GB1355502A - Manufacture of moulds and dies for plastics and similar materials - Google Patents

Abstract

1355502 Making moulds and dies, stamping T I (GROUP SERVICES) Ltd 10 Oct 1972 [10 July 1971] 32515/71 Headings B3A and B3Q A method of forming moulds and dies for making bodies from synthetic resin, rubber or rubber-like material comprises forming the mould or die from a sheet of superplastic metal alloy. A sheet of a superplastic alloy, e.g. an aluminium-zinc euctectoid or an aluminium alloy, is clamped between two pressure chambers 1,2. Clamping rings on the chambers may have serrated mating faces to ensure good sealing between the chambers and sheet. Plain mating faces are sufficient when hydraulic clamping is used. The clamping load is applied by a ram 4 via a pressure plate and a series of pillars. The pressure plate also carries air preheat and cooling chambers 5 for the chamber 1. Each chamber is heated by a 3 kW heater 3 and temperatures of up to 500‹ C. are attained. The chamber 2 contains a forming table 6 operated by a ram 8 and preheat and cooling units 5 for the chamber are located at the base of the apparatus. Pneumatic controls allow either chamber to be pressurized while the other is connected to atmosphere or evacuated. The forming methods used are pressure forming into a female mould or on to a male pattern, plug assisted forming or "snapback'-' forming, Fig. 3 (not shown). Material distribution is improved when pressure forming in the case of a male mould by lubricating the die and in the case of a female mould by applying pressure with the workpiece cold. The moulds may also be made by pressing the superplastic sheet to a pattern of the article to be moulded. The mould may be heat treated to destroy its superplastic properties and it may be strengthened with suitable backing material. The life of the mould or die may be increased by applying a coating of hard chromium plating. The dies made by these methods may be used for casting, injection moulding, extrusion and like processes.