Metallic part fabrication with selective inhibition sintering (SIS) based on microscopic mechanical inhibition

The Selective Inhibition Sintering (SIS) process is an additive manufacturing (AM) technology which builds parts on a layer-by-layer basis. The principle idea of the SIS process is based on the prevention of selected segments of each powder layer from sintering. The purpose of this research is to investigate the fundamentals of the Selective Inhibition Sintering (SIS) process for the fabrication of metallic parts. A SIS-Metal process has been developed based on the microscopic mechanical inhibition principle. In this process the inhibitor, which is a salt solution or a carbohydrate solution (sucrose), is printed in the selected areas of each metal powder layer; the salt re-crystallizes when water evaporates under moderate heat; salt crystals decompose to second phase metal oxide during the sintering cycle; the decomposed solid particles cover the surface of affected metal powder particles and exert a retarding force on the surface movement and prevent the sintering. This thesis presents the results of the conducted research on the inhibition mechanism and control of the SIS process. Experimental results are also presented to demonstrate the capability of the process in fabricating metallic parts with various geometries. The SIS-Metal process has numerous advantages including low cost, minimal shrinkage and deformation effects and independence from polymeric binders which cause shrinkage and adverse effect on sintering furnace. The factors affecting the SIS-Metal process based on microscopic mechanical inhibition are investigated. By the aid of response surface methodology the effective factors are evaluated to improve the part strength, surface quality and dimensional accuracy of the parts made with the SIS-Metal process.