Experimental investigation of hydrodynamic flexible spindle polishing of metal additively manufactured channels

Abstract

Metal additive manufacturing enables fabrication of internal channels with complex geometries, including small diameters and high aspect ratios, optimized for thermal and fluid transfer efficiency. Polishing these channels to improve internal surface finishing is critical to fatigue life, corrosion resistance, and fluid flow efficiency. Existing internal polishing methods are challenged by these complex channels and struggle to produce consistent internal surface roughness improvement, limiting their applicability. A novel hydrodynamic flexible spindle (HydroFlex) polishing process is introduced. HydroFlex uses a high-speed fixed-abrasive grinding wheel driven by a flexible spindle to navigate through complex internal channels for fast, uniform, and controllable material removal for surface improvement. HydroFlex polishing performance depends on process parameters including workpiece material, channel diameter, grinding wheel diameter, rotational speed, and coolant which are interdependent with limited understanding. In this study, Taguchi statistical method was employed to evaluate the influence of HydroFlex process parameters on the polishing performance, with surface roughness, polish uniformity, and maintenance of channel dimension characterized. The grinding forces and wheel motion were measured for mechanistic understanding. As results, grinding wheel orbital motion around the internal surface of the specimen was found to strongly correlate with polishing performance, with more stable wheel motion resulting in better surface finish. The sensitivity analysis indicated that the wheel rotational speed and specimen material had the largest effect on grinding wheel motion and polishing performance. In performance testing, HydroFlex was able to reduce the surface roughness of a 100 mm long additively manufactured AlSi10Mg channel by 86 % to 1.58 μm in five minutes of polishing. The sample surface finish uniformity and channel circularity were improved by 24.7 % and 43 %, respectively, with the channel diameter widening by only 1.2 %. These results suggest that HydroFlex is an effective, efficient polishing process for additive manufactured internal channels with inherent controllability and adaptability for surface uniformity and dimensional integrity.