University of Bordeaux (France)
Today, the separation of the phenomena occurring during machining and in particular the intense friction and shear phenomena of the material is a real challenge. Indeed, the behaviour laws characterizing these phenomena need to be improved. The laws thus established have to take into account the material microstructure and must be finely characterized. To do this, the various phenomena must be isolated and decoupled as much as possible to allow this characterization. This is particularly true in machining where the intense friction phenomena at the chip tool interface (secondary shear zone) or workpiece tool interface (cut surface) must be isolated from the adiabatic shear phenomena present in the primary shear zone.
Major steps in the work
The aim of this ESR is to examine phenomena occurring in the cutting zones by carrying out kinematic and temperature fields measurements during cutting or friction on three types of materials: Ti64, Inconel 718 and Al-Li alloys. To achieve this purpose, an experimental bench capable of identifying temperature and kinetic fields during machining or friction, will be developed.
The ESR7 will :
- define this experimental bench to monitor material flow and temperature gradient in both zones where chip formation or friction at the tool-chip interface occurs,
- specify the experimental experimental benchmark to identify the largest range of strain, strain rate and temperature that occurs during machining or tool/chip interface friction phenomena.
The device, which is innovative in its philosophy, will be designed to be a high-capacity linear tribometer, based on a principle of progressive loading in order to be able to know the evolution of the microstructural transformations during the chip formation The tests carried out should make it possible to:
- isolate friction phenomena in order to elaborate new laws of friction behaviour complementary to the laws of material behaviour,
- analyse chip formation in order to validate the machining conditions generating chip fragmentation, for all studied materials,
- study the adequacy of constituent laws to describe the behaviour of the material under machining conditions, or even develop laws capable of describing the behaviour of metallic materials under the loads generated by machining,
- investigate the interactions between the cutting process (thermomechanical strain, deformation, temperature) and the microstructural evolution during chip formation.
During all these tests, the cutting and friction processes will be analysed by measuring cutting actions (forces and torque at the tip of the tool or the centre of the friction surface), temperatures and material flow using a dynamometer platform, an Infrared (IR) camera and a high-speed camera respectively. To complete the analysis, the chips will be collected and analysed using traditional methods to correlate the in process and post mortem observations. To better approach machining operations such as milling or straight turning some kinematic and temperature fields measurements will be performed in oblique machining configuration.
An analysis of sensitivity to the variation of each parameter must be carried out in machining and in situation of intense friction. Modelling of the behaviour of the results in strain, strain rate and temperature according to the input parameters will then be proposed for each of these cases.
The mechanical and thermal solicitations measured using the developed bench test will be used to validate FEM model developed by ESR5 and ESR6. In addition, ESR7 will have to provide data on the thermomechanical fields and clearly identify the different microstructure genesis, to ESR1 and 2 for the selected alloys.