Fault and cause diagnosis of casting defects: A case study

Abstract

AbstractThe product selected for detailed study was a cored grey iron disc, cast in a five cavity mould, subject to rejection at a highly variable rate. The behaviour of process variables in the sub‐systems of green sand, core making, metal pouring and metallurgical composition was analysed to detect any statistically significant correlations with the incidence of blisters, which was the predominant cause of rejection.To supplement the recorded data and to separate causal factors from correlations, a series of direct experimental trials was conducted to trace a faulty casting to the cavity, mould box, pouring conditions, green sand, cores and metallurgical composition pertaining at the time of actual production.From a progressively accumulated database of some 100 hours of the specific product runs, built up over several months, the production variables and responses were analysed using regression, ANOVA, correlation and factorial experimentation techniques. Three major interventions involving a change in bentonite supply and two modifications to the runner system were accompanied by a reduction of some 60 per cent in the mean level of blister rejects with an improved dispersion.