Powder injection molding : influence of mixing routes

• Main Author: Soh, Wei Xiang.
• Other Authors: Loh Ngiap Hiang
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Manufacturing::Polymers and plastics
• Online Access: http://hdl.handle.net/10356/16148
• Institution: Nanyang Technological University

Powder injection molding (PIM) is a manufacturing process for producing very small parts. There are generally four steps in PIM namely mixing of feedstock, injection molding, debinding and sintering. In this project, the focus is only on the first step, mixing of feedstock. A homogeneous feedstock is desired because it is the basis for the whole PIM process. If not done properly, the whole structure might collapse during debinding or sintering, incurring huge losses. Through Design of Experiments and Analysis of Variance, various factors like mixing temperature, mixing time, powder loading sequence and mixing speed were varied in 2k experiments. In the end, only mixing temperature had significant effect on the response (torques), while the other three factors had little or no influence on the torques. Homogeneity in this project, was assessed using a quantitative method known as Thermogravimetric Analysis (TGA). Through this method, the homogeneity of the feedstock was correlated to the torques during mixing. During mixing, lower torques mean lower viscosity of the feedstock and the binder system will coat the powder more easily. This will result in a more homogeneous feedstock compared to one with higher torques. However in this project, it was found that higher torques gave better homogeneity instead. This could be due to the combination of certain factors and interactions or the degradation of certain binder system components during mixing at high temperatures.