Plenary Lecture

Machining Process and System Stability – A Chaotic Approach

Professor Gabriel Frumusanu
Manufacturing Science and Engineering Department,
“Dunarea de Jos” University of Galati, ROMANIA
E-mail: gabriel.frumusanu@ugal.ro

Abstract: The actual technology demand is to minimize the production time, by using high speed machining (HSM), in conditions of obtaining a good quality of the workpiece surface. The main obstacle in front of this purpose is the cutting process instability. In the up to now accepted theory concerning cutting process stability, the process transfer function is considered to be a real constant, by completely neglecting cutting process dynamics. On the other hand, the behavior of the system mechanical structure is accepted as being linear, which enables to the machining system transfer function to be considered as the amplitude-frequency characteristic of the mechanical structure (possible to be experimentally found). Last evolutions in cutting stability theory are given through a significant large number of researches, concerning especially three investigation directions: new models and methods to study machining processes dynamics; analysis and interpretation of the phenomenology connected to instability of cutting processes; finding concrete solutions to improve cutting processes stability. We can generally remark the tendency to drop off the cutting process classic model and to search for new approaches. Recent developments in Chaos Theory furnished tools to be used for studying the systems having chaotic dynamics: attractors fractal dimension, Lyapunov exponent, Poincare map, bifurcation diagrams etc. Until now, it was revealed the chaotic behavior in the cases of electric circuits, lasers, chemical reactions, fluids dynamics or meteorology, but last hour researches started also to claim the chaotic character of cutting process dynamics; anyway, this process is inherently nonlinear, due to frictional effects, delay dynamics, structural nonlinearities and to loss of contact between the tool and the workpiece. From researches and observations done up to now, the current functioning point of a certain machine-tool can be referred to its stability limit by modeling with chaotic models the time evolution of the machining system & process parameters (e.g. the cutting force). This lecture refers to the machining process and system stability, when the two elements (process and system) are treated as a unique entity. To fulfill this objective, the following steps were done: 1) an appropriate type of chaotic model was found, by experimental research, to describe the entity dynamic behavior; 2) numerical simulations were realized by using the adopted model; 3) the simulation results were compared to the observations done on the real system functioning, in the corresponding situations.

Brief Biography of the Speaker:
Gabriel Frumusanu graduated a 5 years Mechanical Engineering degree program at “Dunarea de Jos” University of Galati (1987); PhD in Industrial Engineering - at “Dunarea de Jos” University of Galati (1999); Training stages at: “Ecole des Mines de Paris”, CEMEF, Sophia-Antipolis – France (1992); “Universita degli Studi di Padova”, Padua – Italy (1997); “Ecole Nationale Superieure des Artes et Metiers“, Angers – France (2002). Research fields: numerical modeling of manufacturing processes and surfaces generation; cutting processes dynamics; metals cold forming (deep drawing, extrusion, orbital volumetric cold forming). Professional experience: 1988 – 1990 – Engineer responsible of equipments maintenance at Cold Rolling Mill from Galati Iron and Steel Company; 1990 – 2000 – Assistant-professor at “Dunarea de Jos” University of Galati, Manufacturing Science and Engineering Department; 2000 – 2004 – Associate-professor, in the same department; 2004 up to present – Professor, in the same department.
Prof Frumusanu participated in over 20 research projects supported by Romanian Ministry of Education and Science; author / co-author of over 20 scientific or didactic books; over 100 scientific papers written or co-authored, published to International / National Conferences proceedings (France, Hungary, Israel, Moldavia) and Journals. Invited professor at “Universita degli Studi di Padova”, Padua – Italy (2006). Member of professional and scientific associations: Romanian Association for Non-Conventional Technologies - ARTN, Romanian Association of Managers and Engineers - AMIER, Romanian Association of Tensometry - ARTENS; Expert of Romanian National University Research Council - CNCSIS and of Romanian Agency for Quality Assurance in Higher Education - ARACIS.