Preparation of feedstock using beeswax binder and SS 17-4PH powder for fabrication process of orthodontic bracket by metal injection molding

Abstract

The need for orthodontic brackets in Indonesia is very high due to the high prevalence of malocclusion sufferers in Indonesia. In this research, orthodontic brackets were fabricated by Metal Injection Molding method using Stainless Steel (SS) 17-4 PH powder and the variation of binder system as the feedstocks. The purpose of this study was to develop the optimum of the local binder systems as the feedstocks preparation for the fabrication of orthodontic brackets. Several parameters that could affect fabrication has been studied, such as: the composition of the binder system with the relation with torque and viscosity of the feedstock. The mixture of Beeswax (BW) as a local raw material, Paraffin Wax (PW), Low-Linear Density Polyethylene (LLDPE), Ethylene Vinyl Acetate (EVA), and Stearic Acid (SA) were mixed with SS 17-4PH powder in various compositions to produce the optimal feedstock properties. The compositions was K1 (PW 64%, HDPE 35%, SA 1%), K2 (30% PW, 30% BW, 30% LLDPE, 5% EVA, 5% SA), K3 (PW 20%, BW 30 %, LLDPE 30%, EVA 15%, SA 5%), and K4 (PW 20%, BW 30%, LLDPE 40%, EVA 5%, SA 5%) with powder loading of 60 vol. %. The feedstocks were injected into orthodontic bracket molds and the effect on their rheological properties was observed. It was found that the composition of the K4 binder system had an optimal torque and viscosity value of 5.63 Nm and 19.43 Pa.s, respectively. Moreover, the torque and viscosity values were close to the values of commercial feedstocks (i.e. 5.52 Nm and 19.04 Pa.s) that produce green parts with a good shape stability and minimum defects. With an excellent Melting Flow Index (MFI) of LLDPE, the feedstock generated a good mold-ability and crack resistance of the brackets. These results indicated that the composition of the K4 binder system is suitable for use as an orthodontic bracket feedstock.