Effect of powder loading on local feedstock injection behavior for fabrication process of orthodontic bracket SS 17-4 PH using metal injection molding

The need for orthodontic brackets in Indonesia is very high due to the high prevalence of malocclusion sufferers in Indonesia. Metal Injection Molding is one of fabrication methods that can be used by obtaining an optimum powder loading in order to produce good feedstock quality for manufacturing orthodontic bracket products. A higher powder loading was able to improve the mechanical properties and tighten dimensional tolerances of products by increasing its density. However, excessive number of powder loading leads to exorbitant viscosity of the feedstock and results in failure of injection process. The aim of this study was to evaluate the performance of Stainless Steel 17-4 PH orthodontic bracket fabrication process, so that the optimum powder loading for local bracket orthodontic manufacturing process could be obtained. In this study, SS 17-4 PH and local binder system (i.e. beeswax, paraffin wax, low linear density polyethylene, ethylene vinyl acetate, and stearic acid with 30, 30, 30, 5, and 5 vol.%, respectively) were used to prepare four kinds of feedstocks at powder loading of 60, 62, 64, and 66 vol.%. The feedstocks were injected into the orthodontic bracket mold and observed the effect on their rheological properties. The results showed that the feedstock with powder loading of 64 wt.% was the optimum one, with optimum torque value of 5.4 Nm resulted from the mixing process that produced green parts with a good shape stability and minimum defects when injection molded.