This study explores the application of Discrete Event Simulation (DES) for optimising the factory flow in an aerospace manufacturing setting. GKN Aerospace's manufacturing facilities aim to increase production efficiency through capital investment and automation, aligned with Lean Manufacturing principles of waste reduction and flow improvement. A target has been set for this work of a 25% throughput increase per month by 2027. Through DES modelling, we replicated the different configurations of an aerospace component manufacturing process flow, capturing key operational constraints such as machine availability, resource allocation, and material handling. A baseline model was developed to reflect the standard configuration of new CNC technology and automated loading and unloading operations, which is followed by scenario analysis to compare the deployment of different configurations of the system. The simulation results provide insights into bottlenecks, resource utilisation, and potential improvements, enabling data-driven decision-making for production ramp-up while supporting a culture of continuous improvement. The findings highlight the effectiveness of DES in mitigating operational uncertainties and optimising manufacturing strategies before real-world implementation. This research contributes to aerospace manufacturing by demonstrating how simulation-driven approaches can enhance efficiency and support strategic investment decisions within a Lean Manufacturing framework.