Flow stress behaviour of ABS (acrylonitrile–butadiene–styrene) at elevated temperature and application to the thermal vacuum forming process

Abstract

A conventional plastic processing method, vacuum thermal forming, is adopted for manufacturing the large-size rear back of the TV set. The candidate material is the widely used engineering plastic, acrylonitrile–butadiene–styrene (ABS). The basic principle of thermal forming process is to place a heated plastic sheet on a die and clamp with a cover plate whose function is to seal around circumference to establish a vacuum or pressurised compartment. Thus, the softened sheet as being preheated will progress towards and fill up the die underneath when vacuum or pressure is applied. The major problem with thermal forming could be the uneven thickness distribution. To tackle this issue, computer simulation can be an advantageous tool to minimise the number of try-and-error experiments. To run computer simulation for thermal forming, flow behaviour of the ABS is needed as the computer input. Thus, stress–strain relation obtained by tensile tests at various elevated temperatures and strain rate is essential for performing computer simulation work. The constitutive equation based on the widely power law was established. The application was applied to simulate the vacuum thermoforming process of a large-size back cover of television set and the major problem of uneven thickness distribution was successfully simulated with suggested prevention design.