A Thermomechanical Model Dedicated to Thixoforming. Application to Semi-Solid Forming

in Solid State Phenomena (2013), 192-193

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase ... [more ▼]

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material [less ▲]

Influence of parameters during induction heating cycle of 7075 aluminium alloys with RAP process

in Solid State Phenomena (2008), 141-143

Thixoforging involves shaping alloys with a globular microstructure in the semi-solid state. To reach this kind of material, the Recrystallisation and Partial Melting (RAP) process can be used to obtain a ... [more ▼]

Thixoforging involves shaping alloys with a globular microstructure in the semi-solid state. To reach this kind of material, the Recrystallisation and Partial Melting (RAP) process can be used to obtain a globular microstructure from extruded material with liquid penetrating the recrystallised boundaries. Induction heating is used to apply the RAP process to slugs. One of the benefits of using this method of heating is the fast heating rate (20°C/s). This paper will help to improve heating parameters by showing their influence on 7075 aluminium alloy recrystallisation. These parameters are the heating rate; heating frequencies-power; presence or not of protective gas; position of the slug in the inductor; energy stored inside the slug; oxide layer on the slug side; chamfer of the slug upper corner. [less ▲]

Alloy Characterization to Adapt Steels to Thixoforming: Study of a High Chromium High Carbon Steel

in Solid State Phenomena (2008), 141-143

This paper deals with the examination of the influence of alloying elements on the thixoformability of a Cr steel. It focuses on the liquid fraction curves of different Cr steels with modifications of ... [more ▼]

This paper deals with the examination of the influence of alloying elements on the thixoformability of a Cr steel. It focuses on the liquid fraction curves of different Cr steels with modifications of composition. The effect of composition modifications was observed. The solid fraction versus temperature has been obtained by a thermodynamics software (MTData) and by Differential Scanning Calorimetry (DSC), limited to low heating rates. MTData permits to obtain information on the influence of alloying elements, with the advantage of the possibility to change the chemical composition very easily. The DSC tests determine the influence of the heating rate on these curves. [less ▲]

A one-phase thermomechanical Model for Semi-Solid thixoforming

in Solid State Phenomena (2008), 141-143

Simulation of thixoforming: comparison of different constitutive equations

in Solid State Phenomena (2006), 116-117

The behaviour of the semi-solid material is complex to simulate and many approaches are proposed in the literature to represent it. In this work, different constitutive equations are studied: the ... [more ▼]

The behaviour of the semi-solid material is complex to simulate and many approaches are proposed in the literature to represent it. In this work, different constitutive equations are studied: the classical Northon-Hoff law, Joly and Merhabian's one [1] and an innovative micromechanical model using homogenisation technique [2]. These constitutive equations have been implemented in the FE code Forge2 (R) to simulate simple forming tests, such as compression and direct extrusion. The load-displacement curves using the three constitutive equations are compared in order to estimate their capabilities. [less ▲]

Thixoforming of carbon steels: Inductive heating and process control

in Solid State Phenomena (2006), 116-117

The development of steel grades for the production of thixoformed parts made a great progress but the process itself is still difficult to control. The most critical point is the inductive heating of the ... [more ▼]

The development of steel grades for the production of thixoformed parts made a great progress but the process itself is still difficult to control. The most critical point is the inductive heating of the billets to assuring a homogeneous distribution of the desired liquid fraction. One of the principle approaches is based on investigations of the thermo-physical properties of steel grades. These data are also used for numerical simulation of the inductive heating. From these results a mathematical model is derived and implemented in the heating chain for controlling the parameters that determines the billet temperature indirectly by computation and not by direct measuring of the temperature. Optimizing the coil geometry leads to an adapted magnetic field assuring a homogenous temperature distribution in the billet considering expected energy losses. We will also present new results of the liquid fraction within the billet as well as the electrical resistivity of the thixotropic steel at high heating rate corresponding to the industrial scale. Last but not least, some new parts made out of adapted steel will be shown. [less ▲]

Steel grades adapted to the thixoforging process : metallurgical structures and mechanical properties

in Solid State Phenomena (2006), 116-117

Thixoforming of steel offers the advantages of casting technology in combination with high mechanical strength that can only be achieved by forging. The progress in establishing this technology in ... [more ▼]

Thixoforming of steel offers the advantages of casting technology in combination with high mechanical strength that can only be achieved by forging. The progress in establishing this technology in industry depends on the success in the development of suitable steel grades. Recent investigations dealt-with the development of steel grades that are especially adapted to the thixoforming process. For this, alloys were developed with a lower solidus temperature and a wider process temperature range compared to classic forging steels. In consequence, the inductive heating process is more tolerant to inaccuracies and for a given liquid fraction the process temperature window is easier to handle. It is desired to obtain great degrees of deformation at rather low forming forces as these parameters determine the size of the needed presses. This behaviour is affected by the present liquid fraction in the slug and the heat transfer between work piece and die. It was detected that variations of the forming force have a direct influence on the quality of the thixoformed parts. In order to make the thixoforming technology of steels competitive versus other forming technologies, the parts must show a favourable microstructure and thus, good in-use properties. In this paper various solutions are compared. The main results obtained in the optimization research, namely, the steel grades adapted to semi-solid forming, the resulting process parameters and the mechanical properties of thixoforming parts will be presented for two exemplary steel grades. By producing a real automotive part, thixoforging of steels with regard to the adapted materials and to the ongoing industrial implementation of this process is proved. [less ▲]

Influence of experimental parameters on properties and microstructure of the steel X210CrW12 in the semi-solid state

in Solid State Phenomena (2006), 116-117

This paper deals with the examination of the steel grade X210CrW12 and its suitability for Thixoforming. In the semi-solid state, the microstructure of this steel consists of a homogeneous distribution of ... [more ▼]

This paper deals with the examination of the steel grade X210CrW12 and its suitability for Thixoforming. In the semi-solid state, the microstructure of this steel consists of a homogeneous distribution of globular particles surrounded by liquid. Additionally, carbides are stabile up to fraction liquid contents of approximately 40%. After quenching, this steel reveals a globular austenitic microstructure with eutectic (former liquid phase) at the grain boundaries. Compression tests permit to determine the influence of different process parameters on the properties and the material behaviour in the semi-solid state. Their influence on the microstructure was investigated but not yet highlighted. Further investigations on this steel allow a fine-tuning to establish optimal process windows of the different thixoforming- and rheoforming-routes. [less ▲]

Thixoforging of 7075 aluminium alloys at high solid fraction

in Solid State Phenomena (2006), 116-117

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5 < f(s) < 1), which involves the processing of alloys in the semi-solid state. 7075 alloy has been used as a feedstock for ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5 < f(s) < 1), which involves the processing of alloys in the semi-solid state. 7075 alloy has been used as a feedstock for thixoforming in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. The microstructure in semi-solid state consists of fine spheroidal solid grains surrounded by liquid. Thixo behaviour allows laminar flow that avoids macro-porosity and other casting defects and gives better mechanical properties; so we can reduce the weight of functional parts. Higher solid fraction of 7075 alloy is less sensitive to temperature, avoids metal splash at high speed, allows laminar flow at high speed and gives a good smooth surface without stick-slip phenomenon. The process is quicker with less energy and so the production rate increases and the tool has longer life. However, high solid fraction promotes freezing flow because of faster solidification and the lack of liquid phase. This freezing flow creates solid/liquid segregation and increases the forming force. [less ▲]