Numerical Simulation On Metal Injection Moulding

Metal Injection Moulding (MTM) is a near net shape technology to manufacture the small intricate parts in 3D shapes. Compared with other fabrication methods, such as die compaction, machining and casting etc, MIM technology has some evident advantages to produce complex components with high mechanical properties and low costs. The MIM technology includes four main stages: 1) mixture of feedstock. 2) injection moulding to get the green parts. 3) debinding stage to remove the binder. 4) final sintering stage to get the condensed part in pure metallic material.As a new manufacturing technology, numerical simulation plays an important role in its efficient applications. Among the simulations of different stages, the simulation of injection moulding is perhaps the most important one. Any defects appearing in this stage will be amplified in the next debinding and sintering stage to corrupt the quality of final parts. The properly chosen process parameters in injection stage, such as the temperature, pressure and well-designed mould configurations, are essential for ensuring the quality of produced parts. The numerical simulation of MIM injection provides a powerful tool to predict the filling state, velocity fields, pressure field and temperature field in the mould cavities at each instant of the injection process. Except for predicting the defects that may happen commonly in the process of polymer injection, the powder segregation effect in MIM injection can be predicted by the simulation based on a bi-phasic model. The segregation effect is the source of collapse in debinding, as well as the warpage and distortion in sintering.For the prediction of powder segregation in injection stage of MIM, the application of mixture theory is necessary, which induces two coupled Navier-Stokes equations. The computation becomes an extremely heavy charge for the traditional algorithms, which prevents severely its real application. To achieve the efficientMIM simulation, a fully vectorial explicit algorithm for simulation of the rilling process is proposed firstly, then the important extension to bi-phasic simulation for the prediction of powder segregation is proposed to realize a fully explicit and vectorial solver. In the new solver for simulation of the bi-phasic injection model, there is no more global solution or the construction of any global matrix except the small operations at element level. In global sense, the computation is carried out only by the vectorial operations. So the computation is very efficient. Moreover, the new solver employs the elements of equal-order interpolations instead of the MINI elements. Incompressibility of the mixture is retained by a corrective feedback operation, with a procedure of systematic smoothing to avoid the possibility of mesh locking. Another smoothing method is proposed to avoid the instability at starting stage of the filling simulation. This instability is caused by the sudden change of filled zone because of the discretization of element model. The developed new solver shows the proper advantages for simulation of the industrial problems in large scale. Furthermore, the software is easy to be parallelized on a high performance system with multi-clusters because of its vectorial feature. The comparison of numerical results with experiments and previous simulations proves the validity and efficiency of new algorithm.