GB543040A - Improvements in or relating to the forming by stretching of sheet metal particularly aluminium and aluminium alloy sheet - Google Patents

Abstract

543,040. Making aircraft. PRESSED STEEL CO., Ltd., and PETHER, A. H. Oct. 25, 1940, No. 15678. [Classes 83 (ii) and 83 (iv)] Angular bending; stretching.-Sheet metal parts, for example the cowlings, fairings and other skin panels for aircraft, of aluminium and its alloys, are produced in a standard power press with a preliminary step of freely bending over a die and then finally stretching the blank to the desired shape over the die, The tapering section 11, Fig. 1, is produced from a sheet 41, Fig. 2, by locating the sheet by holes, situated outside the trim-lines 51, engaging pins 44 in the wooden die 21 secured to a plate 22 supported on the holder 23 on the press bed 24. As the head 27 descends wooden blank holders 25, faced with metal 31 grooved at 49 to prevent slip, bend the sheet round the die till the edges are clamped against wooden spars 45. Air is now admitted beneath the cushion 36 and pins 35 raise the die 21 an amount determined by the setting of screwed collars 54 on side rods to stretch the metal over the die ; the amount of stretch being from 3 per cent. to 6 per cent. In a modification, pressure on the cushion is continuous and the spars 45 are replaced by blank holders supported in a raised position by the cushion during the " bending " part of the stroke after which the cushion yields to effect the stretching.