During the molding of industrial parts using injection molding, the molten polymer flow through converging and diverging sections as well as in areas presenting thickness and flow direction changes. A good understanding of the flow behavior and thermal history is important in order to optimize the part design and molding conditions. This is particularly true in the case of automotive and electronic applications where the coupled phenomena of fluid flow and heat transfer determine to a large extent the final properties of the part. This paper presents a 3D finite element model capable of predicting the velocity, pressure, and temperature fields, as well as the position of the flow fronts. The velocity and pressure fields are governed by the generalized Stokes equations. The fluid behavior is predicted through the Carreau Law and Arrhenius constitutive models. These equations are solved using a Galerkin formulation. A mixed formulation is used to satisfy the continuity equation. The tracking of the flow front is modeled by using a pseudo‐concentration method and the model equations are solved using a Petrov‐Galerkin formulation. The validity of the method has been tested through the analysis of the flow in simple geometries. Its practical relevance has been proven through the analysis of an industrial part.

This paper proposes a new immersed boundary (IB) method for solving fluid flow problems in the presence of rigid objects which are not represented by the mesh. Solving the flow around objects with complex shapes may involve extensive meshing work that has to be repeated each time a change in the geometry is needed. Important benefit would be reached if we are able to solve the flow without the need of generating a mesh that fits the shape of the immersed objects. This work presents a finite element IB method using a discretization covering the entire domain of interest, including the volume occupied by immersed objects, and which produces solutions of the flow satisfying accurately the boundary conditions at the surface of immersed bodies. In other words the finite element solution represents accurately the presence of immersed bodies while the mesh does not. This is done by including additional degrees of freedom on interface cut elements which are then eliminated at element level. The boundary of immersed objects is defined using a level set function. Solutions are shown for various flow problems and the accuracy of the present approach is measured with respect to solutions obtained on body‐fitted meshes. Copyright © 2010 Crown in the right of Canada.

No abstract

Today, hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated so far using the above processes. However, with increasing requirements regarding the embossing surface and the simultaneous decrease of the structure size down into the nanorange, increasing know--how is needed to adapt hot embossing to industrial standards. To reach this objective, a GermanCanadian cooperation project has been launched to study hot embossing theoretically by a process simulation and experimentally. The present publication shall report about an important aspect--the determination of friction during the demolding of microstructures.

SUMMARYThis paper presents a ÿnite element algorithm for solving gas-assisted injection moulding problems. The ÿlling material is considered incompressible and has temperature and shear rate dependent viscosity. The solution of the three-dimensional (3D) equations modelling the momentum, mass and energy conservation is coupled with two front-tracking equations, which are solved for the polymer=air and gas=polymer interfaces. The performances of the proposed procedure are quantiÿed by solving the gas-assisted injection problem on a thin plate with a ow channel. Solutions are shown for di erent polymer=gas ratios injected. The e ect of the melt temperature, gas pressure and gas injection delay, on the solution behaviour is also investigated. The approach is then applied to a thick 3D part. Published in