Putri, I.A.A. et al. 2025. Preventive Maintenance Analysis to Improve the Readiness of Heavy Equipment Hydraulic Excavator Liebherr R9250 & R9350 with Six Sigma Method at PT. XYZ. IJIEM - Indonesian Journal of Industrial Engineering and Management. 5, 3 (Mar. 2025), 701–711. DOI:https://doi.org/10.22441/ijiem.v5i3.22917.