Thermoplastic micro-forming process of bulk metallic glass surgical blades using drawing velocity regulation

Abstract

Drawing velocity is essential in the manufacturing of the multi-facet bulk metallic glass (BMG) knife edges used in corneal surgery since it is one of the factors that can determine good blade profiles in the thermoplastic forming process. The goal of this article is to determine and regulate drawing velocity based on the viscoelastic filament stretching and knowledge of the thermoplastic forming map of BMG. The generation of drawing velocity profile is done in two stages: the initial transient stage before the extensional viscosity stage is fully developed, and the extensional viscosity stage. The controller based on the system identification of the testbed is then optimized from the requirements of the drawing velocity and its implementation feasibility. The control objectives of regulation performance and robustness to modeling uncertainties are posed and solved in an optimal control (H_∞) framework. The proposed controller shows an improvement over other controllers including proportional-integral-derivative controllers in terms of robustness to uncertainties and tracking performance. BMG samples processed from this study result in good quality with improvement of 20% and 54% in X–Y ( $2.2\pm 0.1$ µm) and X–Z ( $1.3\pm 0.1$ µm) straightness and 25% more consistent edge radii ( $46\pm 3$ nm).