This invention relates to bending, in particular but not exclusively to bending metal tubes already nutted and flared such as automotive brake pipes.
There are many applications which make it desirable to have a machine capable of providing successive bends of different configuration in articles such as metal strip, wire, rod or tubing, without the necessity to adjust the machine between bends. One such application is in the manufacture of automotive brake pipes where a complexity of bends may be required which varies from model to model. Economic considerations make it preferable that a single machine should be capable of providing these complex curvatures and also be readily adjustable to bend work-pieces to different formations.
At present brake tubes are bent by use of manual jigs employing conical formers which have grooves of varying radii around which the tubes are bent. Such a bending operation is labour intensive and imprecise, and furthermore the jigs are bulky.
In the present invention a method of bending elongate articles of relatively low cross-sectional area is envisaged, in which the article is longitudinally translated via a bending head which selectively engages with portions of the article to form incremental bend portions, and the final configuration of the article is determined (i) by the number and/or angular extent of the incremental bend portions and (ii) by the extent of translation between successive incremental bend portions. The elongate article may also be rotated about its longitudinal axis during translation and/or bending for the purpose of varying the direction of the bending.
A machine for bending an elongate article such as a brake pipe may comprise a bend head such as for example a die and former arrangement operable to put a controlled angular extent of bend into a short length of the article, and means operable in sequence with operation of the die and former arrangement for advancing the article through the die and former arrangement by a controlled amount to present a further length for bending. The die may be controlled to rock repeatedly over the former so as to put equal incremental bend portions into the article in each bending operation, or alternatively the angular extent of each bend portion may be controlled within an available range by control of the extent of relative movement between the die and former in each bending operation. Means may furthermore be provided whereby the article may be rotated axially by a controlled amount in sequence with its advancement through the die and former arrangement so that the plane of the bend may be varied as required. Work-piece extraction after bending may be achieved by arranging for the die and the former to be pivotable away from one another once a locking means, which is engaged during bending, has been disengaged.
A powered carriage movable by a controllable amount is most conveniently provided for effecting intermittent longitudinal feed of the article to the bending head, the carriage carrying a clamp, preferably of a pivoted lever linkage type, for securing one end of the workpiece to the carriage.
The operating movements of the bend head, which determine the angular extent of each bend portion, and the translational and/or axial rotational movements of the article to be bent, which determine respectively the linear and angular distance between successive bend portions, can most readily be controlled by means of a microprocessor or similar data processing apparatus.
In order that the invention might be well understood, a presently preferred embodiment of the invention will hereinafter be described by way of example only with reference to the accompanying drawings in which:
- Figure 1 shows three typical forms of bent tube;
- Figure 2 shows an embodiment of the invention comprising a tube bending machine;
- Figure 3 shows a carriage and clamp system for the machine of Figure 2;
- Figure 4 is a perspective view of the clamp and carriage of Figure 3;
- Figures 5a and 5b are schematic diagrams of the clamp of Figure 3 shown closed and open respectively;
- Figures 6a and 6b are perspective views of the bend head of Figure 2, Figure 6b illustrating the interfitting of the parts in exploded view;
- Figure 7 is a sectional view of the interfitting parts of the bend head; and
- Figure 8 shows the bend head opened for work- piece extraction.
The machine in the described embodiment is designed to bend tubes such as hydraulic brake tubes of, typically, 3-13mm diameter metal tubing. These tubes are provided to the machine already nutted and flared and so the machine is designed to accept and release the nuts, although similar bending techniques and apparatus could be applied to plain tubing, strip or wire. Figure 1 shows three tubes depicting typical forms which can be produced: the tubes 1 are each provided with end nuts 2.
The general method of bending consists of a procedure in which the tube is fed through a bending head which engages only a small length of the tube and when operated forms an incremental bend portion of predetermined constant angular extent of for example 50 to 7°, in this small length. The bend head is then disengaged from the tube which is fed through the head by a chosen amount and then a further bend made at another point along its length. Repetition of the bend-feed-bend procedure can produce different overall curvatures in the tube dependent on the extent of translation, or feed, of the tube between incremental bends. The minimum radius possible is determined by the degree of bend provided by the bend head and is obtained when the tube is fed by a length equal to the length over which the bend head acts. For larger radii of curvature the feed length between incremental bends is increased. Feeding without operation of the bend head enables straight lengths to be left in the tube. Bends in different planes as shown of Figure 1a are obtained by rotation of the tube between bends, whilst a continuously varying plane, such as a helix shown in Figure 1b, can be obtained by axially rotating the tube by a few degrees in synchronism with the feed of the tube between successive bends. Variation in the curvature by progressively changing the feed lengths between incremental bends gives rise to a 'snail' form as shown in Figure 1c. Since each incremental bend may be formed in the same or a different plane from the adjacent bends, the only constraints on the shape and curvature of bent tubing formed according to the invention are those of minimum bend radius as dictated by the bend head construction, and spatial limitations imposed by the machine itself obstructing the bent tube.
Figure 2 shows the bending machine which consists of a carriage and clamp, indicated generally as 3 and a bend head 4. The bending machine is shown free standing but it may be suspended from a wall or ceiling or be mounted on an arm or gimbal. An important feature of the machine is its compactness, which enables the tube to be bent back on itself through large angles and minimises the aforementioned limitation of the machine bulk restricting the range of curvature.
Figures 3 and 4 show the carriage which comprises a cylindrical body 5 containing a double acting hydraulic cylinder 6 which is attached to an activating member 7 of a pull type lazy-tongs clamp mechanism shown generally as 8. The cylindrical body 5 is provided with lateral wheels 9 which enable it to run in a channel 38 which extends to the bend head 4. The nut at the end of the tube workpiece is accommodated by the clamp 8 and the tube extends forwardly through the bend head 4. A toothed belt 10, which may be seen in Figure 2, extends from pulleys 11 at the base of the machine and around pulleys 12 on the bend head. This belt is driven by a motor 13 and engages with slots on each side of the carriage to transport the carriage upwards (as viewed) and feed tube 1 into the bend head 4. Bent workpieces are removed and new workpieces inserted when the carriage abuts the bend head. Once a new workpiece has been received, belt 10 reverses the carriage 3 away from the bend head back to its starting position to commence transport of the new workpiece into the bend head.
A frame 22 is journalled as shown in Figure 3 within the cylindrical body 5 and is connected through gearing 40, 42 with an electric motor 44 mounted on the cylindrical body 5. The motor 44, preferably a stepping motor, serves for rotating frame 22 and the clamp 8 and the engaged tube by controlled amounts dependent upon signals applied to the motor 44 so that the tube can be bent in various planes. Frame 22 is not translatable with respect to body 5, but actuator 7 is longitudinally translatable by a small amount within the frame under control of hydraulic cylinder 6.
Figures 5a and 5b show schematically the clamp system 8, which consists of actuator 7, levers 14 and 15 and jaws 16 and 17. Levers 14 and 15 are pivotally connected to the actuator by pivot pin 18, lever 14 is pivoted by pin 19 to upper jaw 17, lever 15 is pivoted by pin 20 to lower jaw 16, and jaws 16 and 17 are pivotally connected by pin 21. Lower jaw 16 is bifurcated to accommodate upper jaw 17 and lever 15 between the bifurcations (see Figure 4), and levers 14 and 15 are slotted to fit around actuator 9 at their mutual pivotal connection. Upper jaw 17 is bifurcated in order to accommodate lever 14 and the end portion of frame 22 between the bifurcations.
Jaws 16 and 17 are separated by actuator 7 moving to the left under the influence of hydraulic cylinder 6, from the position as viewed in Figure 5a to the position shown in Figure 5b. This causes levers 14 and 15 and hence jaws 16 and 17 to move apart. Closure of the jaws is accomplished by retraction of the actuator 7 back to the position shown in Figure 5a which moves levers 14 and 15, and hence jaws 16 and 17 back together. The bushing for pivot pin 21 is elongated in the direction of movement of the actuator 7, and this elongation enables the movement of the actuator to translate the lever linkage of the clamp 8 a small distance in the same direction as the actuator movement for a purpose explained hereinafter.
Frame 22 is recessed to accommodate a mandrel insert 23 (Figure 3) on which the end of the tube 1 and nut 2 can be located. Mandrel 23 is interchangeable so that different types of nut may be accommodated. In order to enable rapid interchange of mandrels, the mandrel may be magnetically located and/or 'snap' fitting. When a new workpiece is inserted into the open jaws, the ends of the nut 2 and tube are engaged by the mandrel. The actuator 7 then causes the jaws to close and lastly the lever linkage is translated due to the abovementioned bushing elongation which draws the nut 2 back against the mandrel. On removal of the workpiece from the clamp 8, the translation of the linkage in the opposite direction first pulls the nut away from the base of the mandrel, and then the jaws open.
A resilient bias, for instance applied between pivot pins 19 and 20 biasing jaws 16 and 17 together, may be provided to ensure that the bushing travel is taken at the correct instant with respect to the opening and closure of the jaws to facilitate reception or ejection of the nut 2 on the end of the workpiece.
The bend head 4 is shown in perspective in Figure 6a; Figure 6b is an exploded perspective view of the die, former and frame of the bend head, and Figure 7 is a sectional view showing how these parts interfit. The bend head comprises a die consisting of a bending portion 24 and an actuating portion 25, a former 26 and a frame 27. A double acting ram 28 is linked to the actuating portion 25 of the die for rocking this so as to cause the connected bending portion 24 of the die to rock over the former 26 thereby to bend a tube 1 which is engaged in shaped recesses in the former 26 and bending portion 24 of the die. Ram 28 may have a variable stroke amplitude which is. controlled in conjunction with the required curvature of the tube, e.g. a larger amplitude may be used when a small radius of curvature is desired and vice versa.
Bending portion 24 is connected to actuating portion 25 of the die by a cylindrical extension 24a which passes through a bore 25a in the actuating portion 25. Former 26 has a hollow cylindrical extension 26c which extends through bores 27c in the frame 27 and bore 25c in the actuating portion of the die to secure the die and former to the frame 27. The bending portion 24 of the die is rotatable axially about extension 24a journalled in bore 25a of the actuating portion 25, and former 26 is rotatable axially about extension 26c journalled in bores 27c and 25c. When the head is being used for bending, two locking pins 29 and 30 are inserted, pin 30 passing along the centre of hollow cylindrical extension 26c and into recess 24c in the bending portion 24 of the die, and pin 29 passing through bores 27b in frame 27, through bore 25b in the actuating portion of the die and into recess 26b in former 26. Insertion and withdrawal of these pins is controlled by a solenoid 31., When ram. 28 is operated, the die 24 is rocked over former 26, with pin 30 acting as a pivot. In order to permit this rocking motion the bore 25b in the actuated portion 25 of the die is arcuate in cross- section.
When the bending of a workpiece is finished the nut 2 held in the clamp 8 of the carriage is released, and in order that the workpiece can be removed from the bend head the solenoid 31 withdraws the pins 29 and 30 from their positions locking the bending portion 24 of the die and the former 26, and these parts are pushed open to the positions shown in Figure 8 by the nut 2 as it is pulled through the bend head. As the bending portion 24 of the die rotates upwards about its cylindrical extension 24a, it rotates lever 32 upwards taking one arm of a pivotally connected crank 33 with it. The other arm of crank 33 is pivotally connected to a lever 34 which is in turn connected to the cylindrical extension 26c of the former 26. This lever linkage ensure that both the bending portion 24 of the die and the former 26 open if only one is pushed. A small amount of lost motion is provided in the linkage to accommodate the rocking movement of the die during a bending operation.
The open position of the bend head shown in Figure 8 is maintained by the over centre action of a spring 35 so that a new workpiece can be inserted into the jaws of the clamp 8 situated immediately behind the bend head. A loading mechanism for the new work- piece can be arranged to push the bend head back to the closed position, e.g. by a member pushing the bending portion 24 of the die so that the lever linkage 32, 33, 34 causes the former to follow. The locking pins 29 and 30 can then be inserted and the carriage 3 retracted to its starting position to commence bending the new workpiece.
A microprocessor or other computer control unit shown at 50 in Figure 2 may advantageously be used to synchronise and control the feed and rotation of the tube and operation of the bend head. The microprocessor can be programmed to ensure that, after the last bend, the jaws of the clamp 8 are rotated so that they are correctly aligned for opening without becoming obstructed by the bend head.
In an alternative arrangement for the machine, the bend head and carriage are mounted on the end lever of an articulated lever arm. The workpiece is loaded so that the nut on its first end is resting on a support, the nut at the second end being held in the clamp. As the bent tube emerges from the bend head the articulated arm moves so that the emergent tube is balanced on the support. Computation of the instantaneous centre of gravity of the emergent tube and the relative movement of the arm may be performed by the microprocessor.