A new approach to monitoring thermal fatigue cracks in die casting moulds

Abstract Die casting moulds are exposed to high cyclic temperatures, mechanical loads and severe chemical conditions. Thermal and mechanical loads cause high local stresses and consequently surface cracks. This paper introduces a new approach to establishing thermal fatigue cracks in die casting moulds by measuring the resulting defect-fins on aluminium alloy castings in the actual die casting process. The investigation showed that cracks occurred sooner and were bigger if the mould material had a lower hardness. The maximum depth of the defect-fin observed on the casting due to thermal fatigue crack on the mould with the lowest hardness (42 HRc) at 10000 cycles was 0.37 mm, the maximum width of the defect-fin was 0.76 mm and maximum length was 9.6 mm. The observed cracks were bigger closer to the entrance of melt flow, especially at the places with stress concentrators, due to higher melt temperature and higher melt flow.