GB1564898A

GB1564898A - Shaping ductile sheet metal

Info

Publication number: GB1564898A
Application number: GB4681875A
Authority: GB
Original assignee: TI Superform Ltd
Current assignee: TI Superform Ltd
Priority date: 1976-10-28
Filing date: 1976-10-28
Publication date: 1980-04-16

Description

(54) SHAPING DUCTILE SHEET METAL (71) We, T.I. SUPERFORM LIMITED, formerly known as Superform Metals Limited, a British Company, of P.O. Box 150, Worcester, WRS 8PY, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement : This invention relates to the shaping of ductile sheet materials by the use of fluid pressure difference. The most widely known shaping or forming methods of this class are the vacuum-forming and blowmoulding of plastics but it is also known to form ductile metals in a similar way, by the use of gas pressure, in particular those having, under the right conditions, a very high ductility and commonly known as superplastic alloys.

The use of a fluid pressure difference (usually it is air that is used) is dependent on the sheet material in question being imperforate. However, where openings are required in the finished body it is difficult to form these openings cleanly after shaping, especially where the body is very thinwalled.

According to the invention a method of forming a shaped body from a sheet of superplastic metal is proposed comprising first forming one or more openings in the sheet of metal, backing this perforated sheet with an imperforate sheet of material, raising the temperature of the perforated sheet until it is in a superplastic condition, and shaping the pair of adjacent sheets together by the use of a fluid pressure difference, the imperforate backing sheet being on that side of the pair of sheets which is exposed to the higher pressure.

Where the backing sheet is of a cheap material it can be thrown away after use.

To match the movement of the superplastic metal it must, generally speaking, have closely similar mechanical properties and it is not too difficult to find a suitable cheap material where the superplastic metal is a zinc-based alloy.

However, especially where the superplastic metal is an aluminium-based alloy it may be difficult to find a different and cheaper material for the backing sheet and if necessary one could use a sheet of the same alloy, but imperforate, as the backing sheet. It is wasteful to scrap this every time and so, according to a further aspect of the invention, we propose a method of forming a shaped body from a sheet of superplastic metal, together with a further shaped body from a further sheet of ductile material, comprising first forming one or more openings in the sheet of metal, hack- ing this perforated sheet with an imperforate sheet of ductile imperforate material, raising the temperature of the perforated sheet until it is in a superplastic condition, shaping the pair of adjacent sheets together by the use of a fluid pressure difference, into a first shaped die to form the first-mentioned shaped body from the perforated sheet, the imperforate backing sheet being on that side of the pair of sheets which is exposed to the higher pressure, and then reversing the pressure difference so as to force the imperforate sheet away from the first die, through its starting position, and into a second shaped die to form the said second shaped body, whilst leaving the perforated sheet in the first die.

Thus the backing sheet necessary for use in forming the first body is not wasted as it later forms a further body. In fact both dies may be present throughout the operation, both sheets being clamped together at their peripheries throughout the operation.

Alternatively, after the second operation the imperforate sheet may be removed and transferred to a separate die for forming into a body of the required shape. Indeed there may be situations where two classes of bodies of identical shape are required, one with openings and one without, in which case they can both be made simultaneously in the first step and the second step is not required.

Generally speaking, the shape of body to be made in the second step, that is to say from the imperforate sheet, should be of deeper form that the first body, as the sheet can be stretched further by pressure, but not contracted.

In a further development one may start with a sandwich of one imperforate sheet between two sheets having openings. According to this aspect of the invention a method of forming first and second shaped bodies, each having one or more openings in it, from respective sheets of superplastic metal comprises first forming one or more openings in each sheet, sandwiching between the two sheets a sheet of imperforate ductile material, raising the temperature of the perforated sheets until they are in a superplastic condition, shaping the sandwiched sheets, by the use of a fluid pressure difference into a first shaped die to form the firstmentioned body from one of the perforated sheets, then reversing the pressure difference so that the imperforate sheet and the second perforated sheet are forced away from the first die, through their starting position into a second shaped die to form the said second shaped body from the second perforated sheet.

Some embodiments of the invention will now be further described by way of example with reference to the accompanying drawings, in which.

Figures 1 and 2 show diagrammatically two stages in the formation of a shaped perforated body according to the invention; Figures 3 and 4 show diagrammatically successive stages in the formation of shaped bodies according to the invention with a slight modification; and Figures 5 to 7 show diagrammatically successive stages in the formation of two shaped perforated bodies according to a further modification of the invention.

Referring to Figure 1, a perforated sheet 1 and a backing sheet 2 which is imperforate are clamped together at their peripheries between the apertured clamping plates 3, 4. Secured to the plates 3, 4 are two pot shaped housings 5, 6 defining closed cavities on opposite sides of the sheets 1, 2.

Starting from the position shown in Figure 1, a pressure differential is applied across the sheets 1, 2 by the introduction of a fluid (preferably air) at above atmospheric pressure into the housing 6. The pressure differential forces the sheets 1, 2 to deform into a generally hemispherical shape as shown in Figure 2.

The shaped perforated body formed from the sheet 1 can now be separated from the backing sheet 2, which may subsequently be formed into a further shaoed body of the same or a different shape by the appli cation of further pressure.

Figures 3 and 4 show a method by which both the perforated sheet and the backing sheet may be formed into shaped bodies in a two step operation. In these figures corresponding references have been used for parts corresponding to these in Figures 1 and 2.

A pressure differential is first applied in the direction shown by the arrows in Figure 3 to force both sheets into a first die 7, with the perforated sheet 1 in intimate contact with the die. The pressure differential is then reversed, for example, by exhausting the housing 6. The imperforate backing sheet 2 moves back, due to the decrease in pressure, through its initial position and is inverted to come into contact with a second die 8 which has been brought up behind it as shown in Figure 4.

The perforated sheet 1 remains in the first die 7 during this operation.

The dies 7 and 8 may be of any required shape. The shape of the body to be made from the imperforate sheet should be of deeper form than the first body so that the sheet is stretched further by the pressure.

Figures 5 to 7 show successive stages in a two step operation for forming two bodies of the same or different shapes from perforated sheets. In these figures the same references have been used for parts corresponding to those in the previous examples.

A sandwich of one imperforate sheet 9 between two sheets 10, 11 having openings is clamped at its peripheral edge as in the previous examples. Air at above atmospheric pressure is introduced into the housing 6 and the imperforate sheet 9 together with the perforated sheet 10 is forced into a first die 7, as shown in Figure 6. The pressure is then reversed by evacuating the housing 6. The imperforate sheet will first move back to its initial position against the perforated sheet 11 due to the decrease in pressure and subseauentlv both sheets will be urged into the second die 8 as shown in Figure 7. The imDerforate sheet thus acts as the backing sheet in the formation of two apertured bodies in a two step operation.

The imperforate sheet 9 may be removed from the dies after the shaDing operation, at this Doint having the shaDe of the second bodv, and may then be formed into a third shaDed bodv in a third die.

In the above examples the perforated sheet or sheets and the backing sheet may be of the same material or of different materials having closely similar mechanical pronerties. The material of the perforated sheet may be plastics or a ductile metal surh as a superolastic allov.

The nrocesses described above will normallv be carried out at an elevated tem- perature appropriate to the material used.

Claims

WHAT WE CLAIM IS:-

1. A method of forming a shaped body from a sheet of superplastic metal comprising first forming one or more openings in the sheet of metal, backing this perforated sheet with an imperforate sheet of material, raising the temperature of the perforated sheet until it is in superplastic condition, and shaping the pair of adjacent sheets together by the use of a fluid pressure difference, the imperforate backing sheet being on that side of the pair of sheets which is exposed to the higher pressure.

2. A method according to claim 1 in which the material of the backing sheet is different from that of the perforated sheet but has similar mechanical properties.

3. A method according to claim 1 in which the backing sheet and perforated sheet are of the same material.

4. A method according to any preceding claim in which the shaped body is separated from the backing sheet after the forming operation and, by the application of further pressure to the backing sheet, a further shaped body of the same shape or a different shape is formed.

5. A method of forming a shaped body from a sheet of superplastic metal, together with a further shaped body from a further sheet of ductile material, comprising first forming one or more openings in the sheet of metal, backing this perforated sheet with an imperforate sheet of ductile imperforate material, raising the temperature of the perforated sheet until it is in a superplastic condition, shaping the pair of adjacent sheets together by the use of a fluid pressure difference, into a first shaped die to form the first-mentioned shaped bodv from the perforated sheet, the imperforate backing sheet being on the side of the pair of sheets which is exposed to the higher pressure, and then reversing the pressure difference so as to force the imperforate sheet away from the first die, through its starting position, and into a second shaped die to form the said second shaped body whilst leaving the perforated sheet in the first die.

6. A method of forming first and second shaped bodies, each having one or more openings in it, from respective sheets of superplastic metal comprising first forming one or more openings in each sheet, sandwiching between the two sheets a sheet of imperforate ductile material, raising the temperature of the perforated sheets until they are in a superplastic condition, shaping the sandwiched sheets, by the use of a fluid pressure difference, into a first shaped die to form the first-mentioned body from one of the perforated sheets, then reversing the pressure difference so that the imperforate sheet and the second perforated sheet are forced away from the first die, through their starting position into a second shaped die to form the said second shaped body from the second perforated sheet.

7. A method according to Claim 6, in which the imperforate sheet is removed from the second die after the two steps and is formed into a third body in a third die.

8. A method of forming a shaped body from a sheet of superplastic metal substantially as herein described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

9. A method of forming shaped bodies from sheets of superplastic metal substantially as described with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.

10. A method of forming shaped bodies from sheets of superplastic metal substantially as herein described with reference to and as illustrated in Figures 5 to 7 of the accompanying drawings.