Patent GB-959093-A (GB)
Title: Improvements in or relating to method and apparatus for combined stretch and die forming of metal stock
IPC: B21D25/02
Filed: 1960-11-18
Abstract: 959,093. Stretch forming. CYRIL BATH CO. Nov. 18, 1960 [March 17, 1960], No. 39779/60 Headings B3E and B3Q. A method of cold forming sheet metal stock into an article, e.g. automobile panels, comprises tensioning the stock along only one dimension into a range above its elastic limit, and drawing the stock into the desired shape to form the article between drawing dies substantially coextensive peripherally with that area of the stock from which the article is to be formed to change the cross-sectional shape of the stock in each of two cross-sectional planes mutually perpendicular to each other and to the stock. A machine for carrying out the method comprises a main framework 1, 2 and 3, the top frame 3 supporting a male drawing die 4. A complementary female die 5 is mounted on a rocker arm 7 pivoted at one end to the main frame at 8. The rocker arm is actuated by hydraulic cylinders 12 pivoted to the main frame. The sheet metal stock is gripped at the end of the machine adjacent the pivot 8 by grippers 21 detachably and adjustably mounted on a pivoted head 20. All the grippers are opened and closed simultaneously by fluid pressure means. Alternatively, a single elongated gripper is used. At the other end of the machine a complementary pivoted gripping head 40 carries grippers 41 and the tensioning of the sheet metal stock is effected by a fluid pressure cylinder 45 pivotally mounted in a frame 49 on rocker arms 50. After the initial tensioning of the stock the head 40 is swung downwardly to stretch form the stock over the die 4. This is effected by a fluid pressure cylinder 52 attached to the rocker arms 50. In operation, with the arm 7 in its raised position, the sheet metal stock is gripped by the heads 20 and 40 and fluid pressure is supplied to the cylinder 45 to tension the stock beyond its elastic limit. Fluid pressure is next supplied to the cylinders 12 to close the dies. Due to the gradual closure of the dies progressively from one edge to the other edge in the stretch forming dimension the metal tends to flow in the direction of closure. At the same time the metal is free and unconstrained and unconfined at the die edges which extend in the tensioning direction so that the metal creeps into the dies freely transversely of the tensioning direction and can flow in the tensioning direction as urged so by the die faces and the tensioning means and so readily takes the form of the dies without wrinkling. While the dies are held closed the stock may be given an additional restretch to set the material around the margins. A modified machine, Fig. 10, comprises a frame 70 on which is mounted a male die 71 and a female die 72, both dies being connected together at one edge by a pivot 73. Stretch-forming means 75 is actuated by a fluid-pressure cylinder 78. The die 72 is opened and closed by fluidpressure cylinders 83 and a pressure roll 86 urged downwardly by fluid-pressure cylinders 87 acts on the die 72 to supply the required forming pressure to the dies. The supports 85 for the pressure roll 86 are movable lengthwise of the dies on guideways 89 by fluid-pressure cylinders 90 so that the roll is transversed across the dies at the same time as the forming pressure is applied. In a modification the female dies 94, Fig. 12, is carried on the bed of the machine and the male die 95 is mounted on the pivoted rocker arm. Specification 959,094 is referred to.