Rapid manufacturing techniques in the development of an axial blood pump impeller
Abstract This paper presents a comparison of manufacturing techniques used in the development of an axial blood pump impeller. In this development process the impeller was designed and its performance was evaluated with the aid of computational fluid dynamics (CFD). Prototypes of those designs where the CFD results show promise were needed in sufficient quantities at a low cost for experimental validation of the CFD results. As the impeller is less than 16 mm in diameter with a maximum blade thickness of about 1.5 mm, innovative manufacturing techniques are explored in this paper to determine the best process for quick fabrication of prototypes that are dimensionally accurate, structurally robust and low in cost. Four rapid prototyping techniques were explored. The completed parts were compared on the basis of manufacturing time, quality and strength of parts obtained, manufacturing cost and also in vitro performances. Based on these studies, it was concluded that selective laser sintering (SLS) is the most appropriate method for the quick production of prototype parts for evaluation of pump performance.
3D Printing of Functional Assemblies with Integrated Polymer-Bonded Magnets Demonstrated with a Prototype of a Rotary Blood Pump
Conventional magnet manufacturing is a significant bottleneck in the development processes of products that use magnets, because every design adaption requires production steps with long lead times. Additive manufacturing of magnetic components delivers the opportunity to shift to agile and test-driven development in early prototyping stages, as well as new possibilities for complex designs. In an effort to simplify integration of magnetic components, the current work presents a method to directly print polymer-bonded hard magnets of arbitrary shape into thermoplastic parts by fused deposition modeling. This method was applied to an early prototype design of a rotary blood pump with magnetic bearing and magnetic drive coupling. Thermoplastics were compounded with 56 vol.% isotropic NdFeB powder to manufacture printable filament. With a powder loading of 56 vol.%, remanences of 350 mT and adequate mechanical flexibility for robust processability were achieved. This compound allowed us to print a prototype of a turbodynamic pump with integrated magnets in the impeller and housing in one piece on a low-cost, end-user 3D printer. Then, the magnetic components in the printed pump were fully magnetized in a pulsed Bitter coil. The pump impeller is driven by magnetic coupling to non-printed permanent magnets rotated by a brushless DC motor, resulting in a flow rate of 3 L/min at 1000 rpm. For the first time, an application of combined multi-material and magnet printing by fused deposition modeling was shown. The presented process significantly simplifies the prototyping of products that use magnets, such as rotary blood pumps, and opens the door for more complex and innovative designs. It will also help postpone the shift to conventional manufacturing methods to later phases of the development process.
CFD-Based Design Optimization of the Outlet Stator of a Rotodynamic Cardiac Assist Device
Two designs of an outlet stator for an axial flow left ventricular assist device are analyzed at nominal operating conditions. The original stator assembly (design 1) has significant flow separation and reversal. A second stator assembly (design 2) replaces part of the original tubular outer housing with a converging-diverging throat section with the intention of locally improving the fluid dynamics. Both stator designs are analyzed using computational fluid dynamics (CFD) analysis and experimental flow visualization. The computational and experimental methods indicate persistent regions of flow separation in design 1 and increased surface washing in design 2. However, the improved fluid dynamics of design 2 is accompanied by a significant decrease in pressure recovery as compared to design 1. To resolve these apparently conflicting end point behaviors, CFD-based design optimization is used to evolve the outer housing shape of a third stator assembly to simultaneously reduce flow stasis and maintain a high level of pressure recovery. During the optimization process, several insightful guidelines for designing efficient outlet stators of axial flow turbomachines become evident.