US3520219A - Clamp - Google Patents

Description

July 1 1970 E. H. TREFF 3,520,219

CLAMP Original Filed July 1. 1965 4 Sheets-Sheet 1 Tll:i.l

INVENTOR 0 ffi/VESTfl Teamavyfigyw ATTORNEYS July 14, 1970 E. H. TREFF 3,520,219

CLAMP Original Filed July 1, 1965 4 Sheets-Sheet. 2

INVENTOR ATTORNEYS United States Patent 3,520,219 CLAMP Ernest H. Treif, Fort Washington, N.Y., assignor to F. L. Snnthe Machine Company, Inc., New York, N.Y., a corporation of New York Continuation of application Ser. No. 468,836, July 1, 1965. This application Dec. 18, 1967, Ser. No. 696,55 Int. Cl. B26d 7/02, 7/16 U.S. Cl. 83-453 12 Claims ABSTRACT OF THE DISCLOSURE The present application is a continuation of Ser. No. 468,836, filed July 1, 1965, now abandoned.

This invention relates to die cutting, and has particular reference to that type of cutting in which a sharp edged die, defining the shape desired, is forced through a stack of sheets by a ram or the like.

As commonly practiced, a stack of sheets, such as for example, paper, is secured to a table by clamps. One or more dies is then placed on top of the sheets in a predetermined position, either by hand or by mechanical means, and the stack is positioned under a ram which forces the die into the stack, cutting the material. The cut-out material is then removed from the interior of the die, and the die placed on another part of the stack and the process repeated. As a minimum of the sheet area is available for waste, the clamps must be capable of securing the stack while in contact with a minimum area of the stack.

Although the cutting edge of the die is quite sharp, it must be to some extent wedge-shaped to give it suflicient stiffness to resist the considerable pressure of the ram forcing it through the stack of sheets. It can thus be seen that as it enters the stack, the top sheet is forced to buckle, either within the die, on the outside of the die, or both. The same is true of the sheets underneath, to a lessening degree, right down to the bottom sheet of the stack. Experience has shown that a certain amount of this buckling can occur in the cut-out, that is, in the material on the interior of the die, and still have a satisfactory product, but in general at least some of the buckling or movement must take place in the waste. (The proportion is set by the degree of taper on the inside and outside surfaces of the die.) However, inasmuch as the operation involves a series of successive cuts, it is essential that means be provided for permitting movement of the portion of the stack outside the die, and, at the same time, assure that the next cut will be made on a properly square stack.

With the above considerations in mind, it is a primary object of the present invention to provide a clamp means for securing a stack of sheets against permanent displacement as a cutting die is forced through the stack.

It is a further object of the present invention to provide a clamp means for securing a stack of sheets to a table for cutting with dies which does not interfere with motion of portions of the stack required by the thickness of the die.

It is a further object of the present invention to pro- "Ice vide a clamp for a stack of sheets which permits movement of portions of the stack as required by the thickness of a die being forced through the stack, but presents a properly positioned stack for a succeeding cutting stroke of the die.

It is a further object of the present invention to provide a clamp for a stack of sheets exerting a substantially uniform pressure regardless of the thickness of the stack.

It is a further object of the present invention to provide a clamp for a stack of sheets to be die out which can stop the operation of the cutting process in the event of incorrect positioning of the die over the clamp.

Referring now to the drawings forming part of this specification, a preferred embodiment of the present invention is shown in the various figures, in which:

FIG. 1 is a plan view of a table with a stack of sheets clamped thereon, with the outlines of the desired die cut product indicated;

FIG. 2 is an elevation, in an enlarged scale of one of the clamps shown in FIG. 1, the clamp being in the open position;

FIG. 3 is a plan view of the device shown in FIG. 2, on a similar scale;

FIG. 4 is a view similar to FIG. 2, but with parts broken away;

FIG. 5 is a section, taken on line 5-5 of FIG. 4, looking in the direction of the arrows.

FIG. 6 is a sectional elevation taken on line 6-6 of FIG. 3, looking in the direction of the arrows, showing the device in operative or clamping position;

FIG. 7 is a view similar to FIG. 2, but With the parts of the clamp in engagement with the stack and displaced by reason of the adjacency of a die passing through the stack of sheets;

FIG. 8 is a view taken on line 88 of FIG. 7, with parts broken away; and

FIG. 9 is a fragmentary view taken at line 9-9 of FIG. 7, looking in the direction of the arrows.

Referring first to FIG. 1, a stack of sheets 10 is supported on a suitable table, and secured thereto by means of clamps 11. By means of a suitable die, the sheets are reduced to a number of die cut shapes. In the particular arrangement shown, a series of envelope blanks, all the same size, is produced. This is not necessarily the case, as economy of stock might dictate the use of two or more dies to better utilize the paper available. A little consideration will show that the proper procedure in cutting the blanks laid out in FIG. 1 would be to start at the left and cut vertical rows until three rows have been removed, which will leave the three right-most blanks to be cut. By this procedure it can be seen that the material to be operated on is at all times securely held by the two clamps 11, until the two uppermost right-hand blanks alone remain. They can then be cut out one by one, without disturbing each other unduly.

However, such an arrangement is not always economical, and it could very well happen that an arrangement might be adapted such that blank A must, by reason of the arrangement of other pieces, be cut out before blank B. If this is done, the waste material at C will be forced to the right by the die as it severs the stack. 'It must be restored to the position it originally had before the blank B can be severed correctly. The novel mechanism herein disclosed accomplishes this result, among others.

Referring generally to the views showing the clamp in an enlarged scale a base portion 14 is provided having slots 15 which are utilized to secure the clamp to the press table 16 at the point desired. Integral with the base 14 are a pair of pintles 17, having aligned bores receiving a pin 18. The pin 18 serves as a support for an abutment piece 19, as perhaps best shown in FIG. 6. This abutment piece is a generally flat member pivoting about the axis of pin 18. It is provided with a surface which, as shown in FIG. 2 and elsewhere, is normally perpendicular to the plane of the table, and serves as a stop against which the stack of sheets is jogged, and against which it is clamped.

In order to maintain the perpendicular position of the face 20, a rod 21 is secured to the base 16, as by means of threads in its lowermost portion and a jam nut 22. The rod passes through an opening 24 in the portion 25 of the abutment piece 19. A spring 26, between the washers 27, is of such length that when the nuts 28, 29 are run down sufficiently to bring the. face 20 in the proper position, the upward force of the compressed spring is suflicient to hold the abutment piece in position as a new stack of sheets is jogged into place. As a matter of fact, the determining factor for the strength of spring 26 when compressed to its working length is also determined by another factor which will appear later.

The structure so far described accurately positions the stack of sheets as they are placed on the table. Additional structure is utilized to clamp the stack in place. A clamping lever 30 having a pair of downwardly extending flanges 31 is pivoted to the abutment piece 19 by a pin 32 extending through the flanges 31 and the piece 19. This pin may be secured against axial displacement by means of a set screw 33 in the piece 19, if necessary. At one end, the lever 30 is provided with a finger portion 34, which may have its lower face roughened, as at 35, in the portion engaging the top sheet of the stack. It will be realized that the clamp finger 34 is intended to contact a waste portion of the stack, and consequently the roughened surface does no harm to the finished product. Although the finger can be of any extent desired, it is preferable that it be as small as feasible, to interfere as little as possible with placement of the cutting die, and in consequence it has been disclosed as shown in FIG. 3 as comparatively narrow and closely adjacent to the abutment piece 19, as one of its functions is to hold the stack of sheets against the surface 20".

Near its opposite end from the. finger portion 34, the lever 30 is provided with a pair of notches 36, one on each side of the region occupied by the abutment piece '19, into which the ends of piston rods may fit, to move the lever in a clamping direction. For moving the lever in the opposite direction, a pair of springs 37, attached to pins 38 secured to the lever and pins 39 attached to the base 14 may be employed.

The mechanism disclosed for exerting clamping pressure requires fluid pressure, either hydraulic or pneumatic, and was selected in preference to such devices as spring toggles and the like for the reason that the force available is constant regardless of the height of the stack (within the operating range of the device), and also the operator is not required to reach over to the clamps to actuate them. A unitary casting 40 comprises in general two cylinders and means for attaching them to the rest of the structure.

The casting, as best shown in FIGS. 2, 4, 5, 6, and 9, is in the form of a pair of parallel generally cylindrical portions 50, joined by a strut 51 of triangular cross-section. A pair of lugs '52, 53 project from one end of the casting, and these lugs are pierced for passage of the pin 18, the casting thus having a pivotal movement about an axis common with the abutment member 19. Each of the cylindrical portions is provided with a bore 54 within which a piston 55 operates. Each of these pistons may be maintained in fluid tight engagement with the Walls of the corresponding bore 54 by any convenient means, such as an elastomeric O-ring 56. A suitable cylinder head 57 is provided for each cylinder, through which the piston rods 58 extend. Each piston rod 58 may be provided with a suitable ending 59, for engagement with the notches 36. As can be seen from the structure so far described, actuation of the piston and cylinder assemblies by pressure within the cylinders will cause clamping movement of the lever 30. Conversely, release of the pressure within the cylinders will permit the springs 37 to lift the finger 34 to its idle position as shown in FIG. 2.

For the purpose of activating the piston and cylinder assembly, a conduit '60 may be provided, in communication with the interior of each cylinder. In the shown form, each cylinder is provided with an opening 61 into which is threaded a conduit 60, and a drilled hole 62 communicates with the interior of each cylinder. Although two conduits are. shown, one may be suificient, and the two inlets shown therefor merely convenient in hooking up the proper source of pressure and relief.

For the purpose of restraining movement of the clamping lever in a clamping direction to such an extent that the piston contacts the cylinder head, a pin 65 may be inserted in the abutment piece in the path of movement of the finger 34.

The general operation of the device should now be clear. Given the parts in the position shown in FIG. 2, a stack of sheets 10 may be placed on the press table and squared up by jogging against each surface 20 of the abutment pieces 19. Pressure is then applied to the cylinder and piston assemblies, and the clamping member moves down to the position shown in FIG. 6. When a cut is made near a clamp, as best shown in FIG. 7, the abutment member 19 and the clamping lever move, against the compression of spring 26. After the die is withdrawn, the spring 26 urges the parts into the position shown in dot and dash lines in FIG. 7.

There is, however, a very important action which is not particularly obvious from the disclosed structure, but which is of considerable importance to the successful operation of the device. Considering the device in the position shown in FIG. 6, it can be appreciated that if the pressure within the cylinder is increased sufficiently the reaction of the finger portion on the top of the stack will cause pivoting of the abutment piece about the pin 18, the parts then taking the position shown in FIG. 7 (assuming, of course, that either the finger slips or the stack moves). Thus, at any pressure less than that required to cause such movement, the eifectiveness of the spring 26 is lessened by an increase in the pressure in the cylinders.

It is desirable, for the purposes set forth at the beginning of this specification, that the movement shown in FIG. 7 be available, but at the same time, it is necessary that after the die is withdrawn the parts take the position shown in FIG. 2. The force required for producing such return to normal depends upon the material being cut and other factors. However, measurements of theoretical forces are not necessary. By changing the spring 26 on an empirical basis, and changing the pressure applied to the cylinders, a satisfactory balance is readily arrived at, which satisfies the requirement that the abutment piece be rigid enough when the clamp is open to remain stationary as a stack of sheets is jogged in place, yielding enough to permit the movement shown in FIG. 7 when the clamp is in operative position, and still retaining enough resistance to such movement to properly hold the stack and return the waste to its original position when the die and the cutout material are removed.

Up to this point, no consideration has been given to the particular type of press on which the clamp is to be employed. It is useful in that type of press in which the die is manually placed by a skillful workman for each successive cut, in that he can program the various cuts taking into consideration that he can take a out near a clamp which is not the final cut, and have the waste yield and return to support the remaining stock for a subsequent cut. In that type of machine employing a die attached to the press ram for vertical movement with mechanical or electrical positioning of the die before a cutting stroke, the same considerations apply. However,

in such applications, there are further problems which the structure of the present invention is particularly Well adapted to overcome.

In setting up, which is in some machines a trial and error procedure, a relatively minor misjudgment by the operator can cause the die to descend on the finger of the clamp. This is particularly likely to happen in a press which rotates the die as well as translates it, for the limits of translating movement of the die must perforce be sufficient to bring the edge of the die to the edge of the sheet, and rotation of the die can then cause it to project beyond the sheet edge. In addition to this, certain types of die positioning mechanisms are subject to a sort of progressive inaccuracy or creep, which the operator controls by watching the finished product and making appropriate adjustments. However, it is not particularly obvious to him when the die comes dangerously close to the clamp. Of course, if the die hits the clamp, it is unusable unless resharpened, and the press is disabled until the die can be replaced.

Accordingly, the structure indicated in FIGS. 2 and 3 has been incorporated in the disclosed structure.

Between the nut 28 and the nut 29 there may be supported a metal strap 165, extending over the vulnerable parts of the clamp, as shown in dot and dash lines in FIG. 3, and in full lines in FIG. 2. It can be seen that the errant die will strike the strap 165 and still have a distance to travel before endangering the clamp. It is necessary, therefore, only to provide a suitable electrical circuit, completed upon contact between the die and the strap, adapted to cause cessation of the downward movement of the die carrying rarn to afford complete protection for the clamp and die. It is to be noted that a definite space is provided between the strap and the uppermost parts of the clamp, to take care of the inertia or lost motion permitting motion of the ram after actuation of the stopping mechanism.

Another solution to this problem would be to substitute for the metal strap 165, a very soft conductive layer such as lead (not shown), which is fastened to the top of abutment piece 19 and to the clamping finger 34. A thickness of approximately one quarter of an inch of this material is sufiicient to provide safe operation and is still sufiiciently strong to withstand the repeated contact of the outside ejectors (such as soft rubber blocks) which periodically fall on top of the clamp.

What I claim is:

1. An improved clamp for holding a stack of sheets on a table when the sheets are to have a plurality of sections cut therefrom, said clamp comprising an abutment against which the side of the stack may be positioned, said abutment being normally perpendicular to the plane of the table and movable in a direction away from the side of the stack during the cutting thereof, gripping means coacting with said abutment to hold the top of the stack during the cutting thereof and means coupling said abutment and said gripping means in coacting relationship.

2. A clamp as in claim 1 wherein said abutment is pivotably movable.

3. A clamp as in claim 1 including means normally urging said abutment in a direction towards and into engagement with the side of the stack.

4. A clamp as in claim 3 including stop means limiting movement of said abutment in a direction towards the stack.

5. A clamp as in claim 4 wherein said stop means is adjustable.

6. A clamp, as in claim 3 wherein said urging means is a spring.

7. A clamp as in claim 1 wherein said stack gripping means is pivotably movable into and out of engagement with the top of the stack.

8. A clamp as in claim 1 wherein said stack gripping means is pivotably mounted on said abutment.

9. A clamp as in claim 1 including force applying means acting on said gripping means to move said gripping means into engagement with the top of the stack during the cutting thereof.

10. A clamp as in claim 9 including return means acting on said gripping means in a direction opposite to said force applying means, said return means acting to move said gripping means out of engagement with the top of the stack when said force applying means is not operative.

11. A clamp as in claim 10 wherein said force applying means includes means for utilizing fiuid pressure and said return means is a spring.

12. Means for holding a stack of sheets on a table comprising, in combination:

(a) an abutment having a surface for engaging and aligning the side of the stack in a substantially vertical plane;

(b) a member having a portion arranged to clampingly engage the top of the stack;

(c) :means supporting said abutment surface and said member portion in engagement with the side and top of the stack, respectively, said support means including means permitting movement of said abutment surface in a direction away from the side of the stack after alignment thereof.

References Cited UNITED STATES PATENTS 670,876 3/1901 Hammond 269157 1,957,711 5/1934 Heyman 83-367 2,589,033 3/1952 Baumgartner 83-467 3,032,209 5/1962 Mead 83-453 X 3,166,308 1/1965 Thumim 269303 FOREIGN PATENTS 870,119 12/ 1941 France.

ANDREW R. JUHASZ, Primary Examiner U.S. Cl. X.R. 83-467; 269303

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