Influence of tilt filling on Weibull modulus of 2L99 aluminium investment castings

Abstract

A detailed investigation has been made of the tilt pouring of investment castings in order to reduce oxide film entrainment and hence improve their reliability. A computer controlled tilt casting machine has been developed to fill moulds using single and multi stage cycles. Metal flow during mould filling has been simulated using Flow 3D software and confirmed using real time X-ray radiography of moulds. Large numbers of test bars have been tilt poured in 2L99 (Al–7Si–0·4Mg) alloy. Castings have also been produced using top and bottom gated gravity filled moulds for comparison. The scatter in the breaking stresses has been analysed using the Weibull statistical technique to give the Weibull modulus λ. Top gated gravity filling gave relatively unreliable castings (λ=23), but this was significantly improved by bottom gating (λ=49). Fast single stage tilt filling gave λ in the range 30–45 depending on the rotation speed and an optimised multi stage tilting cycle increased λ to 55.