Thesis Topic

Experimental Investigation and Modeling of Overheating in Aerospace Alloys during Milling

Abstract

Finishing machining plays a key role in the quality of mechanical components, particularly in the aerospace industry where in-service performance requirements are critical. Beyond simple geometric shaping, these operations modify the mechanical and microstructural properties of machined surfaces. These alterations, referred to as surface integrity, directly govern the functional properties of components, especially their fatigue resistance. Among the potential defects, overheating phenomena, characteristic of thermal overexposure, represent a critical issue due to their particularly detrimental impact on in-service behavior.

In this context, the control and prediction of surface integrity remain limited by the complexity of the underlying physical mechanisms and by the empirical nature of current industrial approaches. This PhD work aims to address this issue by relying on a deterministic causal approach, intended to establish robust relationships between operating conditions, thermomechanical loads, the internal material state, and the resulting surface properties.

First, a literature review enabled the identification of the dominant mechanisms governing surface integrity and highlighted the major role of residual stresses and microstructural evolutions. The investigated overheating cases revealed contrasted degradations depending on the material, with the formation of hardened and brittle layers for Ti-6Al-4V, and over-aging phenomena for 7xxx series aluminum alloys.

A first contribution of this work consists in the development of a cutting force model allowing the decomposition of forces into contributions associated with chip formation and ploughing. This approach introduces intermediate parameters representative of the tool edge/workpiece material pair, facilitating the analysis of the influence of tool edge micro-geometries. An experimental methodology based on variable uncut chip thickness tests was also proposed, enabling a robust identification of the model parameters with a reduced number of experiments.

Based on this framework, an analytical modeling of local thermomechanical loads was developed to estimate pressures and heat fluxes within the shear zones. The results highlighted the significant influence of tool edge micro-geometries on the magnitude of thermal fluxes. In addition, an original concept of thermal cycling was introduced to quantify heat accumulation effects in machining operations, where the final surface temperature results from multiple cutting passes. Its application to experimental cases made it possible to identify kinematic configurations prone to overheating.

Finally, a hybrid modeling approach was implemented to predict the evolution of the internal material state from the identified thermomechanical loads. The simulations reproduced the thermal and mechanical fields beneath the machined surface. Quantitative correlations between the thermal history and material properties, such as hardness and electrical conductivity, were established, enabling the characterization and prediction of overheating effects in helical milling configurations.

Overall, this work demonstrates the relevance of a causal approach for understanding and predicting surface integrity in machining. It opens perspectives for the development of robust predictive tools combining physics-based models and experimental data, with the aim of achieving improved control of manufacturing processes.

Keywords

Milling, Orthogonal cutting, Micro-geometry, Surface integrity, Overheating, Modeling.

Doctoral advisors

• Gérard POULACHON - Director,
• RITOU Mathieu,
• Frédéric ROSSI
• BIREMBAUX Hélène.

Partners

• Airbus
• LS2N

Project

N/A

Funding

• CIFRE

Start

3rd of April 2023

Expected end

18th of May 2026