GB2174329A - Punch retainer - Google Patents

Abstract

A punch retainer 10 has a retainer body 18 provided with a vertical through bore 36 therein to receive the shank 38 of a punch 40. The upper face portion 64 of the body 18 through which the bore 36 extends is offset downwardly from and parallel to the remaining portion 22 of the top face of the body to form a seat for a hardened steel backing plate 20 which is 2 permanently mounted on the body. After the backing plate 20 is secured to the body 18, a through hole 76 is formed in the backing plate accurately concentric with the axis of the punch bore 36. The retainer 10 is adapted to be accurately located on a die shoe 14 by means of an accurately located pin 78 projecting downwardly from a blind hole 80 in the die shoe 14 and having a close fit with the hole 76 in the backing plate 20. The body 18 has two further through bores (60, Fig. 4) for screws to secure the retainer to the die shoe and, for non-circular punches, a second locating pin 82. <IMAGE>

Description

SPECIFICATION Punch retainer This invention relates to punch retainers.

In punching holes in metal workpieces each punch is normally mounted in a retainer which is in turn mounted on a die shoe in a press. The punch retainer normally comprises a steel body having a through bore in which the shank of a punch is removably secured. In one form of punch retainer a hardened steel backing plate is interposed between the retainer body and the die shoe to prevent the punch from being driven into the soft steel of the die shoe. In another form of punch retainer, instead of utilizing a hardened steel backing plate, the upper end of the bore in the retainer for the shank of the punch is enlarged to form a conical cavity and a tubular plug having a slightly smaller conical head is press fitted into the punch bore.

Regardless of whether the retainer utilizes a backing plate or a plug to absorb the impact force of the punch, in order to punch accurately located holes in a workpiece it is essential that the punch retainer be very accurately positioned on the die shoe because the workpiece to be punched is accurately positioned relative to the die shoe.

Position accuracy of the retainer is best obtained through the use of dowels. In the case of punches for round holes, this accuracy can be obtained by a single dowel in the retainer and the die shoe accurately aligned with the axis of the bore for the shank of the punch. In the case of noncircular punches, at least two widely spaced dowels are preferably utilized to accurately locate the retainer on the die shoe.

When a tubular plug having a conically shaped outer end is located at the upper end of the punch bore in the retainer, a dowel in the center passage of the plug is arranged to engage and accurately position the recess in the die shoe to locate the retainer on the die shoe. While this arrangement eliminates the need for a backing plate, experience has shown that it is suitable only for very light work.

With large holes or holes in thick metal, such plugs have a tendency to penetrate into the soft steel of the die shoe. Thus, such plug arrangements have very limited application.

When a backing plate is utilized between the body of the retainer and the die shoe, in order to produce accurately located holes in a workpiece, it is essential that the backing plate is accurately located relative to the retainer body and also relative to the die shoe. This normally requires at least two dowels for removably positioning the backing plate on the retainer body and also one or more dowels for accurately locating the retainer on the die shoe.

The stamping industry has established standard sizes for punches and retainers. Industry standards have been established with respect to the diameter and length of punch shanks. This in turn determines the standards for diameter and length of the punch bore in the punch retainer. Industry standards also specify the thickness (vertical dimension) of the assembled retainer body and backing plate.

Accordingly, to enable interchangeability of punch retainers it is necessary that the retainers are dimensioned to adhere to industry standards. The thickness dimension of a punch retainer is important from the standpoint of strength.

Consequently, the strength of the retainer body, which is softer and tougher than the hardened backing plate, is, to a large extent, determined by its thickness. Accordingly, to the extent that the backing plate does not reduce the thickness of the retainer body, the retainer has greater strength.

The present invention has for an object the provision of a compact, high strength punch retainer which is readily interchangeable with other retainers that are made according to the dimension specifications of industrial standards.

Another object of the present invention is to provide a punch retainer that can be precisely located on a die shoe while requiring a minimum of very precisely maintained locating surfaces, holes and dowel pins.

A further object of the present invention is to provide a punch retainer having a permanently mounted backing plate capable of absorbing the thrust of the punch without penetrating into the soft die shoe and which at the same time does not detract from the strength of the retainer body.

The present invention resides in a punch retainer comprising a body having parallel top and bottom faces and a pair of opposite side faces, said body having adjacent one end thereof a through bore perpendicular to said top and bottom faces and disposed laterally between said side faces, a backing plate seated on the top face of said body, means fixedly and substantially permanently securing the ba#cking plate on the retainer body, said backing plate having a bore therethrough substantially smaller than and accurately concentric with said bore in said body for receiving a dowel pin adapted to project upwardly into a registering bore in the die shoe and a pair of vertically extending, laterally spaced through bores in said body for receiving screws to secure the retainer on the mounting face of a die shoe.

The invention will be further described by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a vertical sectional view of a punch retainer of the present invention taken along the line 1-1 in FIG. 2; FIG 2 is a top plan view of the retainer taken along the line 2-2 in FIG 1; FIG. 3 is a sectional view taken along the line 3~3 in FIG. 2; and FIG. 4 is a sectional view taken along the line 4~4 in FIG. 2.

In the arrangement illustrated in the drawing a punch retainer 10 is secured to the mounting face 12 of a die shoe 14 by a pair of cap screws 16. Punch retainer 10 includes a body 18 and a backing plate 20. Body 18 of retainer 10 has flat parallel top and bottom faces 22,24, respectively. As shown in FIG. 2, body 18 has a pair of side faces 26 which converge to a rounded apex 28. Body 18 has a second pair of side faces 30 which extend from the ends of the divergent faces 26 and converge through a rounded apex 32. The adjacent ends of the surfaces 26,30 are interconnected by rounded surfaces 34.

Between the converging faces 26 and adjacent the apex 28 body 18 is formed with a circular through bore 36 which is perpendicular to the planes of the top and bottom faces of the body. Bore 36 is sized to receive with a close fit the cylindrical shank 38 of a punch 40 having a noncircular lower punching end 42. Punch 40 is adapted to be releasably retained in bore 36 by a roller 44 engaging an inwardly inclined face portion 46 on the shank of the punch. Roller 44 is biased into engagement with the inclined face 46 by a compression spring 48, the lower end of which bears downwardly on roller 44. The upper end of spring 48 is engaged by a cylindrical spring retainer 50. Roller 44, spring 48 and retainer 50 are housed in a cavity 52 in body 18.The upper end of spring retainer 50 is transversely slotted as at 54 to accommodate a wire or rod 56 seated in holes 58 in body 18 at each side of cavity 52. The holes 58 extend laterally from the opposite side of cavity 52 to the bores 60 for the retainer cap screws 16. The top face of body 18 is vertically slotted laterally outwardly from the bores 60 as at 62 to permit insertion and removal of the wire or rod 56 from within the holes 58. When the rod or wire 56 is engaged with the spring retainer 50 as shown in the drawing, the retainer 50, spring 48 and roller 44 are retained in their assembled condition within retainer body 18.

The steel backing plate 20 is preferably substantially harder than the retainer body 18. The flat bottom face of backing plate 20 is seated on a flat face 64 which is offset downwardly from and parallel to the top face 22 of retainer body 18. The top face 66 of backing plate 20 is flush with the top face 22 of body 18. As is best illustrated in FIG. 1 and 2, backing plate 20 overlies the upper end of bore 36 and is coextensive in size and shape with the portion of the top face of body 18 which lies to the left of the bores 60, as shown in FIG. 2. The top face portions 22,64 of body 18 are connected by a perpendicular shoulder 68 which extends transversely across the body 18 in line with the junctions between the converging faces 26 and the curved surfaces 34 of body 18.

Backing plate 20 is permanently secured on the face 64 of body 18 by a pair of soft metal dowels 70 that are extruded or otherwise firmly pressed into registering openings 72,74 in backing plate 20 and body 18, respectively. After the backing plate 20 is secured to the retainer body 18 in this fashion, a through hole 76 is formed in backing plate 20 at a location accurately concentric with the axis of bore 36. The hole 76 is adapted to receive with a close fit one end of a dowel pin 78, the other end of which is received with a close fit in a registering and accurately located blind hole 80 in the die shoe 14.

Since the end 42 of the punch is noncircular, it requires a second dowel pin 82 to properly orient the retainer 10 on the die shoe. Dowel pin 82 extends into a blind hole 84 in die shoe 14 and a registering through hole 86 in retainer body 18. It will be noted that dowel pin 82 is located on the side of bores 60 opposite bore 36. The lower portion of the hole 86 is threaded, as at 88, to receive a jack screw, such as shown at 90, when it is desired to remove the retainer from the die shoe. Jack screw 90 is also adapted to be threaded upwardly into a threaded opening 92 at the lower end of cavity 52 for raising roller 44 out of engagement with the inclined surface 46 on punch 40; when it is desired to withdraw the punch from the bore 36 in the retainer 10.

With the above-described arrangement it will be observed that the backing plate 20 is permanently affixed to the retainer body 18, and it is therefore a relatively simple matter to accurately locate the dowel pin opening 76 in the backing plate accurately concentric with the axis of bore 36. Accordingly, when the retainer is removed from the die shoe by threading a jack screw such as shown at 90 into engagement with the lower end of dowel pin 82, the backing plate 20 remains with the retainer body 18 and a subsequently used punch in the retainer body is automatically centered at the proper position by interengaging the dowel pin 78 with the opening 76 in the backing plate 20. It will also be appreciated that the backing plate 20 has an area substantially greater than the area of bore 36 and is therefore amply capable of sustaining large impact forces on the punch without penetrating into the soft steel of the die shoe 14. At the same time, the backing plate 20 occupies somewhat less than half the top area surface of the retainer block 18. Thus, a substantial portion of the retainer block has a vertical dimension (thickness) of a maximum value, thereby rendering the retainer as a whole very strong.

Claims (13)

1. A punch retainer comprising a body having parallel top and bottom faces and a pair of opposite side faces, said body having adjacent one end thereof a through bore perpendicular to said top and bottom faces and disposed laterally between said side faces, a backing plate seated on the top face of said body, means fixedly and substantially permanently securing the backing plate on the retainer body, said backing plate having a bore therethrough substantially smaller than and accurately concentric with said bore in said body for receiving a dowel pin adapted to project upwardly into a registering bore in the die shoe and a pair of vertically extending, laterally spaced through bores in said bodyfor receiving screws to secure the retainer on the mounting face of a die shoe.

2. A punch retainer as claimed in claim 1, wherein the top face of said body has a portion adjacent one end thereof and through which the bore in said body extends offset downwardly and parallel to the remaining portion of said top face, said backing plate being seated on said offset portion which overlies the open upper end of said bore, the top face of said backing plate being accurately flush with the adjacent remaining surface portion of the top face of the body to form a continuous flat surface on the retainer for coplanar abutting engagement with a flat mounting surface on the die shoe.

3. A punch retainer as claimed in claim 2, wherein said laterally spaced bores extend through said remaining top surface portion of the retainer body.

4. A punch retainer as claimed in claim 3, wherein said shoulder is defined by a straight line extending between said side faces.

5. A punch retainer as claimed in claim 3 or 4, wherein said shoulder extends transversely across the top face of the body along a line spaced between said first-mentioned bore and the last-twomentioned bores.

6. A punch retainer as claimed in claim 5, wherein said last-mentioned bore in the body is a through bore and the lower end portion thereof is threaded to receive a jack screw.

7. A punch retainer as claimed in any of claims 2 to 6, wherein said two surface portions of said top face are interconnected by an upright shoulder.

8. A punch retainer as claimed in claim 7, wherein said shoulder extends continuously from one of said side faces to the other.

9. A punch retainer as claimed in claim 8, wherein said downwardly offset surface portion extends from said shoulder to said one end of the retainer body and from one side face of the body to the other side face thereof.

10. A punch retainer as claimed in any of claims 2 to 9, wherein said body has a vertical bore in said remaining portion of said top face adjacent the other end thereof for receiving a dowel pin to project upwardly into a registering bore in the mounting face of a die shoe.

11. A punch retainer as claimed in any of claims 1 to 10, wherein said means securing the backing plate on the body comprises a pair of dowel pins extending through the backing plate into said body.

12. A punch retainer as claimed in claim 10, wherein said body is formed with blind holes for receiving said pair of dowel pins.

13. A punch retainer constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.