Decoupled Molding

Differing theories discussed primarily in the U.S. and termed Decoupled Molding contradict the physical principles of process optimization since it always leads to a stagnation of the melt and thus to undesirable process conditions or to different boundary layer thicknesses (= different shrinkage conditions) due to conscious deceleration of the filling before the switchover to holding pressure. 

Groleau R, Groleau M. The fundamentals of decoupled molding. IMM Almanac 2005. 

R. Launsby et. al, DOE decoupled molding part I Process centering and validation from the plastic s point of view. Conference proceedings of SPE ANTEC 1999, (1999)... 

The parts were made by setting up a 2-stage decoupled molding process in which velocity and position were used for the filling phase, and hold pressure and time were used for the packing and compensation phases. All parts were produced using a Boy 35A injection molding machine. A full part was achieved and the coinjection portion of the experiment followed. 

This effect is fully corroborated by a dart drop test (DIN EN ISO 6603-2) with a 100 J dart and injection molded plates of 2 mm thickness, as shown in Fig. 18.24. In particular, the absorbed energy during the puncture event for the weak PP-g-MAH interphase is more than doubled compared to the normal composite without decoupling (moderate interphase). 

Lipscomb et al. (1988) have shown that the flow kinematics in complex flows can be strongly affected due to fibers. However, in the injection molding simulation for flows in narrow channels, the effects can be neglected, and an orientation-flow decoupled simulation approach is used. To understand in which situations the decoupled simulation is allowed, we need to classify the flow regimes. Tucker (1991) has identified four regimes of suspension flows. His classification was based on two dimensionless numbers. The first is the particle number defined by... 

Consider a set of typical values in the injection molded composites (p — 10%, Ur = 20, Cj — O.OOland s = 0.01. FromEqs. 5.48 and 5.50, assmning the fibers are aligned, we obtain Np = 6.4 and (5 = 0.1. Then we have Np3 = 0.064. The flow belongs to regime one, and hence decoupled flow and fiber orientation calculations will be allowed. This will be the case for many, but not all, injection molding simulations for fiber-filled composites. 

Often, only small series are produced, so the standard mold is often left on the injection molding machine while the mold inserts are exchanged for other small series. In these cases, the cavity pressure and cavity temperature sensors have to be automatically decoupled with the mold insert otherwise, the entire mold must be disassembled to replace the sensors. 

Currently, the CVFEM and CONNFFESSIT methods are decoupled. We will combine them together to carry out the transient viscoelastic flow simulation in the micro-injection molding. 

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