The production of PET flakes in the Peruvian textile industry faces productivity limitations associated with operational inefficiencies of the grinding mill. The diagnostic analysis identified three critical sources of performance loss: prolonged blade changeover times, a high share of set-up time within the process cycle time, and low operational availability of the mill. To address these limitations, the Lean Manufacturing tools 5S and SMED were applied and validated through discrete-event simulation using Arena, comparing the As-Is and To-Be scenarios. The results show a reduction in set-up time to 121 minutes (–38%) and in cycle time to 132 minutes (–11%), together with an increase in mill availability to 90.2% (+7%), which enabled productivity to rise from 36.21 to 54 kg/H-h (+39%). These findings confirm the effectiveness of the proposed approach in improving the operational performance of the PET flake production process