer diameter of the punch
And the inner diameter of the hole of the die are pressed into the hole of the die.
2.1 times or more of the outer peripheral wall thickness of the work before being 2.8
Since it is less than double, the dimensional accuracy of the inner diameter of the work and
The wall thickness of the cylindrical part of the workpiece is increased while maintaining the roundness.
Be done. By increasing the thickness of the workpiece in this way,
In the present yoke manufacturing method to be formed, the mounting portion has a flat plate shape.
Even if the inner diameter accuracy and roundness of the work are maintained,
By increasing the wall thickness of the cylinder, the yoke can be finally formed.
Therefore, it is possible to place the workpiece during machining and
It is easy to take out and carry, and work efficiency is improved.
In addition, the tensile stress in the direction along the axial direction of the work is
The thickness of the workpiece is increased without causing
In addition, the accuracy of the inner diameter of the workpiece and
Since it can be kept within the difference range, the wall thickness increases.
It is a simple drawing process that does not occur
It is possible to increase the amount of magnetic flux passing inside the material of
The rotation torque of the motor can be improved. Also,
In the case of simple drawing, anticipate the reduction in wall thickness in advance.
And a thick metal flat plate must be used, but this production
With the method, it is not necessary to allow for the reduction in wall thickness,
The strike becomes cheap.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing the structure of a thickening die 10 (hereinafter simply referred to as "die 10") according to an embodiment of the present invention. As shown in this figure, the main mold 10 includes a lower mold 14.
A cylinder portion 16 having an opening at the upper end is formed on the lower mold 14. A flat plate-shaped backing plate 18 having an outer diameter dimension sufficiently smaller than an inner diameter dimension of the cylinder portion 16 is placed substantially in the center of the bottom portion of the cylinder portion 16.
The backing plate 18 is on the backing plate 18.
Similarly, the punch plate 20 having the outer diameter dimension sufficiently smaller than the inner diameter dimension of the cylinder portion 16 is placed. A circular hole 22 is formed in the center of the punch plate 20 so as to penetrate along the thickness direction of the punch plate 20. A punch 24 is provided inside the circular hole 22 of the punch plate 20. The punch 24 has a columnar shape whose outer diameter is slightly smaller than the inner diameter of the circular hole 22. The end of the punch 24 on the side where it is inserted into the circular hole 22 has a planar shape that is cut along the direction orthogonal to the axis, and penetrates the circular hole 22 to abut the upper surface of the backing plate 18. . On the other hand, the end opposite to the end inserted into the circular hole 22 is a substantially hemispherical spherical portion 26. The outer diameter of the punch 24 is set to the inner diameter of the product (that is, the inner diameter of the workpiece 70 after processing).

A cushion plate 28 as a mounting portion is mounted on the punch plate 20. Although the outer diameter of the cushion plate 28 is smaller than the inner diameter of the cylinder portion 16, the backing plate 18 described above is used.
And sufficiently larger than the outer diameter of the punch plate 20. Between the axially intermediate portion of the outer peripheral portion of the cushion plate 28 and the end portion of the cylinder portion 16 on the bottom side, the flange portion 3 extends outward in the radial direction of the cushion plate 28.
0 has been extended. The outer diameter dimension of the cushion plate 28 at the portion where the flange portion 30 is formed is set to be slightly smaller than the inner diameter dimension of the cylinder portion 16,
The cushion plate 28 can slide along the axial direction of the cylinder portion 16.

A circular hole 32 as a through hole is formed in the center of the cushion plate 28 in the radial direction. The inner diameter of the circular hole 32 is approximately equal to the inner diameter of the circular hole 22 of the punch plate 20 described above, and the spherical portion 26 side of the punch 24 penetrates. Therefore, the cushion plate 28
Is guided by both the cylinder portion 16 and the punch 24,
It can slide along the axial direction of the cylinder portion 16 and the punch 24.

Further, on the end face of the lower mold 14 at the open end,
A ring-shaped stopper 34 is provided. Stopper 3
In No. 4, the inner diameter dimension is larger than the outer diameter dimension of the cushion plate 28, but smaller than the outer diameter dimension of the cushion plate 28 at the portion where the flange portion 30 is formed. Therefore, when the cushion plate 28 slides toward the open end side of the cylinder portion 16 along the axial direction of the cylinder portion 16 and the punch 24, the flange portion 30 contacts the stopper 34, and the cushion plate 28 is not slid further. Restrict.

Further, as shown in FIG. 1, a plurality of through holes 36 are formed in the bottom portion of the cylinder portion 16 so as to penetrate toward the side opposite to the open end of the cylinder portion 16. These through holes 36 are provided at equal intervals along the circumferential direction of an imaginary circle centered on the center of the bottom of the cylinder portion 16, and a cushion rod 38 is arranged through each through hole 36. One end of the cushion rod 38 is in contact with the end of the cushion plate 28 on the side facing the bottom of the cylinder portion 16,
The other end is inserted into a cylinder (neither shown) as a cushion pressure adjusting means for moving the cushion rod 38 along the through hole 36, and by adjusting the hydraulic pressure, water pressure, gas pressure such as air, etc. in the cylinder. The cushion rod 38 can be slid.

On the other hand, above the lower mold 14, a flat plate-shaped upper mold 5 is provided.
0 is provided. The upper die 50 is held by a slider (none of which is shown) of the pressing device, and the slider is circular hole 22 by the driving force of the driving means provided in the pressing device.
By moving along the axial direction of, the contacting / separating movement is performed with respect to the lower mold 14. A die holder 52 is fixed to the lower die 14 side end of the upper die 50, and a die 54 is further fixed to the die holder 52 and the lower die 14 side end. The punch 2 described above is provided substantially in the center of the die 54.
4 is formed with a hole portion 56 penetrating along the axial direction of the die 4, and the die 54 is moved to the die holder 52 so that the hole portion 56 and the hole portion 56 are coaxial with the punch 24 along the axial direction of the punch 24. It is attached.

The inner diameter of the hole 56 is the same as that of the main mold 10.
Is smaller than the outer diameter of the workpiece 70 before machining, and the radius of curvature of the upper end portion of the workpiece 70 before machining (that is, the radius of curvature of the corner portion formed by the bottom portion of the workpiece 70 and the cylinder portion 74). Larger than the center diameter of. Therefore,
In the state where the punch 24 is inserted inside the hole 56, the plate thickness dimension of the workpiece 70 before processing is 2.1 times or more and 2.8 times between the inner peripheral part of the hole 56 and the outer peripheral part of the punch 24. Below, the gap L having a dimension of preferably 2.4 times or more and 2.5 times or less is formed. In particular, regarding the inner diameter of the hole 56 and the outer diameter of the punch 24, the above conditions are satisfied, and the drawing ratio in the thickening drawing of the work 70 is 85%.
It is preferable to set the inner diameter dimension of the hole portion 56 and the outer diameter dimension of the punch 24 so as to be 90% or less.
Confirmed experimentally.

Further, in the vicinity of the lower mold 14 side end of the inner peripheral portion of the hole 56, there is formed a curved portion 58 having a predetermined radius of curvature and gradually increasing in inner diameter toward the lower mold 14 side.

Further, as shown in FIG.
Is provided with a holding shaft 60. Holding shaft 6
No. 0 penetrates the upper die 50 and the die holder 52 along the axial center positions of the punch 24 and the hole portion 56 described above along the axial direction thereof, and the punch 24 and the hole portion 56 are driven by the driving force of the driving means of the press machine. Can be moved relative to the die 54 along the axial direction of the. A pressing block 62 is provided at the end of the pressing shaft 60 on the lower mold 14 side. The pressing block 62 has the work 7 at the end on the lower mold 14 side.
It is a curved surface corresponding to the bottom shape of 0.

Next, the operation and effect of the present embodiment will be described through the description of the thickening drawing process of the work 70 using the die 10.

The work 70 processed by the main mold 10 has a bottomed cylindrical shape whose bottom is substantially hemispherical in the previous step (that is, a normal drawing step, etc.) and the open end of the cylinder 74. Has a flange portion 7 extending outward in the radial direction.
2 is formed.

When the work 70 is set in the mold 10, first, the cushion rod 38 is slid on the lower die 14 until the flange portion 30 comes into contact with the stopper 34 by the cushion pressure adjusting means of the pressing device.
While being slid toward the side, the upper die 50 is moved in the direction of separating from the lower die 14, and the die 54 is sufficiently separated from the end of the lower die 14 on the upper die 50 side. In this state, the flange 72 and the end of the cushion plate 28 on the upper die 50 side face each other, and
Work 70 so that work 70 and circular hole 32 are substantially coaxial
Is placed on the cushion plate 28.

Next, from this state, the upper mold 50 is moved to the lower mold 14
When the work 70 is moved in the direction of approaching, the bottom of the work 70 comes into contact with the curved portion 58 of the die 54. From this state, when the upper mold 50 is further moved toward the lower mold 14,
The die 54 pushes down the cushion rod 38 via the work 70 and the cushion plate 28 against the pressure of the cushion pressure adjusting means, and the cushion plate 28 slides toward the bottom side of the cylinder portion 16. As a result, the punch 24 is inserted into the work 70. When the cushion plate 28 slides in this way, the cushion plate 28 contacts the punch plate 20 and the punch plate 20 restricts the cushion plate 28 from sliding, as shown in FIG. In this slide-restricted state, the pressing shaft 60 slides toward the lower mold 14 and the pressing block 62 presses the inner bottom portion of the work 70 against the spherical surface portion 26 of the punch 24.

When the upper die 50 is further moved from this state, the work 70 is pressed into the hole 56 of the die 54. Since the inner diameter of the hole portion 56 is smaller than the outer diameter dimension of the workpiece 70 before processing, the workpiece 70 is pressed into the hole portion 56 and compressed by being drawn to reduce both the inner and outer diameters. The thickness of the work 70 increases. In addition, in conjunction with the movement of the upper mold 50 at this time, the pressing shaft 60 slides to a predetermined position in a direction away from the lower mold 14. Further, when the work 70 is to be press-fitted into the hole 56 of the die 54, the corner portion of the lower open end of the hole 56 is located radially inward of the work 70 near the bottom of the work 70 and at the open end (that is, Press downward). The bottom of the work 70 that receives such a pressing force generates a force to escape upward, that is, into the hole 56 of the die 54. As a result, the bottom of the work 70 is punched by the punch 24.
Extends away from the upper end (that is, the spherical surface portion 26) of the. Further, at this time, a compressing force directed downward (that is, the downward 14 side) is applied to the work 70 by the descending die 54, but as described above, the drawing in the thickening drawing process with the main die 10 is performed. By setting the inner diameter of the hole portion 56 so that the lower limit of the ratio is 85%, the buckling of the work 70 due to the compressive force acting on the cylindrical portion 74 is prevented. It should be noted that when the die 54 descends, it is located inside the work 70 in the radial direction and at the open end (that is, below) near the bottom of the work 70.
The radius of curvature of the corner portion of the lower open end of the hole portion 56 that applies a pressing force to is changed depending on the inner and outer diameters of the work 70, but is preferably about 5 to 15 mm.

Here, in FIG. 3, the die clearance (that is, the difference between the inner diameter of the hole portion 56 of the die 54 and the outer diameter of the punch 24 in proportion to the wall thickness) and the wall thickness increase rate (that is, machining). The graph shows the results of experimentally examining the relationship with the ratio of the thickness after processing to the thickness before processing). As shown in this graph, when the die clearance is set in the range of 2.1 to 2.8 times the wall thickness of the tubular portion 74, the increase rate of the wall thickness becomes 1 time or more, and the die clearance is further increased. When it is set in the range of 2.4 to 2.5 times the wall thickness of the cylindrical portion 74, the increase rate of the wall thickness shows a peak. Based on the above results, in the mold 10, the difference between the inner diameter of the hole portion 56 of the die 54 and the outer diameter of the punch 24 is 2.1 times or more the wall thickness of the cylindrical portion 74 of the workpiece 70 before processing. Since it is 2.8 times or less, preferably 2.4 times or more and 2.5 times or less, the thickening drawing described above (that is, the work 7
In the step of press-fitting 0 into the hole portion 56), the wall thickness of the cylinder portion 74 of the work 70 is sufficiently increased without applying tensile stress to the cylinder portion 74, and the inner diameter of the cylinder portion 74 of the work 70 is increased. It is possible to keep dimensional accuracy and roundness within a predetermined tolerance range. Therefore, when the workpiece 70 processed in this manner is used as a housing that also serves as a yoke of a motor, a housing formed by merely drawing (that is, drawing without increasing the wall thickness of the workpiece 70) is used. In comparison, the amount of magnetic flux passing through the inside of the material of the housing can be increased, and the rotational torque of the motor can be improved. Further, in order to obtain the same effect as that of the housing formed by using the main mold 10 in a housing formed by only drawing, a thick metal flat plate must be used in advance in consideration of the decrease in the wall thickness. However, when the mold 10 is used, it is not necessary to anticipate the decrease in the wall thickness, so the manufacturing cost becomes low.

After the thickening drawing is completed in this way, so-called mold opening is performed to take out the work 70 from the mold. At this time, first, the upper mold 50 is lifted so as to be separated from the lower mold 14. Then, the upper die 50 is moved in the direction away from the lower die 14, and the die 54 is sufficiently separated from the end of the lower die 14 on the upper die 50 side. As a result, the work 70 comes out of the hole 56. Next, the cushion rod 3 is adjusted until the flange portion 30 contacts the stopper 34 by the cushion pressure adjusting means of the pressing device.
8 is slid toward the lower mold 14 side, and the punch 24
Escapes from the work 70. Here, in the mold 10,
As described above, the difference between the inner diameter dimension of the hole portion 56 of the die 54 and the outer diameter dimension of the punch 24 is 2.1 times or more and 2.8 times or less the wall thickness of the cylindrical portion 74 of the workpiece 70 before processing, It is preferable that the thickness is increased by 2.4 times or more and 2.5 times or less (that is, the step of press-fitting the work 70 into the hole 56).
At the same time, the wall thickness of the cylinder portion 74 of the work 70 is sufficiently increased without applying tensile stress to the cylinder portion 74, and the inner diameter dimensional accuracy and the roundness of the cylinder portion 74 of the work 70 are within a predetermined tolerance range. In this mold 10, the end of the cushion plate 28 on the side of the upper mold 50 is simply a flat plate. Therefore, the work 70 in this state is merely placed on the cushion plate 28, and the work 70 can be easily taken out.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a thickening drawing die according to an embodiment of the present invention.

FIG. 2 is a sectional view corresponding to FIG. 1 in a thickened drawing state.

FIG. 3 is a graph showing the relationship between die clearance and wall thickness increase rate.

[Explanation of symbols]

10 Thickening die 24 punch 28 Cushion plate (mounting part) 32 circular holes (through holes) 54 dice 70 work 72 Flange

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) B21D 24/00 B21D 22/28 B21D 22/22

Claims (4)

(57) [Claims] 1. A substantially flat plate shape from the opening end flange portion bottomed cylindrical which extends workpiece is placed from the open end
And the through-hole formed in the placing part corresponding to the open end of the work on the side opposite to the work through the placing part.
A punch is inserted into the workpiece by al through small-diameter hole portion than the inner diameter the outer diameter of the workpiece is coaxially formed with respect to the punch, along the axial direction of the through hole And a die for press-fitting the work into the hole by moving the hole relatively closer to the placing part, and the inner diameter of the hole and the outer diameter of the punch.
The difference between the size and the thickness of the outer peripheral part of the work is 2.1.
If the workpiece is machined after being doubled to 2.8 times or less,
A thickening and drawing die , characterized in that the increase rate of the wall thickness is 1 time or more . 2. The inner diameter of the hole and the outer diameter of the punch.
The difference between the dimension and the wall thickness of the outer peripheral portion of the work is 2.4.
The die for thickening and drawing according to claim 1, wherein the die is made to be not less than twice and not more than 2.5 times . 3. The punch is provided with respect to the placing portion.
The thickened diaphragm according to claim 1, wherein the thickened diaphragm is relatively slidable along a through hole of the mounting portion.
Processing mold. 4. A bottomed bottom having a flange extending from the opening end.
A cylindrical work piece is placed on a substantially flat plate-like placement portion, and the work piece is placed from the side opposite to the work piece through the placement portion.
Punch through the through hole formed in the mounting section
The hole that is smaller than the outer diameter of the work is inserted into the punch.
The die formed coaxially to the
And relatively move it to press the work into the hole.
By doing this, the work is thickened and drawn, and the motor
A method of manufacturing a yoke for forming a yoke, wherein a difference between an inner diameter of the hole and an outer diameter of the punch is calculated.
2.1 times or more and 2.8 times the wall thickness of the outer circumference of the work
Increasing the wall thickness of the workpiece after machining
A method for manufacturing a yoke, characterized in that the rate is set to 1 time or more .