Micropowder injection molding: investigation of powder-binder separation using synchrotron-based microtomography and 3D image analysis

Micropowder injection molding (μ-PIM) is one of the most promising processes of mass production for the fabrication of small complex shaped ceramic or metallic parts with high sintered density. However, dimensional accuracy of finished parts is difficult to achieve because of extremely high shear rates during the injection molding process. This promotes the separation of powder and binder even in highly homogeneous feedstocks leading to a particle density variation in the green part causing anisotropic shrinkage during sintering. The main objective of this study is to investigate the effect of the powder particle distribution in injection molded green metallic microparts with respect to the molding parameters using synchrotron microtomography (S-μCT) and three-dimensional (3D) image evaluation. Image analysis has been performed using the MAVI software package. To get information about the allocation of the metal particles along the sample the 3D CT-scans have been segmented and statistically analyzed via spatially resolved size distributions. Furthermore, the spatial arrangement of the particles has been investigated using the so-called summary statistics from the area of point process statistics. The results show that variations in the size distribution of the metal powder particles can be detected and give consistent evidence for a monotonic increase in particle size with distance to the injection point. In order to give recommendations for the choice of parameters as well as tool construction, knowledge about the causes for separation effects is essential. This study shows that S-μCT is a well-adapted analytical tool to investigate the powder-particle distribution in μ-PIM.