Dry film thickness and appearance are the main quality improvements that can be achieved by an automated painting system in the manufacturing process. This study presents the spray coating process for aircraft parts using a gantry robot with an automated spray-painting gun to control the spray path, thus achieving the desired coating layer thickness. The experimental results show that the 3-gun atomization spray method, with high capacity airflow and outstanding atomization characteristics, poses the challenge of achieving an even thickness of the overlapping spray pattern from three separate guns, minimizing the paint material consumption and controlling the dry film thickness within the given specification and standard. The optimization was performed to control the spray path and material consumption with a 3-gun spray method to achieve the optimum setting for the spray nozzle to workpiece height to obtain the target thickness. The results show that replacing the manual process with the automated painting process can increase the speed by up to 30-40%, reduce the setup time and increase the capacity of the painting booth. The development of this system can achieve the desired thickness specification, increase productivity and provide safer, more effective and ergonomic working conditions.