Preliminary failure examination of a plastic-injection mould part

Résumé

The paper studies the failure of a mould-part for the hot-forming of plastics, by injection. The mould’s component was manufactured from AISI H13 and was intended for the production of plastic cups for cylindrical aluminium cans, used for coffee packaging. The tool belongs to a system that produces simultaneously four pieces per cycle. It exhibited a single uniform through thickness crack, after five millions working-cycles, where the lifetime was expected to be ten millions cycles. The paper refers to the preliminary examination of the failed tool surfaces. Data concerning the manufacture, processing and operation of the part were collected and a complete photographic file was created. Non-destructive testing was performed, including hardness measurements, inspection with fluorescent penetrating fluids. Chemical analysis was carried out and the material used to make the tool was identified. The paper presents conclusions on the crack initiation and propagation and the main causes that led to the premature failure.