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

• Applicant: Professor Dr.-Ing. Jürgen Fleischer
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 439709829

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.

• DFG Programme: Research Grants