Precharge placement

Hence, it is desirable to drill holes after the part is molded. Otherwise, mold-ed-in holes should be located in zones of low stress. A key parameter to knit line formation is the precharge location. If possible, multiple precharge or uneven precharge placements should be avoided. Mold filling analysis before manufacturing may be useful to design the precharge specification. 

In real processes, the initial coverage of the mold by precharge material usually is about 50%, and a material flow is not avoidable. Hence, the optimization by process simulation may be useful to avoid problems. For example, precharge placement can be optimized so that the fibers in the final product would be aligned in the loading direction or the anisotropy in fiber orientation would be less significant in the zone of high stress. 

In general, the fiber separation is more significant as the fiber content and fiber length are increased. Moreover, the fibers that are oriented parallel to the flow direction are more susceptible to fiber separation than the fibers that are oriented normal to the flow direction. Even in the case of SMC-CR or XMC, this phenomenon often is observed if continuous fibers are aligned in the parallel direction to the principal flow direction (see Fig. 3.21). If continuous fibers are aligned in the perpendicular direction to the principal flow, the fibers tend to buckle or bend due to the flow-induced drag force. Hence, the precharge placement usually covers nearly 90% of the mold surface in the case of SMC-CR and XMC. 

---