Injection molding and mechanical simulation united

In our example, we explain the process and the advantages of combined structural mechanics and injection molding simulation

In this sub-process, the first step of an integrative combined structural mechanics and injection molding simulation for a plastic rotor is described. The propeller is made of Polybutylene terephthalate (PBT) with an addition of 30% short glass fiber to enhance the mechanical properties of the material. A crucial aspect of this process is the Moldflow simulation of the filling behavior, aiming to analyze the injection behavior of the plastic material during the injection molding process.

The main objective of the simulation lies in the precise calculation of the fiber orientation tensor. This tensor provides insights into the alignment of the glass fibers in the injection-molded rotor and is crucial for predicting the mechanical properties of the end product. Through the detailed analysis of the filling behavior, optimal conditions for the injection molding process can be determined to achieve optimized alignment of the glass fibers and thus maximize the mechanical properties of the material in the plastic rotor. This integrative approach enables precise design and quality control of the rotor, significantly enhancing the performance and durability of the end product.

Following the Moldflow simulation of the filling behavior, preparation for the two subsequent simulations is carried out – first the linear elastic and then the integrative simulation. For the elastic simulation, the most important material parameters are already available. The modulus of elasticity of 9323 MPa and the Poisson’s ratio of 0.2 are considered according to the data sheet specifications. Also relevant is the elongation at break of 3%, which will serve as a critical parameter for the material behavior in the subsequent simulation.

For the integrative simulation, the information from the previously calculated fiber orientation is utilized. An elastic-plastic material model is implemented, taking into account the fiber orientation. The Tsai Hill failure criterion is integrated as the basis for evaluating the failure behavior of the material.

Linear elastic simulation:

In the linear elastic analysis, the result is scaled to the elongation at break. Red areas exceeding the elongation at break are considered critical. The evaluation indicates that at maximum speed (10000 rps), the elongation at break is only exceeded in a few elements in the radius. The majority of the wall thickness remains below the critical elongation at break, indicating generally good structural integrity.

Integrative simulation:

The evaluation of the integrative simulation is based on the failure indicator defined by the Tsai Hill failure criterion. A value of 1 is considered critical for material failure. At a load of 60% of the maximum speed (6000 rpm), it is observed that in more than two-thirds of the wall thickness, failure, i.e., exceeding the strength, occurs. In comparison, the linear elastic approach at the same speed does not show any failure. This disparity underscores the importance of the integrative simulation, which provides more detailed insights into material behavior under more realistic conditions.

The conducted simulations of the plastic rotor, particularly the linear elastic and integrative simulations, have provided valuable insights into the material behavior under various loading conditions. The linear elastic simulation, based on classical material models, demonstrates overall satisfactory structural integrity at maximum speed, with only isolated elements exceeding the elongation at break.

In contrast, the integrative simulation highlights the importance of detailed consideration of fiber orientation and elastic-plastic material behavior. The Tsai Hill failure criterion identifies critical failure areas, especially at 60% of the maximum speed, where more than two-thirds of the wall thickness are affected by strength exceedances.

Additionally, it should be noted that in the linear elastic calculation, the modulus of elasticity from the datasheet was used, determined according to DIN 527 standard. This standard describes an injection-molded tensile bar, where it should be considered that due to high orientation, material properties may be overestimated, and failure limits should not be considered due to the nonlinearity of the plastic.

Furthermore, it is worth highlighting that the material is not only elastically plastic but also, depending on the fiber orientation, provides a mechanical response for every possible degree of orientation.

The integrative simulation proves to be essential as it portrays more realistic conditions and reflects the actual material behaviors more accurately. The consideration of fiber orientation and the application of an elastic-plastic material model enable a more precise prediction of failure areas that may be overlooked with classical linear elastic models.

Especially in the development of plastic components, such as the examined rotor, precise understanding of failure mechanisms is crucial. The integrative simulation helps identify potential weaknesses early on and establish optimal material and manufacturing parameters. This is not only relevant for the safety and performance of the end product but also significantly contributes to reducing development times and costs. Overall, the integrative simulation underscores its importance as an indispensable tool in precise material characterization and product development.