METHOD OF BENDING A METAL PLATE

Abstract

A plate workpiece having an edge is bent with a press having a stationary upper die with a lower face and a vertically and horizontally movable lower die with an upper face. With the upper face of the lower die spaced below the lower face of the upper die, the workpiece is fitted between the dies such that the edge of the plate bears in a horizontal direction on the upper face of the lower die and an upper face of the plate bears upward on a portion of the lower face of the upper die. Then the lower die is moved vertically upward toward the upper die at a predetermined vertical rate while the lower die is shifted horizontally synchronously in the direction at a predetermined horizontal rate such that the plate edge engaging the lower-die upper face does not shift there along during upward movement.

Description

FIELD OF THE INVENTION

The present invention relates to method of bending a metal plate. More particularly this invention concerns such a method for making a workpiece from which welded pipe can be made.

BRIEF DESCRIPTION OF THE DRAWING

The prior art and the invention are described below in more detail with reference to the drawing in which:

FIG. 1 illustrates a prior-art method;

FIG. 2 illustrates another prior-art method; and

FIG. 3 illustrates the method of the present invention

BACKGROUND OF THE INVENTION

In order to make welded pipe, a piece of flat normally steel plate is first bent into a shape of U- or C-section. Then the two longitudinally extending plate edges are pressed together and welded, forming a closed tube. The first step therefore involves bending up both the edges of the starting workpiece that has a pair of opposite and parallel planar faces.

This initial bending is typically done in a bending or crimping press having a stationary upper die with a lower face whose shape is roughly that of a quarter cylinder, corresponding to the desired final shape of the respective workpiece edge after pressing. The press also has a lower die with an upper face and some sort of actuator means for at least vertically displacing the lower die upward.

For the bending operation the workpiece edge is positioned between the die faces and the lower die is raised. This action deforms the edge into an upwardly curving shape. Obviously, both longitudinal edges of the plate are thus deformed to the desired U- or C-section, and then the workpiece is run through several rollers that further deform it into the desired closed circular shape.

One problem with most prior-art systems as described below is that the plate edges are damaged and/or deformed to have an edge burr that interferes with the subsequent welding process and that also produces a lump at the weld seam.

To remedy this, U.S. Pat. No. 7,735,348 describes a method where at the start of the crimping process the lower face of the plate contacting working face of the lower die comes to rest flatly against an abutment that can rock or pivot. This flat contact is maintained during the entire crimping process in that as the lower die moves straight upward, the abutment pivots and the plate workpiece slides on the abutment in face, not line, contact.

An approach comparable to this is known from GB 1,537,055 and shown in FIG. 1. Here, a crimping press 2 is used to deform a flat plate workpiece 1 from an initial basically planar shape, that is with upper and lower faces lying in parallel horizontal planes, shown in solid lines to a shape with one edge upwardly curved into a part-cylindrical shape as shown in broken lines. This type of bending is applied to both longitudinal edges of the workpiece 1 so that it can be formed subsequently into a welded or open seam pipe. The press 2 has an upper die 3 and an lower die 4 respectively having a lower face 7 and an upper face 6, shaped as complementary part cylinders centered on respective parallel horizontal axes. The upper die 3 is stationary and the lower die 4 is shiftable vertically in a straight line as shown at H_V.

Initially the plate 1 is fitted between the dies 3 and 4 with the lower die 4 in the solid-line lower position such that the one lower longitudinal edge of the workpiece contacts the upper face 6 of the lower die 4 at line or position 5. Workpiece advance in direction D is then stopped and the lower die 4 is raised as shown by H_V to the broken-line upper position. During this movement the workpiece corner slides on the face 6 of the lower die 4 along path s from position 5 to position 5′. This action forms a burr on the lower longitudinal edge of the workpiece 1.

What is thus effected in the illustrated solution is a bending stroke without horizontal motion and this results in relative motion between the plate 2 and the lower die 4 when there is high face pressure between the lower die 4 and the plate workpiece 2.

FIG. 2 shows another previously known solution for crimping plate 1 in a crimping press 2 known from DE 10 2007 012 316. Here the difference from the solution of FIG. 1 consists in the fact that the lower die has a face 6′ that, while part-cylindrical, is not complementary to the face 7 but instead is part-cylindrically convex. Here also, a horizontal vector H_H is superimposed on the vertical upward vector H_V. This is aimed at minimizing ridge formation. Consequently, the result again is that during the intended crimping of the plate the starting contact position 5 shifts in the course of the crimping operation along the face 6 of the lower die 4 to position 5′. The displacement path s is again along an arc.

What thus occurs in the solution of FIG. 2 is a bending stroke with superimposed horizontal motion by the lower die 4, and this does in fact enable the face pressure to be reduced. A disadvantageous aspect, however, is that there is a high relative motion between the end edge of the plate and the face of the lower die. The workpiece 2 is left with a hard-to-weld edge.

A similar solution is disclosed in EP 1 958 712.

What cannot be accomplished by any of the previously known solutions in sufficiently reliable fashion is for the bent edge of the strip to have the desired shape. Instead, a burr or flash formation can result when high stresses occur in the edge region of the plate during the crimping process and yield processes result.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved method of bending a metal PLATE.

Another object is the provision of such an improved method of bending a metal PLATE that overcomes the above-given disadvantages, in particular that largely avoids any burr formation at the workpiece edge, leaving it nearly perfectly square and smooth.

SUMMARY OF THE INVENTION

A plate workpiece having an edge is bent with a press having a stationary upper die with a lower face and a vertically and horizontally movable lower die with an upper face. With the is upper face of the lower die spaced below the lower face of the upper die, the workpiece is fitted between the dies such that the edge of the plate bears in a horizontal direction on the upper face of the lower die and an upper face of the plate bears upward on a portion of the lower face of the upper die. Then according to the invention the lower die is moved vertically upward toward the upper die at a predetermined vertical rate while the lower die is shifted horizontally synchronously in the direction at a predetermined horizontal rate such that the plate edge engaging the upper face does not shift along the upper face during upward movement.

In practice this is simultaneously done to both of the longitudinal edges of the workpiece. Subsequently the workpiece, which has been bent into a C- or U-shape, is fed to a plurality of roller benders and a welder that form it into a closed circular shape and weld the two longitudinal edges together.

The horizontal motion by the lower die is preferably effected by at least one hydraulic actuator. A piston-cylinder system can be advantageously employed as the hydraulic actuator.

The face of the lower die contacting the plate is usually of concave form. In one development, provision is made that the curvature of the face of the lower die is not constant, which aspect provides the ability to use different regions of the die for different curvatures of the plate.

The face of the upper die contacting the plate is usually of convex form; here again, provision can be made whereby the curvature of the face of the upper die is not constant.

During crimping, the plate is preferably fixed in the lowermost region of the upper die relative to this die.

Finally, a control means working with or without feedback controls the vertical and horizontal movement of the lower die in such a way that a specified functional correlation exists between vertical and horizontal motion.

With the proposed solution a plate strip required to create an open seam pipe, in particular, a large-diameter pipe, can be bent in an ideal fashion into a cylindrical shape, the joint of the plate faces, in particular, can be formed optimally, that is free if any flash or burrs.

This is accomplished in that any sliding motion is prevented after of the initial contact of the plate on the face of the lower die. Thus, no material that is under high mechanical stress during the crimping process is drawn out and no burr is created.

Advantageously, wear on the face of the lower die is also significantly reduced by the proposed procedure since no relative motion results at the line contact between the face and the plate.

The welding operation, by which the joint points of the plate are joined, can thus be implemented under optimal conditions and is not hampered by a burr.

SPECIFIC DESCRIPTION

As seen in FIG. 3, where elements identical to FIGS. 1 and 2 have the same reference numerals, a horizontal vector H_H of movement is superimposed on the vertical movement vector H_V of the lower die 4 when the plate 1 is bent. Here the faces 5 and 6 are not part-cylindrical, but their curvature is not constant, that is their radius of curvature changes from one angular end to the other.

More particularly this horizontal motion H_H is synchronized to the vertical motion H_V such that the contact region 5 determined at the start of the bending operation between lower die 4 and plate 1 remains the contact region between the lower die 4 and the plate 1 during the entire bending operation, that is the plate 1 does not slide on the face 6 during the bending operation. In and between the lower solid-line position of the lower die 4 and the upper broken-line position, the contact region 5 is stationary on the face 6 of the lower die 4. As a result, there is no significant deformation of the material at the edge of the plate. Burr formation is thus reliably prevented.

A control means or controller 9 is provided to coordinate the vertical lifting motion H_V with the horizontal motion H_H. This controller 9 is linked to a vertical actuator 10 that effects the vertical lifting motion H_V, and a horizontal actuator 11 that effects the horizontal motion H_H. An algorithm or curve path is stored in the controller 9 that specifies a corresponding horizontal motion for each point of the vertical lifting motion. This can then be operated in a closed-loop or feedback-type control system using appropriate horizontal- and vertical-movement sensors 12 and 13 connected to the controller 9.

As a result, there is no shifting of the contact line 5 as in FIGS. 1 and 2.

Claims

1. A method of deforming a plate workpiece having an edge with a bending press having a stationary upper die with a lower face and a vertically and horizontally movable lower die with an upper face, the method comprising the steps of:

with the upper face of the lower die spaced below the lower face of the upper die, fitting the workpiece between the dies such that the edge of the plate bears in a horizontal direction on the upper face of the lower die and an upper face of the plate bears upward on a portion of the lower face of the upper die; and

synchronously moving the lower die vertically upward toward the upper die at a predetermined vertical rate while shifting the lower die horizontally in the direction at a predetermined horizontal rate such that the plate edge engaging the upper face does not shift along the upper face during upward movement.

2. The method defined in claim 1 wherein the upper and lower faces are complementary and the lower die is shifted upward until the workpiece is held in surface contact with both faces.

3. The method defined in claim 2 further comprising the step of

holding the plate between the faces after the workpiece is in surface contact with both faces.

4. The method defined in claim 1 wherein the lower face is downwardly convex and the upper face is upwardly concave.

5. The method defined in claim 4 wherein the curvature of the lower face is not constant.

6. The method defined in claim 4 wherein the curvature of the upper face is not constant.

7. The method defined in claim 1, further comprising the step of

clamping the plate against horizontal movement after the edge contacts the upper face and during upward movement of the lower die.

8. The method defined in claim 1 wherein the press includes a controller that sets the rates in accordance with a stored correlation between the vertical rate and the horizontal rate.