Super plastic forming apparatus and method

Abstract

A cooling apparatus for a component formed by super plastic forming including a gas source configured to supply a gas to an interior space of the component via a gas inlet, a gas outlet configured to allow the gas to exit the interior space, and a gas column connected to the gas outlet and configured to compensate for changes in an external pressure acting on the component.

Claims

1. A cooling apparatus for a component formed by super plastic forming, the cooling apparatus comprising: a gas source configured to supply a supplied gas to an interior space of the component via a gas inlet; a gas outlet configured to allow the gas to exit the interior space; and a gas column connected to the gas outlet at a connection point, the gas column being configured to compensate for changes in an external pressure acting on the component, wherein the gas column is a substantially vertically aligned structure and at least a portion of gas column is at a greater height than the connection point of the gas column and the gas outlet, wherein a vertical height of the gas column is greater than a width of the gas column, and wherein the gas column is at least partially filled with a column gas.

2. The cooling apparatus as claimed in claim 1, wherein the gas source is configured to supply the supplied gas until the component cools to a stabilisation temperature.

3. The cooling apparatus as claimed in claim 1, wherein the gas inlet is a pipe or tube connected to an inlet hole in the component.

4. The cooling apparatus as claimed in claim 3, wherein the inlet hole is a pre-existing hole adapted to have the supplied gas introduced therethrough during super plastic forming.

5. The cooling apparatus as claimed in claim 1, wherein the column gas at least partially filling the gas column is the same gas as the supplied gas supplied by the gas source.

6. The cooling apparatus as claimed in claim 1, wherein the gas column comprises an opening at an upper portion thereof and the external pressure acts on an upper surface of the column gas in the gas column.

7. The cooling apparatus as claimed in claim 1, wherein the column gas in the gas column has a higher density than air.

8. The cooling apparatus as claimed in claim 1, further comprising a control valve configured to control the exit of the supplied gas or the column gas from the apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

(2) FIG. 1(a) is a cross sectional view of an example super plastic forming process involving two layers;

(3) FIG. 1(b) is a cross sectional view of an example super plastic forming process involving three layers;

(4) FIG. 2 is a schematic view of an example cooling apparatus for a component formed by super plastic forming, and

(5) FIG. 3 shows a flowchart of an exemplary method of cooling a component formed by super plastic forming.

DETAILED DESCRIPTION

(6) FIG. 1(a) illustrates a method of super plastic forming a component 10, showing the materials before and after forming, and the resulting component 10. In FIG. 1(a), the component 10 is formed from two sheets of material: an upper sheet 11a and a lower sheet 11b. In one example, the sheets 11 are formed from titanium. In further examples, the sheets 11 are formed from aluminium.

(7) A plurality of bonding zones 16 are defined on the sheets 11, at which the sheets 11 are to be diffusion bonded together. In one example, the bonding zones 16 are defined by applying a coating 14 to either or both of the sheets 11 in the areas of the sheets 11 which are not to be diffusion bonded. Particularly, the coating 14 is applied to the surfaces of the sheets 11 which are disposed facing each other during the forming process. In other words, the coating is applied to either or both of the lower surface of the upper sheet 11a and the upper surface of the lower sheet 11b. The coating 14 therefore acts as a mask, defining the bonding zones 16. In one example, the coating 14 is applied to the or each sheet 11 using screen printing.

(8) The sheets 11 are heated to the transition temperature of the material using a suitable heating means. For example, the heating means may comprise a platen which is heated using an electrical resistance heating system. When the sheets enter a plastic state which allows them to be easily moulded and formed, as well as allowing them to be diffusion bonded. In examples where the sheets 11 are formed from titanium, the transition temperature is around +925° C. In examples where the sheets 11 are formed from aluminium, the transition temperature is around +495° C.

(9) The heated sheets 11 are then placed in a mould 30 or a die. The mould 30 defines one or more recesses 31, which correspond to the desired shape of the finished product 10. A clamp 20 applies a force at one or more clamping points 21 to secure the heated sheets 11 in the mould.

(10) Once secured within the mould 30, a gas is introduced at high pressure between the sheets 11. The gas is supplied by a suitable gas source. In one example, the gas is an inert gas. In one example, the gas is argon. In one example, the gas is introduced via a small, needle-like tube inserted between the sheets 11. In one example the gas is introduced between the sheets at a pressure of approximately 6 Megapascals (60 bars).

(11) The gas forces apart the sheets 11 in the non-bonded areas (i.e. the areas where the coating 14 has been applied). Accordingly, the sheets 11 effectively inflate within the mould 30, with the gas causing the sheets 11 to conform to the shape of recesses 31 of the mould 30. The resulting component 10 comprises one or more internal spaces or cavities 15 in the non-bonded areas between the sheets 11.

(12) FIG. 1(b) shows a similar method of super plastic forming a component 10. However, in FIG. 1(b), the component 10 is formed from three sheets 11: an upper sheet 11a, a lower sheet 11c, and a middle sheet 11b disposed between the upper sheet 11a and the lower sheet 11c.

(13) In the example shown in FIG. 1(b), bonding zones 16 are defined on the surfaces of the sheets 11 which are disposed facing another one of the sheets 11. In other words, the coating 14 is applied to either or both of the lower surface of the upper sheet 11a and the upper surface of the middle sheet 11b. The coating 14 is also applied to either or both of the lower surface of the middle sheet 11b and the upper surface of the lower sheet 11c.

(14) The sheets 11 are heated and clamped in the mould 30 in a similar way to that described above with reference to FIG. 1(a). Again, the gas is introduced at high-pressure between the sheets 11, and the outer sheets 11a and 11c conform to shape of the mould 30. The gas causes the middle sheet 11b to form internal sectional walls within the component 10, defining a plurality of cavities 15 therebetween.

(15) It will be understood by those skilled in the art that the number of sheets 11, the number and position of the bonding zones 16, and the shape of the mould 30 may be varied according to the desired shape and internal structure of the resulting component.

(16) In one example, the component 10 is formed using a super plastic forming apparatus comprising the heating means, the mould and the gas source.

(17) Once formed, the component 10 is removed from the mould 30 whilst still hot, and then cooled using a cooling apparatus 100, which is described below with reference to FIG. 2. It will be understood that, in further examples, the super plastic forming apparatus comprises the cooling apparatus 100. In such examples, the component 10 may be cooled in the mould 30, rather than after removal from the mould 30.

(18) The cooling apparatus 100 comprises a gas source 110, a gas inlet 111, a gas outlet 112 and a gas column 120.

(19) The gas source 110 is configured to supply a gas to the interior space 15 of the component 10 via the gas inlet 111. In one example, the gas is an inert gas. In one example, the gas is argon. In one example, the gas inlet 111 is a pipe or tube connected to an inlet hole in the component 10. The inlet hole may be the same inlet through which gas was introduced at high-pressure between the sheets 11 during the above-described super plastic forming.

(20) The gas outlet 112 is configured to allow the gas to exit the interior space 15 of the component 10. Accordingly, a stream of gas is passed through the component 10 during cooling. In one example, the stream of gas is supplied until the component has reached the stabilisation temperature. In an example where the component is formed from titanium, the stabilisation temperature is approximately +550° C. The supply of gas prevents air entering the interior space 15 of the component, thereby preventing oxidisation caused by the hot internal surfaces of the component 10 reacting with oxygen in the air.

(21) The supply of the gas to the interior space 15 of the component 10 exerts a pressure on the interior space 15, hereinafter referred to as the internal pressure. At the same time, an external pressure P acts on the outer surfaces of the component. Typically, this external pressure is the ambient atmospheric pressure. It will however be understood that the cooling apparatus may be situated in an environment where the external pressure is not the ambient atmospheric pressure, but is instead a different external pressure is maintained.

(22) It will be understood that the external pressure P varies according to climatic conditions. If the internal pressure and the external pressure P are not equal during cooling, the component 10 may deform or distort.

(23) The gas column 120 is connected to the gas outlet 112, and acts to equalise the internal pressure and external pressure P. The gas column 120 is a substantially vertically aligned structure, having a height h greater than the width of the column. The vertical orientation of the gas column 120 results in gravity acting on the gas contained therein, the weight of the gas thereby providing a pressure in a downward direction.

(24) In one example, the gas column 120 is filled with the same gas which is supplied by the gas source 110. The gas column 120 is open to the atmosphere at an uppermost point 121. The gas contained in the gas column 120 has a higher density than air, and so is not contaminated by the oxygen in the air, and nor does the gas in the column 120 escape. For example, argon gas has a density of approximately 1.6 kg/m.sup.3 compared to air, which has a density of approximately 1.2 kg/m.sup.3.

(25) In one example, the height h of the gas column 120 is calculated to achieve a desired pressure at the base of the column.

(26) In one example, the apparatus 100 also comprises a control valve 130. The control valve 130 is connected to the gas outlet 112, and is configured to control the exit of the gas from the apparatus 100. In one example, the gas column 120 is connected to the outlet 112 at a position between the component 10 and the control valve 130.

(27) In use, the component 10 is connected to the inlet 111 and the outlet 112. The gas source 110 supplies gas to the interior space 15 of the component 10, so that a gas stream is passed through the interior space 15. The gas passes out of the component 10 via the outlet 112, and out of the apparatus via the control valve 130.

(28) In use, any variation in the external pressure P is compensated for by the gas column 120, thereby ensuring that the internal and external pressures remain substantially equal. If the external pressure P reduces, the excess internal pressure is vented from the upper end 112 of the column 120. If, on the other hand, the external pressure P increases, the weight of the gas in gas column 120 acts to increase the internal pressure. Accordingly, the effects of variation in ambient pressure are minimised.

(29) FIG. 3 shows a flowchart of an example method.

(30) The method comprises a first step S301 of supplying a gas to the interior space 15 of the component 10. The method comprises a second step S302 of allowing the gas to exit the interior space 15 via the outlet 112. Accordingly, a stream of the gas is supplied to the interior of the component. The method further comprises a step S303 of compensating for changes in atmospheric (i.e. external) pressure P using a gas column 120 connected to the outlet 112. Accordingly, the internal and external pressures acting on the component remain substantially equal.

(31) The above-described apparatuses and methods provide an advantageous method of cooling a component formed by super plastic forming. Such components, and particularly components having a large surface area compared to the thickness of the material from which they are formed, are susceptible to distortion during cooling caused by a difference in the internal and external pressures acting on the component. The above-described apparatuses and methods provide a simple and cost-effective way of compensating for changes in the external pressure acting on the component, for example due to changes in climactic conditions. Accordingly, the need for expensive, complicated and fragile control systems and valves is obviated.

(32) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(33) All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

(34) Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(35) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.