STUDY OF THE DEGRADATION OF POLYETHYLENE GLYCOL IN INCONEL 718 FEEDSTOCK DURING POWDER INJECTION MOULDING PROCESS

Metal injection moulding (MIM) has over the past decade established itself as a competitive manufacturing process to produce in large quantities small precision components with complex shape which would be costly to produce by alternative methods (Enneti, 2012). MIM is a process which combines the versatility of plastic injection moulding with the strength and integrity of machined, pressed or otherwise manufactured small, complex metal parts. MIM consist in shaping powder particles in injection process and then sintering them. MIM make use of the plastic moulding concepts to shape powder-polymer feedstock into the required geometry. During the injection phase, segregation appears in the feedstock and defects will be appear in the component during the sintering. To limit this effect a vast variety of binder systems have been developed (Enneti, 2012) to improve the homogeneity of feedstocks and limit segregation. Binder is formulated as a mixture of different organic or inorganic substances with several functions. Binder has the main commitments of giving the necessary rheological behavior to the feedstocks for injection moulding to transport the powder particles into the mould cavity and the cohesion of the green part (Enneti, 2012). The goal of this study is to characterize and understand the chemical behavior of feedstocks during the phases of mixing and injection. First the binder was studied. Then based on these results the characterization of the feedstock was made. For this a study of the chemical behavior and interactions on feedstocks based on polyethylene glycol (PEG) and Inconel 718 powder was investigated by Fourier Transform InfraRed spectroscopy (FTIR) (Hidalgo et al., 2013). That methodology was also investigated to study the thermal behavior of the binder at a temperature close to the temperature of mixing and injection. Analyzes shows the thermal degradation of the PEG is not affect by the components of the feedstocks. No chemical interactions between the powder and the binder are revealed. The thermal degradation of the PEG appears during the mixing process and change the rheological behavior of the binder. This result shows the necessity to develop another formulation of binder to preserve the PEG.