PIPE BENDING MACHINE

Abstract: A pipe bending machine comprises a bending head (12) for engaging a pipe (1), drive means for displacing the bending head so as to bend the pipe through an angle, and means for co-operating with the bent portion of pipe once the bending force has been removed, in order to determine the actual angle through which the pipe has been bent. This may serve to measure the angle through which the pipe springs back, to enable the control system to predict through what angles the head must turn the pipe to achieve desired angles of bend in the pipe, and to check that actual formed bends are sufficiently accurate relative to desired angles.

Description: PIPE BENDING MACHINE FIELD OF THE INVENTION This invention relates to a pipe or tube bending machine. BACKGROUND AND SUMMARY OF THE INVENTION In the use of pipe bending machines, the pipe or tube will tend to spring back once the bending force is removed after effecting the bending operation. Thus in practice the pipe will exhibit a bend of a slightly small¬ er angle than that through which the machine has displaced the pipe. The angle through which the pipe will spring back will depend upon the overall angle through which it has been bent. For a particular size of pipe of a parti¬ cular material, it is possible to predict the spring- back for all bend angles once two bends of substantially different angles (say 20° and 120°) have been effected in a sample of the pipe and the spring backs for these two bends measured: corrections can then be made for all the bends required in pipes of the same size and mater- ' ial so as to take account of the predicted spring-back and ensure that each bend will be formed to the actually required angle. Hitherto this setting up operation has involved removing the sample pipe or pipes from the machine and measuring the spring-back angles either manually or by means of a separate measuring machine, and then effect- ing the corrections by entering new data into the controls. I have now devised an improved arrangement in a pipe bending machine, for measuring and taking account of spring-back. In accordance with this invention, there is provi- ded a pipe bending machine comprising a bending head for engaging a pipe and drive means for displacing the bend¬ ing head so as to bend the pipe through an angle, and means for co-operating with the bent portion of pipe once the bending force has been removed, in order to determine the actual angle through which the pipe has been bent. In order to determine the actual angle through which the pipe has been bent, an arrangement may be provided which is capable of turning to align with the bent portion of the pipe and has an associated means for indicating its angular position. This arrangement may comprise a mechanical feeler arrangement or an optical system. Alternatively, a camera may be provided to view the pipe from above. For example, the camera may be mounted so as to be movable until the camera is viewing the bent portion of pipe, and a digital indication of the bend angle provided. The camera may be driven under numerical control to its required position, from the data which determines the angle through which the bending head was turned, or may reach this position through an adaptive procedure. The camera may instead be mounted beyond the front of the machine. Once the bend has been effected, the machine may then advance the pipe an appropriate distance (being the known distance of the camera in front of the machine) such that the bend in the pipe is aligned with the camera, then the pipe is clamped up to the bending head and the camera used to determine the actual angle of the bend. The camera may be mounted for movement cross-wise of the machine so that it can be moved out of way when not in use. In particular, the camera may be used before any bend is made on the pipe, with the pipe advanced to project out the front of the machine: the camera is now used to determine accurately the vector for the axis of the unbent pipe and can further be used to determine the width or diameter of the pipe, the latter providing data for use subsequently in defining the true centre line of the bent pipe. In a computer numerically controlled machine, a digital indication of the angle through which the pipe has actually been bent can be provided, and compared with¬ in the control system with the command angle or angle thro¬ ugh which the bending head had been turned. The machine can automatically carry out two bends of significantly different angles (e.g. 20° and 120°) in a sample pipe, and its control system automatically calculate predictions for the spring-back at all bend angles, and automatically correct for all bends which are to be formed under a par¬ ticular part-program. The facility can also or instead be utilised as an in-progress check on the bends being formed on a part. In particular, once the spring-back discrepancy has been measured in respect of a bend, the machine may automatically re-engage the pipe and bent it further, sufficient so that (taking account of the predi- cted further spring back if necessary) the bend in the pipe will be to the required angle. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of this invention will now be described by way of examples only and with reference to the accompany- ing drawings, in which: FIGURE 1 is a diagrammatic plan view of a pipe bend- . ing machine in accordance with this invention; FIGURE 2 is a diagrammatic section on the line II-II of the machine of Figure 1; FIGURE 3 is a diagram of the bending head after a bend in a pipe has been formed; FIGURE 4 is a sectional view on the line TV-TV of of Figure 3; and FIGURE 5 is a plan view of the bend head of a modi¬ fied machine having a camera to determine the bend angle. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figures 1 and 2 of the drawings, there is shown a pipe bending machine of the draw bending type. The machine comprises a- horizontal machine bed 9 mounting a bending head 10 at its forward end. This bending head comprises a bending die 12 of generally cylindrical form and mounted for rotation about its axis A, which is dis¬ posed vertically. The bending die 12 is formed with an annular groove 14 which is semi-circular in section, and is provided with a short, flat-faced, tangential exten- tion 12a_ which has a groove forming a tangential extension of the groove 14. A clamp block 16 is provided to co¬ operate with the bending die extension 12a, and is formed with a semi-circular section groove l6a_ across its face, so that it can clamp a pipe 1 against the bending die. The clamp block 16 is mounted to an arm 18 for sliding movement by an hydraulic actuator 17 towards and away from the bending die extension 12a_: the arm 18 is mounted for rotating about its axis A of the bending die 12 so that it will turn with the bending die during bending operation. The bending head 10 further comprises a pressure die 20 mounted to the machine bed 9 and having a flat front surface formed with a semi-circular section groove co¬ operating with the groove 14 of the bending die 12. This pressure die 20 is movable towards and away from the bend¬ ing die by an hydraulic' actuator 21, and is mounted so that it will move lengthwise of the pipe 1 during a bend- ing operation. A wiper die 22 may also be provided, fixed to the machine bed 9, positioned opposite the pressure die 20 and shaped at its forward end to fit close to the bending die 12. The flat surface of the wiper die 22 which faces the pressure die 20 is formed with a semi- circular section groove co-operating with the groove of the pressure die 20. The bending machine further comprises a pipe or tube holder 26 mounted to a carriage 24 which is mounted for sliding movement along the length of the machine bed 9 under the power of a motor 25 and via a drive belt 25a. for example. The pipe holder 26 comprises a cylindrical body through which, in use, the pipe 1 extends, and is provided with a collet 26a_ which can be applied to grip the pipe. The pipe holder body is rotatable about its axis and coupled to a drive motor 27 for effecting this rotation. The bending machine also comprises a mandrel 28 carried at the end of a'mandrel rod 30, the mandrel being positioned in the pipe 1 to support the latter internally immediately upstream of the bend being formed, in use of the machine. The mandrel rod is mounted by a holder 31 to the machine bed beyond the trailing end of the pipe being processed. The machine is controlled by a computer numerical control system 50. In use, with a pipe 1 over the mandrel 28 and mandrel rod 30 and held in the pipe holder 26, then firstly the control serves to advance the carriage 24 to position the pipe 1 correctly, relative to the bending head, ready for the first bend to be made in the pipe 1. Then the pressure die 20 is advanced to press the pipe against the bending die 12 and wiper die 22, and the clamp¬ ing block is advanced to clamp the pipe 1 securely against • the bending die extension 12a. Next the bending die 12 and clamp arm 18 are turned together around the axis A of the bending die (and through the angle required), for example by a drive motor 45 applying power to a spindle 40 on which the bending die 12 is mounted (Figure 2). During this step the pressure die 20 slides forwardly in following a displacement of the pipe 1 which occurs, in the region of the bending head 10, as the bending die 12 turns. The clamp block 16 and the pressure die 20 are then retracted to free the pipe 1 from the bending die 12. After measurement of the actual bend angle and any correction for spring-back (as will be described below), the clamp arm 18 is returned to its initial position by a drive motor 47 coupled to it, the clamp arm 18 being journalled about the spindle 40. After completing the first bend in the pipe in this manner, the carriage 24 is advanced an appropriate amount so as to position the pipe 1 correctly for the next bend. The bending die 12 is returned to its initial position by its drive mo-tor 45 and the pressure die 20 is also returned to its ori¬ ginal position. If the next bend in the pipe 1 is to be effected in a different plane from the first bend, then the pipe holder 26 is turned through an appropriate angle. The next bend in-the pipe 1 is then carried out in the same manner as just described, and the whole sequence of steps is repeated for all the following bends which are to be made in the pipe 1. The entire operation of the machine is under compu¬ ter numerical control from the control system 50, inclu¬ ding in particular the measured displacements of the carr¬ iage 24, pipe holder 26 and bending die 12 and the applica¬ tion/release movements of the clamp block 16 and pressure die 20. In addition to the structure and operation of the pipe bending machine of Figures 1 and 2 so far described, arrangements are provided for measuring the actual bend angle and carrying any corrections for spring-back. Thus, once the bending die and bending arm come to rest, after turning through the predetermined bend angle to effect a bend in the pipe 1, the clamp 16 is released, allow¬ ing the pipe to spring back. Figure 3 shows in the dotted line position to which the pipe 1 is bent, and in the full line the position to which it springs back. The bending arm 18 is now turned back so as to align with the pipe in its sprung-back position. This movement of the bending arm 18 may be effected manually, and the correct positioning established or check- ed by a visual inspection. However, in the example shown in Figures 1 to 4, a probe 41, 42 is provided on the bend¬ ing arm 18 and, once the clamp 16 has been released, this probe is pivoted up about its axis PR for its two flat fingers 41, 42 to engage the side of the pipe tangentially: each finger 41, 42 includes a detector, so as to indicate if only one or other of them contacts the pipe 1 (indicating a misalignment) or if both of them contact the pipe 1 (indi¬ cating that the bending arm-18 is aligned with the pipe). The probe 41, 42 may be pivoted up manually, but the bending arm is provided with a rotary position encoder for giving a digital output signal indicating the angular position of the bending arm 18 when the alignment position is estab¬ lished: this output is provided to the compute numerical control system 50 of the machine, which serves to control the drives and displacements of the bending die, bending arm, clamp, carriage and pipe holder in accordance with a program or part-program defining the profile to which a pipe is to be formed. Instead of being manually displaced for aligning with the sprung-back pipe 1, the bending arm 18 may be under automatic control of the control system 50 for this operation. For example, once the clamp 16 is released, the bending arm 18 may be driven back through an angle approximating to an expected spring-back angle: then the probe 41, 42 may be advanced automatically under the system control, which then serves to detect if both fingers 41, 42 of the probe make contact with the pipe 1. If one finger only makes contact, the bending arm 18 is turned through a small angle (in a direction determined by which finger 41 or 42 contacted the pipe 1) and the probe is used again: this procedure " is repeated until the probe indi¬ cates that the bending arm 18 is aligned with the sprung- back pipe 1. Then the control system 50 automatically reads the angular position of the bending arm 18. As previously described, once the spring-back angle of a particular bend has been determined by the control system 50, this may cause the clamp 16 to be re-applied and the bending die 12 turned further, so that (taking into account the predicted further spring-back if necess¬ ary) the bend in the pipe 1 will now be to the required angle. This can be repeated for each bend to be formed in a particular part. However, in a setting up operation, two bends (say at 20° and 120°) can be made in a sample pipe, the spring- back for each of these being determined as described above. The control system 50 is then able to predict the spring- back for all bend angles and to apply a correction in respect of all bends to be made in accordance with a part- program for pipes of the same size and material, correc¬ ted data being written in automatically. Moreover, the arrangement enables an in-process check to be made on each bend being formed, and if necessary to re-bend any which are not sufficiently close to the required bend angle. Any repeating inaccuracies can be detected and used to correct automatically the angles through which the bending die is being driven. An electronic or video camera may be employed in¬ stead of the arrangement which has been described for deter¬ mining the actual angle of bend. As explained above, the camera may be mounted so as to be movable in order to align with the bent portion of the pipe. The data which determines the angle through which the bending head was turned may be used to drive the camera under numerical control to the appropriate position, then the actual angle or offset angle of the bent portion of the pipe determined. The camera may reach this position through an adaptive proce¬ dure: for example, in the case of a camera with self- scanning array, the arrangement may be that the camera determines if the received image is at its centre of view or, if not, produces an error signal which is used to drive the camera until the image is centered. The self- scan array determines accurately and automatically the angle at which the bent portion of pipe lies. As shown lines in Figure 5, the camera VC may be mounted beyond the front of the machine and is preferably movable (for example cross-wise of the machine) so that it can be moved out of the way when not in use. The camera may preferably be movable under numerical control with respect to at least two axes, say cross-wise and lengthwise of the machine, or one linear axis and one rotational axis. In the example shown, the camera is movable (lengthwise of the machine) on a carriage 35 along a track 36 and this carriage is movable (cross-wise of the machine) along tracks 37.. Once the bend has been affected, the machine may then advance the pipe 1 an appropriate distance out of the front of the machine and then the pipe 1 is clamped to the bending die 12 and the camera VC moved in to view the bent portion of pipe 1 in order to determine its actual angle automatically. In particular, the camera VC may ' :be used before any bend is made in the pipe 1, with the pipe 1 advanced to project out of the front of the machine: the camera VC is then used to determine accurately the vector for the axis of the unbent pipe 1 and also the width or diameter of the pipe 1. This vector may be determined as the average of a number of unbent pipes. The diameter data may be used subsequently for defining the true centre line of the bent pipe. With the camera VC moved under numerical control, its actual position is always known accurately. From this data, plus the video data (giving the angle of the rec- eived pipe image), the actual pipe angle can be determined accurately even if the camera is viewing an intermediate bent portion of the pipe. It will be appreciated that the advancement of the pipe 1 is also under numerical con¬ trol: each advancement may position the pipe 1 ready for the next bending operation, the camera being moved (in accordance with the advancement data) so that it views the pipe portion bent in the previous bending operation. The system in accordance with this invention may be combined with arrangements for monitoring and/or com- pensating for pipe-elongation which occurs upon bending.

Claims: CLAIMS 1. A pipe bending machine comprising a bending head (12) for engaging a pipe (1) and drive means (45) for dis¬ placing the bending head (12) through an angle, and means (e.g. 30 or VC) for co-operating with the bent portion of pipe (1) once the bending force has been removed, in order to determine the actual angle through which the pipe (1) has been bent. 2. A pipe bending machine as claimed in claim 1, com¬ prising an element (e.g. 18) movable manually to align with the bent portion of pipe (1) and provided with means for then providing an output signal representing the angu- ' lar position of said element. 3. A pipe bending machine as claimed in claim 1, comprising an element (e.g. 18) and an automatic control system for moving said element to align with the bent por¬ tion of pipe (1) and provided with means for then providing an output signal representing the angular position of said element. 4. A pipe bending machine as claimed in claim 1 or 2, in which said element includes a mechanical feeler arran¬ gement (41, 42). 5. A pipe bending machine as claimed in claim 1 or 2, in which said element comprises an optical system. 6. A pipe bending machine as claimed in claim 1, com- prising a camera (VC) mounted beyond the front of the machine, serving to view the bent portion of pipe and determine its angle of bend. 7. A pipe bending machine as claimed in claim 6, com- ■ prising drive means for displacing the camera (VC) from a remote position to a position viewing the bent portion of pipe (1) . 8. A pipe bending machine as claimed in claim 6 or 7, in which the camera (VC) serves to view the bent por¬ tion of pipe (1) upon advancement of the pipe and its re- engagement with the bending head ready for the next bend to be formed in the pipe. 9. A pipe bending machine as claimed in any preceding claim, including a control system (50) arranged to compare the actual measured bend angle with the angle through which said bending head (12) had moved the pipe (1) to form that bend, and from this calculate angles through which the bending head (12) should actually turn the pipe in-order, allowing for spring-back, to form actual bends of predeter¬ mined angles in the pipe. 10. A pipe bending machine as claimed in any one of claims 1 to 8, including a control system (50) arranged to compare the actual measured bend angle with the angle through which said bending head (12) had moved the pipe (1) to form that bend, and serving to cause the bending head (12) to re-engage the bent portion of pipe (1) and bent it a further amount, depending on said comparison, so that allowing for further spring-back the pipe will exhibit a bend of desired angle.

Inventors: GARDNER ROBERT FREDERICK, GARDNER, ROBERT, FREDERICK
Applicants: GARDNER R F, GARDNER, ROBERT, FREDERICK
Application year: 1986
Main classification: B21D7
IPC codes: B21D7