Methodology for increasing the uniformity of fiber-injection-molded preforms

由于资源和能源的稀缺，交通部门对燃料消耗和排放的立法更加严格，以及人们环保意识的增强，近年来，系统高效的轻型结构的重要性显著增加。纤维增强塑料（frp）由于具有密度比非常好的刚度和强度而具有很高的潜力。目前，由于大规模生产的材料和制造成本高，frp的使用受到限制。长纤维增强半成品在包层等半结构应用中是一种具有成本效益的替代方案。对于长纤维预制体的制造，目前使用的是顺序工艺，其中轮廓是从非织造布和垫子上切割出来的，这些非织造布和垫子可以作为二维半成品以卷货的形式提供，并连续成型。这与相应的浪费密切相关，从而导致更高的材料成本。此外，还有直接工艺，特别是纤维喷涂工艺。直接生产三维长纤维预制体的一种很有前途的方法是纤维注射成型工艺，而不需要二维半成品的中间步骤。该工艺通过气流将纤维吹入封闭模具中，可以在不切割废料的情况下生产三维成型的长纤维半成品。这个过程有可能局部调整纤维结构的密度。使用纤维注射成型作为预成型工艺的一个障碍是迄今为止可实现的纤维结构的均匀性，这导致在随后的渗透过程中出现问题。为了经济地使用纤维注射成型工艺制造预制体，必须提高预制体的均匀性。在上述初步工作的基础上，将对气流的喷射过程进行更详细的研究。尽管纤维囊炎的形成导致纤维体积流动不恒定，但通过均匀填充注塑模具可以获得更均匀的性能。因此，目标是通过控制与注射过程相关的参数来积极影响过程，以实现均匀的纤维沉积。计划的调查应对了解注射参数和产生的预制体性能，特别是均匀性之间的相互作用作出重大贡献。

Due to the scarcity of resources and energy, stricter legislation regarding fuel consumption and emissions in the transport sector and the growing environmental awareness among the population, the importance of system-efficient lightweight construction has increased significantly in recent years. Fiber-Reinforced Plastics (FRPs) have a high potential due to their density-specific very good stiffness and strength. Currently, the use of FRPs is limited due to the high material and manufacturing costs in mass production. Long fiber reinforced semi-finished products represent a cost-effective alternative in semi-structural applications such as claddings.For the manufacturing of long fiber preforms, currently sequential processes are used, where the contour is cut from nonwovens and mats, which are available as two-dimensional semi-finished products in the form of rolled goods, and consecutively formed. This goes hand in hand with corresponding waste, which leads to higher material costs. Additionally there are direct processes, in particular the fiber spraying process.A promising approach for the direct production of three-dimensional long fiber preforms without the intermediate step of two-dimensional semi-finished products is the fiber injection molding process. The process allows the production of three-dimensionally formed long fiber semi-finished products without cutting waste by blowing fibers into a closed mold by means of an air stream. This process has the potential to locally adjust the density of the fiber structure. One impediment to the use of fiber injection molding as a preforming process is the uniformity of the fiber structure achievable to date, which leads to problems during subsequent infiltration.In order to use fiber injection molding process for economically manufacturing preforms, the uniformity of the manufactured preforms must therefore be improved. Based on the shown preliminary work, the injection process by the airstream in particular will be investigated in more detail. More homogeneous properties are to be achieved by uniform filling of the injection mold despite the inconstant fiber volume flow caused by the formation of fiber bunions. The aim is therefore to actively influence the process by controlling the parameters relevant to the injection process in order to achieve a uniform fiber deposition.The planned investigations shall make a significant contribution to understanding the interaction between the injection parameters and the resulting preform properties, uniformity in particular.