GB2263081A

GB2263081A - Superplastic forming of sandwich panel

Info

Publication number: GB2263081A
Application number: GB9226451A
Authority: GB
Inventors: Takayuki Tsuzuku
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1992-01-10
Filing date: 1992-12-18
Publication date: 1993-07-14
Anticipated expiration: 2012-12-18
Also published as: GB2263081B; JPH05185169A; GB9226451D0

Abstract

A method for making a metallic sandwich panel, in which the cost of the forming dies is reduced relative to prior art methods, machining to adjust the sheet thickness of the face sheets after shaping is avoided, freedom in the design of the panel is made possible, and panels having smooth outer surfaces can be produced. According to the invention, a work piece (6) is formed by disposing a core sheet (1) between face sheets (2) and bonding the sheet (1) with the sheet (2) in a zig-zag pattern. Dummy sheets (4) are superposed on the outside of the face sheets (2), a fluid pressure is applied between the sheets (1 and 2) of the work piece (6) to shape the latter jointly with the dummy sheets (4), which sheets are effective to increase the deformation resistance and are removed after shaping. The dummy sheets serving to prevent creases or recesses in the facing sheets (2) during superplastic deformation. <IMAGE>

Description

METHOD FOR MAKING METALLIC SANDWICH PANELS BACKGROUND OF THE INVENTION: 1. Field of the Invention: The present invention relates to a method for making a metallic sandwich panel which is required to have a light weight and a high mechanical strength.

2. Description of the Prior Art: A method of making a metallic sandwich panel of the so-called precursor bonding type, in which a sandwich panel was shaped after face sheets and a core sheet interposed therebetween were bonded at necessary locations, and utilizing superplasticity, was such that after a core sheet 01 and face sheets 02 were bonded, an upper die 7 and a lower die 8 were disposed, and shaping was effected by applying a fluid pressure P to the spaces between the core sheet 01 and face sheets 02 as shown in Fig. 2.

The fluid pressure P for superplastically shaping the above-mentioned core sheet acts a similar force also to the face sheets 02, hence deformation would arise also in the face sheets 02, and at the time of finishment of shaping when the face sheets 02 come into tight contact with the dies 7 and 8, in some cases creases or recesses 03 would be produced in the face sheets 02 due to surplus expansion of the face sheets 02.

In order to prevent creases and recesses 03 produced in these face sheets 02, heretofore, a die slide system, a sheet thickness control system and a material (deformation resistance) control system as will be described in the following have been investigated.

The die slide system is such system that in order to cause only a core sheet 01 to be shaped while face sheets 02 are kept in tight contact with upper and lower dies, the upper die 7a and the lower die 8a continue to slide at a predetermined speed until a sandwich panel being shaped attains a final shape as shown in Fig. 3.

In Fig. 2, a cross-section view during shaping is shown at (a), and a perspective view after completion of shaping is shown at (b).

The sheet thickness control system is such system that by selecting a sheet thickness of the face sheets 02 thick as compared to the core sheet 01, the deformation resistance of the face sheets is made relatively large, and thereby only the core sheet 01 is made to deform.

In addition, the material property (deformation resistance) control system is such system that by employing face sheets 02 having a large deformation resistance at a predetermined shaping temperature as compared to that of the core sheet 01, deformation of the face sheets 02 when the core sheet 01 is superplastically shaped, is prevented.

In the method of making a metallic sandwich panel of precursor bonding type and utilizing superplasticity, the above-mentioned three systems all have an effect of preventing creases and recesses produced in the face sheets.

However, at the same time they have the following shortcomings respectively, and they involved the problems that in order to prevent creases and recesses, a freedom in design relating to a combination of a panel configuration, a core/face sheet-thickness-ratio, material property and metallurgical structures of the core and face sheets and the like, and further a resultant panel performance had to be sacrificed.

(1) In the die slide system, restriction to applicable panel configurations is large, also a die structure apparatus is complicated and is extremely high in cost.

(2) In the sheet thickness control system, restriction to a core/face sheet-thickness-ratio is large, and in most cases, after shaping, machining to adjust the sheet thickness (thinning by machining) is necessary.

(3) In the material property (deformation resistance) control system, restriction to a combination of material property and metallurgical structures of a core sheet and face sheets is large, and in many cases, selection of material property (metallurgical structure) matched to requirements for a performance of a panel would become impossible.

SUMMARY OF THE INVENTION: It is therefore one object of the present invention to provide a method for making a metallic sandwich panel of precursor bonding type and utilizing superplasticity, which is free from the problems as observed in the above-described systems which have been heretofore investigated.

Another object of the present invention is to provide a method for making a metallic sandwich panel of precursor bonding type and utilizing superplasticity, which can manufacture a metallic sandwich panel without being subjected to any restriction to material properties, metallurgical structures and sheet thicknesses of a core sheet and face sheets.

Still another object of the present invention is to provide a method for making a metallic sandwich panel at a low cost without sacrificing a panel performance.

A method for making a metallic sandwich panel according to the present invention is characterized by the steps of disposing a core sheet between face sheets, bonding the sheets in a zig-zag pattern to form a work piece, superposing dummy sheets on the outside of the face sheets, thereafter disposing dies on the outside of the work piece, applying a fluid pressure to shape the work piece jointly with the dummy sheets, and removing the above-mentioned dies and dummy sheets after completion of shaping.

In the above-mentioned method according to the present invention, owing to the fact that dummy sheets are superposed on the outside of the face sheets at the time of shaping a work piece by applying a fluid pressure between the sheets, the effect of increasing the deformation resistance against a fluid pressure is revealed by the dummy sheets rather than the face sheets themselves as is the case with the method in the prior art.

Consequently, protruding deformation of the face sheets would be reduced, a sufficiently small curvature can be maintained, and even at the time of finishment of shaping, surplus expansion of the face sheets would not be produced.

From the above-mentioned reasons, according to the present invention, a die structure and an apparatus are simple and cheap, machining for a thickness of face sheets after shaping is unnecessary, furthermore there is no restriction to a combination of material properties, metallurgical structures and thicknesses of face sheets and a core sheet, hence a freedom in design of a panel is greatly improved, and a method for making a metallic sandwich panel having smooth outer surfaces, which are effective not only for appearance but also for improvements in a structural performance, can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 shows one preferred embodiment of the present invention, Fig. l(a) being a schematic crosssection view of a work piece under the state where face sheets and a core sheet have been bonded in a zig-zag pattern and additionally dummy sheets have been superposed on the outside of the face sheets, Fig. l(b) being a schematic cross-section view of a work piece during superplastic shaping (in a right half portion), which also shows, as a contrast, a work piece not including dummy sheets during superplastic shaping in a left half portion, and Fig. l(c) being a schematic perspective view of a work piece showing the state where a metallic sandwich panel has been superplastically shaped and completed according to the present invention; ; Fig. 2 shows a heretofore known method for making a metallic sandwich panel, Fig. 2(a) being a schematic cross-section view of a work piece during superplastic shaping, and Fig. 2(b) being a schematic perspective view of a metallic sandwich panel manufactured through the heretofore known method; and Fig. 3 is a schematic cross-section view showing a work piece during a shaping process (a left half portion) and after finishment of shaping (a right half portion) in the die slide system for making a metallic sandwich panel in the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT: Now one preferred embodiment of the present invention will be described with reference to Fig. 1.

The preferred embodiment shown in Figs. l(a), l(b) and l(c) is the case where a 3-sheet type sandwich panel formed by providing face sheets 2 on the both surfaces of a core sheet 1 is manufactured, and the core sheet 1 and the face sheets 2 are both made of Ti-6AQ-4V alloy having a sheet thickness of 1.0 mm.The face sheets 2 are disposed on the both surfaces of the above-mentioned core sheet 1, the core sheet and the face sheets 2 are bonded at predetermined bonding portions 5 to form a work piece 6, then after dummy sheets 4 made of Ti-6AQ-4V alloy having a sheet thickness of 2.0 mm have been superposed on the both surfaces of the same work piece 6 as shown in Fig. l(a), an upper die 7 and a lower die 8 are disposed above and under the work piece 6 and the spaces between the core sheet 1 and the face sheets 2 are pressurized by a gas pressure P as shown in the right side portion of Fig. l(b), and after the dummy sheets 4 have been brought into tight contact with the upper die 7 and the lower die 8, the upper die 7, the lower die 8 and the dummy sheets 4 are removed.Then a superplastically shaped panel as shown in Fig. l(c) can be obtained.

It is to be noted that in order to make it possible to compare the shapes of the face sheets 2 and the core sheet 1 during superplastic shaping between the case where the dummy sheets are present and the case where the dummy sheets are not present, Fig. l(b) shows these two cases in the right side portion and in the left side portion, respectively.

In the above-described preferred embodiment, if the bonding portions 5 between the face sheets 2 and the core sheet 1 are assumed to have a diameter of 10 mm and a pitch of 56 mm, then a gas pressure P necessitated for shaping the core sheet 1 at a rate of strain of about E =2 x 1O sec 1 is about P = 0.01 kgf/mm2.

An amount of deflection of the face sheet 2 at the position between the bonding portions of the face sheets 2 and the core sheet 1 caused by this shaping pressure, is about 2.7 mm in the case where the dummy sheets 4 are not superposed, but it is about 0.9 mm in the case where the dummy sheets 4 are superposed, and if the amount is converted to an elongation of the face sheet 2, the elongation is about 1% in the former case, but it is about 0.1% in the latter case.

In the case where the dummy sheets 4 are superposed, owing to the fact that the face sheets 2 would almost not deform during superplastic shaping as described above, even at the time of finishment of shaping, creases and recesses caused by surplus expansion of the panel surfaces would not be produced as shown in Fig. l(c), and so, a metallic sandwich panel having smooth surfaces can be manufactured.

While the face sheets 2, core sheet 1 and dummy sheets 4 all employed Ti-6AQ-4V alloy as their material and the sheet thickness was chosen to be 1 mm for the face sheets 2 and core sheet 1 and to be 2 mm for the dummy sheets 4 in the above-described preferred embodiment, the material and the sheet thickness could be chosen arbitrarily, and for instance, if Ti-6A#-2Sn-4Zr-2Mo alloy which has a further large hardness at the superplastic temperature of the Ti-6A#-4V alloy, is employed for the dummy sheets 4, it is possible to reduce the sheet thickness of the dummy sheets 4.

While the prevention of generation of creases and recesses through the previously-described method known in the prior art was effected by making the face sheets themselves have an effect of increasing the deformation resistance, in this preferred embodiment it was conceived that the effect of increasing the deformation resistance of the face sheets 2 is made to be possessed not by the face sheets 2 themselves but by the dummy sheets 4 superposed on the face sheets 2.

In other words, by superposing dummy sheets 4 having a large thickness or a high hardness on the both surfaces or one surface of the work piece 6 (a laminated body of a face sheet 2, one or more core sheets 1 and a face sheet 2) and superplastically shaping the dummy sheets 4 jointly with the work piece 6, the dummy sheets 4 act to reduce protruded deformation of the face sheets 2 and to maintain a sufficiently small curvature.

Consequently, even at the time of finishment of shaping, surplus expansion of the face sheets 2 would not be produced, and a metallic sandwich panel having smooth outer surfaces which are free from creases and recesses, can be formed.

Through the above-described method, it has become possible to manufacture a metallic sandwich panel having smooth outer surfaces which are effective not only to improve an outer appearance but also to improve a structural performance such as a rigidity against out-ofsurface bending or the like, in which a die structure and an apparatus for manufacture are simple and cheap, machining to adjust the thickness of tre face sheets after shaping is unnecessary, furthemore there is no restriction is no restration to a combination of materials, metallurgical structures and sheet thicknesses of face sheets an a core sheet, a freedom in design of a tane is greatly imprved, and deformation of the face sheets at the ime of superplastic shaping is prevented.

while the present invention as been described in detail above or the basis o one preferred embodiment of the invention, it is a matter of corpse that the present inventIon should not be limited to the illustrated embodiment.

Claims

1. A method for making a metallic sandwich panel consisting of the steps of disposing a core sheet between face sheets, bonding them in a zig-zag pattern to form a work piece, superposing a dummy sheet on the outside of each face sheet, thereafter disposing dies on the outside of said work piece, shaping said work piece jointly with the dummy sheets by applying a fluid pressure between the sheets of the work piece, and removing said dies and said dummy sheets after completion of shaping.

2. A method for making a metallic sandwich panel according to Claim 1, wherein each said dummy sheet has a greater thickness that said face sheet.

3. A method for making a metallic sandwich panel according to Claim 1 or 2, wherein each said dummy sheet is made of material having a larger deformation resistance than said face sheet.

4. A method for making a metallic sandwich panel substantially as hereinbefore described with reference to Figs. 1 (a) to (c) of the accompanying drawings.

5. A metallic sandwich panel made by a method according to any preceding claim.