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[September 2004]
Follow-on Project on Ceramic Investment Casting
Getting the moulded dimensions of high performance metal alloy components correct is crucial to cost reduction through, on the one hand, minimising rejection on dimensional grounds or, on the other, by avoiding having to undertake excessive amounts of machining.
However, to make effective dimensional predictions requires a surprising amount of data on the alloy and mould systems being employed. Two years ago NPL (Teddington, Middx, England) successfully completed a project with industry which obtained the thermophysical properties of representative ceramic casting mould materials and of nickel superalloys through the melting range.
NPL has now embarked on a follow-on project, coordinated by DAF Associates, with greater focus on the dimensional stability of ceramic mould materials. This project is examining the size changes in these complex layered ceramic structures resulting from natural sintering, thermal expansion and flexural and compression creep at temperatures and stresses representative of casting.
Mould materials have been specially made for the project by the collaborating industrial members (proprietary systems) and by the University of Birmingham IRC in Advanced Materials (agreed generic systems).
Marked differences in behaviour have so far been found between the different systems, with different risks of distortion occurring in different temperature regimes. It is hoped to compare the laboratory data with data from casting trials on simple shapes. A valuable compilation of comparative data will be produced by the end of project.
For more details, e-mail: peter.quested@npl.co.uk
ENDS