Preparation And Application Of A Newwater－soluble MIM Binder System

Metal injection molding(MIM) is an advanced near net shape process in efficiently producing complex parts and its key technique is binder design. In this paper, the development of MIM and MIM binder were reviewed, among which water-soluble binder system is a green one with good environmental effect and has promising perspective due to its cheap, fast and unpolluted debinding methods.Firstly, the design of the new binder system was discussed, and polyethylene goycol(PEG) was chosen as the water-soluble ingredient, polyoxymethylenes(POM) and polymethyl methacrylate(PMMA) as the polymer ingredients according to the calculation of solubility parameters and their mixing free energy and the result of their mixing tests. It was shown that PEG-POM was a thermodynamic compatibility system and the mixture had good flowability but bad dissolubility in water; PEG-PMMA was a technical compatibility system and had excellent dissolubility but bad flowability. Thus a new three-ingredient system PEG-POM-PMMA of technical compatibility was designed and expected to have good flowability and dissolubility at the same time. A series of PMMA were prepared by suspension polymerization to study the influences of molecular weight of PMMA on the binder's properties and the result showed that the best molecular weight was 98.4X104. The influences of temperature, initiator and molecular weight regulator on molecular weight of PMMA were also studied.Secondly, the properties and application of PEG-POM-PMMA binder were studied systematically. The results showed that the flowability and wettbility of the binder were good and the feedstock was homogeneous. The water debinding of greenpart was excellent for more than 75% PEG could be removed safely in 80癈 water within 2.5 hours. PEG, POM and PMMA could be removed fully above the sintering temperature due to their good pyrolytic properties. The mechanical properties of sintering samples molded by the new binder system were good, among which the density of 7.92g/cmJ and elongation of 68% were especially high, which was much better than that of using wax-based binder system. The test of moldingshowed that PEG-POM-PMMA binder system had good overall properties and was worthy of application.