ALUMINUM FORMING METHOD

Abstract

A method for forming a component to a target shape from an aluminium blank workpiece is disclosed, the method comprising: (a) cold forming an aluminium blank workpiece between a set of dies, thereby producing a component fully or partially formed to a target shape; (b) solution heat treating the fully or partially formed component by heating to or above a solution heat treatment (SHT) temperature and substantially maintaining that temperature until SHT has been completed, thereby producing a solution heat treated fully or partially formed component; and (c) quenching the solution heat treated fully or partially formed component whilst held between a set of dies, wherein holding between the dies may provide additional forming at the same time as quenching, to produce a component fully formed to the target shape.

Claims

1. A method for forming a component to a target shape from an aluminium blank workpiece, the method comprising the steps of: (a) cold forming an aluminium blank workpiece between a set of dies, thereby producing a component fully or partially formed to a target shape; (b) solution heat treating the fully or partially formed component by heating to or above a solution heat treatment (SHT) temperature and substantially maintaining that temperature until SHT has been completed, thereby producing a solution heat treated fully or partially formed component; and (c) quenching the solution heat treated fully or partially formed component whilst held between a set of dies, wherein holding between the dies may provide additional forming at the same time as quenching, to produce a component fully formed to the target shape.

2. The method according to claim 1, wherein: in step (a) the aluminium workpiece is cold formed at a temperature between 0 and 100 degrees centigrade, preferably from 15 to 30 degrees centigrade.

3. The method according to claim 1, wherein: the temperature of the cold forming step (a) is controlled by the set of dies, and/or temperature treatment of the aluminium blank workpiece in a step prior to cold forming in step (a).

4. The method according to claim 1, wherein: the component formed in step (a) is partially formed to the target formed component shape and the partially formed component is fully formed to the target formed component shape during quenching in step (c).

5. The method according to claim 1, wherein: the component formed in step (a) is formed to from 20% to 100% of the target formed component shape.

6. The method according to claim 1, wherein: the set of dies are provided with a grip with one or more protrusions configured to grip the workpiece during forming and thereby control the flow of the workpiece during forming, and wherein one of step (a) and step (c) of the method further comprise using the grip to grip the workpiece during forming.

7. The method according to claim 1, wherein: the set of dies used in step (a) is a first set of dies and the set of dies used in step (c) is a second set of dies, or wherein the set of dies used in step (a) and the set of dies used in step (c) are the same set of dies.

8. (canceled)

9. (canceled)

10. The method according to claim 1, wherein: the aluminium blank workpiece is at least one of fully or partially annealed or is in a T4 or a T6 temper condition state.

11. The method according to claim 1, wherein: the aluminium blank workpiece used is an aluminium alloy.

12. The method according to claim 1, wherein: the aluminium blank workpiece used is a heat-treatable aluminium alloy or a non-heat-treatable aluminium alloy.

13. The method according to claim 1, wherein: the aluminium blank workpiece is one of an AA2XXX, AA6XXX, or AA7XXX series alloy.

14. The method according to claim 1, wherein: the aluminium alloy is an AA5XXX series alloy.

15. The method according to claim 1, wherein: the aluminium blank workpiece used is annealed aluminium alloy sheet and is an AA6082 aluminium alloy in an O condition state.

16. The method according to claim 15, wherein: the solution heat treating step (b) further comprises heating the component formed in step (a) to a temperature within the range from 450 to 600 degrees centigrade.

17. The method according to claim 1, wherein: after step (b) the solution heat treated fully or partially formed component is rapidly transferred to the set of dies in step (c) within from 1 to 20 seconds.

18. The method according to claim 1, wherein: in step (c) the set of dies are maintained at a temperature of between 0 to 250 degrees centigrade.

19. The method according to claim 13, wherein: in step (c) the quenching is carried out to a temperature of below an artificial ageing temperature of the material if the material is a heat-treatable aluminium alloy or to a temperature below a metallurgically stable temperature of the material if the material is a non-heat-treatable aluminium alloy.

20. The method according to claim 1, wherein: in step (c) the quenching is carried out at a rate of from 15 degrees centigrade per second and above to 200 degrees centigrade per second and above.

21. The method according to claim 1, wherein: the method further comprises a step of artificially aging the formed component to obtain improved mechanical properties.

22. The method according to claim 1, further comprising: using a lubricant to lubricate the interface between the set of dies and the workpiece in step (a) and the set of dies and the fully or partially formed component in step (c).

23. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which FIGS. 1a and 1b show a set of dies suitable for use with the invention in a closed and open position, and

[0043] FIG. 2 shows a temperature-time profile of an aluminium alloy workpiece formed in accordance with an example of the invention.

DETAILED DESCRIPTION

[0044] A detailed description of an example method of the first aspect shall now be given in relation to forming a component in a target shape from a blank of a fully annealed aluminium alloy sheet (hereafter referred to as “the workpiece”) in the O condition state, making reference to FIG. 1. The following detailed example describes forming a blank of fully annealed aluminium, however, the method disclosed herein could also be effectively used to form partially annealed aluminium blanks or blanks made from other aluminium alloys.

[0045] The workpiece is initially received by a first die tool. The workpiece may be fed into the first die tool from a roll of annealed aluminium alloy sheet whereby the blank is formed by cutting the sheet to appropriate dimensions upon receipt thereof in the die tool, or may have been pre-cut to desired dimensions.

[0046] The first die tool may be a forming die tool of the conventional type for cold forming such as that shown generally in FIGS. 1a and 1b at item 100. FIGS. 1a and 1b show a forming die tool in the open and closed position respectively, and which comprises corresponding punch plate 102 and cavity (die) plate 104 parts configured to fit together in a male and female relationship respectively so that, when pressed together (as shown in FIG. 1b) with the workpiece 112 therebetween by a press part thereof, a component is formed out of the workpiece 112 to form an intermediate component.

[0047] The die tool comprises one or more grip sets shown generally at items 106, configured to grip the workpiece during the forming process. The grip sets 106 help to control flow of the metal during forming and prevent or at least minimise wrinkling of the workpiece 112 during forming. The grip sets 106 come in two parts 106a and 106b which are positioned around the edges of the plates 102 and 104, and above and below the workpiece 112. When brought together, parts 106a and 106b are configured so that they clamp and grip the workpiece 112. Grip sets 106 may comprise a drawbead set which assist the grip sets 106 in gripping the workpiece 112 during forming. A protrusion part 108 of the drawbead set is configured to protrude from the grip so that when clamping the workpiece (as shown in FIG. 1b) it enters a depression part 110, and catches the workpiece therebetween thereby providing improved grip of the workpiece by forming a tortuous path which holds the workpiece. The intermediate component formed in the first step may or may not be matching in shape to the desired target shape, i.e. the component formed in the first step may be fully or partially formed to the target shape. The first die tool 100 may or may not comprise a liquid cooling system to maintain the temperature of the punch and cavity plate parts to a desired temperature.

[0048] The first step in the method is a cold forming step shown generally at item (1) in FIG. 2, and is carried out under typical cold forming conditions. The cold forming step is carried out at cold forming temperatures, e.g. room temperature (around 20 degrees centigrade). By using O condition annealed aluminium alloy as the work piece, the forming speed is in the range of 1 millimetre per second to 200 millimetres per second. Conventional lubricant of the type suitable for cold forming processes can be used for this cold forming process.

[0049] The intermediate component is removed from the first die tool and, in a second step (shown generally at item (2) of FIG. 2), is heated to at or above the material's SHT (between 450 to 600 degrees centigrade for annealed aluminium alloy) and soaked at that temperature until SHT has been completed and a solution heat treated intermediate component has been formed. Soaking time at temperature for solution treatment depends on the type of alloy and may be determined experimentally using known techniques. There is no specific requirement for the transfer time between removing the intermediate component formed by the first die tool in the first step and heating the intermediate component in the second step.

[0050] Once SHT is completed, in a third step shown generally at item (3) in FIG. 2, the solution heat treated intermediate component is transferred and positioned between closed dies of a second die tool for quenching and a second forming step.

[0051] In this example, the second die tool comprises punch and die plates of the same shape as the first die tool, although they may differ in other embodiments. If the component was fully formed to the target shape in the first cold forming step then there is no additional forming when the dies close around the component, but the closed dies act to prevent any distortion that may occur from the quenching step. If the component was fully formed in the first cold forming step but becomes distorted before the second forming step, e.g. during SHT, then the second forming step may recover the component back to the target shape.

[0052] The solution heat treated intermediate component is transferred to the second die tool as quickly as possible as soon as heating is no longer being applied thereto, e.g. within 1-10 seconds. The forming speed in the third step is in the range of 50 millimetres per second to 500 millimetres per second. The pressure for holding the set of dies is in the range of 1 megapascal to 30 megapascals. The holding time (i.e. the time the workpiece is held between the closed die tool at the required pressure) is in the range of 2 seconds to 15 seconds.

[0053] The temperature of the punch and cavity plate parts of the second die tool are at room temperature when the solution heat treated intermediate component is placed therebetween. Heat energy will transfer to the second die tool from the solution heat treated intermediate component when between the closed second die tool. The second die tool is configured so that the temperature of the parts contacting the intermediate component stays below 150 degrees centigrade. Liquid cooling may be employed by the second die tool to control the temperature thereof. The solution heat treated intermediate component is rapidly cooled as it is held between the closed second die tool, preferably at a rate of over 15 degrees centigrade per second, in order to prevent the formation of coarse phase. In other words, the component being formed inside the second die tool is quenched. Alternatively, the solution heat treated intermediate component may be rapidly cooled after the second step (after SHT and before entering the second die tool). Accurate control of the cooling rate is not necessary so long as it is above 15 degrees centigrade per second. Factors to consider which may affect cooling rate are blank size, blank thickness, holding pressure etc. The second die tool may comprise a grip in accordance with that described above in relation to the grip of the first die tool.

[0054] The particular quenching rate should preferably be selected based on the particular alloy being used and the final mechanical and corrosion requirements of that component. For example, a 2xxx or 7xxx alloys such as 2024 may require fast quenching of >50 degrees centigrade per second or even >200 degrees centigrade per second in order to achieve good corrosion resistance. Alternatively, a less sensitive alloy such as 7020 may be quenched slower to allow lower quench forces or less accurate or simpler tooling to be used. A lubricant may be applied to the first and/or second die tool in order to reduce interface friction between dies and workpiece to improve formability. The lubricant for the first die tool may be any lubricant suitable for use in cold forming processes, and for the second die tool may be any lubricant suitable for use at both the elevated temperatures the workpiece will be at initially when received by the second die tool and the rapid cooling temperatures of the quenching process.

[0055] An additional artificial ageing step (not shown in FIG. 2) may be introduced at the end of the process as a finishing step for heat treatable aluminium alloy components, to enable precipitation hardening and thereby achieve increased hardness and strength.

[0056] The shape of the first and second die tools (i.e. the shape of the punch plate and cavity (die) plate) may be substantially identical to each other or may be different in their shape. Differences in shape may be used to promote partial forming in the first cold forming step, e.g. the shape of the first die tool may be 20-100% towards the shape of the target shape, to produce a partially formed intermediate formed component and the shape of the second die tool may match the target shape (i.e. 100% of the target shape). If the first and second die tools are the same then partial forming in the first forming step may be achieved by varying forming variables such as forming force and time. The second die tool may be shaped to “over form” the solution heat treated intermediate formed component to account for any distortion effects expected to occur after forming. In this way, it is possible to use the same die tool or different die tools to produce an intermediate formed component which is 20-100% towards the shape of the target shape for the formed component in the first (cold) forming step, and to achieve a formed component which is 100% of the target shape for the formed component in the second forming step. The way in which the degree of shaping (the percentage towards the target shape) in the first and/or second die tools is determined is not limited, but may include measuring dimensions, e.g. using a 3D scanner, and then comparing the measured values with the corresponding values of the target shape.

[0057] The method disclosed herein is a notable departure from the conventional methods of forming aluminium alloy. Those skilled in the art will appreciate that the presently disclosed method teaches by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawing should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of scope of the method, which, as a matter of language, might be said to fall there between.