Numerical optimisation of the gating system of a titanium alloy inlet valve casting

Abstract

The research described in this dissertation investigates the feasibility of casting inlet valves for an internal combustion engine using Ti6Al4V alloy. The engine valves operate in an extreme environment under high thermal cycles – this requires a material that can withstand such exposures. Ti6Al4V is the most common titanium alloy with high temperature creep and fatigue resistant behaviour, however, it is not all positive. Ti6Al4V alloy also yields many difficulties with respect to processing especially when the material is cast. It is therefore important to gain a thorough understanding of the pouring and solidification characteristics of this material. The main focus of this work was to investigate and optimise feeding and geometrical parameters to produce valves that are free from defects, especially porosity. An in depth analyses of the parameters that influenced the casting quality was performed, and it was found that casting orientation, inlet feeder geometry, initial and boundary conditions all played a vital role in the final results. These parameters were individually investigated by performing detailed numerical simulations using leading simulation software for each of these cases. For each case, a minimum of ten simulations was performed to accurately determine the effect of the alteration on casting soundness and quality. Furthermore, the relationships (if any) were observed and used in subsequent optimised simulations of an entire investment casting tree. The change of geometric orientation and inlet feeder diameter and angle showed distinct relationships with occurrence of porosity. On the other hand, alteration in the pouring parameters, such as temperature and time, had negligible effect on occurrence or position of porosity in the valve. It was found that investigating individual parameters of simple geometry and then utilising these best-fit results in complex geometry yielded beneficial results that would otherwise not be attainable.