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United States Patent 3,914,975
Kawano October 28, 1975

Hydraulic press brake


A hydraulic press brake is disclosed having a stationary die cooperating with a movable die or punch to perform a bending operation on an elongated workpiece. Movement of the punch is effected by means of a pair of first hydraulic piston-cylinder units each of which is located proximate to one end of the punch. At least one second hydraulic piston-cylinder unit acts on the stationary die at a location intermediate the ends thereof to impart a convex bend to the fixed die to compensate for any concave bending of the movable die during a bending operation, thereby maintaining the surfaces of the fixed and movable dies substantially parallel. Pressurized hydraulic fluid is fed to the first and second hydraulic piston-cylinder units through feed conduits leading from a common pump, with a pressure reducing valve being interposed in the feed conduits between the pump and the second hydraulic piston-cylinder unit.

Inventors: Kawano; Susumu (Isehara, JA)
Assignee: Amada Company Limited (Isehara, JA)
Appl. No.: 05/512,943
Filed: October 7, 1974

Foreign Application Priority Data

Dec 25, 1970 [JA] 45-117685

Current U.S. Class: 72/389.5 ; 100/258A; 100/269.1; 425/214; 425/394; 425/411; 425/412; 425/451.2; 72/453.13; 72/473
Current International Class: B21D 5/02 (20060101); B21D 007/06 ()
Field of Search: 72/389,441,462,429,380,385,386,453,473 100/258A,269R,258R

References Cited

U.S. Patent Documents
3163105 December 1964 Pearson
3550425 December 1970 Cailloux
3587286 June 1971 Fritsch
3668919 June 1972 Hongo
Foreign Patent Documents
1,452,818 Nov., 1970 DT
Primary Examiner: Lanham; C. W.
Assistant Examiner: Crosby; Gene P.
Attorney, Agent or Firm: Thompson, Birch, Gauthier & Samuel

Parent Case Text


This application is a continuation-in-part of U.S. application Ser. No. 358,125 filed May 5, 1973, now abandoned, which in turn is a continuation of U.S. application Ser. No. 209,771 filed Dec. 20, 1971, now abandoned.

I claim:

1. A hydraulic press brake comprising: stationary frame means supporting an elongated die; movable ram means carrying an elongated punch, said punch being adapted to cooperate with said die in performing a bending operation on an elongated workpiece positioned therebetween; first hydraulically actuated means acting on said movable ram means at locations proximate to the ends thereof for moving said ram means and punch towards said stationary frame and elongated die during a bending operation; second hydraulically actuated means acting on said stationary frame means at a location intermediate the ends of the die supported thereon, said second hydraulically actuated means being operative to bend said stationary frame means and die convexly to thereby compensate for concave bending of said punch and ram means during a bending operation; hydraulic pump means; conduit means connecting said hydraulic pump means to said first and second hydraulically actuated means; and pressure reducing valve means in said conduit means between said pump means and said second hydraulically actuated means, said pressure reducing valve means being operative to reduce the pressure of the hydraulic fluid being applied to said second hydraulically actuated means in proportion to the pressure of the hydraulic fluid being applied to said first hydraulically actuated means.

2. The apparatus as claimed in claim 1 wherein said first and second hydraulically actuated means comprise piston-cylinder assemblies.

In a conventional press brake of the type provided at both of its ends with pressurizing cylinders for pressing an elongated punch or movable die against a workpiece placed on an elongated stationary die, the accuracy of the bending operation and the resulting dimensions and shape of the workpiece are adversely affected by the mechanical characteristics of the workpiece, e.g., tensile strength, elastic limit, yield point, as well as the resilient characteristics of the workpiece. For example, when a conventional press brake is operated with use of an elongated punch and an elongated die, the downward forces on the punch are exerted at the ends respectively of the ram supporting the punch and the stationary frame supporting the die. Thus, the punch has a tendency to warp upwardly in a concave manner, whereas the stationary die has a tendency to warp downwardly in a concave manner, because of the resistance of the workpiece to bending. As a result, the lower surface of the punch tends to part from the upper surface of the die. The resulting product is distorted (as shown in FIG. 2) with warps 5 and 7 at the central portions thereof.

Attempts have been made at solving the above problem by increasing the thickness of the central portion of the ram supporting the movable punch. This arrangement can only be employed, however, for the bending of certain materials of a specified bending resistance. Inaccurate bends are still likely to result when materials of different kinds are being bent with greater resistances to bending.

A general object of the present invention is the provision of novel and improved means for obviating the problems noted above. This and other more specific objects and advantages of the present invention will become more apparent as the description proceeds with the aid of the accompanying drawings wherein:

FIG. 1 is a front view, with portions broken away, of a hydraulic press brake embodying the concepts of the present invention, and including a schematic illustration of the hydraulic system;

FIG. 2 is a perspective view of a typical product bent in accordance with conventional techniques;

FIG. 3 is a perspective view showing a typical punch and cooperating lower die;

FIG. 4 is a view in side elevation of the apparatus shown in FIG. l; and

FIG. 5 is a sectional view of a reducing valve employed in the hydraulic system schematically depicted in FIG. 1.

With reference now to the drawings, 9 denotes a lower stationary frame carrying a lower die 3. Reference characters 11, 13 and 15 denote hydraulic mechanisms or cylinders which are mounted on a rigid plate 16 secured to the frame 9 at locations intermediate the ends of the die 3. The hydraulic mechanisms 11, 13, 15 are provided respectively with piston and piston rods 11p, 13p and 15p which exert an upward force on the die 3 through the frame 9. In the embodiment herein disclosed, three such hydraulic mechanisms are disclosed, although it will be appreciated that this number may be varied without departing from the spirit and scope of the invention.

The ram 17 carrying the upper punch or die 1 is constructed with a thicker central portion in accordance with known techniques to minimize any upward or concave warping during a bending operation.

The frame 9 is pivotally carried on horizontal fixed pins 19, 21, the said frame having an elongated opening or slot 23 to accommodate pine 21. This arrangement permits the frame 9 to bend upwardly or convexly when an upward force is exerted thereon by the hydraulic mechanisms 11, 13 and 15.

Hydraulic mechanisms 33, 35 are positioned to exert downward forces on the ends of the ram 17 carrying punch 1. A pump P is driven by motor M and draws hydraulic fluid from a tank T. The fluid is pumped through conduits 30, 29 to mechanism 33, through conduits 30, 31 to mechanism 35, and through conduits 30, 29, 27 and thence through conduits 39, 41 and 43 to hydraulic mechanisms 15, 13 and 11. A pressure reducing valve 25 is located in conduit 27 between the hydraulic mechanisms 15, 13, 11 and pump P.

The pressure reducing valve 25 is of a type wherein the amount of pressure reduction may be optionally selected so that any desired pressure may be obtained in proportion to the pressure being applied to the hydraulic mechanisms 33, 35. FIG. 5 shows one such typical pressure reducing valve 25 wherein P.sub.1 is a high pressure inlet, P.sub.2 is a reduced pressure outlet, P.sub.3 is a port for a pressure gauge, t is a piston and S is a spring. With this arrangement, any increase (or decrease) in pressure P.sub.1 is accompanied by a proportional change in pressure P.sub.2. Although not shown, it will be further understood that the conduits 37, 39, 41 and 43 are provided with appropriate check valves.

In view of the above, it will now be seen that since the stationary frame 9 and the lower die 3 are pressed upwards by the hydraulic cylinders 11, 13 and 15, during a bending operation, they do not warp downward as shown by C.sub.c in FIG. 1, but warp as shown by curve C.sub.b so as to follow the warp of the punch 1 and the ram 17 as shown by curve C.sub.a. Thus the hydraulic press brake of the present invention is characterized in that the upward warp of the stationary frame and the die carried thereon follows the warp of the ram and the punch to avoid such oppositely directed warps of the upper and the lower dies which might otherwise separate the punch from the lower die at the center, thereby obviating the defects that characterize products bent in accordance with conventional techniques as shown in FIG. 2.

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