Plastics and moulds

One of the stages more critical in the process of forming polymer composites by injection of resin (LCM), is the impregnation of the fiber on the inside of the mold for resin. Total impregnating fabric of reinforcement is essential to maximize the properties mechanical of the final piece. The edge effect is a phenomenon that inevitably occurs during mold filling loaded with fiber and occurs in the gaps remaining between the layers of tissue and the walls of the mold. These gaps create channels by where the permeability is much higher and as a result the flow by them is much greater than for the rest of the cast. The main consequence of this effect is the loss of control over the filling of the mold, which makes it impossible for a correct simulation of the filling and the anticipation of the field of pressure on the mold.

Traditionally this effect has been considered as a factor of undesirable and unavoidable, work, however, in recent years has been that this effect can be used to reduce the pressure of injection or decrease the time of injection. If you inject vacuum the edge effect helps guide at the forefront of progress towards the point of emptiness, which is generally located at an intermediate point of the piece.

For a correct numerical simulation of the filling phase, using a Darcy flux, becomes necessary to characterize the edge effect through the definition of an equivalent permeability in the channels of the mould where there is no fiber. Permeability is a difficult measure, but which is essential for a correct simulation of the process of forming. There are numerous methods to measure, either by means of experimental techniques, using numerical techniques or as a combination of both.

The present paper is intended to model the edge effect and characterize an equivalent permeability using experimental techniques, which will then be used to simulate the filling by a finite element technique developed by the authors.

For monitoring the progress of the resin front will be used a mold prototype that allows the recording of the video-fill sequence. This mold is built in one of its acrylic glass halves and the other half is reproduced a preferred channel for the passage of the flow of resin that simulates the edge effect. We will work with different dimensions of channel and different conditions of filling (pressures and flow rates).

Use a material type sandwich (rovicore) as preform and different thicknesses of it. The injection with silicone oil with a viscosity similar to the polymer resins used in MCL and a quasi-Newtonian behavior. The method is also valid for any other material or geometry.

Information obtained from this study should serve as a basis for the calculation of the channels of filling filling by vacuum and a correct estimate of the equivalent permeability.

[1] S. Bickerton, S. g. Advani, Experimental Analysis and Numerical Modeling of Flow Channel Effects in Resin Transfer Molding. Polymer Composites, Vol. 21, no. 1, (2000).

[2] Moon-Kwang Um, Sang-Kwan Lee, A Study on the Determination of In-Plane Permeability of Fiber Preforms. Polymer Composites, Vol. 20, no. 6,(Dec._1999).