Julien Monnet "Process optimisation of tungsten carbide components realised by micro electro discharge milling and characterization of the induced mechanical properties"

Julien Monnet PhD works : "Process optimisation of tungsten carbide components realised by micro electro discharge milling and characterization of the induced mechanical properties"

Abstract : This thesis focuses on the study of micromechanical components realization by micro-milling electro discharge machining (µEDM) and on the evaluation of the mechanical properties induced by this process. The production of micro-components with high mechanical properties in terms of hardness or elasticity responds to a significant demand increase on miniaturized systems.
The first part of this work focuses on the optimization of process control parameters. The study demonstrate the feasibility of manufacturing micromechanical components made of tungsten carbide (WC-Co) by µEDM. The implementation of a design-of-experiment method allowed us to identify the most influent parameters.
The second part of this work concerns the study of the component mechanical properties on a micrometer scale. The objective is to verify the erosion process impact on the elasticity and toughness properties. A test methodology is designed. A tenacity characterization test is developed: microbeams, made by µEDM and notched by focused ion beams, are loaded on a nano-indentation cell. Using the observed failure load, a critical stress intensity factor is then identified using a 2D finite element numerical model.
Finally, a demonstrator is manufactured. It uses an elastic component made of tungsten carbide: a watch movement beam spring. From this demonstrator, an image correlation study is done and associated with a Bernoulli beam model. The results obtained are compared to a numerical simulation of the beam spring’s behaviour. These results validate the good quality of the numerical simulation. This image correlation method can also be used to monitor the health of a component in service, or to evaluate its elastic properties.

Jury composition : 

Sébastien THIBAUD, PR1,  Université Franche-Comté, PhD Director

Fabrice RICHARD, Maître de Conférences, Université Franche-Comté, PhD CoDirector

Yves GAILLARD,  Maître de Conférences,  Université Franche-Comté, PhD CoDirector 

Karl DEBRAY, Professeur, Université de Reims Champagne-Ardenne,  Reporter

Sylvain MEILLE, Professeur, INSA Lyon,  Reporter

Gérard POULACHON,  Professeur,  ENSAM Cluny, Reviewer

Localization : Amphithéâtre Jules Haag,  ENSMM, 26, Rue de l'Epitaphe - 25000 Besançon