As long-time partners, the ArcelorMittal Global R&D research centre in Montataire, which specialises in automotive applications, and UTC have created this joint laboratory in 2019, which is supported by the Hauts-de-France Region and partly funded by the ERDF (also calle Enedis- power grid management). The work carried out within the framework of FuseMetal focuses on the welding of 3rd generation high strength steels and the modelling of additive manufacturing processes. The 6 PhD students, Elise, Daoming, Héléna, Marcia, Ghassen and Ana Julia present their research work in the laboratory.
Ghassen Dali, a 3rd year PhD student, is conducting a thesis on the modelling and simulation of metal additive manufacturing for metallurgical and process optimisation.
“My thesis project started on October 1, 2020, and is part of the laboratory’s strategy to develop and strengthen its skills in the field of additive manufacturing (3D printing), which is a focal point of the FuseMetal joint laboratory. Indeed, this technology has a promising potential because it allows the production of complex and non-traditional geometries, thus bypassing the design/manufacturing constraints imposed by conventional processes, shortening development cycles and reducing costs. On the other hand, additive manufacturing processes can lead to defects during and after manufacturing (instability of the liquid bath, porosities, delamination between layers, heterogeneous properties). To remedy these drawbacks, the use of simulation software is recommended in order to reduce the number of tests required to produce a part that complies with the technical specifications in 3D printing.) I am therefore working on the simulation and modelling of 3D printing of steels. The aim is to develop so-called predictive digital models. The model will be able to better describe the relationships between the operating parameters, the properties of the material and the manufacturing state of the final part.
Marcia Meireles, a 3rd year PhD student, is conducting a thesis on the experimental identification of the links between process parameters, thermal cycles and metallurgical transformations during the additive manufacturing of steels.
“My thesis work concerns the study of an additive manufacturing process for parts (3D printing). This consists of manufacturing 3D parts by adding successive layers of molten material. This process is very promising in the industrial sector because it allows the manufacture of parts with very complex geometries, while avoiding additional assembly phases and produces very little waste. Thus, 3D printing is a process that combines remarkable and unique capabilities. The material I am studying is a type of steel developed by ArcelorMittal specifically for 3D printing. Indeed, to obtain parts that meet the requirements of their application, it is essential to understand the effect of the chosen printing parameters on the quality of the parts. This is why, in my thesis, I study the physical phenomena that take place during 3D printing and evaluate their effects on the final characteristics of the parts. Thus, the goal of my studies is to be able to manufacture 3D parts in an optimal way.”
Daoming Yu, a 3rd year PhD student, is conducting his thesis on the optimisation of 3D printed hot stamping tools.
“My research project focuses on the topological optimisation of hot stamping tools obtained by metal additive manufacturing. Hot stamping is a forming process in which a metal sheet is first heated in an oven to a temperature of approximately 900°C. The sheet is then shaped at high temperature in a press and, thanks to intense cooling (in contact with cold tools), metallurgical transformations allow the final part to have high mechanical characteristics (the final part is case-hardened). Thanks to the high mechanical properties thus obtained, it is possible to reduce the thickness of the parts, which makes it possible to lighten the vehicles. Ultimately, fuel consumption and CO2 emissions will be reduced. In addition, this process has several other advantages: it allows complex geometries to be formed, requires less press pressure, the parts do not show springback, etc. Because of these advantages, hot forming is a widely used forming process for the manufacture of automotive parts. In the hot forming process, the tool is particularly complex, as it incorporates a cooling circuit. It seemed important to us to evaluate the potential of additive manufacturing to produce these stamping tools. In particular, this technique can be used to optimise the cooling circuit and thus improve the efficiency of the hot stamping process. The objective is to develop a unified procedure for designing forming lines, including the design of tools by combining modelling of the forming process and topological optimisation, freeing the constraints imposed by machining and taking into account the constraints imposed by additive manufacturing. This procedure is tested on prototype tools to validate the viability of the proposed solutions in terms of conformity and tooling performance.
Elise Champolivier, a 2nd year PhD student, is conducting a thesis with experimental and numerical studies on modelling and scale transition for the prediction of the shaping of laser assembled structures.
“For several years now, car manufacturers have been constantly challenged to reduce the consumption of their vehicles while maintaining their performance in terms of safety. ArcelorMittal is developing new solutions to meet these objectives by combining two technologies: Laser-Flattened Blanks and 3rd generation ultra-high strength steels. The Laser Flap Blank technology consists of joining steel sheets of different grades, thicknesses or coatings by laser welding. The assembled sheets are then shaped to obtain the shape of the automotive part: this is the stamping stage. Coupled with the use of very high strength steels, this technology makes it possible to lighten automotive parts with the same performance while maintaining their strength properties. My PhD thesis focuses on the study of the formability of Laser-Flattened Blanks made of 3rd generation steels. My work consists of studying the mechanical behaviour of the welds of these assemblies during the forming stage in order to define recommendations and failure criteria that manufacturers can apply to the design of their parts. The study is based on experiments that allow the feeding of models The study is based on experiments that feed into numerical models with the aim of developing predictive models for the behaviour of laser welded assemblies.
Ana Julia Vasconcelos de Moreira, 3rd year PhD student, is carrying out a PhD thesis on the evolution of local microstructures of 3rd generation steels in the presence of strong thermal and chemical gradients.
“My thesis focuses on the study of the joining of two identical or different 3rd generation steel sheets by laser welding for the manufacture of automotive parts. In order to meet the requirements of the automotive industry regarding weight reduction and improved mechanical performance. In addition to meeting these requirements, laser welding technology makes it possible to design automotive parts with specific properties where they are needed. The challenge lies in the change in the characteristics and behaviour of the steels around the weld seam, due to the high temperatures reached during laser welding followed by rapid cooling. Consequently, I am studying the different areas of the different steel assemblies designed by ArcelorMittal, in order to identify and understand the origin of the mechanical and metallurgical defects and thus be able to optimise the laser welding process.