This research investigates the effects of cathodic voltage, degreasing deposition time, and concentration on the thickness of paint layers in cathodic electrocoating (KTL) processes in automated cathodic electrodeposition line through the design of experiments (DOE). By integrating electrochemical theory with materials science, this study elucidates the mechanisms governing film formation during electrocoating, specifically focusing on how variations in voltage and deposition time influence deposition kinetics and layer morphology. Theoretical considerations reveal that increasing cathodic voltage enhances the mobility of charged particles within the electrolyte, leading to increased deposition rates. Experimental results indicate that at a degreasing concentration of 15 g L−1, the optimal cathodic voltage yields a maximum layer thickness of 21.42 μm. This thickness corresponds with the observed electrokinetic effects, including particle aggregation and accelerated deposition at higher voltages. Further analysis demonstrates a linear relationship between concentration and resultant thickness, suggesting that concentration plays a pivotal role in layer uniformity and adhesion properties, critical for the durability and performance of the coating, and surface morphology in industrial sectors.