Christophe Czarnota

Statistical approach for modeling abrasive tool wear and experimental validation when turning the difficult to cut Titanium Alloys Ti6Al4V

Tool wear and tool failure are critical problems in the industrial manufacturing field since they affect the quality of the machined workpiece and raises the production cost. Improving our knowledge of wear mechanisms and capabilities of wear prediction are therefore of great importance in machining. The three main wear modes usually identified at the tool/chip and the tool/workpiece interfaces are abrasion, adhesion and diffusion. Besides, because of their difficult experimental analysis and measurements of their friction interface features (such as temperature, pressure, particles embedded in the contact …), understanding mechanisms that govern these wear modes is still incomplete. The objective of this research work is to develop a new wear model in which abrasive particles are assumed embedded between the tool and the chip at the interface. These particles are considered with a conical shape and are characterized by two main geometric parameters: the corresponding apex angle and size. The wear particles can be seen as a non-metallic inclusions or wear debris generated during the machining process. A probability density function has been adopted to describe the fluctuation of the size and the apex angle of particles in the tool/chip contact area. The influence of the used statistical distribution has been analyzed depending on which law has been adopted: Gaussian or Weibull. The Volume of the removed material per unit of time was chosen, in this study as the main abrasive wear parameter and detailed on a parametric study. Finally, wear tests were carried out with an uncoated WC-Co carbide tool machining a Ti6Al4V titanium alloy to validate the proposed approach.

Experimental Parameters Identification of Fatigue Damage Model for Short Glass Fiber Reinforced Thermoplastics GFRP

In the present work, a new polycyclic fatigue damage model is formulated and applied for short glass fibre reinforced thermoplastics. The model is able to capture experimental trends observed for the considered composites. The damage growth description involves a set of 20 parameters in the case of a complete 3D –structure. In the current paper, it is considered the particular case of a displacement controlled fatigue tensile test involving 4 damage parameters. The present contribution is a first approach of parameter identification. It is considered a least squares sense based cost function and homogeneous fatigue tests performed on a short glass fibre reinforced polyamide. The identified set of parameters appears to be not depending on the adopted initial values. The model as the parameters determined by the minimisation algorithm, are validated on a fatigue test performed with a different loading condition.

New stochastic wear law to predict the abrasive flank wear and tool life in machining process

Tool wear and tool failure are some of the main critical problems in industrial manufacturing fields since they affect the quality of the machined part and raise production costs. Improving our knowledge of wear mechanisms and capabilities of wear prediction are therefore of great importance in the machining process. Abrasion, adhesion and diffusion are usually identified as the three main wear modes at the tool–chip and the tool–workpiece interfaces. From an experimental point of view, the analysis of mechanisms that govern the wear process is still difficult to conduct. The objective of this research work is then to develop a wear modeling focusing on the abrasive wear mode at the tool–workpiece interface. This wear phenomenon is assumed to be closely linked to the microstructure’s material workpiece and caused by hard conical particles trapped into the contact between the cutting tool and the workpiece. The proposed model is based on an analytical approach including a statistical description governing the distribution of particles with conical shape embedded in the contact area. The volume of the removed material per unit time was chosen in this study as the main parameter to describe abrasive flank wear mode. A parameter V b 0 was introduced as the sudden flank wear which occurs in the former few cutting instants. A parametric study has been conducted that highlights the slight effect of the adopted value. The effect of the cutting conditions (cutting speed, pressure) at the tool flank that has a major influence on the wear rate, was deduced from a numerical study on the 42CrMo4/WC-Co tool–workpiece combination. Finally, a wear criterion has been proposed to estimate the tool life in order to address the concerns of industries.

Effect of coating materials on thermal loading in machining difficult‐to‐cut materials

The analysis of machining of difficult‐to‐cut materials is a challenging problem. This is due to the hard environment through which the cutting tool has to operate. This environment includes extreme mechanical loadings coupled to intense thermal gradients. This combination limits the tool life even in the presence of several protective tool coatings. This paper deals with a study on the effect of coating materials on thermal loading and tool wear. For the purpose, the study analyzes the temperature field inside the tool and its evolution at the tool‐chip interface. Results indicate that the temperature rise into the insert is depending on coating materials, in the vicinity of the tool rake face. It therefore controls cutting tool life since intensity of wear at the tool surface is directly proportional to the local efficiency of heat removal. This in turn depends on the effective values of the thermal conductivities of the tool substrate and of the coating material, as on the heat transfer coefficient.