Mathematical and numerical modelling of core injection for investment casting applications

Cademartori, Stefano (2019). Mathematical and numerical modelling of core injection for investment casting applications. University of Birmingham. Eng.D.

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Abstract

Defects in the ceramic cores used for casting internal features in gas turbine blades are usually only visible at the end of the manufacturing process. This thesis aims to shift the paradigm in ceramic injection mould die design by providing an alternative to the traditional trial and error development of complex moulds. The method developed will empower core manufacturers to gain an unprecedented insight into the process leading to reduced costs and waste while improving the manufacturing line efficiency.
The work was carried out by first determining the key defects observed in the production of cores. This was achieved by means of statistical analysis of years of production scrap, the use of an instrumented die to investigate the material and injection machine behaviour during injection and a careful literature review.
The result of this study suggested that the defects were related to the presence of process induced material anisotropy. This hypothesis was verified using different techniques including microstructural analysis and X-ray computed tomography (XCT). Strong particle orientation, phase segregation and consequent density and porosity variations were found in different core sections.
Computational Fluid Dynamics (CFD) analysis was used to predict defects in cores, together with the filling and solidification of large and complex industrially relevant core geometries. Manufacturing trials using short shots were carried out to validate the transient flow patterns of the paste. Analysis of the modelled solidification, shear rates, stagnation points and phase migration has driven die and process optimisation to give commercial benefit in a production environment. Finally, the initial stage of a further investigation into the weld line conditions, that occur at the junctions of the multiple fronts formed during core injection, is presented.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

Supervisor(s):