Machining and Metal Forming
The research on the USIMEF axis (machining and shaping) is part of the overall theme of establishing links between manufacturing processes and the maintenance in service of mechanical parts. The activities carried out concern the processes of machining by removal of material (cutting tool or abrasive water jet), additive manufacturing and shaping of sheets by plastic deformation, mainly for aeronautical structural parts. The concept of “surface” integrity is at the heart of the activities of the USIMEF axis. This integrity of “surface” can be defined by 3 descriptors: geometric (topology of surface condition), mechanical (evolution of residual stresses), microstructural (evolution of the microstructure and deformation rate in the material). The combination of these three factors determines the fatigue life of the part. However, the manufacturing operations modify these three descriptors in a very variable way depending on the material, the process, the operating conditions… In the studies carried out, it is necessary to evaluate the surface obtained according to the 3 descriptors, to develop models and to propose recommendations. Specific work on the characterisation of these descriptors is also carried out and is the subject of a separate theme).
Topic 1: MULTI-AXIS COMPLEX PROCESSING
The work carried out under this theme aims to :
- – Optimize the machining of left surfaces by toric milling. Automatic method of cutting the surface in Muti-zones to apply a strategy of machining in parallel planes with different machining directions.
- – Optimize the tool trajectories for the machining of the left surfaces using tools from differential geometry and artificial intelligence. Development of two software libraries: (i) the DGL (Differential Geometry Library) focused on the manipulation of left curves and surfaces (Bézier, splines, NURBS, …) with the tools of differential geometry (normal, curves, main directions, …); (ii) the jCAM (java Computer Aided Manufacturing) centred on the business aspects: machines, tools, center-tool surfaces, trajectories, etc. Application framework development: Cosmo (Complex Surface Machining Optimisation)
Topic 2 : DRILLING OF PILES MULTI-MATERIALS
The activities carried out under this theme are concerned with the characterisation and modelling of the phenomena involved in the drilling of multi-material materials and stacking. The objective is to establish the relationships between operating parameters, process indicators (mechanical actions, vibrations) and compliance with quality criteria, in terms of geometry but also in terms of “surface integrity” and health matters. This work applies not only to conventional drilling, but also to innovative drilling processes: Forced Vibration Assisted Drilling (PAVf); Orbital Drilling (PO) and High Speed Orbital Drilling (POGV).
Topic 3 : INNOVATIVE PROCESSES
Topic 3-1 : Innovative strategies of manufacturing
- – Machining by pushing: methodology for balancing cross-sectional efforts and limiting dynamic problems such as bending or tool vibration
- – Drawing: drawing of different types of materials (magnesium alloys, aluminium alloys, titanium alloys). Influence of tool geometry on cutting forces. Process optimization (tools, cutting conditions, trajectories)
Topic 3-2 : Abrasive Water Jet Machining
Optimization of machining process control by abrasive water jet :
- – Simple shape machining (pockets) and variable depth left surfaces
- – Mastery of operating parameters and development of machining strategies
Topic 3-3 : Additive manufacturing
Optimization of the quality of nickel base superalloy parts (In718 LC) obtained by laser melting technology of metal powders. Test campaign by definition of elementary test pieces, technology and a demonstrator to control quality and productivity.
Topic 3-4 : Mid-Hot Shape (400°C – 500°C) Ti6Al4V Sheet Metal
The development of metal sheet forming processes for automotive or aeronautical structures at temperatures between ambient and high temperatures, requires consideration of complex behaviour of materials (anisotropic elasto-viscoplastic behaviour) in order to provide geometric information (elastic feedback, distortion) and post-stress statesto study the influence of process parameters. This is particularly the case for the semi-hot forming of Ti-6Al-4V titanium alloy at temperatures of 400 – 500°C. In this temperature range, the anisotropic plastic behaviour of the Ti6Al4V alloy is characteristic of the deformation mechanisms present at room temperature and are combined with the improvement in formability brought about by the increase in temperature. The use of a plastic model with anisotropic hardening and kinematic evolution improves the prediction of stress states and post-forming elastic return.
Topic 4 : MULTI-PHYSICAL AND MULTI-MATERIAL DIGITAL SIMULATION OF PROCEDURES
Topic 4-1 : Hot Shaping
This involves taking into account the coupling effects (thermal-mechanical) in the behaviour of sheet metal and tooling material as well as in the behaviour of sheet metal/tool interfaces over a wide range of temperature and deformations in shaping operations. A first example is the case of hot shearing (550°C – 900°C) of 22MnB5 hardening steel sheet by X70CrMOV5-61 HRc steel blades. The work resulted in the first 2D-DP models of the shearing operation taking into account the thermo-mechanical coupling in sheet metal and tools. They thus make it possible to propose a first thermal and mechanical analysis of local stresses during the operation and to evaluate the influence of the thermal effect on the mechanical stress of the blades. The link between the high stress level and the high temperature values is observed in the process of creating the plate bulge, and then, to a lesser extent, the displacement of the maximum stress around the cutting edge. These results are consistent with the experimental study developed on the hot shear module of the ICA MEFISTO equipment.
Topic 4-2 : Representative elementary cup
The implementation of experiments instrumented on small scales has developed in recent years with a view to validating numerical simulations of cutting phenomena. Indeed, the complexity of the thermomechanical loads involved (speeds, and high temperatures) has necessitated increasingly sophisticated measurements of the tool-point kinematic and thermal fields. The work therefore focused on the simultaneous measurement of these quantities in a submillimetre context and at deformation rates of the order of 103s-1, using a specific cutting device (DEXTER bench) and a coupled vision/characterization device (VISIR)
Topic 5 : Integrity of surface
In order to study the influence of machining and processes on fatigue life of parts, the “surface” integrity descriptors (geometric, mechanical and microstructural) are widely analysed, and specific work on the definition of relevant descriptors, and their measurement/evaluation. It is necessary to establish the relationships between the conditions of implementation of the processes and these relevant descriptors on the one hand, and then between these descriptors and fatigue behaviour. The 3D topology of the surface condition and residual stresses are particularly studied.
Topic 6 : Learning games
In addition to process research activities, the team also pays particular attention to the transmission of knowledge in connection with the training of future technicians and engineers in the mechanical engineering field. From this constant desire came an innovative training tool in the field of CN machining: MECAGENIUS. It is a virtual action learning companion that allows you to discover a manufacturing workshop, learn how to machine parts on CNs and manage a manufacturing project in a virtual workshop. The game is available online here.