US3461762A - Punch and die unit - Google Patents

Description

F. DENI ET Al-v Aug. 19, 1969 PUNCH AND DIE UNIT Filed March 6, 1967 INVENTOR. FRAN/4. DEN/ AH @im FN f T wv, A E

United States Patent Ol Wanda, N.Y., assignors to Unittool Punch & Die Co.,

Inc., Buffalo, N Y., a corporation of New York Filed Mar. 6, 1967, Ser. No. 621,054 Int. Cl. B26d 7/06, 5 08 U.S. Cl. 83-143 6 Claims ABSTRACT F THE DISCLOSURE A punch and die unit including a holder having a central body portion and spaced arms with a die mounted on one of the arms and a punch unit mounted in opposition thereto on the other of the arms with the punch unit including an outer punch guide encircling an inner punch guide encircling a punch, with a first lifter spring interposed between the arm and the outer punch guide and a second lifter spring interposed between the inner and outer punch guides and a stripper spring interposed between the inner punch guide and the punch to provide a high feed clearance in a low open height press.

BACKGROUND OF THE INVENTION The present invention relates to an improved punch and die unit for providing a large feed clearance for a workpiece in a low open height press.

By way of background, a punch and die unit consists of a holder having upper and lower arms and a die mounted on one arm in opposition to a punch mounted on the other. This unit is mounted on a punch press which has a ram or the like which moves between an upper position and a lower position to drive the punch into engagement with a workpiece located on the die. The distance of the ram above the base on which the punch and die unit is mounted when the ram is in its uppermost position is called the open height of the press. The distance of the ram above the base when the ram is in its lower position is called the shut height. The distance between the open height and the shut height is the feed clearance for placing the workpiece between the punch and the die.

In the past, Workpieces requiring a large feed clearance could generally only be punched on presses having a high open height. Such presses are generally more expensive and are not as widely used as low open height presses. Therefore, the punching of workpieces requiring a large feed clearance was generally limited to the owners of presses having a sucient open height to accommodate high clearance punch and die units. However, in certain instances to overcome the requirement for high open height presses, that is, in order to punch workpieces requiring a high clearance on a low open height press, certain punch and die units decreased the area of lateral contact between the punch guide and the holder on which it was mounted, as will become more apparent hereafter, thereby sacrificing the lateral stability of the punch in the holder, which, in turn, was conducive to shorter punch life. It is with an improved punch and die unit which overcomes the foregoing shortcomings of the prior art that the present invention is concerned.

SUMMARY OF THE INVENTION It is accordingly one object of the present invention to provide an improved punch and die unit which provides a large feed clearance in a punch press having a relatively low open height while also supporting the punch in an extremely stable manner against lateral forces.

Another object of the present invention is to provide an improved punch and die unit capable of having a prolonged life because the relative movements between the various parts of the punch are greatly reduced over the 3,461,762 Patented Aug. 19, 1969 relative movements required in conventional punch structures for equal amounts of punch travel, the life of the unit being proportional to the relative travel between the moving parts. Other objects and attendant advantages of thepresent invention will readily be perceived hereafter.

The improved punch and die unit of the present invention includes a holder having upper and lower arms connected by a central body portion. A die is mounted on the lower arm. A punch unit is mounted on the upper arm in opposition to the die. The punch unit consists of an outer punch guide which is mounted for axial sliding movement within a bore in the upper arm. An inner punch guide is mounted within the outer punch guide for axial sliding movement relative thereto, and a punch is mounted within the inner punch guide. An outery lifter spring is interposed between the outer punch guide and the arm and an inner lifter spring is interposed between the inner and outer punch guides. A stripper spring is interposed between the inner punch guide and the punch. The total amount of travel of the punch during operation is the sum of compression of the inner and outer litfer springs and the stripper springs.

Since the stripper spring fits within the outer punch guide and within the outer lifter spring, the lengths of the stripper spring and outer lifter spring which telescope eliminates that much of the height required in conventional structures in which the springs are placed end-to-end in series. This permits a punch and die unit which is capable of providing a high feed clearance to be placed in a press having a relatively low open height.

In addition, since the inner punch guide travels relative to the outer punch guide and the outer punch guide travels relative to the holder, the total travel is the sum of the individual relative travels so that no one part travels a relatively long distance. Since the Wear of each of the parts is directly proportional to the amount of its travel, the present unit will wear longer than a unit in which the travel is not divided into increments.

Furthermore, the outer punch guide moves into the zone between the upper and lower arms during punching to thereby provide lateral support to the inner punch guide which in turn provides lateral support to the punch. This produces less unsupported distance of the punch than was obtainable in the prior art, thereby further prolonging punch and holder life and also enhancing the accuracy of punching inasmuch as the punch is not subjected to the lateral forces to which it was previously subjected when unsupported. The present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF 'I'I-IE DRAWING -DESCRIPTION OF THE PREFERRED EMBODIMENTS The improved punch and `die unit 10 of the present 'invention includes a holder 11 fabricated from suitable cast steel and having a central body portion 12, a lower arm 13 and an upper arm 14. The undersurface 15 of lower arm 13 is placed on the bed of a punch press and is secured thereto by a bolt (not Shown) passing through slot 16 therein.

Mounted on the outer end 22' of lower arm 13 is a. substantially cylindrical die 17 having a concentric bore 1S therein which merges with `duct 19 terminating at aperture 20. Die 17 has a stem 22 which is received in bore 23 of lower arm 13. The pieces which are punched out of the base 21 of workpiece yW will fall through bore 18 and be discharged from conduit 19.

-Mounted in the end portion 24 of upper arm 14 is a punch assembly 25, which is in alignment with die 17. The punch assembly 25 contains structure which permits a large feed clearance to be obtained for workpiece W, the feed clearance being the distance between undersurface 26 of arm 14 and the top 27 of die 17. This large feed clearance is necessitated by the fact that workpiece W is essentially of channel-shape in cross section and has a leg 28 which must t between the lower surface 26 and top 2'7 of the die. It will be appreciated that the punch assembly 25 must be retracted to the position shown in 'FIGURE 1 in order to permit workpiece W to slide laterally into the position shown in FIGURE 1.

The punch unit 25 is capable of providing the large amount of feed clearance required above while also providing a low open height, that is, a relatively small distance from the top 29 of punch 30 to the lower surface of arm 13. This permits the punch and die unit 10 to lit into a low open height press while providing the feed clearance heretofore obtainable only with larger presses. As will become more apparent from the ensuing description, a high open height is not required with punch and die unit 10 because a portion of stripper spring 31 is telescoped within outer lifter spring 32, whereas in the prior art, as exemplified by FIGURE 4, the stripper spring 31 and lifter spring 39 were placed end-to-end in series and therefore required more height.

'In the improved unit of the present invention, punch 30 is mounted on upper arm 14 by means of an outer punch guide 33, which is a substantially cylindrical member, which is mounted for relative sliding movement in bore 34. Outer punch guide 33 in turn includes a lower portion 35 having bore 36 therein which receives the lower portion of inner punch guide 37 in sliding relationship. A shoulder 38 is formed in outer guide 33 and serves as a `resting surface for inner lifter spring 39 which bears on the undersurface of collar 40 formed at the top of inner punch guide 37 and biases inner punch guide to the position shown in FIGURE l. Mounted within the counterbore 41 of outer punch guide 33 is a stripper spring 31 having its lower end bearing on the upper surface of collar 40 and its upper end supporting annular collar 43 surrounding the upper end of punch 30 and retained against movement upwardly relative thereto by C-ring 44. Collar extensions 40 and 43' of collars 40 and 43, respectively, center stripper spring 31 on punch 30. The outer punch guide 33 is biased to the position shown in FIG- U-RE 1 by lifter spring 32 which is interposed between the upper surface of holder end 24 and collar 45I formed integrally with outer punch guide 33.

As noted above, with the improved unit of the present invention, there is a 'telescoped relationship between the outer lifter spring 32 and stripper spring 31. However, with a conventional punch and die assembly, such as shown in FIGURE 4, the placing of the lifter spring 39 and stripper spring 31 in series causes the distance between the top 29 of the punch and the base 15 of the holder to be greater than in the embodiment shown in the open position of FIGURE 1, as noted above, by an amount which is equal to the overlapping of the lengths of the stripper spring 31 and the outer lifter spring 32 of FIGURE 1. In the conventional structure of FIGURE 4, the distance of the top 29 of punch 3(1p above base 15' would be equal to the sum of the following elements: The height of portion 22" of lower arm 13', the height of die 17 above the upper die surface of portion 22, the feed clearance, that is, the distance between the top 27 of die 17 and the lower surface 26 of arm portion 24'; the height of arm portion 24'; the length of lifter spring 39' which raises the punch guide 40 a sufficient amount to cause the lower end of the punch to be raised to at least surface 26', and the length of the stripper spring 31. In the device of FIGURE 4 there is only a single punch guide 40 rather than the telescoped guides of the present invention.

It can readily be seen that because of the overlap or telescoping of stripper spring 31 within outer lifter spring 32, there is a shortening of the distance between the top 29 of punch 30 and base 15 over that which would otherwise be required if the lifter spring and the stripper spring were placed in series, as shown in the conventional device of FIGURE 4. In the conventional device depicted in FIGURE 4, the lower end of the lifter spring 39 bears on the top of the holder arm. However, certain prior devices reduced the required open height for a given feed clearance by counterboring the upper arm so that the lower end of the lifter spring rested on a shoulder within the upper arm of the holder. This procedure reduced the lateral bearing area between the punch guide and the holder, which, in turn, lessened the lateral support therebetween.

At this point it is to be noted that the length of the lifter spring in all of the foregoing devices is dictated by the amount of lifting which must be provided to the punch in order to cause it to retract suiciently to permit the workpiece to be inserted between the upper arm and the die. As noted above, the reason that the device of FIGURES 1 and 2 is capable of providing a lower open height is because of the telescoping of stripper spring 31 and lifter spring 32.

From FIGURE 2 it can be seen what happens when the ram causes the punch to move from its open position of FIGURE 1 to its closed position of FIGURE 2 where it is in engagement with the workpiece. In this instance the following occurs: The inner lifter spring 39, being weaker than outer lifter spring 32, will compress to the position shown in FIGURE 2 from the expanded position shown in FIGURE l as the punch 30 is driven downwardly. This will cause a small relative movement between inner punch guide 37 and wall 36 of outer punch guide 33. After spring 39 has been totally compressed, continued downward movement of punch 30 will cause outer lifter spring 32 to compress to the condition shown in FIGURE 2 from its expanded condition shown in FIG- URE 1. The compression will continue until such time as the lowermost surface of inner punch guide 37 engages the workpiece base 21 resting on die 17. A comparison of FIGURES 1 and 2 shows that inner punch guide 37 will protrude from outer punch guide 33 the amount shown in FIGURE 2 and thereafter inner punch guide 33 will protrude downwardly beyond undersurface 26 of the holder to the position shown in FIGURE 2. Thus, a situation exists where the total amount of movement of punch 30 from the position shown in FIGURE 1 to the position shown in FIGURE 2 is realized as a result of the sum of the relative movement between inner punch guide 37 and outer punch guide 33 and the relative movement between outer punch guide 33 and bore 34 of the holder 11. Since the total movement is the sum of two increments of movement, the relative travel between each of the various parts is less than the total travel which would be experienced if only a single punch guide were used rather than the inner and outer punch guides shown in FIGURES l and 2. Since the total amount of wear is proportional to the amount of relative travel, it will be appreciated that the punch unit shown in FIGURES 1 and 2 will wear much longer than a conventional punch unit. In addition, it is to be noted that outer punch guide 33 by extending downwardly to the position shown in FIGURE 2 from the position shown in FIGURE 1 provides lateral support to inner punch guide 37 to maintain the lateral stability of guide 37 and lower portion of punch 30, notwithstanding the large feed clearance which is obtainable when the punch unit 2S is in the position shown in FIGURE l. It is also to be noted that the linear supported distance between inner punch guide 37 and outer punch guide 33 is substantially the width of the end 24 of the holder 11, that is, there is no great amount of loss of support while obtaining the large feed clearance.

After the punch unit reaches the position shown in FIGURE 2, continued downward movement of the ram on the top 29 of punch 30 will result in the movement of the end 46 of the punch through the base 21 of the workpiece while the surrounding area is held against die 17 by the lowermost portion of inner punch guide 37. This final movement is against the bias of extremely heavy stripper spring 31. When the ram moves upwardly at the finish of its stroke, the stripper spring 31 will be the first to expand to forceably withdraw the end 46 of the punch from the workpiece. After spring 31 has expanded, the outer lifter spring 32 will expand thereafter inner lifter spring 39 will expand so that the punch 'assembly 25 will return to its open position shown in FIG- URE 1.

It will be noted that the inner lifter spring 39 may be eliminated and a greater overlap may be provided between the lifter spring 32 and stripper spring 31. In this case collar 40 would rest on a shoulder such as 38 which would have to be higher to cause the lower end of guide 37 to be retracted to the position of FIGURE l. While this type of construction would still provide the low open height of the present invention, there would be a sacritice in that the outer punch guide 33 would have to travel the entire distance from the position shown in FIGURE 1 to the top surface of the die. This would require a larger amount of relative travel between punch guide 33 and bore 34, which would increase the wear therebetween in proportion `to the greater relative travel. However, a device such as described in this paragraph is within the scope of the present invention inasmuch as it provides a lower open height.

It can thus be seen that the improved punch and die unit of the present invention is manifestly capable of achieving the above enumerated objects and while preferred embodiments of the present invention have been disclosed, it will readily be appreciated that it is not limited thereto but may be otherwise embodied within the scope of the following claims.

We claim:

1. A punch unit comprising a holder having first and second spaced arms connected by a central body portion, means on said first arm for supporting a die, a bore in said second arm, a punch assembly mounted on said second arm in opposition to said first arm, said punch assembly comprising punch guide means mounted for sliding movement in said bore, first lifter spring means effectively positioned between said punch guide means and said second arm for biasing said punch guide means away from said first arm, a punch mounted for relative sliding movement in said punch guide means, a stripper spring effectively positioned between said punch and said punch guide means, with a portion of said stripper spring being mounted in overlapping relationship relative to said first lifter spring means to provide a high feed clearance in a low open height press, said punch guide means comprising an outer punch guide mounted for sliding movement in said bore, an inner punch guide, means mounting said inner punch guide for sliding movement within said outer punch guide, said punch being mounted within said inner punch guide, said sliding movement between said inner punch guide and said outer punch guide providing a compound incremental movement for prolonging life of said punch assembly, said means mounting said inner punch guide for sliding movement including second lifter spring means located between said outer punch guide and said inner punch guide and said stripper spring being located between said inner punch guide and said punch, whereby both said rst and said second lifter spring means are caused to compress when said punch is moved toward said first arm to cause said outer punch guide to provide lateral support for said inner punch guide to provide lateral support for said inner punch guide in the space between said first and second arms and cause the distance of relative travel between said outer punch guide and said second arm and the distance of relative travel between said inner punch guide and said outer punch guide to each be less than the total distance of travel of said punch to thereby tend to minimize the wear between the relatively movable parts.

2. A punch unit as set forth in claim 1 wherein a first collar is formed on said outer punch guide, and wherein said first lifter spring means encircles said outer punch guide and is interposed between said second arm and said rst collar, and wherein a second collar is formed in said inner punch guide and a shoulder is formed on the inside of said outer punch guide and said second lifter spring means is interposed between said second collar and said shoulder, and wherein a third collar is located on said punch and said stripper spring is located between said second and third collars.

3. A punch assembly comprising punch guide means, a punch mounted for sliding movement within said punch guide means, first lifter spring means mounted relative to said punch guide means for biasing said punch guide means relative to a holder, stripper spring means mounted in overlapping relationship to said first lifter spring means and effectively interposed between said punch and said punch guide means, said punch guide means including an outer punch guide and an inner punch guide, means mounting said inner punch guide for relative sliding movement within said outer punch guide, and second lifter spring means effectively interposed between said outer punch guide and said punch.

4. A punch assembly as set forth in claim 3 wherein said stripper spring means is interposed between said inner punch guide and said punch and wherein said secondlifter spring means is interposed between said inner punch guide and said outer punch guide.

5. A punch assembly as set forth in claim 4 wherein said lifter spring means is located in encircling relationship to said outer punch guide, a first collar on said outer punch guide for engaging one end of said lifter spring means, a second collar on said inner punch guide, a shoulder in said outer punch guide, said second lifter spring means being positioned between said shoulder and said second collar, a third collar on said punch, and said stripper spring means being located between said second and third collars.

6. A punch assembly as set forth in claim 3 wherein said outer punch guide includes an upper end and a lower end and wherein said inner punch guide includes an upper end and a lower end and is normally biased to a first position wholly within said outer punch guide by said second lifter spring means, said inner punch guide being dimensioned so that said inner punch guide can slide to a second position relative to said outer punch guide where said lower end of said inner punch guide extends beyond said lower end of said outer punch guide while said upper end of said inner punch guide remains within said lower end of said Outer punch guide to cause said lower end of said inner punch guide to provide support to said punch when said punch extends beyond said lower end of said outer punch guide.

References Cited UNITED sTATEs PATENTS 2,758,560 10/1956 Hirson 83-588 FOREIGN PATENTS 647,163 12/1950 GreatBritain.

JAMES M. MEISTER, Primary Examiner U.S. Cl. X.R. 83-588, 635

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