Calculation of fiber breakage during different stages of injection molding process

Injection molding is a widely used manufacturing process for producing complex plastic parts with high precision and efficiency. When reinforced with fibers, typically glass or carbon, these plastics exhibit enhanced mechanical properties, such as higher stiffness, strength, and dimensional stability. However, one significant challenge in fiber-reinforced polymer (FRP) injection molding is fiber breakage, which can compromise the intended performance of the final product. Moldex3D gives the possibility to calculate the fiber breakage during different stages starting from the screw barrel. This will provide the users the possibility to reduce the fiber breakage by adjusting the process parameters.

Fiber breakage occurs primarily during the various stages of the injection molding process. As the material flows through narrow gates, runners, and mold cavities, fibers experience additional mechanical stresses that lead to breakage. Areas like screw barrels, nozzles, and gate regions are critical locations for fiber degradation due to intense shear and elongational flow.

The shortening of fibers during injection molding reduces their aspect ratio, directly affecting mechanical properties of the final product. Shortened fibers offer less reinforcement, leading to reduced stiffness and strength. On the other hand, uneven fiber lengths and orientations can cause non-uniform mechanical behavior across the part. Critical applications, such as automotive or aerospace components, may fail to meet stringent requirements due to reduced fiber integrity.

In Moldex3D, it is possible to consider the fiber degradation in the process and calculate the fiber length distribution in the cavity in CAE mode or Machine mode. In both cases, it is possible to choose whether the solver takes the screw in the consideration or not. When screw-induced fiber breakage is not selected, the breakage calculations first start from the sprue. On the other hand, it is still possible to select this option in CAE mode and the Solver will consider a screw with a certain length. Below you can see an example of a log file from Moldex3D for fiber breakage including the screw. Moldex3D uses tha Phelps-Tucker Fiber Length Attrition model. The breakage Parameters involve CD, CB, and S. The user has the possibility to define these parameters based on literature or their experiments or use the default settings in the software. In the image below, you see the default settings for long glass fibers.