Minimum Amount of Binder Removal Required during Solvent Debinding of Powder-Injection-Molded Compacts

Unsatisfactory dimensional control, distortion, and defects are frequently observed in powder-injection-molded parts, particularly after the solvent and thermal-debinding processing steps. One of the reasons is that the amount of soluble binder removed during the first step, solvent debinding, is not great enough to form interconnected pores throughout the compact, particularly in the core region. Thus, blistering, cracking, and bubbles can form easily during the subsequent thermal debinding. To determine the minimum debinding fraction required for solvent debinding, at which point interconnected pore channels are formed at the center, modeling of the distribution of the remaining soluble binder in the compact was established. The actual distribution, which was obtained by measuring the binder content layer by layer with the soxhelt extraction method, is in good agreement with the model. The modeling, bubble test, and fluorescence dye-penetration analysis show that, regardless of the compact thickness, the minimum bulk debinding fraction needed is consistently approximately 59 pct, yielding a local debinding fraction of 37 pct and a porosity of 8.5 pct at the center. This porosity is close to the value at which pores in a sintered compact transform from open to closed at the beginning of the final stage of sintering.