| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 88 === Powder injection molding (PIM) has become a popular process in producing complex-shaped parts. However, the undesirable dimensional control and the wide tolerance of the parts remain an obstacle to further promoting this technology. The objective of this study was to investigate the causes of the tolerance control problems by measuring the in-situ dimensional change and deformation behavior of PIM specimens during debinding and sintering using a self-designed laser dilatometer and a conventional thermal dilatometer. The results can be divided into the following parts：
First, during the solvent debinding, swelling was observed when compacts were immersed in the solvent. Three major factors were found to be responsible for the expansion of the specimens: dissolution of soluble binder into the solvent, reaction between insoluble binder and solvent, and thermal expansion due to the temperature rise of the specimen itself. The amount of expansion was related to the thickness of the sample, the amount of the binder, and the temperature employed.
During the subsequent thermal debinding, the dilatometric analysis showed that the specimen shrank in the early stage between 250C and 370C, not because of sintering, but through the loss of N, C, and O in the carbonyl iron powder. At temperatures between 370C and 450°C, the specimen expanded due to the carburization of the iron powder. The length change was also influenced by the heating rate, debinding atmosphere, and the amount of the backbone binder.
In addition, the results of deformation tests show that the backbone binder (LDPE) contributed to the strength of the specimen during solvent debinding. However, the softening of the backbone binder resulted in the slumping and failure of the specimen during thermal debinding. And, it determines that the final shape retention capabilities at both debinding stages are mainly controlled by the thermal debinding process.
Based on the above results, it was found that the powder loading, backbone binder content, solvent debinding temperature, and phase transformation are the key parameters on the dimensional control of the PIM compacts. In this study, one standard deviation of ±0.02% ( 1σ) can be achieved for 2×10×100mm rectangular specimens made from carbonyl iron powders.
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