Apparatus for and method of forming curved panels

Abstract

Aluminium panels curved in mutually orthogonal x, y and z dimensions are made by stretch forming. A former ( 34 ) for use in this process comprises a plurality of steel bars ( 60 ) extending generally in the y direction and mutually spaced apart in the x direction. The bars ( 60 ) are held in side rails ( 62 ) and ( 64 ), which are formed with holes ( 66 ) to receive the bars ( 60 ), and flexed over an intermediate rail ( 68 ). Thus each bar ( 60 ) is curved in a yz plane. The holes ( 66 ) and the seats for the bars on the intermediate rail ( 68 ) each lie on a curve in an xz plane. So located, the bars ( 60 ) combine to define an envelope which is curved in mutually orthogonal x, y and z dimensions. When an aluminium sheet is stretched over the former ( 34 ), it takes up the shape of this envelope.

1 . Apparatus for forming from sheet material a panel curved in mutually orthogonal x, y and z dimensions, which apparatus comprises:
 two side rails and an intermediate rail between the two side rails, all said rails extending generally in the x direction; and   a plurality of bars held by the side rails to extend generally in the y direction and be mutually spaced apart in the x direction;   wherein the side rails and the intermediate rails are relatively configured and arranged so that the bars are flexed thereby to form a plurality of curves in yz planes and the apices of the curves in the yz planes form a curve in the xz plane.   
   
   
       2 . Apparatus for forming a panel as claimed in  claim 1  wherein the bars each have substantially the same cross section. 
   
   
       3 . Apparatus for forming a panel as claimed in  claim 1  wherein each bar is held at or adjacent its ends in openings formed in the side rails. 
   
   
       4 . Apparatus for forming a panel as claimed in  claim 3  wherein the openings in the side rails comprise holes for the respective bars each formed to extend along the curve in the yz plane of the bar it holds. 
   
   
       5 . Apparatus for forming a panel as claimed in  claim 4  wherein said holes are mutually spaced apart in the y direction along a curve in the xz plane. 
   
   
       6 . Apparatus for forming a panel as claimed in  claim 4  wherein each said opening comprises a lengthwise slot holding a plurality of said bars. 
   
   
       7 . Apparatus for forming a panel as claimed in  claim 1  wherein each bar is flexed over a seat on the intermediate rail, said seats being mutually spaced apart in the y direction along a curve in the xz plane. 
   
   
       8 . Apparatus for forming a panel as claimed in  claim 1  wherein there is more than one said intermediate rail. 
   
   
       9 . Apparatus for forming a panel as claimed in  claim 8  wherein there is more than one said side rail each side of the intermediate rail or rails. 
   
   
       10 . Apparatus for forming a panel as claimed in  claim 1 , which apparatus comprises:
 a former defining a surface curved in mutually orthogonal x, y and z dimensions;   two clamps extending generally in the y direction and mutually spaced apart in the x direction to clamp sheet material at opposite ends of said former; and   a jack operable to drive said clamps apart and stretch the clamped sheet material over said surface;   wherein one or each said clamp is carried on a frame pivoted about an axis extending generally in the y direction and rearward of said former, whereby when the clamps are driven apart the sheet material is pulled rearwards onto said surface.   
   
   
       11 . Apparatus for forming a panel as claimed in  claim 10  wherein said jack is arranged between said clamps to bear on each thereof. 
   
   
       12 . Apparatus for forming a panel as claimed in  claim 10  wherein each said clamp comprises first and second members arranged to receive said sheet material therebetween and a source of pressurised fluid arranged to drive the second member towards the second member thereby to clamp the sheet material, each said clamp including a flexible membrane between the second member and the source of pressurised fluid. 
   
   
       13 . A method of forming from sheet material a panel curved in mutually orthogonal x, y and z dimensions, wherein said method comprises:
 arranging a plurality of bars to extend generally in the y direction and be mutually spaced apart in the x direction;   flexing the bars to form a plurality of curves in the yz plane;   locating the bars so that the apices of the curves in the yz planes form a curve in the xz plane; and   stretching said sheet material over said bars.   
   
   
       14 . A method of forming a panel as claimed in  claim 13  wherein:
 the sheet material is clamped along edges extending in the y direction at opposite ends of said former and the clamped edges are driven apart to stretch the clamped sheet material over said surface; and wherein   one or each said clamped edge is driven arcuately about an axis extending generally in the y direction and rearward of said former, whereby the clamped sheet material is pulled rearwards onto said surface.   
   
   
       15 . A method of forming a panel as claimed in  claim 14  wherein the panel is reinforced by stringers applied to the convex face of the panel while its concave face is on said former. 
   
   
       16 . A method of forming a panel as claimed in  claim 15  wherein each said stringer is made from a length of box section made flexible by kerfing before application to the panel. 
   
   
       17 - 19 . (canceled)