EXPERIMENTAL CHARACTERIZATION FOR IMPROVING ENERGY PERFORMANCE AND SUSTAINABILITY IN INDUSTRIAL MANUFACTURING PROCESSES: FLEXOGRAPHIC PRINTING AND ROBOTIC FRICTION STIR WELDING

This PhD thesis presents a comprehensive investigation into the energy performance and optimization potential of two advanced manufacturing processes: flexographic printing and robotic friction stir welding (FSW). Despite their increasing industrial relevance, a detailed understanding of energy consumption patterns, subsystem-level behaviour, and optimization potential remains limited, particularly for flexographic printing systems and robotic FSW applications. To address this gap, the research adopts a detailed, sub-unit level analytical framework combined with life cycle-oriented assessment methods to quantify energy demand, emissions, and efficiency improvements under varying operational conditions.For flexographic printing, the study evaluates various production job scenarios using solvent-based and water-based inks. Key parameters, including electrical energy demand, thermal behaviour, natural gas consumption, compressed air usage, and waste heat potential, are analysed at the process sub-unit level to assess their influence on overall system performance. The results identify waste heat from the drying process as the primary energy hotspot, representing the largest opportunity for energy recovery and efficiency improvement. Significant variations in energy consumption across subsystems are observed, with strong dependence on printing job characteristics (ink type, number of colour stations, and ink coverage) and process parameters (machine production speed, ventilation fan speed, and process air temperature). Water-based inks achieve electrical energy performance comparable to solvent-based inks; however, their overall natural gas demand remains higher due to increased thermal requirements associated with water evaporation, even under optimized recirculation conditions.Building on this analysis, the thesis proposes and evaluates a heat recovery system (HRS) for the drying units of the flexographic printing machines. The findings confirm that the HRS achieves substantial reductions in specific thermal energy consumption (24.41 to 43.8% for water-based inks and 27.8 to 32.9% for solvent-based inks), with only minor increases in electrical energy demand for ventilation fan units due to pressure drop. The integration of variable speed drives (VSDs) for the chiller enables adaptive operation, reducing electricity consumption and contributing to overall system efficiency. Net CO₂ emission reductions range from 19 to 36% for water-based inks and 21 to 26% solvent-based inks, respectively. Economic assessment for HRS demonstrates strong feasibility, with payback periods between 0.39 and 2.06 years, benefit-cost ratios up to 27:1, and consistently positive net present values across all scenarios. The system shows exceptional robustness under varying economic conditions, with optimal performance observed under double-shift operation.In parallel, the thesis addresses a critical research gap in the energy characterization of robotic FSW systems. Through experimental analysis and detailed power profiling at the subunit level, the study quantifies the specific energy consumption of robotic FSW under diverse process conditions. The results indicate that strategic selection of process parameters and workbench positioning can achieve energy savings of up to 57%, when comparing the best-case and worst-case operating scenarios, without compromising weld quality. A predictive energy model is developed based on welding speed, axial force, and workbench coordinates, enabling energy-aware process planning and scheduling.Overall, this research demonstrates that significant energy and environmental improvements can be achieved through system-level analysis, process optimization, and the integration of energy-efficient technologies. The findings provide valuable insights for advancing sustainable manufacturing practices and support the industrial adoption of optimized flexographic printing and robotic FSW systems.