Page 84 - eBook_Proceedings of the International Conference on Digital Manufacturing V2

Proceedings of the International Conference on Digital Manufacturing –
Volume 2

Keywords: semi-solid metal processing, thixotropic, ferrous,
non-ferrous.

INTRODUCTION

SSMP relies on the principle of thixotropy, where materials
exhibit solid-like behaviour under low shear stress but transition
to a fluid-like state when subjected high shear stress (Czerwinski,
2006). The formal development of SSMP began at MIT in 1971.
Experiment with the Sn-15%Pb alloy found that applying shear
during solidification reduced stress compared to just cooling it.
This was crucial in establishing SSMP principles. The research
also found that viscosity increased as temperature dropped, but
higher shear rates led to lower maximum viscosity, which was
essential for developing SSMP techniques (Czerwinski, 2006;
Ahmad, Naher & Brabazon, 2014; Salleh, Omar, Syarif &
Mohammed, 2013; Rosso, 2012; Razak, Ahmad, & Rashidi 2020;
Jiang et al., 2020; Chang et al., 2020). Commercial applications
of SSMP began in the 1980s, particularly in aluminium casting
(Kirkwood, Suéry, Kapranos, Atkinson & Young, 2010).
Companies explored thixo and rheo techniques to produce high-
quality components with better mechanical properties. Rheo
technique was developed to create non-dendritic slurries directly
from molten metal, enabling efficient mass production with fewer
defects. Meanwhile, the thixo technique involves the creation of
the globular microstructure feedstock billet for SSMP. The thixo
technique became popular due to its ability to produce near-zero
porosity components. Recent advancements have led to
continuous rheoconversion methods that improve slurry
production efficiency using liquid mixing techniques in
specialised reactors (Czerwinski, 2006; Chang et al., 2020;
Kirkwood, Suéry, Kapranos, Atkinson & Young, 2010; Rogal &
Garzel, 2019; Tajudin, Ahmad, Alias, Razak & Alang, 2023).
Figure illustrates significant milestones in the historical
development of SSMP.

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