Thierry Barriere

Experimental and numerical analysis on sintering behaviours of injection moulded components in 316L stainless steel powder

Abstract The sintering behaviours of injection moulded components in 316L stainless steel powder are investigated by means of the bending and dilatometric tests in the furnace. Various thermal cycles are realised for different tests. The experimental results are used to determine the parameters of uniaxial viscosity and sintering stress in the viscoplastic constitutive law, which is important for description of the sintering behaviours. The sintering models are implemented into the finite element solver, incorporated with the identified parameters, to simulate the size change and shape distortion of powder injection moulded components during the sintering process. The sintering simulation takes into account the green inhomogeneity caused by powder binder segregation in the previous injection process. The simulation results for the sintering process of a three-dimensional wheel component are compared with the experimental ones. It proved validity of the sintering model and the approaches for parameter determination proposed in the study.

Mechanical and functional properties of Invar alloy for μ-MIM

Abstract Micrometal injection moulding (μ-MIM) is a promising alternative for fabricating micro parts. Low coefficient of thermal expansion Fex–Ni1−x alloys are suitable to meet high dimensional stability with temperature keeping acceptable mechanical properties. However, these alloys are sensible of elements contamination during the debinding and sintering stages, and their dimensional stability and mechanical properties could be affected. The present work studies the effect of using combinations of debinding and sintering atmospheres in the micropowder injection moulding of Invar 36 feedstocks based on cellulose acetate butyrate binders. Microtensile specimens were successfully injected. Densification and microstructure at different conditions were linked with mechanical and physical properties of the parts. The processing conditions, and thus, the residual C, O and especially H influence severely these properties.

Simulation of micro injection moulding with emphasis on the formulation of feedstock viscosity : use of non-equilibrium molecular dynamics for the determination of viscosity of multi-body fluid

The need for prediction of shear viscosity of fluid in particle charged‐Micro Injection Molding at mesoscale, by modelling a whole system particle‐polymer with inter‐dependencies, permits to establish a more realistic feedstock viscosity formulation. The applicability of non‐equilibrium molecular dynamics (NEMD) is investigated for the determination of shear viscosity of melts composed of particles/polymers in microcavities. NEMD is used to simulate planar Poiseuille flow of metallic particle‐polymer melt. Simulations are carried out using molecular dynamics simulation package ESPResSo. The variation of viscosity face to temperature is in agreement with theoretical results. Simulations are compared to experiments. The equivalent viscosity formulation is tuned according to NEMD simulation results, and implemented in a MIM solver built up by the authors. MIM simulations are compared to previously implemented simulations using another equivalent viscosity formulation based on experiments for the case of mono...

Particle‐polymer Interactions Analysis For Metal Powder Injection Molding Feedstock: A Molecular‐dynamics Simulation With Dissipative Particle Dynamics Using ESPResSo

The applicability of Dissipative Particle Dynamics is investigated for the rheological study of melts composed of particles/polymers in microcavities for micro injection moulding. The need for prediction of rheological parameters of fluid in Particle charged‐Micro Injection Molding is of great importance so far as this would give crucial information concerning, e.g., spatial arrangement of polymeric chains and metallic particles and possible segregation effects. Complex fluids like polymer melts have macroscopic behaviour that greatly depends on their microstructure. The dynamics of a complex fluid is fundamentally affected by its microscopic structure. A complex fluid is no longer completely described by the Navier‐Stokes equation, but described by so‐called Fokker‐Planck equations. A fluid is represented by interacting particles. These particles are allowed to move in a continuous space. Each particle carries certain information pertaining to the flow like the volume of the fluid, or only the mass of the fluid. The equations of motion can also be defined through Newton’s laws of motion as in molecular dynamics. Simulations are carried out using molecular dynamics simulation package ESPResSo.

Modeling, Simulation, and Experimentation of Fatigue Behavior in Amorphous Solids

Amorphous solids, such as certain polymers, alloys, and polymer-based composites,are increasingly used materials in engineering components and thus, their fatigue behavioris of utmost importance. The article presents a unified approach suitable for modeling bothisothermal high cycle and low cycle fatigue behavior. The emphasis is placed on the ductilefatigue in which fatigue damage represents the material degeneration during the creation ofmicro-cracks governing majority of the total fatigue life (up to 95%). The model’s capability fortechnologically important polycarbonate (PC) polymer is addressed. The results, in accordancewith experimental observations, favor ductile fatigue behavior, i.e. damage fields remain smallfor most of the fatigue life and do not cause the macroscopic stress reduction. Due to thisproperty, fatigue life of an entire structural element can be evaluated by exploiting singlelocations at which the fatigue damage decisively emerges.

Multiphysic coupling and full cycle simulation of microwave sintering applied to a ceramic compact obtained by ceramic injection moulding

ABSTRACT Microwave sintering represents the coupling of multiple physical phenomena. It involves the distribution of electromagnetic fields, heat generation by electromagnetic effects, heat conduction in the material, and evolution of the densification in the sintered components. This paper describes the mathematical models and the numerical methods used to simulate the complex sintering process. Simulation results are provided for the prediction of shrinkage and evolution of the relative density of the sintered materials. A full cycle simulation of the microwave sintering process have been realized on the COMSOL Multiphysics finite element software platform. This work provides an important approach to studying the process of microwave sintering. The simulation results for sintering submicron zirconia powders are compared with experimental results in terms of the relative densities of the sintered material.

Unconventional methods of sintering Inconel 718 MIM samples

In this investigation, three different ways of sintering Inconel 718 MIM samples are compared. The conventional way of sintering in a furnace will be compared to FAHP and microwave sintering. The difficulty of these two methods is to be able to control the shrinkage of the sample and so its shape. These methods have yet not been investigated with a super alloy powder and so, the effects of a high sintering rate on a MIM sample. By accelerating the sintering kinetics, the thermal behavior may be modified. Hence, the behavior of the Inconel 718 sintered by field assisted and microwave sintering has been investigated. The sintered samples were all injected from a feedstock composed of a fine particle Inconel powder and a binder principally composed of CAB and PEG. They were debinded into water for 24h and put in a furnace at 500°C during 2 hours. The heating rate of the furnace was set to 5°C/min until 1290°C during 2 hours. The heating rate of the FAHP was set to 50°C/min until 1250°C during 15 minutes. The microwave samples were sintered around 1300°C during 1 hour, the temperature was increased progressively by steps of 100°C. The effects of the different process on the microstructure and the mechanical properties are then compared. There was no difference in distribution of pores between the conventional sintering and the FAHP sintering but a finer grain size showed better hardness. The microwave sintering of a MIM sample is more complex and the best properties were not obtained.

Development and Characterization of Inconel-Based Mixtures for Metal Injection Molding Applications

In this paper, the development of a new mixture, called feedstock, based on nickel super-alloys for Metal Injection Molding (MIM) is presented. This feedstock, which will be used to obtain metallic parts for the aeronautic industry, is a mixture of the appropriate, environmentally friendly polymers and metallic powders. Many scientific problems should be taken into account. For example, it requires tight control of the process to achieve the strict chemical and physical properties, because of the application in aeronautic industry. Another difficulty is the large dimension and functional requirement of manufactured components, which subject to the high mechanical and thermal constraints. Additionally, the use of a biodegradable polymer makes the process more delicate because of its thermo-physical properties.Copyright

An optimization strategy for the determination of material and process parameters to avoid segregation defects during metal injection powder

An explicit 3D software “FEAPIM” has been developed at LMARC to perform efficiently the injection simulation to predict and simulate a segregation effect in the mixture flows during MIM, and segregation is the most defect in metal injection molding. In order to reduce it on suggest optimization strategy.A cost function is first defined to account it, and optimization strategy has been developed using the Design Of Experiments (DOE) to find the most influent parameters. Four sensitive parameters are found : Powder volume fraction, Interaction coefficient, Powder density, and Binder density. In order to decrease the computational cost associated to optimization, the response surface, using the Moving Least Square Approximation (MLSA), is used to approximate the cost function. Then a genetic algorithm is coupled with this response surface to obtain the optimal values in reasonable time. The optimization strategy proposed in this paper has been applied to the tensile test. Optimization results are compared to...