Hydraulic Presses

Abstract

Method and apparatus for controlling a hydraulic press having a row of hydraulic cylinder/ram assemblies for applying pressure in a workpiece of elongate form. The pressure of one cylinder/ram assembly adjacent one end of the workpiece is controlled in dependence upon the ratio of the length of the end portion of that workpiece over the length of the zone covered by that one cylinder/ram assembly.

Description

This invention relates to hydraulic presses and has particular, although not exclusive, reference to pipe-forming presses.

In one known method for the production of pipes for the transmission of gas, oil, etc., a workpiece in the form of a flat plate is deformed into a U-shape by a first press and is then transferred to a second and separate press where the U-shaped plate is further deformed into an O-shape.

Known O-form press designs are of the laminated frame type in which a row of cylinder assemblies are mounted within individual sub-frames comprising the press structure. The cylinder assemblies are adapted to provide movement of an upper tool assembly relative to a lower stationary tool assembly which is mounted below the upper assembly and passes axially through the sub-frames. The lower tool assembly is adapted, in use, to receive the U-shaped plate from equipment outside the press, whereupon the press cylinder assemblies are actuated to advance the upper tool assembly to further deform the U-shaped plate into an O-shape. The upper tool assembly is then withdrawn and the O-section tube is conveyed out of the press for subsequent welding, testing, etc.

Pipes made in this way can vary in length up to a maximum determined by the length of the press tool assemblies. However, when the length of the workpiece is less than this maximum value, the ends of the tools and tool supports will overhang the ends of the workpiece and consequently will not be reacted on by the workpiece during the deforming operation. This can create a potentially excessive bending moment in the tool support structure, and in known presses this has been overcome by unloading those cylinders which act beyond the plate extremities.

However, this method is not satisfactory where the plate extremity terminates below an operative cylinder, and in this case it has been found that the pipe end is frequently deformed to a greater extent than the main body of the pipe. Furthermore, because the pipe end deflects further than the main body, a bending moment is imparted to the upper tool support member and the upper tools which necessitates the use of excessively heavy press parts.

According to the present invention, a method controlling a hydraulic press having a row of hydraulic cylinder/ram assemblies for applying pressure to a workpiece of generally elongate form includes the step of controlling the pressure exerted by one, or two or more adjacent cylinder/ram assemblies, under which a portion of one end of the workpiece extends, in dependence upon the ratio of the length of the said end portion of the workpiece which extends into a zone over which the force exerted by the said one, or two or more cylinder is effective, to the length of the zone measured in a direction along the longitudinal axis of the press. Preferably, the method includes the further step of ensuring that the ratio of the pressure exerted by the said one, or two or more adjacent cylinder/ram assemblies to the pressure exerted by any other cylinder/ram assembly under which the workpiece extends fully, is equal to the aforesaid length ratio. A first signal representative of the pressure exerted by the said any other cylinder/arm assembly and a second signal representative of said length ratio can be fed to comparator means the output from which is used to control the pressure exerted by the said one or two or more cylinder/ram assemblies. The second signal can be produced by sensing means used to detect a reference point on the workpiece such as the leading or trailing edge thereof.

The pressure exerted by one, or two or more adjacent cylinder/ram assemblies under which a portion of the other end of the workpiece extends may also be controlled in dependence upon a similar length ratio.

Apparatus for carrying out the aforesaid method may include a row of hydraulic cylinder/ram assemblies for applying pressure to the workpiece, and means for enabling the pressure of one or, two or more adajcent cylinder/ram assemblies associated with one or each end of the workpiece to be controlled in the aforesaid length ratio. The said means can comprise sensing means for providing a first signal representative of said length ratio, means for providing a signal representative of the pressure in said any other cylinder/ram assembly and comparator means for receiving said signals and producing an output for controlling the pressure in said one or two or more cylinder/ram assemblies. The sensing means can be adapted to detect a reference point on the workpiece such as the leading or trailing edge thereof.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings which illustrate an O-forming hydraulic press and in which:

FIG. 1 is a sectional elevation of the press along line I--I of FIG. 2;

FIG. 2 is a part section along line II--II of FIG. 1;

FIG. 3 is a part section along line III--III of FIG. 1; and

FIG. 4 is a diagrammatic representation of a control system for the press shown in FIGS. 1 to 3.

As described in the Specification of our co-pending Patent Application Ser. No. 283,167, the press frame 1 shown in FIGS. 1 to 3 incorporates a series of sub-frames comprised of plates 2 held in fixed spacial relationship by bolts 3 and diaphragms 4.

Mounted within the sub-frames are a number of cylinder/ram assemblies each incorporating a moving cylinder block 5 and a fixed ram 6 to which assemblies hydraulic medium is fed through connections 7 and passageways 8. The cylinder blocks are returned by the rams 9 of fixed cylinders 10.

The movable upper tools 11 of the press are mounted in the cylinder blocks 5 and the fixed lower tools 12 are mounted in supports 13.

Referring now to FIG. 4 cylinders A, B, C and D are connected to a source of hydraulic power schematically indicated as pump 14 and a related control means including a by-pass valve 15 and a pressure relief valve 16. Control valves 17A, 17B, 17C, 17D are provided to isolate their respective from the hydraulic power supply.

Cylinder E is connected to a separate source of hydraulic power indicated as pump 18 and a related control means including a by-pass valve 19, a pressure relief valve 20 and control valve 22.

As shown in FIG. 4, the space between the upper and lower tool sets has been divided into zones A.sub.1, to E.sub.1 ; these zones represent the area of the tool set over which the force from each respective cylinder may be said to be operative. Thus, for example, the zone A.sub.1, represents the area of the tool set over which the force from cylinder A may be said to be operative.

Sensing means 23a to 23d are provided to detect the trailing edge of the plate and sensing means 24 are provided to detect the position of the leading edge of the plate. These means may be of any known form, i.e., electrical, mechanical or hydraulic and may be limit switches, photo cells, digitisers, etc.

The signal from sensing means 24 which represents the position of the leading edge of the plate in relation to the right-hand end (as seen in FIG. 4) of zone E.sub.1 is transmitted to a comparator means 25.

Furthermore, a signal representing the pressure in cylinders A, B, C and D, i.e., the line pressure from pump 14, is also fed into the comparator means 25.

The outgoing signal from the comparator means 25 is the product of the value of pressure in cylinders A, B, C and D multiplied by the ratio of the plate length in zone E.sub.1 to the axial length of zone E.sub.1 and is transmitted to the control means of pressure regulating valve 21, thus controlling, as explained in more detail below, the pressure in cylinder E in the desired ratio to the pressure in cylinders A, B, C and D.

Preferably, a pressure feed back signal 26 is taken from the pressure line to cylinder E and transmitted to the comparator means 25 where the signal representing the actual pressure obtained may be compared with the aforesaid control signal to pressure regulating valve 21. If there is a discrepancy in the two values, the control signal is adjusted accordingly whereby the desired pressure is obtained.

The press operates as follows:

Conveying means (not shown) transport a partially deformed U-shaped plate (not shown) axially, in the direction of arrow 27, into the press between the top and bottom tools until the sensing means 23a detects the trailing edge of the plate. The conveying means is then stopped and the plate lowered on to the bottom tool with its trailing edge coterminus with the right-hand extremity (as seen in FIG. 4) of zone A1. Assuming that a portion of the leading end of the plate extends into zone E.sub.1, then the length of that portion is determined by sensing means 24 and an appropriate signal is transmitted to the comparator means 25.

As the cylinders A, B, C, D and E advance to deform the U-shaped plate, a signal proportional to the pressure in line 14 is received by comparator means 25 and a signal representing the desired value of pressure for cylinder E is transmitted in the manner described above thus controlling the pressure to cylinder E from pump 18.

The U-shaped plate is thus formed into an O-shape between the press tools with the pressure in the cylinders A, B, C and D determined by the resistance to deformation of the main body of the product and the pressure in cylinder E controlled in relation to the pressure in cylinders A, B, C and D in the ratio of the plate length in zone E.sub.1 to the length of zone E.sub.1. That is, if the plate length in pressure zone E.sub.1 is three-quarters of the length of zone E.sub.1, the pressure in cylinder E is maintained at three-quarters the pressure in cylinders A, B, C and D.

Should the plate length be reduced to less than the distance between the right-hand end of zone A.sub.1 and the right-hand end of zone E.sub.1, the trailing edge of the plate is arranged to be coterminus with the right-hand end of zone B.sub.1 by utilising sensing means 23b and cylinder A is unloaded by means of control valve 17A. The above operational procedure is then repeated.

Providing that adequate control facilities are incorporated, further reductions in plate length may be accepted. In these cases, however, it is preferable that the pipe is kept sensibly central between the axial ends of the press and therefore it would be expedient for the hydraulic power, control and sensing means described above for cylinder E to be duplicated for cylinder D, thus providing separate and variable pressure control for cylinders D and E. In this case the sensing means 24 could be used to detect the length of plate extending into either zone D or E.

The press described above could also be modified to incorporate power supply and control means providing a proportional reduction of pressure over two or more adjacent cylinders at one end of the press, thus permitting the use of reduced press power over a longer end portion of plate where the pressure in these cylinders in relation to the pressure in the principal cylinders is in the ratio of the length of plate within the combined pressure zones to the length of the pressure zones.

It will be evident that the measures described above providing proportional pressure variations at one end of the plate could be applied to both ends thereof.

It will be understood that whilst reference has been made above to designs of presses in which the upper tool is supported and powered by a moving cylinder assembly as described in more detail in the Specification of our co-pending Patent Application No. 283,167, the control means described may be applied to any press of known design in which a number of axially mounted rams act directly or indirectly upon a press tool.

It will be further realised that although the trailing edge of the plate is used as a reference point in the press described, this point may be selected anywhere along the length of the plate.

It will also be understood that the comparator means may be of any suitable type, i.e., mechanical, hydraulic or electrical.

In the above description it has been assumed that the force from each cylinder is operative over a particular zone or area such as A.sub.1. It will be appreciated, however, that these zones do not represent the total area over which each cylinder is effective and, in practice, the force exerted by each cylinder will in fact extend beyound the illustrated zones. Furthermore, in conventional presses where the rams, and not the cylinders, are movable and are attached to a common beam or tool support, the forces from the rams will spread through the tool support to an even greater extent depending, of course, on the depth of the tool support.

It will be appreciated that an advantage of the methods and apparatuses described above is that the workpieces are deformed symmetrically and that the press tools are not subjected to excessive bending moments.

Claims

What we claim is:

1. A method of controlling a hydraulic press having a row of hydraulic cylinder/ram assemblies for applying pressure to a workpiece of generally elongate form including the step of controlling the pressure exerted by at least one adjacent cylinder/ram assembly, under which a portion of one end of the workpiece extends, in dependence upon the ratio of the length of the said end portion of the workpiece which extends into a zone over which the force exerted by the said cylinder is effective, to the length of the zone measured in a direction along the longitudinal axis of the press.

2. A method as claimed in claim 1, in which the length of said zone is defined by the axial extremities of the pressing surface presented by the said one cylinder/ram assembly.

3. A method as claimed in claim 1, including the further step of ensuring that the ratio of the pressure exerted by the said one adjacent cylinder/ram assembly to the pressure exerted by any other cylinder/ram assembly under which the workpiece extends fully, is equal to the aforesaid length ratio.

4. A method as claimed in claim 3, in which a first signal representative of the pressure exerted by the said any other cylinder/ram assembly and a second signal representative of said length ratio are fed to comparator means the output from which is used to control the pressure exerted by the said one cylinder/ram assembly.

5. A method as claimed in claim 4, in which the said second signal is produced by sensing means used to detect a reference point on the workpiece such as one of the edges thereof.

6. Apparatus for carrying out the method as claimed in claim 1, including a row of hydraulic cylinder/ram assemblies for applying pressure to the workpiece, and means for enabling the pressure of one adjacent cylinder/ram assembly associated with at least one end of the workpiece to be controlled in the aforesaid length ratio.

7. Apparatus as claimed in claim 6, in which said means comprises sensing means for providing a first signal representative of said length ratio, means for providing a second signal representative of the pressure in said any other cylinder/ram assembly and comparator means for receiving said first and second signals and producing an output for controlling the pressure in said one cylinder/ram assembly.

8. Apparatus as claimed in claim 7, in which said sensing means are adapted to detect a reference point on the workpiece such as one of the edges thereof.