GB2326834A

GB2326834A - Hydro-forming installation

Info

Publication number: GB2326834A
Application number: GB9714072A
Authority: GB
Inventors: Bernard Louis Ciossy
Original assignee: BAS EN BASSET SOC IND DE
Current assignee: BAS EN BASSET SOC IND DE
Priority date: 1996-02-06
Filing date: 1997-07-04
Publication date: 1999-01-06
Anticipated expiration: 2017-07-04
Also published as: FR2744380A1; GB2326834B; GB9714072D0; FR2744380B1

Description

HYDRO-FORMING INSTALLATION The invention relates to hydro-forming, which is a process for the production of metal components from hollow blanks made by stamping from a metal sheet, which process comprises combining an axial mechanical buckling action with a radial deformation carried out in a mould and by means of a hydraulic action performed in the blank, this hydraulic action being defined, as much in value as in synchronization, by the change in the volume of the component, while maintaining its thickness, with respect to the shortening of the blank by the buckling action.

In practice, hydro-forming is carried out using installations comprising: - a buckling jack rigid with one of the supporting beds of a press and carrying a thrust member which receives the blank and is capable of shaping the base of the final component, - at least one mould in several parts, defining the external shape of the final component, - a closure head which tightly closes off the opening of the blank under force, - an hydraulic circuit for controlling the deformation of the blank, the branch of the circuit passing through the closure head and opening into the blank being connected to a control piston, - and means for coordinating the control of the volume of the blank with the buckling thereof as a function of the reduction in its length.

In general, the coordinating means comprise a cam, on the profile of which rests a roller mounted at the lower end of the control piston, controlling the change in the volume of fluid in the blank. This cam is linked in translation to a control jack feeding the buckling jack. Thus, any displacement of the control jack, and therefore of the buckling jack, causing longitudinal shortening of the component entails displacement of the cam and, as a consequence, displacement of the piston of the control jack supported on this cam. As a result, the change in volume of the fluid in the blank is synchronized with the shortening of this blank, and has a positive or negative value which depends on the profile of the cam, which is itself determined as a function of the conditions of deformation of the component.

This production technique allows components which are regular both in their geometry and in their dimensions to be obtained. However, it has disadvantages relating to the control and functioning thereof.

Since the profile of each cam is defined by the curve of the change in volume of the component with respect to its shortening and such that the internal surface of the blank is constant whatever the deformation of this blank, for each new production it is necessary to define, by calculation, some precise points of the curve of the cam, subsequently to connect these points by curve sections and, finally, to adjust the final curve by carrying out shaping trials on the press until the expected result is obtained. This procedure has been mastered well, but is long and tedious.

During functioning, and because of the high pressures acting by reaction on the control piston, the roller which cooperates with the profile of the cam is subjected to high stresses, which cause wear and deterioration thereof, leading to frequent replacements.

Another disadvantage of this installation results from the presence of the cam. In fact, because of its arrangement outside the movable elements of the press, and, for example, outside the toggle links which press the closure head on the blank, this cam requires distancing of the control jack from the blank and necessitates lengthening of the corresponding branch of the hydraulic circuit. The result of this is an increase in the inaccuracies due to swelling of the tubes and conduits of this circuit under the very high pressure therein.

Furthermore, the numerous mechanical components in the coordination means add mechanical inertias which have an influence on the reproducibility of components such that, to obtain regular components, it is necessary, at the end of the controlled hydro-forming operation, to subject the component to an increased pressure pressing it against the stamp. This operation, which is carried out by a so-called calibrating cylinder connected to the control circuit, increases the production time.

An object of the present invention is to provide a hydro-forming installation which remedies these disadvantages, while being safe and reliable in its functioning and very easily adaptable to a change in production.

To this effect, in the installation according to the invention, the means for coordinating the control of the internal volume of the blank comprise: - a detector which measures the linear displacements of the buckling jack and converts them into electrical signals, - a numerical control which drives the feed valve of the control jack as a function of the information from the detector of displacement of the buckling jack, and according to a predetermined relationship between the instantaneous height of the blank and the instantaneous internal volume of this blank, - and a feedback detector which measures the linear displacements of the regulating jack and converts them into electrical signals, this detector being connected to the numerical control by an electrical circuit.

With this arrangement, synchronization of the regulation of the volume of fluid in the blank with respect to the shortening of this blank is ensured by electronic means which react to a regulating law which can be modified very easily to each change in production by simple adjustment of values entered into the programmer of the numerical control. This advantage is particularly important since it enables the time for adjustment to each new production to be reduced, not only by eliminating machining operations on the profile of the cam, but also by reducing the time required for modification of the regulating law during the trials required for verifying consistency between this law and the actual deformation of the component.

Moreover, the elimination of any intermediate mechanical means eliminates the risks of breakdown and unintentional interruptions in production, and enables the length of the hydraulic circuit, and therefore inertias and inaccuracies, to be reduced. The reliability and the reproducibility thus obtained enable the final calibrating operation and the corresponding cylinder to be eliminated, which has the effect of reducing the production time and, in parallel, reducing the cost of the press, while simplifying it.

The feedback detector verifies the actual instantaneous position of the calibrating piston and, if necessary, enables this to be adjusted so that the regulating law is observed.

In one embodiment of the invention, the body of the control jack is fixed against the upper cross member of the press support, and the chamber arranged in the body for the control piston communicates, by an internal channel in this body, with a channel arranged in the cross member, while the latter channel is connected to the branch of the circuit which opens into the sealing head by a telescopic tubular column interposed between this head and the cross member.

With this construction, the hydraulic control circuit is particularly short, and above all is made up of channels which, arranged in massive and resistant components, have little susceptibility to swelling under the action of the high pressure flowing through them during the hydroforming operation.

Other characteristics and advantages will emerge from the following description, with reference to the accompanying drawings showing, by way of example, one embodiment of the installation according to the invention.

Figure 1 is a view, in transverse cross-section, showing the essential elements of part of the installation of the invention; Figures 2 to 7 are fragmentary side views, in cross-section, showing various phases of deformation of a blank, and Figure 8 is a graph showing the curve of the change in internal volume of the component of Figures 2 to 7 as a function of its shortening.

In Figure 1, reference number 2 designates the frame of a press comprising a bench 3 and an upper cross member 4. The bench 3 is integral with the cylinder 5 of a buckling jack 6. The piston 6a of the jack bears on a thrust member 8 which slides up in the cylinder 5, the upper surface of which is machined and shaped at 8a to form the base of the component. The cylinder 5 is fed by a circuit 9 from a control cylinder 10.

Mould elements 12 are associated with the thrust member 8. In the embodiment shown, these elements are in two parts and are intended to serve as the area of support at the widened edge 1 3a of the blank 13 when this blank is pinched by a plug 14 forming part of a closure head 15.

The closure head is connected to the upper cross member 4 by a system of toggle levers 16 which enable the plug 14 to be pressed with force against the widened edge 1 3a of the blank.

The plug 14 has an axial channel 17 therethrough which communicates with the channel 18 of a hydraulic circuit. This circuit comprises a supply branch A comprising a non-return valve 19 arranged in the head 15, and a conduit 20 for fluid supply, in particular water, provided from an electrically controlled valve 22, and a branch B for connection to a control jack 28. This branch comprises a telescopic column in two parts, 23a, 23b respectively, connecting the channel 18 to the upper cross member 4. The upper element 23b of the column opens into a receiver 24 which communicates via a channel 25 arranged in the upper cross member 4 with a channel 26 arranged in the body 27 of the control jack 28. This control jack is a pressure multiplication jack having a piston, the head 29 of which is mounted free in translation in a cylinder 30 fed at each side respectively by hydraulic circuits 32 and 33, and a rod 34 guided in translation by the body 27 and movable in a pressurizing chamber 35. The above-mentioned conduit 26 and a conduit 36, which forms part of an overflow and degassing circuit comprising a driven valve 37 and an evacuation circuit 38, open into this chamber.

The circuits 32 and 33 which feed the control jack are connected to an electrically controlled distributor 39, while the circuit 40 driving the valve 37 is fitted with an electrically controlled distributor 42.

According to the invention, coordination of the hydro-forming operation, that is to say the axial mechanical action of shortening of the blank 13, with the hydraulic action which effects radial expansion of this blank with control of its deformation, is performed by a system comprising a numerical control 50, a detector 52 of displacement of the buckling jack 6 and a detector 53 of displacement of the control jack 28. The detectors 52 and 53 are connected to the numerical control by circuits 54 and 55 respectively. Likewise, the valve 22 and distributors 39 and 42 are connected to this numerical control by circuits 56, 57 and 58 respectively.

In the embodiment shown, each of the detectors 52, 53 is made up of an encoding wheel, not shown, fast for rotation with a pinion 60, 62 which engages with a rack 63, 64 fixed for movement with the piston 6a of the buckling jack 6 and with the piston 29 of the control jack 28. These connections are shown as being effected by rods 7 and 65 respectively, connected to pistons 6a and 29 respectively, but any other connecting means can be used, provided that all displacements of a piston are communicated to the corresponding rack.

The coordinating means, constituted here by the numerical control, has the function of ensuring perfect simultaneity between the shortening action performed by the buckling jack and the widthwise deformation action performed by the hydraulic fluid in the blank, and, consequently, controlling the pressure and the volume of the fluid in the blank such that the internal surface area thereof, and thus its thickness, remains constant.

In practice, this control, which takes into account the changes in volume of the blank in the course of its deformation, as shown in Figures 2 to 7 for the production of a grooved pulley from a blank in the form of a cup, is governed by a predetermined relationship, or the regulating law corresponding to the curve C of Figure 8. This curve, which represents the change in volume of the blank, indicated on the ordinates, with respect to its shortening, plotted on the abscissae, is peculiar to each component and is in general defined by extrapolation from a few points P1 to P6, for each of which the height H1 to H6 is known and the volume Vitro V6 is calculated.

In the installation of the present invention, the values P1 to Pn are introduced into the programmer of the numerical control, which is provided with software which determines the intermediate values. These intermediate values are adjusted during trials carried out on the press.

It may be noted that, by contrast with current installations which require modification of the profile of a cam, the precise definition of the programming law does not require any handling or machining other than performance of trials on the press. A considerable saving of time during each change in production results.

To produce a component by means of this installation, the blank 1 3 of the component is first positioned on the mould elements 12, the means for closing the closure head are then activated such that the plug 14 presses firmly on the tapered edge 13a of the blank on the mould elements 12. At this stage, the numerical control 50 intervenes via the valve 22 of the feed circuit 20 to proceed with filling of the blank 13, but also of the entire hydraulic circuit. During this phase, the valve 37 is brought into the open position by the distributor 42 to proceed with emptying of the air, and evacuation of the overflow. At the completion of filling, the valves 22 and 37 are brought into the closed position such that the hydraulic circuit is closed at each of its ends.

At this stage, the numerical control 50 triggers functioning of the control jack 10 which, via the circuit 9, feeds the chamber of the buckling jack 6 in order to cause displacement thereof upwards in the direction of the arrow 11 in Figure 1.

Due to the detector 52, the displacements of the buckling jack 6 are detected at every instant, transformed into electrical signals and fed to the numerical control 50 which, in parallel, via the circuit 57, activates the distributor 39 which controls feeding of the control jack 28, this being displaced in the direction of the arrow 31 in Figure 1. The rod 34 of this jack, which penetrates into the chamber 35, generates a flow of fluid, which is forced at a predetermined pressure into the blank 13. It can be seen that for some components which instantaneously have positive changes in their volume, the control jack 28 can be displaced in the opposite direction to the arrow 31.

All the displacements of the control jack 28 are measured by the feedback detector 53 and transmitted, in the form of electrical signals, via the circuit 55 to the numerical control 50, which can thus react instantaneously via the distributor 39 to adjust the position of the control jack 28 with respect to the regulating iaw, so that the deformation of the blank 13 is always effected without reducing its thickness and with the internal surface area maintained.

At the end of this deformation operation, the component is finished and does not have to be subjected to a calibrating operation.

At the end of the production cycle, the hydraulic circuit is drained, at least partly, by activating the driven valve 37, and the closure head is then raised to provide access to the component.

It can be seen from the above that the means, which, according to the invention are electronic, for coordinating the mechanical and hydraulic actions of the hydro-forming operation, allow the simultaneity sought to be obtained, due to the combination of the numerical control with the two detectors 52, 53 which measure exclusively the linear displacements of the buckling and control jacks. Furthermore, and independently of the ease of control during each change of component, these coordinating means clear the structure of any mechanical part, such as a cam and its displacement means, and, by bringing the control jack 28 closer to the upper crossbar 4, enable the elements of the hydraulic circuit to be realized in massive and non-deformable components 15, 23a, 23b, 4 and 47, and the length of this circuit to be reduced, which eliminates all the disadvantages caused by swelling of the channels and hydraulic inertias.

With these means, the press is less expensive, changes to the moulds are facilitated, while the components obtained are more precise and less expensive.

Claims

1. An installation for the production of components by hydroforming, comprising: a buckling jack integral with one of the supporting beds of a press and carrying a thrust member which receives a blank and is capable of shaping the blank to form the base of the final component, at least one mould in several parts, defining the external shape of the final component, a closure head, which tightly closes off the opening of the blank under force, an hydraulic circuit for controlling the deformation of the blank, the branch of the circuit passing through the closure head and opening into the blank being connected to a control jack, and means for coordinating the control of the volume of the blank with the buckling as a function of the reduction in the length of this blank, the coordinating means including a detector which measures the linear displacements of the buckling jack and converts them into electrical signals, a numerical control which drives the feed distributor of the control jack as a function of information from the detector of displacement of the buckling jack, and according to a predetermined relationship between the instantaneous height of the blank and the instantaneous internal volume of this blank, and a further detector which measures the linear displacements of the control jack and converts them into electrical signals, this further detector being connected to the numerical control via an electrical circuit.

2. An installation according to Claim 1, wherein each detector is made up of an encoding wheel linked for rotation to a respective pinion, each pinion engaging with a rack linked respectively in translation to the piston of the corresponding jack.

3. An installation according to either of Claims 1 and 2, wherein the body of the control jack is fixed against an upper cross member of the press bed, and the chamber arranged in the body for the control piston communicates, by an internal channel in this body, with a channel arranged in the cross member, the latter channel being connected to the circuit of the closure head by a telescopic tubular column interposed between this head and the cross member.

4. An installation according to Claim 3, wherein the hydraulic circuit arranged in the closure head is connected, inside this head, to a fluid-supply circuit.

5. An installation according to either of Claims 3 and 4, wherein the chamber of the control jack communicates via a channel with a driven valve, accommodated entirely within the body of the jack.

6. An installation for the production of components by hydroforming, comprising a buckling jack adapted and operable to shape a hollow blank by axial deformation thereof, means for applying fluid pressure to the hollow interior of the blank to cause radial expansion of the blank during the axial deformation thereof, means for producing electrical signals representative respectively of the instantaneous height and volume of the blank, and numerical control means arranged to receive said signals and serving to control operation of the fluid-applying means as a function of the displacement of the buckling jack according to a predetermined desired relationship between said height and volume.