11 juin 2025
- Energetics, aerodynamics and intensification of plasma arc cutting jets / PhD Defense Frederic CAMY-PEYRET
Doctorant : Frederic CAMY-PEYRET
Date et lieu : le 11 juin à 14h00 ; amphi N°3 - Centrale Méditerranée
Résumé : The plasma cutting process of electrically conductive materials is one of the three main thermal cutting processes for sheet metal, along with laser and oxy-cutting. This process has gradually spread in industry since the 70s, and is now essential in construction and metal fabrication activities. Improvements in this technology have historically been made by industrial equipment manufacturers using a highly empirical and technological approach, probably due to the lack of fundamental R&D of the sector, and more likely the complexity of the multi-physical phenomenology of the plasma jets in consideration. These can be described as an under-expanded jet at the outlet of a millimetre-sized sonic nozzle, at one’s throat a strongly ionized plasma column is heated above 20000 K by the passage of electrical current.
The complexity of the object of study lies in the numerous physical effects, often themselves difficult to apprehend separately, which may a priori contribute to determining the structure of the plasma jet: thermodynamic properties and transport coefficients of the plasma, geometry of the nozzle and its aerodynamics, pressure, swirl intensity, turbulence, radiative transfers at high temperatures, electrostatic and electromagnetic coupling between the current passage and the plasma, electrodes behaviour... Since the 2000s, largely in collaboration with the public research scholar community, some industrial players have engaged in more fundamental and scientific approaches to better understand and describe these technological objects, an approach to which the author has contributed for 25 years.
After a summary of the career and research work carried out or supervised by the author in the close by disciplines of fluid mechanics, combustion, materials, and processes, the issue addressed in this thesis manuscript will therefore focus on the energetics and the phenomenology of transferred arc plasma jets applied for cutting. This topic is the most populated cluster of my experience as an industrial researcher, and also a subject whose multi-physics nature has greatly benefited from the experience acquired in studying other problems.
We will introduce to the reader the technologies and processes, we will cover the experimental and numerical simulation tools and methods we have utilized and contributed to develop, we will study the energy scales at work in plasma cutting compared to the competing laser process, and detail the mechanisms of energy supply and distribution to the sheet. We will then showcase the advances in the understanding of the constriction of the plasma column through the description of nozzle physics down to the sonic throat, before going farther downstream by analysing the structure of the under- expanded plasma jet developing between the nozzle outlet and the sheet metal workpiece. We finally draw conclusions on how to control the plasma jet power density to favour cutting accuracy.
Keywords: plasma cutting process, electric arc plasma, energy efficiency, metal sheet cutting, under-expanded supersonic plasma jet, aerodynamic adaptation, thermal plasma thermodynamics, high-flux heat transfers, power density, intensification
Jury
Stéphane PELLERIN / Professeur, Université d'Orléans / Rapporteur
Luc VERVISCH / Professeur, INSA de Rouen / Rapporteur
Françoise BATAILLE / Professeur, Université de Perpignan Via Domitia / Examinatrice
Philippe ROBIN-JOUAN / Fellow Expert, GE Vernova / Examinateur
Sergey GAVRILYUK / Professeur, Aix-Marseille Université / Président du jury
Eric SERRE / DR CNRS, M2P2 / Examinateur
Pierre BOIVIN / CR CNRS, M2P2 / Directeur de thèse
Pierre FRETON / Professeur, Université de Toulouse / Co-directeur de thèse
Bernard LABEGORRE / Senior Expert, Air Liquide / Membre invité
