Study on Agar Binder for Metal Injection Molding

Abstract

This paper proposes agar as metal injection molding (MIM) binder in stead of usual plastic binders, expecting simple MIM process without debinding. Agar is natural material extracted from seaweeds and it can keep water in its structure. And agar is soluble in water at near 100°C and gelation of aqueous solution takes place at around 40°C. More the transformation is reversible. Firstly thermal stability, solubility into water and viscosity were examined and it was found agar up to 30% can be solved into water. Secondly titanium green compacts with agar binder were formed by uniaxial pressing and then they were sintered without debinding process. Obtained sintered compacts did not have any cracks on the surface at all. Finally 20 pieces of titanium samples with agar binder were injected. The density distribution of samples was within 5%. Then these were sintered at 1200°C for 1 hour in vacuum and, from the measurements of density and hardness, it is concluded that agar binder is available for MIM process.