Effect of powder particle shape and size distributions on the properties of low-viscosity iron-based feedstocks used in low-pressure powder injection moulding

Abstract

Low-pressure powder injection moulding (LPIM) is a cost-effective manufacturing technology used to fabricate complex-shaped parts with high mechanical properties at low-or highvolume production. This research work presents an experimental approach to investigate the debound/sintered properties of iron components produced by the LPIM process using iron-based powders exhibiting different particle shapes and size distributions. Four lowviscosity feedstocks were mixed and injected into a rectangular mould cavity before being thermally wick-debound and finally sintered using identical debinding and sintering cycles. This study confirms that both irregular and spherical iron powders can be shaped via the LPIM process. The solid loadings obtained with these two powder morphologies, varying from 58 to 62 vol.-%, represent expected values. The trend in the density values obtained with irregular (∼6.6 g/cm 3 ) and spherical (∼7.5 g/cm 3 ) powders was validated by metallographic observations.

Comparative Analysis of Methods for Determining the Critical Binder Volume Concentration in Hard Metal Pastes

“…One way to optimise this parameter is by determining the critical binder volume concentration (CBVC), which is a widespread practice in ceramic and powder metallurgy. This quantity has been determined by a variety of methods for alumina [1]- [3], kaolin and alumina [4], zirconia [5], zirconium silicate [6], [7], stainless steel [5], [8]- [13], gas atomised Invar 36 alloy [14], [15], bonze and Inconel [16]- [18], carbonyl iron [19], titanium [20], [21], tungsten carbide [22]- [28] and other feedstocks. This paper focuses on the CBVC determination via various methods for a hard metal extrusion paste mainly comprised of nano-sized tungsten carbide, cobalt, and a proprietary organic binder.…”

Research Progress on Low-Pressure Powder Injection Molding

“…The binder system greatly influences the mixing, injection, and debinding steps. However, powder characteristics such as particle size, particle size distribution (PSD), and shape also determine the feedstock processability and the final sintered properties [46][47][48][49]. Water and gas atomization are two standard methods for producing irregular and spherical powder particles, respectively.…”

“…For example, if micro-parts or parts with microfeatures are to be shaped, the particles should be smaller than 1 μm for the cavity to be adequately filled [25]. However, LPIM is quite versatile, and it can also be used for parts with dimensions as large as 165 mm [49]. Additionally, Majdi et al [49] used the LPIM approach to make iron parts using four different irregular particles (5.0 < d 50 < 18.3 µm) and spherical (d 50 = 4 µm) iron-powders and a standard binder system containing paraffin wax (PW), carnauba wax (CW), stearic acid (SA), and ethylene vinyl acetate (EVA).…”

“…However, LPIM is quite versatile, and it can also be used for parts with dimensions as large as 165 mm [49]. Additionally, Majdi et al [49] used the LPIM approach to make iron parts using four different irregular particles (5.0 < d 50 < 18.3 µm) and spherical (d 50 = 4 µm) iron-powders and a standard binder system containing paraffin wax (PW), carnauba wax (CW), stearic acid (SA), and ethylene vinyl acetate (EVA). The four feedstocks were injected into a rectangular mold cavity.…”

“…For example, if micro-parts or parts with microfeatures are to be shaped, the particles should be smaller than 1 µm for the cavity to be adequately filled [25]. However, LPIM is quite versatile, and it can also be used for parts with dimensions as large as 165 mm [49].…”