Doctoral Thesis: Energy efficiency of machine tools

ENERGY efficiency has been classified as one of the key technological advancements necessary for European industries to grow and stay competitive on the global market. Latest developments in this field have been reviewed and compared. Despite the effort of the scientific community there is still a considerable field for improvement, e.g. regarding synergy of existing methodologies into a coherent multi-level approaches. This work attempts to provide such perspective as well as necessary tools and methods. Firstly, an experimental characterization approach to collect and process relevant energy data and assist in further analysis is introduced and energy models of the key machine tool components are introduced. Minimal energy-time functions are used to represent an elementary part of processing cycle: a workpiece feature. Energy framework is proposed as a mean to describe a generic discrete-manufacturing process using a hierarchical optimization architecture. System level model, which incorporates knowledge of system performance, reliability, energy-saving policies and machine level energy functions, is developed and integrated with the energy framework. Developed methodology is demonstrated and validated on an industrial case study taken from liquid valve manufacturing plant. It concerns a flexible transfer milling machine, which is modelled using proposed hierarchical energy optimization framework and put into a system context using a generalized threshold model. Economical aspects of the system, namely part price, energy cost tool life and inventory cost are included in the analysis. The thesis concludes with remarks on developed methodologies, reports the findings coming from the case study, best energy reduction strategies and hypotheses about further developments.