Micro-injection molding is one of the most promising technologies in plastics processing. With a growing trend towards miniaturization, the demand for parts within the micrometer range is increasing. Furthermore, these should integrate several functions in one part.
For over a decade now SIGMA Engineering GmbH, Aachen, Germany, has been involved in research projects to predict the behavior of molded materials in micro-sizes. When the size of the part gets smaller, effects which are irrelevant in the macro-world, such as surface tension, start to be important. Particularly the heat exchange between mold and melt must be modeled exactly. Several material models have been integrated into SIGMASOFT® to capture the material behavior at low scale-sizes in injection molding simulation. Hahn Schickard in Stuttgart, Germany, has been using SIGMASOFT® since 2007 to support the part design in micro applications. The software is used to predict the filling pattern, the fiber orientation, the presence of part defects, and also to simulate in-molded stresses. Amongst the applications is the prediction of warpage and deformation, where simulation results have proved to correlate closely with reality. The software is also used to predict the filling pattern in critical parts and to identify early possible mechanical defects in mechanically loaded regions, such as voids or welding lines. In one particular case, a micro magnetic sensor array was to be produced. In this application, a case had to be produced to hold a complex magnetic chip. It was critical to accurately predict the position of welding lines during the part filling, as well as to analyze the part distortion, to avoid possible performance problems in the application. According to Tobias Grözinger, Engineer at Hahn Schickard responsible for modeling and reliability, “With a SIGMASOFT® Virtual Molding analysis it was possible to minimize the risk of welding lines by optimizing the part thickness, as well as to determine that the deformation in the placement planes was uncritical”.
