Enhancement of the Weld Line Strength of Injection Molded and fiber reinforced Components by Means of a Novel Mold Technology

• Applicant: Professor Dr.-Ing. Christian Bonten
• Subject Area: Plastics Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536598071

In injection molding, complex three-dimensional components can be produced cost-efficiently. The filling of the mold has a significant influence on the later properties of the part. However, different phenomena weakening the mechanical properties of the plastic material can be observed. Weld lines are such a problem, especially in the case of complex parts. These occur when the melt has first been divided and then, e. g. after flowing around an obstacle, the two melt streams meet again. Especially with fiber-reinforced plastics, weld lines are challenging. While the macromolecules of the polymers still can cross the interface through Brownian motion even after the screw has stopped, this is not possible with fibers. In the past many different concepts have been developed to address this problem, but often with great effort and usually only for specific applications. The aim of the proposed project is to develop a comparatively simple process which increases the weld line strength of the injection molded component. For that a ram is to be integrated into the die wall close to the weld line. When retracted, the ram allows the melt to enter a secondary cavity. From there the ram pushes it back into the area of the weld line area directly after filling. As a result of this, the former orientation of the macromolecules and fillers in the weld line is destroyed by the counter-flow and the weld line is blurred. In order to implement this approach, first of all, the mechanism during the push-back of the melt must be understood and modeled. Orientations, especially fiber orientations, play a special role here. One method will be to simulate the process with the help of tracer particles. Also, an experimental study and the use of fiber orientation analysis will help to evaluate the real process. This will reveal the influence of the different process and geometry parameters on the reorientation of the fibers. The knowledge gained will be used to build an experimental mold that will validate the implementation in reality. In addition, the influences of different materials, process parameters and component geometries will be investigated. Finally, a model is to be created, which makes it possible to ideally apply the new method to any component geometry and material. Thus, the results of the project are a new method for improving the weld line strength, an extended understanding of the processes during the application of this technique and a model applicable for prediction and design of the new technology.

• DFG Programme: Research Grants