MIM工件之尺寸穩定性與緻密性之研究
The study of dimensional stability and densification for PIM parts
Date Issued
2004
Date
2004
Author(s)
Shu, Guo-Jiun
DOI
zh-TW
Abstract
Powder injection molded (PIM) parts usually incur large amounts of shrinkage after sintering due to their low solid content and resulting poor dimensional stability. This problem is further aggravated when a high shrinkage rate occurs or when the furnace temperature is not uniform. To alleviate this dimensional control problem, the effects of the phase transformation, sintering temperature, and heating rate were investigated. The results show that when an abrupt volume change occurs, as happens during the alpha-gama phase transformation of iron, the dimensional stability deteriorates. This problem gets worse when the density of the part is low. By slowing down the heating rate in the region where the high shrinkage rate occurs, avoiding the phase changes, and adding alloying elements to broaden the temperature range of the phase transformation, the dimensional control of ferrous PIM compacts can be improved.
316L stainless steels usually use relatively coarse atomized powders. Thus, high-temperature sintering and, sometimes, liquid phase sintering is needed in order to get densities greater than 95%. With the formation of the liquid phase, the dimensional control problem occurs, despites of its beneficial effect of increasing the sintered density. To improve the dimensional control, a slow heating rate and dual phase sintering are recommended.
Carbonyl iron powders are the most widely used raw powder in PIM components owing to their high driving forces for sintering. However, the cost of this powder is relatively high. To improve the competitiveness of the PIM process, coarse iron powders, which are much more economical, were mixed with fine carbonyl iron powders in an optimum ratio of 6/4 in this study. This replacement of fine carbonyl iron powders did not change the kneading and molding behaviors significantly. The solvent and thermal debinding rates of the compacts that contain 100% and 40% fine powders also showed little difference. Such debinding results, which are contrary to the general belief, suggest that the particle size is not the critical factor in the debinding of PIM compacts. The debinding rate is more likely controlled by the diffusion of the soluble binder in the solvent (for solvent debinding) and the decomposition rate of the backbone binder (for thermal debinding).
High sintered densities can still be attained in the compact with mixed powders after
Subjects
燒結緻密性
燒結
金屬粉末射出成形
脫脂行為
粉末大小
alpha相穩定元素
熱膨脹儀
尺寸穩定性
particle size
Powder injection molding
dimensional control
debinding behavior
dilatometer
alpha phase stabilizer
densification
sintering
Type
thesis