Threshold Concentration of Surfactant Agent in Feedstocks Used for Low-Pressure Powder Injection Molding

Abstract

In this work, 32 different feedstocks formulated from four different stainless steel powders and two wax-based binder systems (paraffin wax and beeswax), for which the proportion of two different surfactant agents was varied from 0 to 5 vol.% (stearic acid and oleic acid), were obtained. The viscosity of the feedstocks according to the shear rate was measured using a rotational rheometer. The moldability of the mixtures was assessed using the injected length following real-scale injections. The results show that the influence of surfactant agents on viscosity depends on the main binder constituent used in the feedstock formulation. The moldability of paraffin wax–based feedstocks was significantly affected by the proportion of the surfactant agents, whereas that of beeswax-based feedstocks was not affected by the presence of stearic acid or oleic acid. It was confirmed that as little as 0.20 vol.% of stearic acid or oleic acid in paraffin wax–based feedstock is enough to produce the surfactant effect, leading to a significant increase in the moldability of feedstocks (e.g., fourfold longer injected length). This threshold concentration of surfactant agent in paraffin wax–based feedstocks was also established with different powder grades, shapes, and sizes. For feedstocks containing paraffin wax and surfactant agents, the presence of a discontinuity in the viscosity profiles was confirmed not to be an experimental artifact because the phenomenon was reproduced using three different measurement approaches.

Optimization of the printability envelope of low-viscosity powder-binder feedstocks used in material extrusion 3D printing

“…These constituents are extensively used in the LPIM process as the surfactant, main carrier and thickening agent (Gonc, 2001), respectively. SA was added to enhance the chemical links between the powder and binder (Li et al , 2007; Ali et al , 2020). Thanks to its low viscosity, constant rheological properties and low cost (Waesche et al , 2007), PW was used to ensure the fluidity of the feedstocks (Waesche et al , 2007).…”

Research Progress on Low-Pressure Powder Injection Molding

“…The surfactant is another component essential for binder systems used in LPIM [122]. The surfactant could create a thin surface layer between powder particles and binder constituents.…”

Effect of surface modification of metal powders (by aluminum stearate) on the properties of metal injection molding feedstock

“…Their functions are to keep the polarity of metal powder consistent with the binder system, improve powder agglomeration, enhance the powder-binder compatibility and bonding, and reduce the cracking caused by shrinkage during MIM molding. Ali et al 17 found that adding 0.2vol% stearic acid (SA) or oleic acid in the wax-based binder system is enough to produce the effect of the surface modifier and significantly improve the fluidity of the feedstock. Momeni et al 18 found that in the process of 4605 low-alloy steel powder injection molding, with the continuous increase of surfactant SA, the feedstock showed higher sensitivity to the shear rate.…”