US3759130A

US3759130A - Replaceable tip shear proof punch

Info

Publication number: US3759130A
Application number: US00243696A
Authority: US
Inventors: C Patterson
Original assignee: Mate Punch and Die Co
Current assignee: Mate Punch and Die Co
Priority date: 1972-04-13
Filing date: 1972-04-13
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18

Abstract

A shear proof punch with heel aligning structure formed as a part of the punch tip retainer but without difficult machining tolerances.

Description

United States Patent H Patterson Sept. 18, 1973 REPLACEABLE TIP SHEAR PROOF PUNCH [75] Inventor: Clinton E. Patterson, Minneapolis, [56] Reierences cued Minn. UNITED STATES PATENTS 3,348,443 l0/l967 Smith et al 83/635 X [73] Ass'gnee r t 3,296,905 1/1967 Killaly 83/635 x Filedi P 1972 Primary Examiner.|. M. Meister N Attorney-L. A. MaCeachl'On [57] ABSTRACT [52] U.S. Cl 83/637, 88330663958, 8834/6536, A Shear proof punch with heel g g Structure [51] Int Cl 1/12 formed as a part of the punch tip retainer but without 58 Field of Search 83/635, 637, 684-690, machmmg mle'ances' 7 Claims, 7 Drawing Figures REPLACEABLE TIP SHEAR PROOF PUNCH BACKGROUND OF THE INVENTION This invention relates to a form of cutting die and punch arrangement in which the punch has elements that prevent it from becoming misaligned with the die when only a portion of the punch is actually cutting. This form of punch has become known in the trade as a shear proof punch. The elements that keep the punch aligned with the die are known as heels. They are members that are spring loaded to extend below the surface of the punch when it is not cutting and which are forced to retract until their lower surface forms a portion of the cutting punch only if there is material to be cut in their path. When no material forces the heel to retract, it precedes the balance of the punch tip into the die to assure that the punch will not move laterally as a result of cutting with a portion only of the punch surface. As an economy of language, these punches will be referred to hereafter as shear proofs.

One of the principal drawbacks to the shear proof from the point of view of the user is the rather high expense of punch when made in the conventional manner. One of the more satisfactory methods of making the heels is to make them of rod stock and then cut away whatever portion of the heel as round that does not conform to the shape of the punch for which it will serve as a heel. As a result, the portion of the heel that functions as part of the punch for cutting is asymmetrical. It must be held in an aligned position, therefore, when cutting as part of the punch or when serving as a lateral movement restrainer either one. Most of these heels are currently held in an aligned position by means of small plates that are accurately made and fitted to the side of the punch tip. The plates are held there with cap screws which the most careful makers secure with safety wire. No other means of securing the cap screws seems to assure that the screws will not loosen as a result of running the punch in a press. The complexity of this conventional structure causes the manufacture and assembly of the parts for these shear proofs very time consuming which is to say expensive.

In a manner of speaking, the conventional shear proof is a replaceable tip unit. In fact, however, there is no little value in the retainer of conventional structure, it does not pay to have that part returned to be used again. This invention addresses itself to the solution of both of the problems described above by making a shear proof with a replaceable tip in which the retainer carries the heel aligning structure.

BRIEF DESCRIPTION OF THE INVENTION There are two main features that are particularly important. The first of these is the concept of having the heel aligning structure part of the retainer rather than having it secured directly to the punch tip. The second point is having the reference surface of the retainer, against which the punch and heels bear when they are cutting, spaced vertically from the heels aligning surfaces to reduce the criticality of the machining necessary to make a useable punch. If the heel aligning structure were so near to the reference surface as to have portions of the aligning structure in the same plane as the reference surface or nearly so, those surfaces would have to be at nearly exact right angles to each other for the punch to function well.

The punch tip retainer of this invention is longer than conventional retainers and has fingers which extend down along the sides of the tip. At the ends of these fingers are what are called herein pads. The pads are rather narrow and no portion of them is anywhere near the reference surface horizontal plane. The reference surface of the punch tip retainer against which the punch tip rests to provide the support for the tip to be forced to shear the material being cut by the punch is at a different elevation than any part of the pad on the heel aligning finger. These facts make the machining of the retainer substantially less demanding than it otherwise would be. Thus without generating a nearly impossible machining job, a shear proof is provided in which the heel aligning structure is on the retainer rather than the punch tip.

To assure that the heel aligning structure is in initimate contact with the sides of the punch tip and hence will assure good aligning, the space defined by the pads of the fingers is never larger than the dimensions of the punch tip. It may be smaller to assure close contact between the sides of the punch tip and the finger pads. For this reason the retainer is made from spring steel so that the fingers can yield if need be to accept the tip. Such a fit is assured by giving a nominal dimension to both the tip and the retainer opening that is the same and providing only a minus tolerance for the opening in the retainer and only a plus tolerance for the punch tip. If the tip and the retainer opening were by some chance to exactly match the nominal size, they would fit precisely. Since mostmachining tolerances are a recognition of the impracticality of getting exact dimensions in an economically sound period of time, the tip is almost invariably slightly larger than the opening. The most satisfactory spring steel known presently is called AISI Standard 8-7. I

In at least one form of the device disclosed here, the tip can be removed and replaced in the retainer without removing the retainer from the punch holder of the press.

All of this structure will be described in detail in connection with accompanying drawings which are briefly described as follows:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary side elevation of the invention, a portion of a press and a die;

FIG. 2 is an exploded side elevation of the invention drawn to a smaller scale than the one used in FIG. 1; broken lines shown hidden parts and the alignment of parts;

. FIG. 3 is a bottom view of the punch tip retainer shown in FlG.-l and at the same scale as that figure; broken lines show hidden parts;

FIG. 4 is a vertical section of the retainer shown in FIG. 3 and taken on the line and in the direction of the arrows 4--4; it is drawn to the scale of FIG. 1;

FIG. 5 is a perspective view of the punch tip of figures I and 2 and is shown in a scale that is between those used in those two figures;

FIG. 6 is a perspective view of an alternate form of of the structure shown in FIG. 5 and drawn to the scale of FIG. I; and

FIG. 7 is a vertical section of the punch tip of FIG. 6 and taken on the line and in the direction of the arrows 7-7 in FIG. 6; the tip is shown secured to a retainer and holder that are also shown in section and drawn to the scale of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, is a punch holder that is part of the turret press with which the shear proof punch is used and to which the punch retainer 11 is conventionally secured by a cap screw represented by the broken lines 12. The punch tip is designated 14 and is secured to the retainer by cap screws one of which is represented at 15. There are .four heels, one for each side of the square. Three of these can be seen at 16, 17 and 18. The die is numbered 19 and a sheet material being cut is 20. As is clearly seen in FIG. 1, the sheet material has been cut once and has an opening 21. This opening is misaligned with the opening 22 of the die 19 so that only heel 16 is acting as part of the cutting punch on this stroke. The heels l7 and 18 are seen to be below the surface of the die 19 and into the opening 22 in the die 19. Heel 16 is partially retracted as a result of engaging material 20. Spring 24 which urges heel l6 downward is partly compressed. Because the heel 17 has encountered no resistance, spring 25 is urging heel l7 outward as far as the structure of the tip will allow. Punch tip 14 has not yet engaged the sheet of material 20 as shown in FIG. 1, hence the heels l7 and 18, as well as the heel that is directly across from heel l7 and obscured by heel 17, will be well into the opening 22 of die 19 before the cutting pressure is applied to tip 14.

In FIG. 2, cap screws and 26 fit into the

wells

27 and 28 of retainer 11 and engage threads in tip 14 to hold those two parts together. Heels 16, 17 and 18 and their

respective springs

24, 25 and 29 fit into wells (not shown in FIG. 2) in retainer 11 and engage the

heads

16a, 17a and 18a of the

heels

16, 17 and 18. The springs urge the heels outward as far as the enlarged portion 30 of heel groove 31 for heel 17, for example, will permit. In'FIG. 5, the balance of the heel groove enlargements may be seen at 32, 34 and 35. In addition to heel groove 31 for heel 17 may be seen heel groove 36 for heel. 18. The two

wells

37 and 38 are threaded and receive the cap screws 15 and 26.

Referring now to FIG. 3, retainer 11 has the opening 29 to receive the punch tip 14. It is slightly larger than the punch tip so there is a slight clearance between them. The

fingers

41, 42, 44 and 45 are one the four sides of the opening and engage the four sides of the tip 14 when it is engaged in opening 39. Well 46 is threaded to receive the cap screw 12. Indexing notches 47 and 48are conventional and have no special significance relative to this invention. The

wells

49, 50, 51 and 52 receive the four springs for the heels.

In FIG. 4, the

fingers

42 and 41 are shown clearly to have the

pads

54 and 55 respectively which extend inward from the balance of the fingers. These pads are ground or otherwise machined to be the surfaces which will hold the heels aligned with the punch tip. The bottom 56 of well 39 is a reference surface against which the end 57 of punch tip 14 rests. It will be noted that no portion of

pads

54 and 55 are anywhere near the surface 56 with reference to their vertical positions. For this reason, surface 56 does not have to be pre-' cisely at right angles to the vertical surfaces of the pads as would be the case if the fingers did not have pads and spring fingers. If there were unyielding punch tip contacting and heel aligning members right next to the reference surface, the precision of workmanship that would be required would be extreme.

In FIG. 6 a form of punch tip is shown that varies from that shown and described previously in only one main respect. In FIG. 6 it can be seen that there is an unthreaded well 65 in place of the two threaded

wells

37 and 38 in FIG. 5.

Turning now to FIG. 7, the use of this central well 65 to receive the cap screw 60 which is reached and turned from the cutting end of the tool punch rather than the via the rear of the retainer as in the form of the invention shown in FIGS. l-5. In FIGS. 6 and 7 all parts.

that are the same in form and function to counterparts in the form of the invention shown in FIGS. 1-5 are given the same number designations followed by letter suffixes. Parts that are different in the form 'of the invention illustrated in FIGS. 6 and 7 are given new numbers. In FIG. 6 for example, only the center well 65 is different. All of the other portions of the tip 14a from 300 to 57a are appropriately described by reference to the descriptions of parts '30, 31 etc.

As is clearly shown in FIG. 7, the retainer 11a is held in the punch holder 10a by the cap screw 12a. Cap screw 60 in well 65 uses the lower end of this threaded well 46a to hold the tip 14a in the retainer 11a.

Cap screw 60 has a groove 61 formed in it into which the snap ring 62 fits. Snap ring 62 is no thicker than the very shallow well 64 is deep. The cap screw 60 can turn in relation to the snap ring 62, but there is no axial movement between them or more accurately very little axial movement. All the rest of the parts are essentially the same as their similarly designated counterparts. Because the

heels

16 and 18 have their heads designated as and respectively, the heels in this figure are called 16b and 18b and theirheads 16c and 180.

OPERATION This portion of the application deals with replacing the tips; the punch is used in slotting the same as a conventional punch is used.

Replacement of the tip 14 in the structure shown in FIGS. l-5 is accomplished by removing the punch holder 10 from the press and separating the assembled retainer and tip from the holder by unscrewing cap screw 12. Cap screws 15 and 26 are then accessible and can be removed. It may be necessary to use a mechanical assist to remove tip 14 from the retainer 11. Well 46 will give access to the back of the punch tip so that an arbor press or some other formof mechanical aid can be used to puch the tip free. A new tip can then be pressed into the retainer 1 l.

Screws

15 and 26 are then used to secure the two together and it may then be reassembled to the punch holder.

When the form of the invention shown in FIGS. 6 and 7. is used, the replacement job is still easier. Once the punch holder 10a is removed from the press, it can be turned so the tip 14a is facing up. Access to the cap 60 is immediate'down well 65. Furthermore, as the cap screw is backed out of well 460, snap ring 62 pushes on surface 57a of tip 14a and serves asa built in screw jack to push the tip 140 out of retainer 11a. Cap screw 60 has less length of threads than the distance from the finger pad 54a to the surface 56a of the retainer. Since the sides of well 39a clear the tip 144, only the pads serve to position the tip in the retainer. For this reason, tip 14a can be relieved starting a short distance from pad 54:: toward surface 570. Once tip 14a has been moved to the area of relief, the tension applied by the fingers is greatly reduced or relieved altogether. Tip 140 can be removed with relative ease. Similarly a replacement tip can be removed into retainer 11a rather easily far enough to let cap screw 60 engage the threads of well 460 before the need of a mechanical assist is felt. The cap screw 60 is then engaged and is used to move the tip into the retainer for that portion of the movement during which the friction applied by the spring fingers is severe. The cap screw then with the snap ring serves both as a screw threaded means for aiding in the disassembly and reassembly of the punch.

This completes the disclosure of the invention, and it is now claimed below as required by law.

I claim: 1. A shearproof punch structure including: A. a retainer portion adapted to be secured to a punch holder during use, B. a tip secured to the retainer in a manner allowing them to be separated when desired, C. heels secured to said tip for limited sliding movement relative thereto, D. means for urging said heels to one limit of movement, and E. heel aligning structure secured to said retainer. 2. The shear proof punch structure of claim 1 in which the heel aligning structure is spring fingers hav- 6 ing pads.

3. The shear proof punch structure of claim I in which the tip is releaseably secured to the retainer by means actuated at the cutting face of the punch tip.

4. The shear proof punch structure of claim 1 in which the heel aligning structure is spring fingers and the means for securing the heel and tip together is screw thread means that also can force the tip and retainer apart and draw them together.

5. The shear proof punch structure of claim 1 in which said retainer has a reference surface against which the tip bears when in operable condition and characterized by having the reference surface spaced from the heel aligning structure vertically.

6. The sheer proof punch structure of claim 5 in which the heel aligning structure is spring fingers having pads and the distance between pads is never greater than the corresponding distance between faces of the tip that the pads will engage.

7. The sheer proof punch structure of claim 6 in which the tip and retainer are releaseably secured to each other by a cap screw having a groove in it, and a snap ring in said groove that engages said tip when said cap screw is backed off to push said tip from said retainer; said cap screw head being accessible at the cutting face of said tip.

Claims

1. A shearproof punch structure including: A. a retainer portion adapted to be secured to a punch holder during use, B. a tip secured to the retainer in a manner allowing them to be separated when desired, C. heels secured to said tip for limited sliding movement relative thereto, D. means for urging said heels to one limit of movement, and E. heel aligning structure secured to said retainer.

2. The shear proof punch structure of claim 1 in which the heel aligning structure is spring fingers having pads.

3. The shear proof punch structure of claim 1 in which the tip is releaseably secured to the retainer by means actuated at the cutting face of the punch tip.