J.C. Gelin

3D FEM simulations of shoulder milling operations on a 304L stainless steel

Abstract This paper describes investigations realised to perform simulations of shoulder milling operations on AISI 304L stainless steel using the commercial software LS-Dyna©. A Lagrangian formulation with an explicit solution scheme and a penalty contact algorithm has been used. Many experiments were performed in shoulder milling configurations in order to study the machinability of this material and also to validate the results obtained from the developed 3D finite element model. In the simulations, the material behaviour is modelled with a classical Johnson–Cook law. Some enhancements and simplifications had to be made in geometry, meshing, friction and temperature considerations for limiting the calculation time. The final aim consists to obtain realistic numerical cutting forces for shoulder milling operations.

Improving mould design and injection parameters in metal injection moulding by accurate 3D finite element simulation

Abstract The metal injection moulding (MIM) process combines the well-known thermoplastic injection and powder metallurgy technologies to manufacture small and intricate parts to nearly net shape. The design of injection moulds is a very important stage in such a technology as the mixture of metallic powder and thermoplastic binder is injected in the mould with a viscous behaviour strongly different from the pure polymer injection. To improve the mould design by an efficient numerical tool, an explicit 3D software has been developed to perform efficiently the injection simulation. Taking into account the special behaviour of feedstock in MIM injection, a bi-phasic model is used to describe the flows of metallic powder and plastic binder so as to predict accurately the powder segregation in injection. The volume fractions of metallic powder and plastic binder give directly the evolution of segregation during the injection course. The numerical results are compared with experiments, in which a multi-cavity mould specially designed and realised in our laboratory is used. The segregation zones are well predicted. This specially developed software permits to optimise the mould design and processing parameters to get required components.

Experimental and numerical investigations on properties and quality of parts produced by MIM

Abstract This paper concerns the effect of processing conditions in metal injection moulding on the resultant properties of produced parts. A multicavities mould has been designed and manufactured in the laboratory for performing experiments on 316L based feedstock. A set of experiments covering injection moulding, debinding, and sintering stages have been realised, investigating the main role of the process parameters. The properties of the produced parts are analysed through SEM observations, mass measurements, and tensile and bending mechanical tests. The modelling and numerical simulation of the injection moulding stage has been developed based on a biphasic flow approach of the feedstock mixture. The powder volume fraction is considered as a key variable to describe phase segregation during moulding and allows powder contours to be found after the injection stage. Finally the mechanical properties of the parts are measured and identified. An inverse identification procedure combining experiments and simulation permits the results to be checked.

Application of optimal design and control strategies to the forming of thin walled metallic components

Abstract The paper focuses on approaches for the optimal process control in hydroforming. The main objective is to find by numerical simulation and optimisation the loading curve versus process parameters that minimise the thickness variations and that give the shape for the final part. Different approaches are proposed typically based on optimisation strategies and requiring a sensitivity analysis, or based on a local approximation of the tube thickness versus process parameters using optimisation procedures based on evolution strategies. The results obtained proved the ability of the proposed approach in the analysis of tube hydroforming processes and its potential to handle the numerical process control.

Experiments and Computational Modeling of Metal Injection Molding for Forming Small Parts

Abstract The metal injection molding process is mainly used for manufacturing small metallic components with complex shapes. The process includes four stages and the present study is concentrated on the injection and the densification ones. A multiple cavities mold has been designed and realized that permits to characterize the effects of injection parameters on the final results in terms of shape and integrity. A mechanical model and a set of numerical simulations have been carried out that enhance the experimental results and that allow to access to the influence of the main process parameters. Finally it is shown that computational modeling could be used to help the process designer to produce accurate parts.

Replication of microchannel structures in WC-Co feedstock using elastomeric replica moulds by hot embossing process.

Hot embossing is a net shaping process that is able to produce the micro-components of polymers with intrinsic and complex shapes at lower cost compared with machining and injection moulding. However, the emboss of hard metals, such as WC-Co, is more challenging due to their high thermal conductivity and ease of agglomeration. Thus, a WC-Co alloy mixed with a wax-based binder feedstock was selected. The formed feedstock exhibited pseudo-plastic flow and was successfully embossed (green part). Here, we developed a novel process that is used to replicate polymer microfluidic chips while simultaneously reducing the channel surface roughness of the mould insert, yielding optical-grade (less than 100 nm surface roughness) channels and reservoirs. This paper concerns the replication of metallic microfluidic mould inserts in WC-Co and the parameters associated with feedstock formation via a hot embossing process. A suitable formulation for micro-powder hot embossing has been established and characterised by thermogravimetric analyses and measurements of mixing torques to verify and quantify the homogeneity of the proposed feedstocks. The relative density of the samples increased with processing temperature, and almost fully dense materials were obtained. In this work, the effects of the sintering temperature on the physical properties were systematically analysed. The evolution of the metal surface morphology during the hot embossing process was also investigated. The results indicate that the feedstock can be used to manufacture micro-fluidic die mould cavities with a low roughness, proper dimensions and good shape retention. The shrinkage of the sintered part was approximately 19-24% compared with that of the brown part.

Experimental Analysis and Numerical Simulation of the Flow Behaviour of Thin Polymer Films during Hot Embossing

The geometrical and material properties of polymer components made by polymer hot embossing are largely affected by the embossing pressure and temperature, and depend on physical properties of considered polymers as well as on cavity shapes and roughness. The present paper is focussed on experiments and numerical simulations of the hot embossing processes consisting in the replication of polymers plates on engraved shapes in the metallic plates that are used for the tests. The numerical simulations of the embossing process are realized for 2D or 3D geometries, and provide the way to access to the pressure on the polymer substrate, as a function of the viscosity of the polymers under given pressure and temperature conditions. The ability of the process to fill the cavities depends on the viscoelastic and viscoplastic properties of the polymers, for the temperature and strain range considered. In the proposed analysis consisting of the micro‐indentation of the polymer plate, axisymmetric and 3D FE models ar...

Design of hydroforming processes for metallic liners used in high pressure hydrogen storage

Within the framework of an European project concerning hydrogen storage, one analyze the way to manufacture high pressure tanks (700bars) for hydrogen storage, intended to be embarked for using in motor vehicles. These tanks consist of a metallic liner, which ensure a barrier role compared to the hydrogen atoms as well as a part of the mechanical resistance, and of a composite envelope built by filament rolling up which ensures the complementary part of the mechanical resistance. The paper describes the work completed within this framework, on the basis of the simulation of the hydroforming process thanks to the complete control of the process, in volume of fluid injected. One was thus brought to develop an optimization module based on finite element calculations. This optimization module includes MPI library in order to launch several calculations in parallel on a Linux cluster. It consists in seeking the optimal evolution of the fluid volume injected vs. time to obtain a good quality component. In our case, the optimization criterion is based on the variation thickness of the tube and the possible appearance of necking. It is shown that such a way for controlling the process provide the way to get minimal thickness variation, comparatively to standard optimization approaches where the process parameters are discretized through processing time in a more standard way.

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.

Adhesion Strength Study of Silicone Rubber Compounds to Nylon 66

In recent years, multi-component injection molding has largely developed in the industries. During the manufacturing process, the critical challenge is in achieving an optimum adhesion between the two materials. This study examines the influence of curing kinetics on the interfacial adhesion strength between a silicone rubber and nylon 66 using a rotational rheometer. The evolution of adhesion strength of assembly during the curing behaviour of silicone rubber was measured by tensile test at different curing temperature and different curing time. The results showed a significant increase in adhesion was obtained while either the curing temperature or the curing time increased. In this study, the rheological property of silicone rubber fluid has been also determined by the rotational rheometer. In addition, the kinetics of the curing reaction of silicone rubber has been studied by differential scanning calorimeter.