Wedge-lockable removable punch and die bushing in retainer

FIELD OF THE INVENTION

The present invention relates to an improvement in a retainer such as is conventionally used to secure a tool such as a punch, or, a die bushing (or die or die button), or forming tool, removably in a die shoe.

BACKGROUND OF THE INVENTION

A retainer for a punch (punch retainer) secures the punch held within it to a die shoe, usually the upper, of a punch press so that the punch may be moved downwards into a die bushing with precision, over and over again so that stringent specifications of a punched sheet may be maintained. The die bushing, in turn, is held in a retainer (die bushing retainer) and secured to an opposed die shoe of the punch press. Typically both the retainers are removably secured to their respective die shoes; and the punch and the die bushing are also removably secured in their respective retainers.

For several decades a “ball lock punch retainer” has been used to secure the punch, and in fewer instances, also the die bushing which is more often clamped to the lower die shoe of the press, or tightly fitted into a recess therein. Despite the many problems associated with the use of a spring-biased retaining ball biased against a helical spring held in an angulated elongated passage within the retainer, this is the industrially favored mechanism because of the relatively low cost of manufacturing its components. However, aside from the relatively poor precision with which the shank (upper portion) of such a punch can be positioned, and the tolerable accuracy with which the point (lower portion) of the punch makes a through-passage (“hole” for brevity) of arbitrary cross-section in a sheet of stock being punched, a serious problem is that it is routinely an arduous and frustrating task to release a punch when it is to be replaced. One of the reasons is that repeated operation of the punch distorts the shape of the ball, which then becomes immovably lodged against the punch or against a helical spring against which the ball is biased. The problem of replacing the punch is worse when the ball is sheared, which typically happens when the stripping force exceeds that which the ball can withstand. In operation, punches are routinely subjected to unexpectedly large stripping forces typically cause by galling of the point.

An inherent result of using a ball seat or pocket in the shank of a punch to lock it with a ball is that, the shank of the punch is of necessity, cylindrical. If the point of the punch is non-circular in lateral cross-section, it can be sharpened only until the point is used up and the shank is reached. Moreover, by reason of the clearances required between the pocket and the ball, and the relatively small force exerted by the spring against the ball, it is difficult to maintain concentricity with tolerance less than 0.001 inch. Particularly when the shape of the hole to be punched is other than circular, the shank is not held tightly and non-rotatably in its elongated passage with the result that the play between the ball and the pocket results in slight but unacceptable variations in orientation of the hole punched. These problems are more readily envisioned by reference to

FIGS. 1 and 2

in which the prior art mechanism is briefly described. Moreover, the structural differences and their effect on the forces exerted on a tool to be replaced, when compared to those of the present invention, will more readily be appreciated.

Similar considerations apply to securing a forming tool which operates in a forming press and which forming tool is typically secured in a manner analogous to a punch. A commonly used forming punch has a point for making the desired hole in a sheet of stock, and has an upwardly flared conical portion directly above the tip of the point. The flared portion serves to provide desired concavity. Hereafter, for brevity and convenience, a punch and a forming tool or forming punch, and a die bushing are together referred to by the term “tool”, and are identified individually when specifically referred to.

Referring to

FIGS. 1 and 2

, there is illustrated a retainer block indicated generally by reference numeral

10

and a conventional punch

20

held therein. A forming toot if used, would be analogously held. The retainer block

10

includes a through-hardened backing plate

12

conforming to the upper surface of the retainer block, both being adapted to be secured to an upper die shoe of a punch press or other machine with a punching or forming function by suitable fastening means such as Allen-head screws (not shown). Since a tool (punch or forming) is generally used in a vertical attitude in a punch or forming press, the description herein refers to upper and lower in relation to such attitude. The retainer block

10

is provided with a cylindrical bore or tool socket

14

in which is slidably inserted and removably secured the shank (upper portion)

22

of the punch

20

, the lower portion of which is an oval-shaped point

24

. Block

10

is also provided with a cylindrical bore

15

which is angularly disposed relative to the bore

14

and which extends inwardly and downwardly into the retainer block

10

so as to partially intersect socket

14

. The partial intersection occurs because the lower end of the bore

15

is provided with a stepped surface forming ball seat

13

.

A retainer ball

16

is movably disposed in bore

15

, and a helical compression spring

18

is snugly held in the bore

15

with one end abutting the backing plate

12

so as to urge the ball

16

outwardly of the intersecting portion of bore

15

. Though the ball projects into the socket

14

the ball cannot escape (into the socket

14

). The retainer block is also provided with a through-passage or release-bole

17

through which a thin rod or drift pin is inserted to push the ball upward and move it out of the ball seat

13

when the punch

20

is to be removed. To replace the ball

16

when it gets distorted or damaged, the retainer block

10

is removed from the backing plate

12

and the spring and ball removed through the top of bore

15

.

The shank

22

is provided with a semi-pocket or ball seat

25

shaped generally like a one-half of a falling tear drop viewed in longitudinal elevation, and which is adapted to receive locking ball

16

to releasably lock the punch

20

in the bore

14

. The pocket's upper portion

26

appears as a straight section forming a continuation of the bore

15

; and the lower portion is provided with a return section

28

which is curved upon a radius greater than the radius of the ball

16

so as to connect the deepest part of the pocket

25

to the surface of the shank. When the ball

16

is held in pocket

25

its bottom may be in contact with the ball if the radius of section

28

is substantially greater than that of the ball; or, if the radius of the ball is substantially greater than that of the return section

28

, the extreme edges

34

,

35

of the pocket

25

will contact the ball.

To appreciate the advantage of locking a punch precisely positioned in the retainer block, the problem with using a pocket and retaining ball is illustratively presented in

FIGS. 3 and 4

so it may be more readily visualized. Both problems, namely of securing the tool to the die shoe, and positioning the punch (and die bushing) precisely, is particularly severe with relatively small diameter punches having a shank less than about 7.6 cm (3 ins.) in diameter. A larger diameter shank may be secured and precisely positioned with screws and dowels through the shank and die shoe. In

FIG. 3

is shown a shank

22

A having a pocket

25

A with an arcuate section having a radius substantially greater than that of ball

16

A, allowing the punch to rotate slightly in either direction, as shown by the arcuate double-headed arrow, so that accurate alignment between a non-circular punch and its corresponding die bushing cannot be maintained. In

FIG. 4

, in shank

22

B, the arcuate section of pocket

25

B has a radius smaller than that of ball

16

B so that it engages the corner portions

34

B,

35

B of the pocket in the shank. Under operating conditions which generate high forces, depending upon the relative hardness of the ball and the shank, either one or the other, or both are distorted or damaged; at the very least the extreme edges

34

35

of the pocket are pushed outward as shown at

38

,

39

.

Thus for optimum locking it is desirable to have the diameter of the ball accurately adapted to fit in the pocket so as to have the pocket contact the ball at two opposed points

33

inwardly spaced apart from the edges

34

,

35

as shown in

FIG. 2

, the distance inward being chosen so as to avoid forcing the extreme edges

34

,

35

outwards. Such precision is difficult to achieve in practice, and is proportionately so expensive as to be uneconomical. When achieved it will be evident that, the ball being a sphere, the contact at

33

is essentially point-contact with the surface of the pocket

25

and not substantially different from the point contact between the ball

16

B and shank

22

B with the pocket

25

B.

To avoid using a ball lock mechanism, wedges have been used to lock a punch transversely in a retainer as illustrated in U.S. Pat. No. 3,137,193, the shank is provided with a flat (shank flat) on one side thereof which flat engages a cooperating flat formed on a tapered retaining pin fitting within a transversely extending opening formed in the punch retainer. Since the tapered pin cannot prevent the punch from moving vertically the shank must also be held by a pin the inner end of which has a sloping wedge surface which is adapted to engage a cooperating wedge surface formed on the shank of the punch as a part of a cutout on the opposite side from the shank flat. Even if one accorded this means for holding a punch in a retainer great merit for accuracy, it is evident that such a punch and retainer function to wedge the shank by contact with two inclined surfaces, each of which serve to wedge the shank laterally, not vertically. The inclined surfaces form acute angles with the horizontal in a horizontal plane, that is, “laterally acute”; not with the vertical in a vertical plane, that is “vertically acute”. Moreover, such a mechanism is complicated and expensive to produce. Equally evident is why the ball lock punch retainer is the current standard for the machine tool industry.

In an analogous manner, when it is inconvenient or impractical to clamp a die bushing in a die-receiving hole, or one seeks either to avoid press-fitting a die bushing in the die-receiving hole, or using a ball lock mechanism to do so, the die bushing may be held as shown in U.S. Pat. No. 3,535,967 to Whistler et al. The die bushing is accurately positioned in a flexible retainer into which it is press-fitted and is held in the die retainer block by providing one side of the bushing with a flat surface, the flat cooperating with a corresponding flat on an aligning pin disposed transversely within a transversely extending opening in the die retainer.

The goal of this invention is to provide a locking means for a tool in a retainer block, which locking means will accomplish what the ball lock does, and much more, not only with respect to precision and strength, but also for economy and ease of operation; and to permit quick replacement of the tool by releasing it in its tool-receiving cavity with a force which is proportional to the pitch of threads in the screw means which secures the wedge in its wedge cavity to the backing plate of the retainer block.

SUMMARY OF THE INVENTION

It has been discovered that a conventional ball lock retainer for a tool (punch or die bushing) can be replaced with a tapered holding means such as a wedge-shaped block (“wedge”) having a vertical surface at an acute angle to the vertical center-line of the punch (“vertically acute angle”); the wedge locks the shank and locates it accurately in the retainer; doing away with the spring-biased locking ball a wedge-lockable punch avoids problems arising from lack of precise positioning of the point, and the failure of either the ball or the spring.

It is therefore a general object of this invention to provide a tooling construction comprising in combination, a retainer block, a punch or forming tool and a wedge means; the retainer block having a tool-and-wedge-receiving cavity or passage therein adapted to receive both the punch and the wedge means which, in operation, are locked in position relative to each other, the wedge means being provided with at least one inclined surface inclined from the vertical, and a tool-contacting, preferably tool-mating surface; and, fastening means to releasably secure the wedge within the retainer block so as to lock and unlock the punch in the tool cavity.

It is a specific object of this invention to provide, in lieu of a ball lock mechanism, a retainer block and punch releasably secured for operation in the retainer block, wherein the shank of the punch is non-circular so as to be non-rotatably locked in a predetermined precise position against the correspondingly non-circular tool-mating surface of the wedge when the wedge is translated towards the die shoe; and the upper portion or shank of the punch in lateral cross-section, may be the same as, or different from that of the lower portion or point of the punch.

It is a specific object of this invention to provide a die retainer and die bushing for operation in the die retainer wherein the die bushing is releasably secured in the lower die shoe of a press without requiring clamps or a ball lock mechanism.

It is also a general object of this invention to provide a method for securing a punch or forming punch or die bushing (“tool”) in a retainer block, comprising, forming therein a tool-and-wedge-receiving cavity shaped to provide both a tool cavity and a wedge cavity into each of which is closely received the tool and the wedge respectively; forming a wedge means adapted to be inserted in the wedge cavity, the wedge having an inclined surface (“wedge-inclined surface”); shaping the wedge to provide both a tool-mating surface and the wedge-inclined surface for contact with the retainer block, each surface preferably oppositely disposed relative to the other; assembling the wedge and the retainer block so as to form a tool cavity; inserting the tool within the cavity so as to be closely received therein and slidable relative to the tool-mating surface; and, providing relative movement between the tool-mating surface and the tool, sufficient to releasably lock the tool in the cavity.

It is a specific object to provide corresponding inclined surfaces on the following cooperating surfaces: (i) the wedge-inclined surface and a wall of the cavity in contact with the wedge inclined surface (see

FIGS. 6-9

,

15

); (ii) the tool surface and the wedge's tool-mating surface (see FIG.

10

); or (iii), both (i) and (ii) (see FIG.

11

).

It is a specific object of this invention to provide a method for securing a punch or forming tool in a retainer block, comprising, forming a wedge-shaped cavity in the block wherein at least one surface of the block (“inclined block surface”) is inclined from the vertical; forming a wedge having an inclined surface (“wedge inclined surface”) adapted to slidably cooperate with the inclined block surface, the wedge being shaped to provide a tool-mating surface oppositely disposed relative to the wedge inclined surface when the wedge is inserted into the wedge cavity, the tool-mating surface in cooperation with surfaces of the wedge cavity providing a tool passage within which the tool is to be held; inserting the wedge into the wedge-shaped cavity so that the wedge inclined surface is in contact with the inclined block surface; inserting the tool into the tool passage; and releasably securing the wedge within the retainer block to permit vertical movement thereof relative to the retainer block.

It is a specific object of this invention to provide a method of assembling a tool such as a punch or forming tool in a retainer block therefor, comprising, forming a cavity in the retainer block, the cavity having at least one surface inclined relative to the vertical plane through the tool; inserting a wedge in the cavity closely but slidably fitting the punch or forming tool in the cavity so as to contact a surface of the wedge on the side opposed to the inclined surface; and releasably securing the wedge within the retainer block to permit vertical movement thereof relative to the retainer block.

It is another general object of this invention to provide a method for making a retainer block and a tool adapted to be held in a cavity therein, comprising positioning a block of material in a wire electric discharge machine (“EDM”); programming the machine to cut a tool of desired shaped from within the block with a wire so as to form a tool cavity having an arbitrary cross-section and being open at both the top and bottom of the block; and, programming the machine to cut a wedge of desired shape from within the retainer block with the wire, the wedge having at least one inclined surface inclined from the vertical at an angle from about 1° to about 45° so as to form a wedge cavity; whereby the wedge is releasably insertable in the wedge cavity and the tool, however formed, is releasably insertable in the tool cavity.

It is a specific object of this invention to cut, using wire EDM, not only the wedge, but also the tool-and-wedge cavity from the retainer block using a thin wire having a sufficiently small diameter to provide the desired clearances between tool, wedge and cavity.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and additional objects and advantages of the invention will best be understood by reference to the following detailed description, accompanied with schematic illustrations of preferred embodiments of the invention, in which illustrations like reference numerals refer to like elements, and in which:

FIG. 1

is central vertical, sectional view of a conventional retainer block provided with a retaining ball releasably holding a punch.

FIG. 2

is a cross-section taken along the line

2

—

2

of

FIG. 1

, looking in the direction of the arrows.

FIG. 3

is a diagrammatic sectional view, in the lateral plane, of a ball having a diameter slightly greater than that of the pocket.

FIG. 4

is a diagrammatic sectional view, in the lateral plane, of a ball having a diameter slightly smaller than that of the pocket.

FIG. 5

is a bottom plan view, looking up, at a punch having a cylindrical shank and an oval point, the shank being held in a retainer block with a wedge.

FIG. 6

is a side elevational view taken along the line

6

—

6

of

FIG. 5

, looking in the direction of the arrows, showing a wedge having an inclined wedge surface at an angle θ (theta) which is inclined relative to the vertical center line through the punch, showing a first embodiment for releasably securing the punch.

FIG. 7

is a side elevational view, analogous to that in

FIG. 6

showing a wedge having an inclined wedge surface at an angle θ, but showing a second, alternative embodiment for releasably securing the punch.

FIG. 8

is a side elevational view, analogous to that in

FIGS. 6 and 7

, but showing a third, alternative embodiment for releasably securing the punch held by a wedge having a wedge surface at an obtuse angle α (alpha) relative to the vertical center line through the punch.

FIG. 9

is a side elevational view, analogous to that in

FIG. 8

, showing a wedge having a wedge surface at an obtuse angle α, but showing a fourth, alternative embodiment for releasably securing the punch.

FIG. 10

is a side elevational view, analogous to that in

FIG. 6

, but showing a fifth, alternative embodiment for releasably securing the punch held by a wedge in which its tool-mating surface is at an obtuse angle α (alpha) relative to the vertical center line through the punch, and the opposite surface of the wedge in contact with the wall of the cavity in the retainer block, is vertical.

FIG. 11

is a side elevational view, analogous to that in

FIGS. 6 and 8

, showing a sixth, alternative embodiment for releasably securing the punch, in which embodiment wedge surfaces on opposed sides are oppositely inclined, one at an obtuse angle α, the other at an inclined angle θ.

FIG. 12

is a bottom plan view, looking up, at plural punches in a punch assembly having a common retainer block and backing plate, in which assembly each non-circular shank is held non-rotatably against the wedge's shank-mating surface; the shank is integral with, and has the same cross-section as its point, and the cross-section is of arbitrary non-circular shape.

FIG. 13

is a perspective view of a hexagonal punch illustrating a shank and point with a common cross-section.

FIG. 14

is a top plan view, looking down, at a pair of die bushings in a die bushing assembly for a pair of punches having oval and hexagonal cross-sections respectively, the assembly having a common retainer block.

FIG. 15

is a side elevational view taken along the line

15

—

15

of

FIG. 14

, looking in the direction of the arrows, showing a cylindrical die bushing held by a wedge having a wedge surface inclined at an angle θ (theta) relative to the vertical center line through the punch.

FIG. 16

is a bottom plan view, looking up, at a pair of identical punches in a common retainer block, one punch secured in a retainer block by a partially frustoconical wedge with an arcuate vertical tool-mating surface, the other punch secured by a wedge with a planar inclined wedge surface, two arcuate vertical surfaces, one being a tool-mating surface, and three vertical planar surfaces.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to

FIGS. 5 and 6

there is illustrated a punch

20

having a cylindrical shank

22

, without a ball-receiving pocket, and a point

24

with a substantially oval cross-section. The shank

22

is held in retainer block

30

with wedge

31

. Wedge

31

, in lateral cross-section, has a generally polygonal periphery except for one side

32

which is arcuate, representing the wedge's arcuate, essentially vertical tool-mating surface which is adapted to closely receive the shank

22

. If the shank

22

were rectangular in cross-section, the side

32

would represent a vertical planar surface and the periphery would be linear. The peripheral outline of the mating surfaces is not critical so long as they are in contact to enable the tool to be secured in the retainer block.

The wedge

31

has an inclined surface

36

which is on the opposite side from the surface

32

, and is accurately machined relative to the other surfaces of the cavity; the upper edge of the wedge

31

is represented in phantom outline by the dashed line

14

. The surface

36

is inclined at a vertically acute angle θ relative to the vertical center line through the punch. The term “acute” refers to the included angle (as shown) formed by the intersection of the wedge surface and the vertical plane, as viewed frontally in the lower right quadrant. Since the arms of this angle open and diverge downwards, the wedging surface is referred to as having a “downwardly acute angle”. It will be evident that the angle θ is not narrowly critical as long as it is less than 90° and greater than 0° (relative to the vertical plane), but it will be evident that a much smaller angle, less than 60° will provide an adequate wedging function. Preferably the angle is in the range from about 10 to 45°, the larger angles generally facilitating release of the wedge for any reason, for example, when the punch is to be changed. For most punch retainer combinations the most preferred acute angle is in the range from about 1° to about 20°.

The wedge

31

is received in the retainer block

30

which is provided with a vertically extending through-passage also referred to as a tool-and-wedge receiving cavity

40

sized to closely receive the upper portion or shank

22

and also the wedge

31

having a tool-mating surface

32

. As shown in

FIG. 6

, one wall

41

of the cavity is inclined at the same acute angle as the wedge surface

36

so that the wedge may be moved against and along the wall

41

of the block. Wedge

31

is provided with a through-bore

42

into which a fastening means such as an Allen head shoulder screw

43

is inserted, and a snap-ring

44

is disposed within a circumferentially extending groove cut above the threads. The function of the snap-ring is to retain the wedge in operative relationship with the retaining block and tool, and provide a positive stop against which the wedge's upper surface is biased when the screw

43

is loosened in the backing plate

12

into which the the screw

43

is threaded. The shank

22

is inserted in the passage between the face

32

and the opposed face of the tool cavity

40

. The wedge is so dimensioned that tightening the Allen screw

43

tightly secures the shank in the retainer block. To remove the punch, the Allen screw

43

is loosened and the snap ring

44

will bias the wedge block away from the backing plate

12

sufficiently to free the punch.

Since the purpose of the wedge-inclined surface is to provide the wedging force it is not necessary that the tool-mating surface be opposite the wedge-inclined surface, though it is preferred that it be. As will also be evident, one may avoid the use of a hardened backing plate if the die shoe was adapted to have the retainer block secured to it and a hole was drilled and tapped to receive the Allen screw for translating the wedge means in the block. As will be evident in the embodiments shown in

FIGS. 7 and 8

below, the die shoe would not be required to be threaded. Of course, in practice, one routinely uses a backing plate for convenience and because a die shoe is not adequately hardened.

The backing plate or punch retainer pad

12

is held in operative position against the upper die shoe of a press by retaining means such as Allen head retaining screws

11

which are inserted in through-bores in the block

10

and threadedly secured in the backing plate

12

; dowel pins

19

align the backing plate accurately. It will be appreciated that a through-hardened backing plate is typically provided to save the die shoe (not shown) which is typically not hardened and would be damaged if the retainer block

10

were omitted; though the operability of the invention would not be affected by the absence of a backing plate, were the retainer block secured directly to the die shoe, the useful life of the die shoe would.

Referring to

FIG. 7

there is shown another embodiment in which a wedge

51

is translated within the tool-and-wedge cavity

50

of a retainer block

52

with a screw, such as an Allen head set screw

53

. One wall

54

of the cavity

50

is inclined at a downwardly acute angle θ, as is one face

55

of the wedge which cooperates with the wall

54

to provide the desired wedging force. The upper portion of the wall

54

has a channel-shaped groove cut in it, the length of the channel corresponding to the length of the threads on the set screw

53

. The upper end of the screw

53

abuts the top of the channel at

57

and the head of the set screw abuts the lower surface of the wedge at

58

. The inclined wall

54

of the cavity

50

is threaded to threadedly receive the set screw

53

, so that as the set screw is is rotated in one direction, the wedge is translated upward towards the backing plate

12

, and when the direction of rotation of the screw

53

is reversed, the wedge moves downward. The extent to which the threads (that is, length measured along the inclined wall) are cut in the wall

54

corresponds to the distance the wedge is to travel. As before, tool-mating face

56

of wedge

51

is vertical and arcuate to closely receive the cylindrical shank

22

of the punch

20

. As before the backing plate is secured to the die shoe and in the description of the following additional embodiments for utilizing the wedge, securing the backing plate to the die shoe will not be repeated.

Referring to

FIG. 8

, tool-and-wedge cavity

60

is provided in a retainer block

66

with an inclined wall

64

, and wedge

61

has an inclined surface

65

which cooperates with the wall

64

, each inclined at an obtuse angle α relative to acute angle θ. The term “obtuse” refers to the angle (as shown) formed by the intersection of the wedge surface and the vertical plane, as viewed frontally and measured upward starting at the vertical in the lower right quadrant. This is consistent with the use of the term “acute”. It will be evident that obtuse angle α is the complementary angle of acute angle θ, but oppositely directed as if in mirror image relationship, the mirror positioned in a plane vertical with respect to the paper. For convenience, and to visually convey this relationship, the obtuse angle α of the wedge inclined surface is hereafter referred to as an “upwardly acute angle”. As before, this upwardly acute angle is not narrowly critical as long as it is less than 180° and greater than 90° relative to the vertical plane, but it will be evident that an angle greater than 120° will provide an adequate wedging function. Preferably the angle is in the range from about 135° to 179°, the numerically smaller angles generally facilitating release of the wedge. For most punch retainer combinations the most preferred obtuse angle is in the range from about 160° to about 179°.

An upwardly inclined wedge is particularly suited for use with a punch stripper subjected to higher forces than tolerated by a ball lock mechanism. Wedge

61

is provided with a bore

62

which is partially threaded so that rotation of an Allen screw

63

threaded in the bore, when the end of the screw is biased against the backing plate

12

, translates the wedge up and down. As before, shank

22

is closely received in tool-mating surface

67

. When the screw is rotated so the wedge is translated downwards the wedge locks the shank

22

in position; when translated upwards, the shank is released.

Because the wedge

61

has an upwardly inclined face, the combination of retainer block and wedge is assembled prior to securing it to the die shoe. The screw

63

is threaded in the wedge

61

so that the end of the screw is flush with the surface of the wedge, and this assembly is place on the backing plate

12

. The retainer block

66

is then fitted over the wedge so that the cooperating inclined surfaces are in contact and the wedge is captured. The retainer block is then secured to the backing plate. This procedure is followed in all instances where one of the surfaces of the wedge is upwardly inclined. The advantage of capturing the wedge in the retainer block before it is secured to the die shoe is that the wedge is not misplaced.

Referring to

FIG. 9

, retainer block

75

is provided with tool-and-wedge cavity

70

having an inclined wall

74

, and wedge

71

has an inclined surface

77

which cooperates with the wall

74

, each inclined at an upwardly acute angle θ. Wedge

71

is provided with a threaded bore

72

in which a screw

73

is threaded. One portion

73

′ of the screw

73

is threaded with a left hand thread, and the remaining portion

73

″ is threaded with a right hand thread. Accordingly, the threaded bore in wedge

71

is of opposite “hand” relative to a threaded bore in backing plate

12

, and the screw operates in a manner analogous to a turnbuckle. As before, the wedge is captured in the retainer block

75

before it is secured to the die shoe and shank

22

is closely received in tool-mating surface

76

. When the screw is rotated so the wedge is translated downwards the wedge locks the shank

22

in position; when translated upwards, the shank is released.

Referring to

FIG. 10

, retainer block

85

is provided with tool-and wedge cavity

80

having a vertical wall

84

, and wedge

81

has a vertical surface

83

which cooperates with the wall

84

, each inclined at an obtuse angle α. The tool-mating face

85

of the wedge is inclined at an upwardly acute angle θ and is adapted to closely receive the correspondingly obtusely inclined surface

86

of shank

22

. Since the shank is cylindrical, the inclined surface

86

is arcuate. Wedge

81

is provided with a through-bore

42

into which an Allen screw

43

is inserted and a snap-ring

44

is placed in a groove cut above the threads. As before, shank

22

is closely received in tool-mating surface

85

; and, the wedge

81

is dimensioned so that tightening the Allen screw

43

secures the shank in the retainer block; loosening the screw allows the snap-ring to help move the wedge and release the punch.

Referring to

FIG. 11

, retainer block

95

is provided with tool-and-wedge cavity

90

having an inclined wall

94

, and wedge

91

which has an inclined surface

95

cooperating with wall

94

, each inclined at a downwardly acute angle θ. The tool-mating face

96

of the wedge is inclined at an upwardly acute angle θ and is adapted to closely receive the correspondingly obtusely inclined surface

97

of shank

22

. Since the shank is cylindrical, the inclined surface

96

is arcuate. Wedge

91

is provided with a through-bore

42

into which an Allen screw

43

is inserted and a snap-ring

44

is placed in a groove cut above the threads. As before, shank

22

is closely received in tool-mating surface

96

; and, the wedge

91

is dimensioned so that tightening the Allen screw

43

secures the shank in the retainer block; loosening the screw

43

in the backing plate

12

allows the snap-ring to help move the wedge and release the punch.

In each of the foregoing descriptions of embodiments of the invention, the shank is shown as being cylindrical, as is conventional, and for the common instance where a the point punches a circular hole in a web of stock, the rotation of the shank in its cavity is immaterial if its clearances relative to the die bushing are correctly established. However, in cases where the dimensional tolerances of the cooperating surfaces of the punch, the retainer block and the die bushing are critical and must be tightly controlled, the punched hole is required to be within tolerances less than 25.4 μm (microns or micrometers) or 0.001″ (inch). For example, where the point is non-circular in cross-section and the shank is cylindrical, and the point is to be accurately positioned with a clearance of 12.7 μm or (0.0005″) in a correspondingly shaped die bushing, the cylindrical shank is provided with a flat, and a corresponding mating flat is provided in the wedge's tool-mating surface. When the cross-section of a non-circular punch is the same in its upper and lower portions, the punch cavity in the retainer block is correspondingly shaped with a minimum clearance, typically 12.7 μm. Whether the cross-section of the shank is circular or not, the force with which the wedge secures the punch in the retainer block is much greater than that exerted by a conventional ball lock and spring in the same application with the same size punches. For example, a 9.84 mm (0.25″) ball in the pocket of a punch with a 9.5 mm (0.375″) diam shank and a conventional ball lock and spring, is shattered when a stripping force of 272.7 Kg (600 lbs) is exerted on the punch; the same shank is held with a stripping force of 909 Kg (2000 lbs) when it is secured with a downwardly inclined wedge (FIG.

6

), when slipping of the punch occurred. No such slipping would occur with both an upwardly inclined tool-mating surface and a downwardly inclined wedge-inclined surface (FIG.

11

).

It will also be noted that in embodiments shown in

FIGS. 5

,

6

,

9

,

10

,

11

,

12

and

14

the wedge is held in the tool-and-wedge cavity by a screw which is threaded into the backing plate, but a screw is not so threaded in the embodiments shown in

FIGS. 7 and 8

, though the screw does cooperate with the backing plate to move the wedge in all embodiments except that in FIG.

7

.

Referring to

FIG. 12

there is schematically illustrated a bottom plan view, looking up, of a retainer block

100

in which multiple punches

101

,

102

,

103

, and

104

are commonly held and positioned with dowel pins

19

, then secured against a backing plate with Allen screws

11

. Each punch is a rod of appropriately hardened steel or other metal, the rod having a uniform cross-section, but each rod has a cross-section of different shape. Each rod is secured with a wedge having a correspondingly shaped tool-mating surface to receive a portion of the periphery of the punch. The remaining portion of the periphery is received by a correspondingly shaped tool-mating surface in the wall of the retainer, opposite the wedge. In each of the above wedges, the tool-mating surface is vertical and the opposed inclined surface is at a downwardly acute angle θ. In each case the wedge is vertically translatable in its respective tool cavity to an extent sufficient to release the tool whether punch, forming tool or die bushing.

FIG. 13

is a perspective view of punch

103

which is of substantially hexagonal cross-section, as shown in the combination of wedge and punch identified by reference numeral

103

in FIG.

12

. Approximately one-third of the periphery of the punch is received in a one-third-hexagon-shaped tool-mating surface of wedge

110

, and the remaining two-third is received in a vertical surface of corresponding two-third-hexagon shape which is cut in the retainer block.

Referring to

FIG. 14

there is illustrated a pair of die bushings

105

and

106

secured by wedges

107

and

108

respectively in a common die bushing retainer block

110

which, in turn, is secured to the lower die shoe of a punch press with Allen screws

11

. Each die bushing is non-circular and has a planar upper surface defining a point-receiving through-passage therein to receive a correspondingly non-circular punch accurately positioned relative to the common die retainer block and the corresponding punches. In each case, the wedge inclined surface is accurately machined relative to the non-circular point. The goal is to provide a highly secure and accurate position of the die bushing without having any structural component protruding substantially above the surface of the retainer block

110

, that is, does not interfere with accurately positioning stock on the die retainer block.

Referring to

FIG. 15

there is shown a die bushing

106

having an elliptical tapered through-bore

19

which at the surface of the retainer block provides the precise desired clearance of the elliptical punch it is to receive. One portion of the die bushing

106

is provided with a flat

111

which is held by a corresponding flat surface on wedge

108

. The tool-and-wedge cavity

112

is outlined by the periphery of the die bushing

106

and the wedge

108

, the wall

113

of the cavity being inclined at an acute angle θ to the vertical, this being the included angle between the plane of the inclined surface and the vertical plane through the center of the Allen screw

43

, viewed frontally in the upper left hand quadrant. The tool-mating surface of the wedge being planar and vertical, as before, an Allen screw

43

threaded into the backing plate (not shown) secures the die bushing in position when the screw is tightened, and releases the die bushing when the screw is loosened. As before, this is facilitated with a spring washer

44

interposed between the lower surface of the wedge and the surface of the backing plate.

Though the cross-section of the wedges illustrated in the

FIGS. 5

,

12

&

14

indicate they have been cut from a rectangular block, as would be the wedges cut in

FIGS. 8

,

9

,

10

and

11

, it will be evident, that the wedge could be cut so as to have an arbitrary cross-section (in the lateral plane shown) so long as the tool-mating surface corresponds to the surface of the tool and the wedge inclined surface corresponds to the inclined surface in the retainer block.

Referring to

FIG. 16

there is shown a the shank

22

of a punch held in a tool cavity formed within common retainer block

120

by a partially frustoconical wedge

121

received closely between an inclined surface of a partial cone cut in the retainer block, the surface being scribed and cut at a downwardly inclined angle θ. The conical surface of the partial cone cut in the block corresponds to the conical surface of the conical wedge, the upper outline of which is shown by the dotted line

122

. The surfaces

123

and

126

of the wedge are vertical and planar. The tool-mating surface

124

of the wedge is vertical and arcuate except where it is flatted at

128

, corresponding to the flatted cylindrical surface of the shank

22

. As before, Allen screw

11

and dowel pins

19

secure the retainer block to the die show and an Allen head shoulder bolt

125

with a snap-ring in a groove above the threads, secures the conical wedge to the retainer block

120

so that tightening the conical wedge against the retainer block locks the shank

22

in the block, and loosening the screw

125

releases the wedge and allows it to be moved downwards.

The other wedge

130

in the retainer block

120

is irregularly shaped. It has a planar wedge-inclined-surface the lower edge

131

of which is downwardly inclined at an angle θ, and the upper edge of the surface is indicated by dotted line

132

. Surface

133

is vertical and arcuate, being partially cylindrical, curving outward; tool-mating surface

135

is vertical, arcuate and partially cylindrical curving inward; and surface

134

represents the remaining vertical surfaces of the periphery which are shown as a partial polygon. From a practical point of view, one would choose the shape of the wedge which best suits his purpose for the task at hand, using the shape which is most economically cut.

In each of the foregoing embodiments it will now be evident that machining the wedge and retainer block to provide the tool cavity desired is the key to providing the reliability and precision not routinely available in any prior art tool and retainer combination used for a similar purpose. It will also be evident that the wedge may have plural inclined surfaces, if desired. Though the wedge, punch or die bushing, and retainer block with the appropriate tool cavity may be formed separately by machining them to the desired specifications, a preferred method is forming the tool cavity and wedge essentially simultaneously. This is done by a conventional traveling-wire electrical discharge machine (TW-EDM) in which a thin continuous wire-like elongate electrode is axially caused to travel or is transported from a supply reel to a wind-up (take-up) reel and a retainer block is disposed in juxtaposition with the traveling-wire electrode while electrical energy in the form of time-spaced electrical pulses is supplied across a machining gap formed between the traveling wire and the block in the presence of a dielectric fluid to effect a series of electrical discharges to remove material from the block. As material removal proceeds, the block is displaced relative to the axially transported wire electrode in a prescribed path to produce a desired cutting pattern in the block

Conventional machines designed to execute the TW-EDM process are provided with a pair of support arms extending from a column mounted upright on a base of the machine, one of the support arms guiding the continuous wire electrode unwound from the supply reel into the machining region where the workpiece machining portion is located while the other guides the wire electrode having undergone the machining action continuously to the take-up reel. The axial transportation of the wire electrode is effected by controlled rotary drive comprising feed and brake roller arrangements which also act to stretch the moving wire guided between the support members under a sufficient tension to allow the wire electrode to travel smoothly and accurately in machining position relative to the workpiece. As a result, a block of hardened tool steel may be cut precisely, providing of course the machine is programmed appropriately. Of course, the wedge may be cut from a non-hardened alloy steel which may not need to be hardened, or which may be hardened later. The advantage of cutting the wedge from hardened steel is to minimize the distortion which may occur upon hardening. A machine which is well-adapted to machine the block as desired is a Mitsubishi FX10 which is preferably operated with a wire having a thickness of about 0.254 mm (0.010″). Programming instructions for the machine are used conventionally, and being well known to those skilled in the art, need not be described in greater detail herein.

It will now be evident that the length of the tool being greater than the thickness of a retainer block in which it is to be held, it is not economical to cut the tool from the same block of hardened steel as the retainer block and wedge. For example, for a punch such as shown in

FIG. 6

which is 7.62 cm (3″) long, the thickness of the retainer block is typically 2.54 cm (1″). Therefore, the tool, and preferably many tools, the same or different, are cut from a separate block of adequate longer dimension (7.62 cm) than the block from which the wedge and retainer block are cut (2.54 cm).

Having thus provided a general discussion, described the overall combination of tool and wedge means in detail and illustrated the invention with specific examples of the best mode of carrying out the process, it will be evident that the invention may be incorporated in other tool constructions, several of which are described. The wedge lockable tool has provided an effective solution to an age-old problem. It is therefore to be understood that no undue restrictions are to be imposed by reason of the specific embodiments illustrated and discussed, and particularly that the invention is not restricted to a slavish adherence to the details set forth herein.

Number	Name	Date
2662773	Parsons	Dec 1953
3137193	Whistler, Sr. et al.	Jun 1964
3535967	Whistler, Sr. et al.	Oct 1970
5464299	Schärer	Nov 1995
5881625	Wellman	Mar 1999
5913634	Helig	Jun 1999

Wedge-lockable removable punch and die bushing in retainer

Information

Patent Number

Date Filed

Date Issued

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CPC

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Abstract

Description

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US Referenced Citations (6)