References of "Pierret, Jean-Christophe"
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See detailCharacterization of thixoforming process of 100Cr6 steel
Solek, Krzysztof; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Transactions of nonferrous metals society of China (2010), 20(special 3), 916-920

The main goal of this work is an analysis of the semi-industrial process of steel thixoforming. The process was carried out using industrial equipment. This equipment consists of a heating device ... [more ▼]

The main goal of this work is an analysis of the semi-industrial process of steel thixoforming. The process was carried out using industrial equipment. This equipment consists of a heating device, industrial robots and a hydraulic press. The globular microstructure ensuring thixotropic properties was obtained using the SIMA method. It is one of the simpler and cheaper methods which could be easy applied in case of steel alloys. In this work the hot forged rods, commercially produced from 100Cr6 steel, were used. The first part of the work concerned the determination of the proper temperature range, for thixoforming of 100Cr6 steel. Next, some heating tests were carried out in order to obtain as uniform temperature distribution as possible. Heating process was executed using inductive heating. Microstructure analysis of heated samples reveals globular particles surrounded by liquid phase. Next the thixoforming process was carried out using closed-die forming technique. Completely filled die cavity and good microstructure of the part show that applied process parameters were properly selected. [less ▲]

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See detailStability of steel thixoforging process
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in Transactions of Nonferrous Metals Society of China (2010), 20(Special 3), 937-942

Whereas thixoforming of aluminum and other low melting point alloys is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High temperature ... [more ▼]

Whereas thixoforming of aluminum and other low melting point alloys is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High temperature issues, die wearing and production rate are problems that must be solved and are more and more investigated. This work focus on the study of a thixoforming line stability in the aim of industrialization of the process. The line is fully automated in order to maximize the repeatability of the experiments. Studied parameters are the heating cycle, the slug temperature, the tool temperature and the forming speed. For each of them we will give an order of magnitude of the expected variations in a steady-state process as well as the effects of these variations on the process itself (forming load and parts quality). Three different tools, and so three slugs and parts geometries, have been used in the experiments and are presented. Some mathematical simulations have been realized on the finite elements code Forge2008© with a semi-solid constitutive law and are also compared to the experiments. So the capacity of the model to represent the process stability is discussed as well. [less ▲]

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See detailX38CrMoV5 hot-work tool steel as tool material for thixoforging of steel, numerical and experimental evaluation
Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg; Vaneetveld, Grégory ULg et al

in Transactions of Nonferrous Metals Society of China (2010), 20(Special 3), 713-718

Whereas thixoforming of low melting point alloys as aluminum or magnesium is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High working ... [more ▼]

Whereas thixoforming of low melting point alloys as aluminum or magnesium is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High working temperature, die wearing and production rate are problems that must be solved and are under investigation. The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during the steel thixoforging process in order to determine if classical hot-work tool steel could be an appropriate tool material. This evaluation has been realized thanks to experimental trials and to simulations on the finite elements code Forge2008©. The effect of the loadings on the tool’s failure modes are highlighted and compared to the ones observed in classical hot forging. Beyond this, the failure modes of hot-work tool steel, the X38CrMoV5 or H11, is presented. [less ▲]

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See detailConception of tooling adapted to the thixoforging of high solid fraction hot-crack-sensitive aluminium alloys
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Transactions of Nonferrous Metals Society of China (2010), 20(9), 1712-1718

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. Tooling has to be adapted to this particular ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. Tooling has to be adapted to this particular process to benefit of shear thinning and thixotropic behaviour of such semisolid material. Tooling parameters, as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool. These thermal exchanges influence the high-cracking tendency and the rheology of the semisolid material during forming which affect parts properties. This paper shows, thanks to extrusion tests, how thermal exchanges influence surface quality of thixoforged parts made in 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector. A direct application is the evaluation of surface quality of thixoforged thin wall parts made in 7075 aluminium alloys. [less ▲]

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See detailThixoextrusion of A357 aluminium alloy
Forn, Antonio; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in Transactions of Nonferrous Metals Society of China (2010)

The aim of this work is to attempt the application of A357 Al-Si-Mg cast alloy in the thixoextrusion process, evaluating the different parameters effect. Thixoextrusion offers several advantages compared ... [more ▼]

The aim of this work is to attempt the application of A357 Al-Si-Mg cast alloy in the thixoextrusion process, evaluating the different parameters effect. Thixoextrusion offers several advantages compared to traditional hot-extrusion such as lower pressure, minor friction forces, higher material fluidity, longer tool life, etc. This type of semi-solid process requires high solid fractions (0.5<fs<1). Aluminium alloy A357 is a commercial cast alloy characterized by high strength, ductility and corrosion resistance. It is commonly used for cast production of automotive components and it is also suitable for semi-solid process, due to its ample range of solidification. A357 aluminium alloy has been used as a feedstock for thixoextrusion in order to investigate thixoformability at high solid fraction. Alloys with high solid fraction are less sensitive to temperature drops and allow laminar flow at higher speeds. To know the parameters that improve the mechanical properties of thixoextruded parts, some extrusion tests at constant speeds have been carried out. The results were used as the main criteria for assessing the thixoforming viability of the A357 alloy. [less ▲]

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See detailFriction coefficients evaluation for steel thixoforging
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in Proceedings of The 13th Esaform Conference on Material Forming (2010) - semi-solid processing (2010)

Since the first works on thixoforming, lot of studies have been performed all over the world and the behaviour of the globular semi-solid slurry is now quite well understood. This knowledge had lead to an ... [more ▼]

Since the first works on thixoforming, lot of studies have been performed all over the world and the behaviour of the globular semi-solid slurry is now quite well understood. This knowledge had lead to an industrialisation of the technology for low melting point alloys as aluminium or magnesium. For high melting point alloys as steel, this industrialisation is still a wish but seems closer each year. In the aim of this development of the process, it is important to be able to accurately represent the behaviour of the slurry during thixoforming. In this goal, lot of constitutive models has been proposed during the last years. However, until now there isn’t any study about the friction in the case of thixoforming. This knowledge is needed as friction has an important effect on the flow of the slurry during the shaping. The aim of this work is so to propose a quantification of the friction coefficients for the thixoforming technology thanks to experiments on a dedicated tool and comparison with simulations run on the finite elements code Forge2008©. The friction law is a Coulomb limited Tresca one. [less ▲]

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See detailValidation of a one-phase thermomechanical model for thixoforming of steel by comparison between numerical and experimental results on two semi-solid extrusion tests
Koeune, Roxane ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Yonglin, Kang (Ed.) 11th International Conference on Semi-Solid Processing of Alloys and Composites (2010)

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See detailBenefits of thixoforging hot-crack-sensitive aluminium alloys at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in International Journal of Material Forming (2010), 2

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See detailQuantification de la robustesse du procédé de thixoformage des aciers
Pierret, Jean-Christophe ULg

Doctoral thesis (2009)

This work aims to assess the robustness of the steel thixoforming process by a qualitative and quantitative study of the influence of the parameters involved in the process. Thixoforming is the shaping of ... [more ▼]

This work aims to assess the robustness of the steel thixoforming process by a qualitative and quantitative study of the influence of the parameters involved in the process. Thixoforming is the shaping of metals in the semi-solid state and with a globular microstructure. In this case, one shows that consistency decreases when shear rate increases and that the process parameters leading the behaviour are time dependent. As a key-step of the technology, heating is studied as well as forming. Influences of heating strategy, inductor’s geometry and external conditions are determined by the help of modelling and heating experiments. Handling system between heating furnace and press is also tackled. To study the forming’s relability and sensitivity, three geometries are used : direct extrusion, a rheological study part and an industrial part. Again, practical experiments and modelling are used in a complementary way. Effects of slug’s temperature, forming speed, lubrication and tool’s temperature are analysed. Repeatability of heating and forming are highlighted. The defects and structures obtained in the parts are presented before discussing the thixoformability of steel grades. In particular, qualification of especially designed grades as well as non adapted grades is discussed. Finally, the tooling wear and lifetime issues are detailed as it is one of the mean locks of the technology industrialisation. [less ▲]

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See detailInfluence of the chemical composition on the thixoformability of steels
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in International Journal of Material Forming (2009)

This work deals with the qualification of a variety of steels for their shaping by the thixoforging process. This technology requires setting up a globular microstructure inside the material during ... [more ▼]

This work deals with the qualification of a variety of steels for their shaping by the thixoforging process. This technology requires setting up a globular microstructure inside the material during reheating to a temperature between the solidus and liquidus. As the evolution of the liquid fraction is strongly connected to the steel composition, it is useful to understand how low carbon steel could be alloyed and still thixoformable. The most critical parameter for this is the carbon content. In this study, a theoretical analysis of the phase evolution during the reheating has been performed on the MT Data software to investigate the influence of alloying elements. These first results have been confirmed by Differential Thermal Analysis and by inductive heating experiments on steel slugs. Finally, some parts have been shaped using a thixoforming tool mounted on a hydraulic press. Micrographs of reheated slugs as well as of actual parts are also presented in this paper. [less ▲]

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See detailBenefits of thixoforging hot-crack-sensitive aluminium alloys at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Proceedings of The 13th Esaform Conference on Material Forming (2010) - semi-solid processing (2009)

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular microstructure helps to decrease forming load. But the introduction of a liquid phase in the material is a source of defects that limit mechanical properties of thixoforged parts. One of these defects is the hot cracking for some hot crack-sensitive wrought aluminium alloys. Hot cracking occurs because of strain and deformation during last step of solidification. This paper shows how thixoforging process helps to lower hot cracking tendency without modification of the alloy composition by decreasing strain and deformation due to shrinkage. Different experimental tests by extrusion of 7075 aluminium alloys are used. [less ▲]

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See detailImprovement in Thixoforging of 7075 Aluminium Alloys at High Solid Fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in Solid State Phenomena (2008), 141-143

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<1). 7075 aluminium alloys have been used as a feedstock for thixoforging in order to investigate thixoformability of a ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<1). 7075 aluminium alloys have been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to temperature, avoids metal splash at high speed and allows laminar flow at high speed. Hot tool combined with lubricant tool coating are used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges with the tool. Improved thermal and forming parameters [1-2] will be applied to produce an automotive component by thixoforging and mechanical properties have been measured from tensile samples. High mechanical properties are obtained after T6 thermal treatment. [less ▲]

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See detailSteel Thixoforging: Heat Exchange Impact on the Mechanical and
Becker, Eric; Cezard, Pierre; Bigot, Regis et al

in Solid State Phenomena (2008), 141-143

Steel thixoforging process combines the advantages of performing parts having highly complex shapes and good mechanical properties. These advantages result from the shear thinning flow behaviour of semi ... [more ▼]

Steel thixoforging process combines the advantages of performing parts having highly complex shapes and good mechanical properties. These advantages result from the shear thinning flow behaviour of semi-solids due to microstructure changes during the material deformation. Many parameters such as steel grade, raw speed, slug temperature, tool temperature influence the steel thixoforging process. In this work, we are interested in analysing the influence of thermal conditions as well as ram speed on the flow behaviour and the microstructure of the final parts. To do so, thixo-extrusion tests on a high speed hydraulic press were performed on C38 steels using different ram speeds and different temperatures for the tools. The temperature is measured in the die close to the tool-material interface during the whole process. Correlations between the temperature measurements, the flow profile and the microstructure are discussed. Using the Finite Element code Forge2005, these thixo-extrusion tests are simulated. Using an inverse method, some parameters used in the thermal exchange modelling are identified by successive comparisons between calculated and measured temperatures within the die. [less ▲]

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See detailMetallurgical and mechanical analysis from thixoforging steel shape
Becker, Eric; Bigot, Regis; Langlois, Laurent et al

in International Journal of Material Forming (2008), 1(1), 977-980

Since always, Industry minimizes manufacturing process plan and increases mechanical behaviour. In this topic, the thixoforging process offers important perspectives especially steel thixoforging. It is ... [more ▼]

Since always, Industry minimizes manufacturing process plan and increases mechanical behaviour. In this topic, the thixoforging process offers important perspectives especially steel thixoforging. It is on the way of industrial development between casting and forging process. Previous works have illustrated the importance many parameters such as steel grade, slide speed, slug and tool temperature on the geometry from thixoforging part and of the forming load. This paper completes the previous results. It presents an analysis from mechanical resistance of samples extracted of from thixo-extrusion parts on a high speed hydraulic press. This strength investigation is correlated with metallurgical analysis. Macrograph analyses allow identifying the material yield during the process and the different phases. [less ▲]

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See detailExtrusion tests of 7075 aluminium alloy at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in International Journal of Material Forming (2008), 1(1), 1019-1022

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to a drop in temperature, avoids metal splash at high speed, allows laminar flow at high speed. Hot tool is used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges. To determine the best parameters to achieve maximum mechanical properties in thixoforging of 7075 aluminum alloy, we need to consider the impact of some parameters such as tool temperature, shear rate. For this, we use extrusion tests with constant speed [1] where these parameters are known. The result of this study is that each parameter has its level of impact on the thixoforging: the temperature of the tool and the deformation rate shouldn't be high to avoid cracks. Thermal exchanges between the material flow and the tool have to be reduced to avoid high solidification rate [2]. [less ▲]

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See detailSteel thixoforming, influence of forming parameters on the microstructure
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in International Journal of Material Forming (2008), 1(1), 1011-1014

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the ... [more ▼]

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the process. Among these we could quote liquid fraction, shear rate, shape factor, contiguity, tool temperature, agglomeration level, heating rate, protecting gas, temperature distribution, lubricant. Of course all of these parameters don’t have the same order of importance. In this paper we show the influence of a set of chosen parameters and we highlight their effects on the microstructure and so, on the deformation behavior. The studied parameters are the heating conditions, the tool temperature, the part temperature, the thermal exchanges between the part and the dies and the forming rate. [less ▲]

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See detailRobustness of a thixoforming production line
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in Solid State Phenomena (2008), 141-143

The development of the thixoforming process made great progress since its beginning. But whereas thixoforming of aluminium and other low melting point alloys is now an industrial reality, thixoforming of ... [more ▼]

The development of the thixoforming process made great progress since its beginning. But whereas thixoforming of aluminium and other low melting point alloys is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High temperature issues, die wearing and production rate are problems that must be solved and are more and more investigated. This work is a study of the robustness of a complete thixoforming unit dealing with steel. This flexible unit allows parts of various shapes be formed in conditions close to industrial ones. The study focus on the heating strategy, heat exchanges between the slug and the tool, the feeding and the cycle time. In this work, modelling has been used to simulate heating and feeding. In parallel, experiments have been made to obtain the needed parameters, to validate the modelling and to evaluate the capacities of such a line. [less ▲]

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See detailTHIXOFORMAGE DES METAUX: Mise en forme rapide de pièces fonctionelles “near-net-shape” à design complexe dignes du forgeage!
Rassili, Ahmed ULg; Vaneetveld, Grégory ULg; Pierret, Jean-Christophe ULg et al

Poster (2007, June 14)

Présentation du laboratoire de thixofomage de métaux.

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See detailThixoforming of Steel: New Tools Conception to Analyse Thermal Exchanges and Strain Rate Effects
Cezard, Pierre; Bigot, Regis; Becker, Eric et al

in AIP Conference Proceeding - 10th ESAFORM Conference on Material Forming (2007, April 07)

Through different papers, authors shown that the influence of thermal exchanges was a first order parameter on the semi-solid steel behaviour, and certainly for every semi-solid metallic materials. These ... [more ▼]

Through different papers, authors shown that the influence of thermal exchanges was a first order parameter on the semi-solid steel behaviour, and certainly for every semi-solid metallic materials. These thermal exchanges hide other parameters effect like, for example, the strain rate influence. This paper tries to determine the influence of these two parameters by using a new extrusion device on a hydraulic press. This new tools conception annihilated the influence of the decrease of the punch speed before stopping and permitted to have a constant speed during the experiment. This work also deals with the homogeneous flow during thixoforming of steel and shows the importance to couple initial temperature of the slug with punch speed. This paper presents different conditions which permitted to have a homogeneous flow by keeping a low load. [less ▲]

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