GB2298605A - Forming and aluminium alloy component - Google Patents

Description

FORMING AN ALUMINIUM ALLOY COMPONENT This invention relates to forming aluminium alloy components and in particular to forming such components from metal blanks using a fluid cell press.

It is known to use a fluid cell press in which fluid pressure of the order of hundreds of bar is applied to a rubber diaphragm to form a metal blank to the shape of a tool or former against which the metal blank is formed by the fluid pressure. In this process the sheet metal blank is placed over the former which is itself positioned in a tray which comprises a shallow bath-like receptacle for receiving the diaphragm under pressure. In use the tray is positioned under the diaphragm which is then rapidly pressurised from above to the required forming pressure using hydraulic fluid.

The diaphragm is then caused to expand downwardly into the tray and to apply forming pressure to the metal blank positioned over the former. The metal blank is thus caused to take up closely the shape of the former. The process is fairly rapid, and after holding the forming pressure for, usually, a matter of seconds the pressure is rapidly released and the tray withdrawn from beneath the diaphragm. The formed part may then be removed from the former.

Often a rubber overlay will be interposed between the diaphragm and the blank or blanks to be formed in order to protect the material of the diaphragm. This overlay can also increase the wiping action of the metal blank over the former during forming. Sometimes in addition further individual rubber overlays will be positioned over metal blanks and their formers further to protect the diaphragm and/or to increase the wiping action against the blank during forming.

It is well known to use such fluid cell forming techniques to form mild steel sheet into articles such as vehicle door panels. It is also known to form aluminium alloy articles using this method.

Sometimes trimming of excess material from the metal blank can be achieved during forming by creating hardened trimming edges on the former against which the blank will be pressed by the forming pressure when a shearing action will cause trimming of the material to take place.

It is further known to use such a fluid cell forming press during the manufacture of a domed aluminium alloy sheet component according to the following method. A sheet metal blank is shaped using a router. The blank is then degreased and superannealed and then draw formed against a male forming button in a two-staged forming operation. The semi-formed part is then degreased, waste is trimmed off and the edges are dressed. The dome, as formed, is then hand dressed to remove wrinkling. The part formed article is then pressed for the first time in a fluid cell forming press. The resultant still part formed article is then solution heat treated and subjected to a final fluid cell forming step. Excess waste is then trimmed off by spindling and the formed article is deburred ready for welding to another part along the deburred edges.

It is an object of the invention to provide a forming process for an aluminium alloy component which is reliable and simpler and cheaper to carry out.

According to one aspect of the invention there is provided a method of forming an aluminium alloy component from a metal blank including the steps of solution heat treating a said metal blank; placing the solution heat treated metal blank on a fluid cell forming press having a forming button and at least one metal trimming edge incorporated thereon, and applying forming pressure to the metal blank in an amount sufficient to form the blank to the shape of the forming button and simultaneously to trim at least one edge of the metal blank against the trimming edge.

It has been found, contrary to expectation, that to solution heat treat the metal blank prior to the forming step provides a metal blank of aluminium alloy which shears effectively against the trimming edge whilst still being formable against the forming button in the required manner.

The forming button may be male and may be formed with a double curvature surface.

The trimming edge of the forming button may extend substantially all around the forming button.

The aluminium alloy component may be formed with a component width to depth ratio generally in the region of two to one.

The trimming edge of the forming button may be formed with an overhang of between 8mm and 12mm. This overhand has been found particularly suitable for metal blanks of thickness in the range 1.2mm to 2.5mm.

The trimming edge of the forming button may define one edge of a recess for receiving trimmed off material from the metal component in which the recess may extend for a distance of between 15mm and 20mum from the trimming edge.

The method may conveniently include the step of providing at least one trimming edge for trimming scrap material into more than one piece. This may facilitate removal of the scrap material from a tool of which the forming button forms part.

The method may include the step of providing a draw dam for supporting edges of the metal blank prior to and during the forming operation. Such a draw dam has been found to be particularly beneficial for forming relatively deep components and in particular for forming components where trimming takes place during forming.

The draw dam may be shaped to conform generally to an outline of the finished component. In this way the metal blank will be formed over a forming button at approximately the same rate as it is pressed downwardly over the draw dam by the forming pressure. The resulting frictional force between the metal blank and the draw dam thus helps in stretching the metal over the button during forming.

The method may include the step of positioning an additional rubber overlay over the metal blank prior to forming, the overlay having a profile substantially matching in form that of the metal blank. In practice this step has been found to help the wiping action as previously described.

The rubber overlay may be formed of material, for example polyurethane, having Shore hardness of substantially 50D and may be of thickness substantially loom.

For particularly deep components positioning of a second individual rubber overlay or a second layer of a single composite overlay over the metal blank may be found advantageous. This second overlay or second layer of composite overlay may be of commercial grade rubber which may be of Shore hardness substantially 60A and may be of thickness substantially 20mm.

The forming pressure may be set at between 700 bar and 850 bar for application to a said metal blank of thickness in the range 1.2mm to 1.6mum, and more preferably the forming pressure may be between 725 bar and 825 bar, most preferably substantially 750 bar.

For a said metal blank of thickness in the range 1.6mm to 2.5mm a forming pressure of between 850 bar and 950 bar may be applied, more preferably substantially 900 bar.

For certain components a further forming step on the fluid cell press may be found advantageous. This further forming step may take place on an rover bendw forming button or may take place on a dead form forming button which may be manufactured of laminated wood, for example, hydulignum. It has been found that re forming the component on such a wooden forming button of dead size is just as effective as carrying out the step on an over bend button.

According to a second aspect of the invention there is provided an aluminium alloy component formed according to a method including the steps of solution heat treating a metal blank; placing the solution heat treated metal blank on a fluid cell forming press having a forming button and at least one metal trimming edge incorporated thereon, and applying forming pressure to the metal blank in an amount sufficient to form the blank to the shape of the forming button and simultaneously to trim at least one edge of the metal blank against the trimming edge.

The invention will now be described by way of example with reference to the accompanying drawings of which: figure 1 is a vertical section taken lengthwise through a fluid cell forming press with a tool and blank assembly shown in position ready for forming.

figure 2 is a plan view of a tray for a fluid cell forming press similar to that shown in figure 1 with a tool and blank assembly in position for forming.

figure 3 is a sectioned side perspective view of a forming button and draw dam according to the invention, figure 4 is a plan view of the forming button and draw dam of figure 3, figure 5 is a vertical end section of the forming button and draw dam of figure 3 with a metal blank in position ready for forming, figure 6 shows the section of figure 5 with the metal blank shown partially and fully formed, figure 7 is a three-quarter perspective view of an aluminium alloy component formed on the forming button of figure 3, and figure 8 is a diagrammatic representation of a cutting edge according to the invention.

Referring to the drawings, figure 1 is a typical arrangement of a fluid cell forming press 1 having an aluminium alloy metal blank 2 positioned on a draw dam 3 of a tool assembly 4 ready for forming. The press 1 has two trays 5, 42, for shuttle movement, in which the tool assembly 4 can be placed for forming. The press also has a pair of reels 43, 44 for receiving rubber overlays or "tray pads" 45, 15, respectively during the shuttle movement. The tray pads are unrolled over a tray 42 or 5 as the tray is slid between press plates 11, 39 for forming. The tray 5 has a flat base 6 and sloping sides 7 into which a diaphragm 8 is extended during forming. Beneath the tray 5 is the fixed lower press plate 39.

The diaphragm 8 is held between side members 9 which are sealed to edges 10 of the diaphragm. Above the diaphragm is fluid compressing means including the upper press plate 11 capable of pressurising hydraulic fluid to 1000 bar or more.

Pressurised fluid is fed into a shallow chamber 12 above the diaphragm 8. The fluid exerts a powerful downward pressure on the diaphragm which is consequently stretched downwardly over the metal blank 2 during forming.

Shown positioned on top of the metal blank are first and second rubber overlays 13, 14, and between the diaphragm 8 and the rubber overlay 14 is the "tray pad 15. This is approximately 25mm thick. The rubber overlay 14 is commercial grade rubber of 20mm thickness having a Shore hardness of 60A.

The polyurethane rubber overlay 13 is 10mm thick and has a Shore hardness of 50D. The purpose of the rubber overlays is firstly to protect the diaphragm 8 from splitting during forming, for example against rough or sharp edges; the second purpose is to assist in the wiping action of the forming of the metal blank.

Rubber overlays 13, 14 are optional with the overlay 13 in particular only being applied for deeper components and where simultaneous forming and trimming of the component takes place.

The rubber overlays 13, 14 have profiles substantially matching in form that of the metal blank 2 although being a little larger than same.

During the forming operation the diaphragm 8 is rapidly pressurised by the hydraulic fluid above it to a pre-set pressure of 750 bar. The diaphragm is thus forced downwards into contact with the metal blank 2 which is then formed to the shape of a forming button 16 (see figure 3). Hydraulic pressure above the diaphragm is then rapidly released and the diaphragm returns to its unstretched position shown in figures 1 and 2. The tray may then be withdrawn from underneath the diaphragm and the finished components removed.

Referring now to figures 3 to 7, the aluminium forming button 16 is shown positioned between two sides 17, 18 of the draw dam 3. The sides 17, 18 are tapered on their inner surfaces and extend to a position approximately lcm above the highest point 19 of the button 16. The sides 17, 18 generally follow the contour of the forming button 16 and are generally equi-distant from the forming button along their length. In this way a generally constant frictional force will be applied to edges 20, 21 of the blank 2 during deformation. The button 16 has end supports 40, 41 which define recesses 42, 43 between themselves and trimming edges 25, 26 respectively of the button.

The forming button 16 shown is for one half of an aircraft track can for fitting within the wing. It has a generally curved cross-section with a flattened area 22.

Along each lower edge of the button is a trimming edge 23, 24. Also at each end is a trimming edge 25, 26. In addition further trimming edges 27, 28, 29, 30 are provided for trimming the scrap.

The trimming edges 23, 24 each form one edge of a recess 31, 32 for receiving trimmed off material or scrap from the metal component. Referring to figure 8, the recess extends for a distance of 20mm from the trimming edge. The trimming edges 23, 24 have an overhang of 10mm. These dimensions have been found to be quite critical in the efficient trimming of scrap material from the component.

Similarly, trimming edges 25 to 30 are formed with overhangs and recesses of very similar dimensions to those described above.

Figure 7 shows a finished component 33 which includes four robot welding lead-in tags 34. The component 33 is to be robot welded along the lines 35, 36 to a similar component to form a generally cylindrical track can. The weld lines 35, 36 have been found to be of sufficient quality to allow robot welding without any further finishing operations being necessary.

Trimmed off scrap 37, 38 is shown in figure 6. This can simply be removed by hand from the tool.

In use, as best illustrated in figures 5 and 6, a metal blank 2 is positioned on the draw dam 3 of the tool, rubber overlays 13, 14 are positioned on top of the blank and the tray 5 is then slid between the upper and lower press plates of the press during which the rubber tray pad 15 is automatically positioned over the tray. When the tray is in position under the diaphragm 8 between the press plates hydraulic fluid is pumped into the chamber 12 above the diaphragm which distends the diaphragm downwardly into the tray and against the rubber overlay 14. Continued hydraulic pressure presses on the metal blank 2 (in figure 5) which is then deformed downwardly over the forming button 16 to the intermediate position shown in figure 6. Deformation continues with the blank 2 being further deformed around the button 16 until shearing takes place at all the trimming edges 23-30 whereby the finished component 33 is formed and scrap material is trimmed off and left lying in the tool, as shown by the dotted lines in figure 6. Finished component 33 is then simply lifted off the button and may be ready for welding or, as in this case, is ready for a final finish forming step on a hydulignum wooden button of dead size in the fluid cell forming press.

It has been found that lubrication of the trimming edges 23 to 30 with caster oil gives a cleaner cut edge to the component. The trimming edges are the only parts of the button to which caster oil is applied.

Claims (16)

1. A method of forming an aluminium alloy component from a metal blank including the steps of: solution heat treating a said metal blank; placing the solution heat treated metal blank on a fluid cell forming press having a forming button and at least one metal trimming edge incorporated thereon, and applying forming pressure to the metal blank in an amount sufficient to form the blank to the shape of the forming button and simultaneously to trim at least one edge of the metal blank against the trimming edge.

2. A method as in claim 1 including the step of providing the forming button with a double curvature surface.

3. A method as in claim 1 or 2 including the step of providing a said metal trimming edge on the forming button which extends substantially all around the forming button.

4. A method as in claim 1, 2 or 3 in which the aluminium alloy component is formed with a width to depth ratio of substantially 2:1.

5. A method as in any preceding claim including forming the trimming edge of the forming button with an overhang of between 8mm and 12mm.

6. A method as in any preceding claim in which the trimming edge of the forming button forms one edge of a recess for receiving trimmed off material from the metal component and in which the recess extends for a distance between 15mm and 20mm from the trimmed edge.

7. A method as in any preceding claim including the step of providing at least one trimming edge for trimming scrap material into more than one piece.

8. A method as in any preceding claim including the step of providing a draw dam for supporting edges of the metal blank prior to and during the forming operation.

9. A method as in claim 8 including shaping the draw dam generally to confirm to the outline of the finished component.

10. A method as in any preceding claim including the step of positioning an additional rubber overlay over the metal blank prior to forming, the additional rubber overlay having a profile substantially matching in form that of the metal blank.

11. A method as in any preceding claim including the step of applying a forming pressure of between 700 bar and 850 bar to a said metal blank of thickness in the range 1.2mm to 1.4mm.

12. A method as in any of claims 1 to 10 including the step of applying a forming pressure of between 850 bar and 950 bar to a said metal blank of thickness in the range 1.6mm to 2.5mm.

13. A method as in any preceding claim including the further step of re-forming the aluminium alloy component on a wooden forming button of dead size.

14. An aluminium alloy component when formed according to a method including the steps of solution heat treating a metal blank; placing the solution heat treated metal blank on a fluid cell forming press having a forming button and at least one metal trimming edge incorporated thereon, and applying forming pressure to the metal blank in an amount sufficient to form the blank to the shape of the forming button and simultaneously to trim at least one edge of the metal blank against the trimming edge.

15. A method of forming an aluminium alloy component substantially as herein described.

16. An aluminium alloy component substantially as herein described with reference to the accompanying drawings.