BACKGROUND ART Generally, a stack of laminate (that is also called lamina core) made by stacking laminas is used as a rotor or a stator in generators or motors, and its manufacturing method is well known in the art.

FIG. 1 shows a lamina core in which lamina members L are stacked, and FIG. 2 is a section view taken along II-II line of FIG. 1. Referring to FIGs. 1 and 2, a shaft hole H is formed on the center of the lamina members L. Out of the shaft hole H, a plurality of slots S are formed in a radial direction.

Each of the lamina members L has an interlock tap 101 for interconnection between the members. When the lamina members L are stacked, an interlock tap 101 formed in the upper lamina member L is fitted into an interlock groove 102 of the lower lamina member to bind both lamina members.

The lamina member L is manufactured from a strip stock material by stamping it

with a typical progressive stamping die apparatus. Referring to FIG. 3 that shows an interlock tap forming process in the prior art, an interlock tap punch 10 fixed to an upper press (not shown) is descended and presses a strip stock material 100 supplied on a lower die 20 to a predetermined depth so as to form embossing, thereby forming the interlock tap 101. At this time, the interlock tap punch 10 is inserted into a punch hole 21 formed in the upper portion of the lower die 20 and presses the strip stock material 100 to be plastically deformed, and an edge of the pressed portion is rounded as shown in a partially enlarged view. A gap G between the interlock tap punch 10 and the punch hole 21 is adjusted within the range of about 0.005 to 0.01 mm. If the gap G is too small, the binding power between the lamina members 100 is reduced. To the contrary, if the gap G is too large, more force is required for their binding.

In the conventional progressive stamping die apparatus, the interlock tap punch 10 has a section identical to that of the punch hole 21, except that their sectional sizes are different as much as the gap G. However, if the operation accuracy of the upper press is deteriorated to cause variation in the descending strokes of the punch, an amount of plastic deformation of the strip stock material is also varied accordingly.

However, the conventional interlock tap forming structure is not equipped with a means for sufficiently absorbing such plastic deformation. In addition, as the apparatus is aged, the interlock tap punch 10 does not stamp a center of the punch hole 21 exactly, but punches eccentrically with a predetermined variation from the center. In this case, the embossing may be asymmetrically formed or excessively deviated to one side to cause cracks in the material and not to form the embossing in the other side, thereby not allowing the lamina members to be bound.

DISCLOSURE OF INVENTION The present invention is designed in consideration of such problems of the prior art, and therefore an object of the invention is to provide a progressive stamping die apparatus that prepares a clearance recess of a predetermined width in a punch hole of a lower die in which an interlock tap is formed so that a strip stock material is deformed with being partially pushed into the recess when a punch presses and plastically deforms the material, and a method for manufacturing a stack of laminate.

According to the present invention, since an interlock groove formed in the upper surface of the strip stock material has a shape different from an interlock tap formed in the lower surface thereof, stronger binding power is ensured when binding lamina members. In addition, the interlock tap forming structure according to the present invention is designed to be capable of buffing and compensating though an amount of plastic deformation is locally changed due to descent variation of the punch.

In order to accomplish the above object, the present invention provides a progressive stamping die apparatus, which includes a lower die, on an upper surface of which a strip stock material is supplied; an upper press moved up and down against the lower die for stamping the strip stock material to make a plurality of lamina members; and an interlock tap punch combined to the upper press for pressing the strip stock material to form an interlock tap, wherein a punch hole having a shape corresponding to a section of the interlock tap punch is formed in an upper surface of the upper die with a predetermined gap so that the interlock tap punch is inserted therein, and at least one clearance recess is formed in a part of the punch hole so that the strip stock material is partially pushed therein by means of plastic deformation when the interlock tap is

formed.

In another aspect of the invention, there is provided a method for manufacturing a stack of laminate by using a progressive stamping die apparatus including an upper press combined with an interlock tap punch, and a lower die in which a punch hole having a shape corresponding to a section of the interlock tap punch is formed therein and at least one clearance recess is formed in a part of the punch hole, wherein the method includes (a) supplying a strip stock material between the upper press and the lower die; (b) forming an interlock groove and an interlock tap by moving the upper press down to press the strip stock material into the punch hole, the strip stock material being partially pushed into the clearance recess by means of plastic deformation; (c) generating lamina members by blanking the strip stock material ; and (d) stacking the lamina members while the interlock tap formed in an upper lamina member is fitted into the interlock groove formed in a lower lamina member.

Preferably, in the step (b), the interlock groove corresponding to the section of the interlock tap punch is formed in an upper surface of the strip stock material, and the interlock tap having a clearance projection corresponding to the clearance recess of the punch hole is formed in a lower surface of the strip stock material.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: FIG. 1 is a perspective view showing an example of a general lamina core;

FIG. 2 is a sectional view taken along 11-11 line of FIG. 1; FIG. 3 is a sectional view and a plane view for illustrating the interlock tap forming process of the prior art; FIG. 4 is a side view schematically showing a progressive stamping die apparatus according to a preferred embodiment of the present invention; FIG. 5 is a plane view of a lamina core manufacturing process, schematically shown on a strip stock material, according to a preferred embodiment of the present invention; FIG. 6 is a perspective view schematically showing an interlock tap forming portion of the progressive stamping die apparatus according to a preferred embodiment of the present invention; FIG. 7 is a sectional view schematically showing the progressive stamping die apparatus according to a preferred embodiment of the present invention, in which a hatching portion is corresponding to the section of an interlock tap punch and a solid line is corresponding to a border of the punch hole; FIG. 8 is a sectional view schematically showing that an interlock tap is formed in the strip stock material according to a preferred embodiment of the present invention, in which a solid line designates a border of the interlock groove formed on the upper surface and a dotted line designates a border of the interlock tap formed on the lower surface; FIG. 9 is a sectional view for illustrating operation of a stacking barrel in the progressive stamping die apparatus according to a preferred embodiment of the present invention;

FIG. 10 is a sectional view for illustrating the binding relation of the interlock taps when lamina members are stacked according to a preferred embodiment of the present invention; FIG. 1 la is a plane view showing an interlock tap punch and a corresponding punch hole according to another embodiment of the present invention; and FIG. 11b is a plane view showing an interlock tap punch and a corresponding punch hole according to still another embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that terms and words used in the specification and the claims should not be limitedly interpreted as a common or dictionary meaning, but as meaning and concept according to the technical spirit of the invention, based on the principle that an inventor can define the concept of a term suitably in order to describe his/her own invention in a best way.

Thus, the embodiment stated in the specification and the configuration shown in the drawings are just the most preferable example, not intended to illustrate all of the spirit of the invention, so it should be understood that various equivalents and modifications may be made to replace the example. In addition, a component named with"means"in the specification and claims are not defined with its specific structure and shape, but as a functional and operating meaning to be achieved by it. Accordingly, it should be understood that various equivalents exist within the scope capable of accomplishing such function and operation.

FIG. 4 is a side view schematically showing a progressive stamping die apparatus according to a preferred embodiment of the present invention, and FIG. 5 is a plane view of a lamina core manufacturing process, schematically shown on a strip stock material.

Referring to FIGs. 3 and 4, a lamina member is manufactured by stamping and blanking a long strip stock material 100 with intermittently transferring the strip stock material 100 in the progressive stamping die apparatus. The progressive stamping die apparatus according to the preferred embodiment of the present invention includes a lower die 110 upon which the strip stock material 100 is supplied, and an upper press 120 installed above the lower die 110 to move up and down.

The upper press 120 is designed to make vertical strokes rapidly by means of a well-known press driving means. On the lower surface of the upper press 120, punches 130a, 140a, 150a and 160a having various shapes and functions are mounted to stamp or blank the strip stock material 100 supplied upon the lower die 110. In addition, punch holes 130b, 140b, 150b and 160b corresponding to the punches are formed in the lower die 110.

Furthermore, at the last stage of the process, a blanking pin 170a for blanking the strip stock material 100 to complete a lamina member and a stacking barrel 170b for receiving and stacking the blanked lamina member are respectively provided to the upper press 120 and the lower die 110.

The progressive stamping die apparatus of this embodiment may be designed to conduct a five-stage process, namely using a slot forming portion 130, a counter hole forming portion 140, a shaft hole forming portion 150, an interlock tap forming portion

160 and a blanking portion 170.

In the slot forming portion 130 corresponding to the first stage (I) process, if the strip stock material 100 is supplied upon the lower die 110 by means of a separate supply means, the upper press 120 is moved down. At this time, the pin punch 130a installed on the lower surface of the upper press 120 is moved down and inserted into the hole 130b to perforate a plurality of slots S in the strip stock material 100.

After the slots S are formed, the upper press 120 is moved up, and the strip stock material 100 is then advanced again a predetermined distance by means of the supply means to reach the counter hole forming portion 140 of the stage II. The counter process is for adjusting the sheet number of lamina cores finally stacked, and in the counter process the pin punch 140a perforates the strip stock material 100 to form a counter hole 201 in the suitable number of lamina members L. The pin punch 140a may select one mode between an operating state and a non-operating state by means of a driving means, not shown, which is well shown in the art and not described in detail here. If the counter hole 201 is not required, the pin punch 140a becomes in a non-operating state. In this case, it is possible that an interlock tap is formed in the lamina member in the following process.

If the counter process is completed, the upper press 120 is moved up, and the strip stock material 100 is again advanced a predetermined distance to reach the shaft hole forming portion 150 of the stage III. Like the above processes, the upper press 120 is moved down so that the pin punch 150a perforates a shaft hole H at the center of the strip stock material 100.

After that, the strip stock material 100 is advanced to form the interlock tap 101

at the interlock tap forming portion 160 of the stage IV. Essential parts of the interlock tap forming portion 160 are schematically shown in FIG. 6. As shown in FIG. 6, the interlock tap punch 160a that presses the strip stock material 100 is fixed to a support block 162 combined to the upper press 120, and then moved up together with the upper press 120.

In the lower die 110 positioned below the upper press 120, a punch hole 160b is formed in correspondence to the interlock tap punch 160a. The punch hole 160b has a size that ensures a predetermined gap G from the interlock tap punch 160a, as shown in a plane sectional view of FIG. 7. According to the features of the present invention, at least one clearance recess 161a, 161b, 161c and 161d having a predetermined width is formed in the punch hole 160b. In this embodiment, an example of forming a circular interlock tap is disclosed, and at edges of the punch hole 160b, the clearance recesses 161a, 161b, 161c and 161d are symmetrically formed.

Depth and width of the clearance recesses 161a, 161b, 161c and 161d are suitably selected according to thickness and malleability of the strip stock material 100 to be stamped so that they may sufficient cover the plastic deformation of the material.

If the strip stock material 100 is supplied to the interlock tap forming portion 160, the upper press 120 is moved down to press the material 100, thereby forming the interlock tap 101. At this time, as shown in FIG. 8, an interlock groove 102 having a shape corresponding to the section of the interlock tap punch 160a, e. g. a circular shape, is formed on the upper surface of the strip stock material 100. Meanwhile, when the punch 160a presses the strip stock material 100, the material is embossed by means of plastic deformation and also partially pushed into the clearance recesses 161a, 161b,

161c and 161d, so the interlock tap 101 having at least one clearance projection 101a is formed on the lower surface of the strip stock material 100 as shown in FIG. 8 by a dotted line.

Subsequently, if the strip stock material 100 is advanced to the stage V, the blanking punch 170a installed to the upper press 120 is moved down to blank the material, thereby finally giving a lamina member L. Together with being blanked by the blanking punch 170a, the lamina member L is is inserted into the stacking barrel 170b installed below it and then stacked on another lamina member already stacked therein, as shown in FIG. 9. At this time, the lamina members L are pressed by the punch so that the interlock tap 101 of an upper lamina member L-2 is fit into the interlock groove 102 of a lower lamina member L_1 for mutual binding, as shown in FIG. 10. If, after the predetermined number of lamina members, for example 20 lamina members, are stacked using the same process, a lamina member without an interlock tap is blanked by means of the well-known counter hole forming process and then stacked thereon, a lamina member not stacked any more, but separated. The lamina core stacked as mentioned above is discharged out through a separate discharge hole.

According to the present invention, when the upper and lower lamina members L 2 and L 1 are bound with each other, they are forged with the clearance projection 101a of the upper interlock tap 101 being fitted into the interlock groove 102, thereby improving mutual binding force.

This embodiment is described using a specific lamina core as an example.

However, it is just an example, and it should be understood that there may be applied

various kinds of lamina cores.

The clearance recess may have various sizes and shapes in an interlock tap that may have various shapes in the present invention. For example, clearance recesses 270a and 270b may be formed at both sides of the rectangular punch hole 270 corresponding to the rectangular punch 260, as shown in FIG. 11a. In addition, FIG.

11b shows a section of the punch 370 to form an oval interlock tap, a punch hole 360 corresponding to the section, and a clearance recess 370a formed io a part of the punch hole 360, as an example.

INDUSTRIAL APPLICABILITY According to the progressive stamping die apparatus and the method for manufacturing a stack of laminate according to the present invention, since at least one clearance recess is provided to a part of the punch hole having a shape corresponding to the punch section, the strip stock material is pushed into the clearance recess when the interlock tap is formed. It functions to sufficiently relieve and cover the plastic deformation of the material. For example, though precision of the punch is deteriorated due to aging of the apparatus to cause irregular deformation of the material or focus stress on a local region, the clearance recess may compensate it.

In addition, since the interlock groove corresponding to the section of the punch is formed in the upper surface of the material and the interlock tap with the clearance projection is formed in the lower surface of the material, the interlock tap with the clearance projection is fit into the narrower interlock groove when the lamina members are stacked, thereby giving firm binding force. Accordingly, it is possible to prevent the lamina cores from being separated or deviated in the following procedure.