GB1208729A - A method of forming sheet or plate material - Google Patents

Abstract

1,208,729. Stamping; working at specified temperatures; making dies. PRESSED STEEL FISHER Ltd. 18 Dec., 1967 [23 Dec., 1966; 8 March, 1967; 15 March, 1967], Nos. 57753/66, 10802/67 and 12067/67. Headings B3A, B3Q and B3V. A method of forming a superplastic alloy plate or sheet 44 in a die 19 comprises subjecting one face of the sheet to a liquid 43 that has been heated to within, or above, that range of temperatures at which the alloy becomes superplastic until the sheet has been heated to within this range, and then applying sufficient pressure to the liquid to so sorce the sheet towards the die that the sheet is formed at a strain rate below the critical rate while subjecting the heated liquid and hence the sheet or plate to highfrequency vibrations. Examples of alloys which are superplastic below a certain critical strain rate are the eutectoid alloy of aluminiun and zinc, and the eutectic alloy of silicon and aluminium. The heating liquid 43 may be a molten low-melting-point alloy, an acid or a salt. The sheet may be pre-stretched in a separate operation by vacuum or press forming, or it may be pre-stretched after heating within the superplastic range by pressure applied to the hot liquid with the die 19 retracted, or the sheet may be stretched by a male die. Apparatus for performing the method includes a concrete die 19 with embedded electric heating coils 22, controlled by a thermocouple responsive to temperatures adjacent the forming surface 20, and compressed-air passages for cooling and ejecting the formed sheet, as described in Specification 1,208,730. The die is operated by a pneumatic cylinder 15. A concrete block 24 supports a steel chamber 25 connected by a conduit 31 to a reservoir 32 for the liquid 43. The top of the reservoir is connected, through a regulating valve 37, to a supply 39 of compressed-air and also to a metering valve 40, a metering pump 41 and a pressure release valve 42. Heating coils 26, 33 and 35 are provided controlled by thermocouples 27, 34. A high-frequency signal generator 28 for subjecting the sheet to vibrations above 10 kc./sec. and producing an air bearing between the sheet and die has a horn 29 projecting into the chamber 25. Working at specified temperatures.-The molten alloy and the die-surface 20 are maintained at 260‹ C., the sheet being loosely held between the die and base 24 until contacted by the liquid and raised to 260‹ C. The die is then firmly clamped, the generator 28 energized and highpressure air supplied to the reservoir 32 for effecting the forming operation.