US3702558A

US3702558A - Deflection compensating press brake die support

Info

Publication number: US3702558A
Application number: US178892A
Authority: US
Inventors: Donald G Swenson; George H Trautman Jr
Original assignee: Niagara Machine and Tool Works
Current assignee: Niagara Machine and Tool Works
Priority date: 1971-09-09
Filing date: 1971-09-09
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14

Abstract

Apparatus for eliminating faulty bends in press brakes due to deflection between the ram and bed of a press brake which is greatest at the mid point. A compressible polyurethane member is interposed between the die and bed of the press brake and is of such thickness that it compresses to a degree approximately one order of magnitude greater than the total deflection of the bed and ram at the mid point. The polyurethane member is of substantially the same length and in registry with the bend line of the workpiece. Means are also provided for readily lifting the die member to provide polyurethane inserts of a total length to match the bend line of the workpiece.

Description

United States Patent Swenson et al.

[54] DEFLECTION COMPENSATING PRESS BRAKE DIE SUPPORT [72] Inventors: Donald G. Swenson, Eggertsville; George H. Trautman, Jr., Kenmore,

both of NY.

[73] Assignee: Niagara Machine 8: Tool 'Works,

, Buffalo, NY.

[22] Filed: Sept. 9,1971

[21] Appl. N0.: 178,892.

3,561,241 2/1971 Blain ..72/465 Primary Examiner-Lowell A. A ttomey -Conrad Christel, et; a1.

[ ABSTRACT Apparatus for eliminating faulty bends in press brakes due to deflection between the ram and bed of a press brake which is greatest at the mid point. A compressible polyurethane member is interposed between the die and bed of the press brake and is of such thickness that it compresses to a degree approximately one order of magnitude greater than the total deflection of the bed and ram at the mid point. The polyurethane member is of substantially the same length and in registry with the bend line of the workpiece. Means are also provided for readily lifting the die member to provide polyurethane inserts of a total length to match the bend line of the workpiece.

16 Claims, 3 Drawing Figures PArENTEgmumz 3,702,558

.smzzuorz x mm F16. DONALDYG. SWENS:

I I H.TRA

GEORGE INVENTORS v UTMAN,

ATTORNEYS DEFLECTION COMPENSATING PRESS BRAKE DIE SUPPORT BACKGROUND OF THE INVENTION This invention relates to press brake die supporting means and particularly to novel supporting means which substantially neutralizes the deflection of the punch and die members and thus avoids the production of malformed bends due to deflection of the bed and ram of the press brake.

When a press brake punch and die engage a metal sheet to effect a bend therein, the die and its supporting structure and the punch and the ram to which it is secured all deflect, the ram deflecting upwardly and the bed deflecting downwardly, and since the greatest deflection is at the mid-points of the punch and die, the punch does not enter the die to as great a degree at the mid-point as at the ends of the punch and die. This results in a bend which is of greater included angle at the mid-point of the workpiece than at the ends and produces a bowed or warped workpiece.

Various expedients have been employed in attempts to avoid the objectionable bend formations resulting from the deflection of press brake dies and punches. For instance, some press brake manufacturers build camber into the press bed to compensate for deflection. This expedient obviously can correct for only one set of conditions whereas there are numerous variables such as the thickness of the workpiece, the length of the bend line, the angle of the bend, the kind of material, etc.

Another expedient is to shim the die holder to introduce camber to counteract deflection. This is a tedious, makeshift procedure and, to be effective, would require re-shimming with changes in any of the above variable conditions.

' SUMMARY OF THE INVENTION The present invention provides a convenient and practical arrangement for neutralizing the deflection of the punch and die members and their supporting parts.

In bending metal sheets in a press brake the tonnage per linear inch of bend line is constant over the length of the bend line excepting at the very ends wherelateral contraction of the sheet is unresisted and the tonnage drops off somewhat. This latter effect is of little significance. When the mid portions of the bed and ram of the press brake deflect and the punch accordingly does not enter the die as far as at the ends, the tonnage per linear inch at such mid-points will be less than at the ends of the worksheet. Any die arrangement that insures uniform unit pressure against the workpiece along the entire bend line will produce good bends of constant angle throughout, regardless of the amount of deflection of the bed and ram at their midpoints.

The present invention provides a very close approach to such uniform pressure per inch of bend line along the entire length of the bend by introducing an elastic medium of uniform spring constant per linear inch of die holder, such elastic medium being inserted under the die holder for the length of the workpiece to be bent, that is, between the die holder and the bed of the press brake. This elastic medium may be either continuous or of closely spaced units. The same theoretical results are attained if the elastic medium is interposed between the ram and the punch carried thereby and in fact the elastic medium may be provided between both the punch and ram and between the die and bed.

To achieve the desired results of the present invention, the total vertical deformation of the elastic medium must be a number of times greater than the degree of deflection of the bed and ram of the machine under a given load. The total vertical deformation of the elastic medium should be preferably at least about one order of magnitude greater than the deflection and if a greater order of magnitude is provided, better bends will be produced.

While various materials and dimensions may be employed, successful operation has been achieved by using polyurethane of durometer hardness. A piece two inches square in transverse section and of a length equal to the length of the workpiece along the bend line was interposed between the press brake die and the bed of the press. This produced excellent bend results with standard punch and die units.

By way of explanation, if a given load employing the elastic medium of the present invention would normally produce a total deflection of bed and ram of 0.015 inches, which deflection would be of a degree which would produce unsatisfactory bends, and if such load produced a total approximate vertical compression of the elastic medium of say 0.150 inches at the center of the bend, then the compression of the elastic medium at the ends of the bend would be 0.165 inches. The elastic medium would then exert a pressure at the center of the bend equal to about 90 per cent of the pressure at the ends of the bend line.

This degree of upward pressure exerted against the center of the die by the elastic medium arches the die upwardly at the center toward the punch to a degree which closely matches the upward arch of the punch due to deflection, and thus produces excellent bends. It is to be understood that the more or less matched arching of the punch and die in forming a bend is immaterial as far as curving the workpiece is concerned since this degree of arching is far within the elastic limit of materials which would usually be formed in this manner.

An important feature of the present invention is that the length of the elastic medium acting between the die and bed (or the punch and ram, as the case may be) be of the same length and in vertical registry with the length of the bend in the workpiece. If the elastic medium is substantially longer than the bend line, then the projection of the elastic medium beyond the bend line will arch the portion of the die beyond the bend line and this arching will affect the arching of the die along the bend line to a degree which defeats the purposes of the present invention. Similarly, if the elastic medium is substantially shorter than the bend line, then the die would tend to arch reversely beyond the ends of the elastic medium outwardly to the ends of the bend line, again producing an entirely unsatisfactory result.

With the elastic medium of substantially the same length and in registry with the bend line, the portions of the die projecting beyond the bend line will be under no bending stress and will merely project outwardly in a straight line tangent to the arched portion of the die at the ends of the elastic medium. Thus the inactive portions of the die beyond the bend line do not aggravate the deflection condition within the bend line which they would do if the polyurethane were present between the die and bed beyond the ends of the bend line to cause deflection of the die beyond such ends.

BRIEF DESCRIPTION OF THE DRAWINGS paratus shown in FIG. I viewed from the front of the press brake and showing the die parts in position for operation; and

FIG. 3 is a similar view showing the die element in a raised position for changing polyurethane inserts.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT In FIG. 1 the numeral designates the lower portion of the ram of a press brake and the numeral 11 shows the upper die supporting portion of the bed of such press brake. In the present instance, the ram 10 has attached thereto a conventional punch 12 which is attached to the ram by a horizontal clamp bar 13. All of this construction is entirely conventional.

In FIG. 1 a die member for cooperation with punch 12 is designated 14 and the manner in which die 14 is supported on bed 1 1 is as follows. A pair of die supporting rails are indicated at 15 and 16, rail 15 comprising a base for the die support and rail 16 comprising a top plate. The facing surfaces of rails 15 and 16 are longitudinally recessed as shown in FIG. 1 to receive a longitudinally extending bar 17 of a compressible medium which, by way of example, may comprise polyurethane. In actual practice polyurethane having a durometer hardness of 90 has been found satisfactory for operating under average loading conditions. Again merely by way of example, the bar 17 may be two inches square in transverse section.

As indicated earlier herein it is essential that the length of the compressible medium, in this case bar 17, be substantially the same length as the bend line in the workpiece so that it registers vertically therewith. Specifically, the purposes of the present invention are defeated if bar 17 is of substantially greater length than the bend line in the workpiece so that it supports the die member beyond the workpiece at one or both ends of the bend line. Similarly, the purposes of the present invention will not be attained if the bar 17 is substantially shorter than the bend line. For this reason, it is necessary in the present example to adjust the length of the compressible medium 17 whenever a workpiece having a different length of bend line is to be formed in the press brake.

It is to be understood that the compressible medium 17 may be made up of any number of pieces of polyurethane in end-to-end relationship between the die rails 15 and 16. To facilitate adding or subtracting from the length of the polyurethane member 17 to suit the length of the bend to be formed, means are provided for conveniently lifting top plate 16 of the die rail structure and the die 14 which is carried thereon, leaving the polyurethane compressible member 17 fully exposed for convenient replacement or for additions or removals of portions of the member 17.

The means for thus lifting top plate 16 and die 14 is illustrated in FIGS. 2 and 3 which show the right-hand end of the die structure, viewed at right angles to FIG. 1, but it is to be understood that duplicate lifting mechanism of opposite hand will be provided at the left-hand end of the die structure.

A mounting plate 20 is fixed to each end of base 15 of the die rail structure and has fixed thereto a mounting bracket 21. A pair of plates 22 are fixed to opposite sides of a handle member 23 asby rivets 24 and plates 22 are pivotally connected to hearing portions 25 of bracket 21. A lifting rod is designated 26 in FIGS. 2 and 3 and a link 27 is pivoted to the lower end of rod 26 as at 28 and to an intermediate point on plates 22 as at 29.

Rod 26 is mounted for vertical sliding movement in a bushing 32 carried by bearing formations 33 on bracket 21 and rod 26 is fixed adjacent to its upper end to a bracket 35 which is secured to the end of upper plate 16 of the die rail structure. For adjustably attaching the upper end of rod 26 to bracket 35, a stud 36 is threaded into the upper end of rod 26 and is attached to bracket 35 by a pair of lock nuts 38 which provide axial adjustment of rod 26 relative to bracket 35.

In the position shown in FIG. 2, handle 23 is in a lowered position so that upper plate 16 and die 14 are resting freely on the polyurethane member 17 and the latter may readily compress under vertical loads against the die member upon which the handle members 23 will swing freely toward the ends of bed 11. When polyurethane member or members 17 are to be replaced, added to, or subtracted from, the handles 23 at opposite ends of the die structure are raised to the position illustrated in FIG. 3. The parts will normally remain in this position under the force of gravity by reason of the fact that during this raising movement of handle 23, pivot 29 moves over center with respect to the pivotal connection of plates 22 with bearing formations 25 and this over-center movement is limited by abutment between portions of handle member 23 and link 27, as clearly shown in FIG. 3.

After proper length adjustment of the compressible medium 17 is accomplished to match such length to the length of the line of bend in the workpiece, handles 23 are manually lowered to the position shown in FIG. 2 and the parts reassume the position shown in FIG. 1.

The foregoing provides a very practical and workable arrangement to compensate for the deflection of the bed and ram of a press brake. A more elaborate arrangement which fully compensates for this deflection is to introduce a closely and uniformly spaced row of hydraulic cylinders between the die and bed, or between the punch and ram. These cylinders are interconnected to exert uniform pressures and means are provided so that only the cylinders within the limits of the length of the bend line are operative, the remaining cylinders being bypassed or otherwise cut out of the system.

A preferred embodiment has been described herein and shown in the accompanying drawings to illustrate the underlying principles of the invention but it is to be understood that numerous modifications may be made without departing from the broad spirit and scope of the invention.

We claim:

1. In a press brake having a bed, a ram movable toward and away from said bed, a die mounted on said bed, and a punch carried by said ram, compressible means extending linearly between said die and the bed of the press brake and having a substantially uniform spring constant per inch along said die and having a vertical deformation under a given load approximately one order of magnitude greater than the combined maximum deflection of the bed and ram of the press brake under such given load or greater.

2. A press brake according to claim 1 wherein said compressible means extends substantially the same length as the bend line of the workpiece.

3. A press brake according to claim 2 wherein said compressible means comprises a body of polyurethane.

4. A press brake according to claim 3 wherein said polyurethane has a hardness of approximately 90 durometer.

5. Apparatus according to claim 2 having means at opposite ends of said bed engageable with said die for elevating the same to facilitate adjusting the efiective length of said compressible means to match the length of said bend line.

6. Apparatus according to claim 2 having means at opposite ends of said bed engageable between said bed and said die for raising the latter and maintaining the same temporarily in raised position to permit adjustment of the effective length of said compressible means to match the length of said bend line.

7. A press brake according to claim 1 wherein said compressible means comprises a body of polyurethane.

8. A press brake according to claim 7 wherein said polyurethane has a hardness of approximately 90 durometer.

9. Apparatus according to claim 7 having means at opposite ends of said bed engageable with said die for elevating the same to adjust the length of the polyurethane body to match the length of said bend line.

10. Apparatus according to claim 7 having means at opposite ends of said bed engageable between said bed and said die for raising the latter and maintaining the same temporarily in raised position to permit adjustment of the length of said polyurethane body to match the length of said bend line.

11. In a press brake having a bed and a ram, a die member carried by said bed and a punch member carried by said ram, and compressible means interposed between at least one of said members and its respective carrier and extending linearly along said member, said compressible means having a substantially uniform spring constant along said member and having a total vertical deformation under a given load approximately one order of magnitude greater than the combined maximum deflection of the bed and ram of the press brake under such given load or greater.

12. A press brake according to claim 11 wherein said compressible means extends substantially the same length as the bend line of the workpiece.

13. A press brake according to claim 12 wherein said compressible means comprises a body of polyurethane.

14. A press brake according to claim 13 wherein said polyurethane has a hardness of approximately durometer.

15. A press brake according to claim 11 wherein said com r ssible means com rises' 01 rethane.

16? 1 press brake accoi ding 3) claim 15 wherein said polyurethane has a hardness of approximately 90 durometer.

Claims

5. Apparatus according to claim 2 having means at opposite ends of said bed engageable with said die for elevating the same to facilitate adjusting the effective length of said compressible means to match the length of said bend line.

14. A press brake according to claim 13 wherein said polyurethane has a hardness of approximately 90 durometer.

15. A press brake according to claim 11 wherein said compressible means comprises polyurethane.

16. A press brake according to claim 15 wherein said polyurethane has a hardness of approximately 90 durometer.