Horizontal continuous casting process has been successfully implemented in Alcan for the production of T-ingots of primary aluminium and foundry alloys. Ability to achieve increased productivity targets and reduce production costs relies on a fundamental understanding of key process characteristics and operating parameters. Thanks to the long-standing experience in vertical DC Casting, numerical modelling appeared as a powerful approach to understand phenomena related to metal flow, solidification and ultimately defect formation. As part of a collaborative R&D program, a global model of horizontal casting process, integrating specialized sub-models on critical aspects of the process such as meniscus dynamics, is being developed. Experimental characterization of primary and secondary cooling is performed in parallel with modelling work to provide the information necessary to properly characterize mould heat transfer. This paper will present the development of a 3D process model of T-ingot casting along with its application to solve specific process challenges that have emerged during the first years of production in the plant.