GB2147533A - Stretch forming parts from ductile materials - Google Patents

Abstract

A workpiece 1 of sheet metal is gripped around its perimeter by grippers 3, which are in turn pulled by pullers 4, to stretch the workpiece 1 over a former 2. This stretch forming of the workpiece 1 is carried out under the control of a microprocessor 6, which responds to an output of a scanner 12, which monitors the behaviour of the workpiece 1 during its stretch forming. In this way, shaped parts may be repetitively formed, with a high degree of accuracy. The same production machine is capable of producing parts of varying profiles in response to predetermined programmes. The machine will manipulate the workpiece in addition to the stretching of the workpiece because controlled mobility of the mooring points is included. <IMAGE>

Description

SPECIFICATION Forming parts from ductile materials This invention relates to the forming of parts from ductile materials and is concerned particularly, although not exclusively, with forming parts from sheet metal.

There are very many ways known of working sheet metal. However, for making complex shapes in quantity, the only practical method at the present time is pressing. This involves the use of extremely expensive presses and extremely expensive press tools, which latter are completely dedicated to the production of one particular component. This means that only very large production runs can hope to recoup the expense of press tooling. If only relatively low productions runs are involved, it is usually uneconomical to use sheet metal at all, and cheaper alternatives, such as glass reinforced plastics, are considered. Such materials are chosen for their relative ease of shaping, and not for their mechanical properties, which are generally inferior to those of sheet metal.

It is of course possible to work sheet metal by largely manual processes. However, it is then usually rather difficult to retain a high degree of accuracy in a succession of finished products.

There is no doubt that sheet metal would be used much more widely if there were an economical method of shaping it for relatively low production runs. The present invention aims to provide such a method, and apparatus for performing the method.

According to a first aspect of the present invention, there is provided a method of forming a part from a ductile material, comprising the steps of placing a blank of the material on a former, gripping the blank at predetermined points, pulling the blank selectively at said points to stretch the blank over the former, monitoring the behaviour of the material as the blank is stretched, and controlling automatically pulling of the blank in dependence upon the monitored behaviour of the material, until the blank is sufficiently stretched over the former to form the part.

By monitoring the behaviour of the material as the blank is stretched, and controlling the pulling of the blank accordingly, a high degree of accuracy can be obtained in the finished part, and this accuracy may be re peated.

According to a second aspect of the present invention, there is provided apparatus for forming a part from a ductile material, comprising: a former the shape of which relates to the shape of the part to be formed; gripping means adapted to grip at least part of the periphery of a blank of ductile material when placed on the former; pulling means adapted to exert a pulling force on the gripping means to stretch the blank over the former; monitoring means adapted to monitor the behaviour of the material as the blank is stretched; and control means adapted to receive an output from the monitoring means and to control automatically the pulling means in dependence thereon until the blank is sufficiently stretched over the former to form the part.

The former may be collapsible in order to allow the part to be more readily removed therefrom. Alternatively or additionally, the part may be "blown off" the former by air being directed through holes in the former.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made; by way of example, to the accompanying diagrammatic drawing, the single figure of which illustrates schematically apparatus embodying the present invention.

In the figure, a workpiece 1 of sheet metal is placed on a former 2. Hydraulically powered grippers 3 grip the workpiece 1 around its periphery, at predetermined points. Each of the grippers 3 is connected to an hydraulic puller 4, which is connected to ground (or other reference point) at 5.

A microprocessor unit 6 controls the former 2, the grippers 3 and the pullers 4. To this end, a control line 7 extends from the microprocessor unit 6 to the former 2. Control lines 8 and 9 extend from the microprocessor 6 to the gripper 3, respectively for controlling the gripping function and the position of the gripper 3. Similarly. control lines 10 and 11 extend from the microprocessor 6 to the puller 4, respectively to control the pulling force and the position thereof.

A scanner 12 scans the surface of the workpiece 1, to monitor the behaviour thereof. An output from the scanner 12 is fed via a line 13 to the microprocessor unit 6, which in turn controls operation of the apparatus in response to the output from the scanner 12.

Briefly, the apparatus operates as follows.

Firstly, the workpiece in the form of a suitable blank is placed upon the former 2, and the grippers 3 are operated to grip the periphery of the workpiece 1, at selected points. The pullers 4 are then operated, under the control of the microprocessor 6, to pull the grippers 3, whereby the workpiece 1 is caused to stretch over the former 2. Before stretching, the workpiece 1 has a reference pattern applied to its outer surface, and it is this pattern that is scanned by the scanner 12 as the workpiece 1 is being stretched. As the behaviour of the workpiece 1 is being monitored by the scanner 12 in this way, the microprocessor 6 responds accordingly to control the pullers 4, until the workpiece 1 is eventually stretched into its desired shape of the part to be formed.

It will be appreciated that the illustrated apparatus has been shown to be very simple.

for ease of explanation. In practice, the shape of the former 2 may be much more complex than that shown. and a plurality of pullers 4 may act via grippers 3 to stretch the workpiece 1 in numerous directions.

Various possible features of the invention will now be described in more detail.

Although the workpiece 1 is described as being a blank of sheet metal, it is to be appreciated that it may be a blank of any other suitable ductile material. It may be in sheet, plate, laminate or composite form, and may comprise steel, aluminium, or any other material having sufficient ductility to enable it to be stretch formed. It may be of a plastics material, which may be preformed to a de sires workpiece shape, and then reshaped by the illustrated method. The workpiece could comprise two materials placed together with a bonding agent between them, which are then bonded together as they are stetched by the illustrated method.

It may be appreciated that the workpiece 1 may have an optimum size and shape, depending upon the design of the part to be formed. Thus, the workpiece 1 may be of any geometric shape, and may have any required distribution of thickness. Given the design parameters of the part to be formed, the microprocessor 6 may be adapted to calculate and display optimum parameters for the workpiece 1.

The workpiece 1 may be heated either wholly or locally, before, during and/or after the stretch forming operation. Similarily, it may be wholly or locally or spot-quenched before, during and/or after stretch forming. It may be vibrated, to assist the stretch forming process.

The surface of the workpiece may be coated or treated with chemicals, oils, plastics, etc., before use, to modify the coefficient of friction of the surface and to assist in obtaining the desired shape of the part. The material itself of the workpiece 1 may be treated mechanically, electrically, magnetically, etc., to facilitate the grain forming process. In particular, the molecular structure of the material may be conditioned to facilitate stretching.

The former 2, may be made of any suitable material. By way of example, it may be of steel, aluminium, ferro-concrete, wood, plastic or resin. It may be hollow or solid. It may have a predetermined shape, or may be provided with means whereby the shape of the former may be changed at will (particularly during the stretch forming process). Preferably, means are provided for moving the former (under the control of the microprocessor 6) bodily in 6 degrees of freedom (if required) to achieve the final desired shape of the part being formed.

The former 2 may comprise a base which may be rigid or flexible, and a surface which may be rigid or flexible. Where the former is at least partially flexible, means may be provided for varying the flexibility, under the control of the microprocessor 6. Means may be provided for injecting a controlled amount of fluid through a skin of the former, to assist the stretch forming process.

The outer surface of the former may be coated, impregnated or treated by diffusion, radiation, spraying, etc., to vary the surface coefficient of friction, to assist the stretch forming process.

The former 2 may be heated wholly or locally, and may be vibrated to assist the stretch forming process.

it will be appreciated that the grippers 3 are the means of reacting the load from the former 2 at the perimeter of the workpiece 1, and to this end, they may grip all or part of the perimeter. There may be any desired number of grippers 3, depending upon the particular shape being formed. The grippers 3 may vary their respective gripped areas on the workpiece 1 at any time during the stretch forming process, either individually or collectively. The grippers 3 are preferably movable, each with up to 6 degrees of freedom, under the control of the microprocessor 6. They may employ mechanical, hydraulic, pneumatic, electrical or magnetic forces to grip the workpiece 1, and the actual gripping function may be controlled either automatically or manually.

The grippers may be profiled to adapt to the contours of the workpiece. They may be segmented or curved, or have any other desired shape.

The pullers 4 may comprise any suitable mechanism. However, it is envisaged that a particularly convenient way of providing the pullers 4 is by way of hydraulically powered units controlled by electrically operated valves, under the control of the microprocessor 6. For very delicate stretching operations, pullers 4 with fast response times will be required, and for heavy stretching, high power will be required. The pullers 4 are preferably movable with 6 degrees of freedom.

The scanner 12 may use any suitable system to scan the pattern on the workpiece 1.

For example, it may scan electrically, magnetically or optically, or may use laser measuring techniques. The scanning may be carried out in two or three dimensions. Any other suitable devices for monitoring the behaviour of the workpiece 1 as it is stretched may be employed-for example, strain gauges.

The illustrated apparatus may be self-contained, with its own hydraulic pumps driven by a power source. Alternatively, it may take its hydraulic power from a central pumping station, which feeds a ring main for several similar apparatuses.

The essential function of the microprocessor 6 is to store the desired process parameters for forming a particular part, and then control the various parts of the apparatus to produce the parts. Typically, to make a part for the first time, the apparatus is operated under manual control, to form a test part to a desired specification. It is possible that this might involve more than one attempt, until the desired test part is produced. The sequence of operations of the apparatus necessary to produce the desired test part is then stored in the memory of the microprocessor 6, which can then reproduce the sequence of operations indefinitely, to provide successive identical parts.

However, it is to be appreciated that the microprocessor 6 may provide more sophisticated features. For example, it may store parameters of standard materials, standard shapes, and/or those shapes which are achievable by use of the apparatus. Then, upon inputting to the microprocessor data (such as, for example, a set of three dimensional co-ordinates) defining a required shape, the microprocessor may use the data in its memory to create a sequence of process steps to form the desired part. The microprocessor 6 may provide an indication if the shape of any desired part is not achievable and/or may display the nearest possible achieveable design to a proposed part design.If the initial design of parts is done by CAD (Computer Aided Design) equipment, the microprocessor 6 may be adapted to feed back to the CAD station information as to whether a part design is achieveable, to prevent wasted design effort and time.

Another optional function of the microprocessor 6 is to calculate, from the design of a part, and with reference to known properties of the material of which the part is to be made, an optimum shape of workpiece 1.

The illustrated apparatus may include means for at least partially cutting an aperture in the workpiece 1 before, during or after the stretch forming operation. If made before the end of the stretch forming operation, the initial cuts are so designed as to produce in the final product an aperture of required design dimensions. It will be appreciated that, depending upon when the cutting operation takes place, it may not be necessary to cut through the full thickness of the workpiece 1, and it may be necessary to use cutting tools or a cutting system which may cut through the workpiece 1 to an automatically controlled depth. In particular, it is important that the former 2 is not damaged, and to this end, automatic sensing of the thickness of the workpiece 1 may be employed.The route of the cutter may be controlled by a preformed pattern in the workpiece, or by a buried guide in the former 2.

A programmed or guide-following cutter may also be used to trim the workpiece 1 after it has been formed, in a manner similar to that used for cutting apertures, as mentioned above.

To facilitate the formation of some parts, it may be necessary to roll or iron some areas of the workpiece, and suitable devices such as robotic devices may be employed to this end.

It will be appreciated that robotic devices may be used for cutting operations as mentioned above.

It may thus be appreciated that the illustrated apparatus may be used to form parts from a ductile material in a relatively simpley but reliable manner. In particular, the apparatus may be used to shape parts of sheet metal, involving a capital expenditure on plant which is far below that required for conventional high output metal presses and tools. It is not intended that the illustrated apparatus should replace metal presses as, for high quality and high production items, pressing may still be the best method, at the present time. However, the illustrated apparatus may produce similar and acceptable parts, at much lower cost. It will be appreciated that the illustrated apparatus may be used to produce a variety of different parts in any desired quantity, once the parameters of each desired part are known.Of course, for different parts, it may be necessary to make some changes to the illustrated apparatus, but these changes will involve much less cost than changes involved in sheet metal pressing.

Although the illustrated apparatus is essentially used to stretch form the workpiece 1, it is to be appreciated that, if desired, a dye may be used to mate with the former 1, to effect a pressing operation before, during or after the stretch forming operation. In this arrangement, the former 2 would in effect form part of a dye, whilst pressing is carried out.

In order to provide a decorative and/or protective finish to the part being made, a colour and/or a pattern may be printed or pressed onto the surface of the workpiece 1, to provide after the stretch forming operation a finished part which does not need painting or finishing separately afterwards. A complete materials equivalent of a paint system may be produced during the stretch forming operation to produce a finished part ready for assembly.

It is to be appreciated that, during the stretch forming operation, it may be desired to prevent certain parts of the workpiece 1 undergoing stretching, or further stretching, at any time. To this end, there may be provided clamping means adapted to hold firm any selected area on the workpiece 1 during stretch forming. Such clamping means, in the illustrated example, may be hydraulically powered, or more generally, may be powered in any suitable way. The clamping means would be under the control of the microprcessor 6, and would preferably be movable with up to 6 degrees of freedom.

In one possible arrangement, the former 2 may be disposed within a hemispherical bowl, the internal surface of which provides a mounting for one end of each of the pullers 4, such that the pullers may be moved to any desired point on the internal hemispherical surface, under control of the microprocessor 6. This is to enbç,e that each puller 4 always pulls in a required direction.

It will be appreciated by those skilled in the art that a number of basic stretch forming techniques are known although, to the best of our knowledge, stretch forming in a controlled manner as provided by the present invention is novel. It is envisaged that any known basic techniques for stretch forming may be employed in use for the invention, and by way of example, the readers attention is directed to the publication "Metals Handbook Eighth Edition Volume Four Forming" published by the American Society for Metals (especially pages 239/245 and 392/393).

Claims (27)

1. A method of forming a part from a ductile material comprising the steps of placing a blank of the material on a former, gripping the blank at predetermined points, pulling the blank selectively at said points to stretch the blank over the former, monitoring the behaviour of the material as the blank is stretched, and controlling automatically the pulling of the blank in dependence upon the monitored behaviour of the material, until the blank is sufficiently stretched over the former to form the part.

2. A method according to Claim 1, including the step of at least partially cutting the blank to define the site of an aperture in the formed part.

3. A method according to Claim 1 or 2, including the step of vibrating the blank and/or former during pulling.

4. A method according to Claim 1, 2 or 3, including the step of heating the blank and/or former.

5. A method according to any preceding claim, including the step of treating the surface of the blank and/or former to modify the coefficient of friction thereof.

6. A method according to any preceding claim, including the step of varying the shape of the former.

7. A method according to any preceding claim, including the step of varying the points at which the blank is gripped, and/or varying the magnitude and/or direction of the forces which pull the blank.

8. A method according to any preceding claim, wherein the behaviour of the material is monitored by strain gauges and/or by applying a reference pattern to the blank and scanning the pattern.

9. A method according to any preceding claim, wherein the monitored behaviour of the material is represented by electrical signals, and an electronic processor is arranged to receive said signals and control automatically the pulling of the blank in dependence thereon.

10. A method according to Claim 9, wherein the procesor contains stored parameters representing desired values, and the pulling of the blank is controlled automatically until measured parameters of the monitored behaviour of the material coincide with said stored parameters.

11. A method according to Claim 10. including the preliminary steps of forming a test part by a method which is in accordance with Claim 1 except that the pulling of the blank is not controlled automatically, and, when the test part has been formed to a desired specification, entering its parameters into a memory of the processor as said stored parameters.

12. A method according to Claim 9, 10 or 11, wherein the processor contains stored information on the properties of materials and/or on standard shapes and/or on those shapes which are achievable in use of a method according to Claim 1.

13. A method according to Claim 9, 10. 11 or 12, wherein the processor receives data on the design of a desired part, and calculates and displays a corresponding design that can be made by a method according to Claim 1.

14. A method according to Claim 13, wherein said desired part is an existing part which is scanned by a scanner, and data from the scanner is fed to the processor.

15. A method of forming a part from a ductile material, substantially as described herein.

16. Apparatus for forming a part from a ductile material, comprising: a former the shape of which relates to the shape of the part to be formed; gripping means adapted to grip at least part of the periphery of a blank of ductile material when placed on the former; pulling means adapted to exert a pulling force on the gripping means to stretch the blank over the former; monitoring means adapted to monitor the behaviour of the material as the blank is stretched; and control means adapted to receive an output for the monitoring means and to control automatically the pulling means in dependence thereon until the blank is sufficiently stretched over the former to form the part.

17. Apparatus according to Claim 16, including means for at least partially cutting the blank to define the site of an aperture in the formed part.

18. Apparatus according to Claim 16 or 17, including means for vibrating the blank and/or former.

19. Apparatus according to Claim 16, 17 or 18, including means for heating the blank and/or former.

20. Apparatus according to any one of Claims 16 to 19, wherein the shape of the former is variable.

21. Apparatus according to any one of Claims 16 to 20, wherein said monitoring means comprises strain gauges and/or scanning means.

22. Apparatus according to any one of Claims 16 to 21, wherein said control means comprises an electronic process.

23. Apparatus according to Claim 22, wherein the processor contains stored parameters representing desired values, and is adapted to control the pulling means automatically until the output of the monitoring means coincides with said stored parameters.

24. Apparatus according to Claim 22 or 23, wherein the processor contains stored information on the properties of materials and/or on standard shapes and/or on those shapes which are achievable in use of a method according to Claim 1.

25. Apparatus according to Claim 24, wherein the processor is adapted to receive data on the design of a desired part and to calculate and display a corresponding design that can be made by a method according to Claim 1.

26. Apparatus according to Claim 25, including a scanner for scanning an existing part as said desired part and feeding data thereon to the processor.

27. Apparatus for forming a part from a ductile material, substantially as hereinbefore described.