Conference Funding for Undergraduate Women Students at WPI (2023-24) – Currently Funded Students

Caitlyn Harrington

Conference: Manufacturing Science and Engineering Conference (https://event.asme.org/MSEC)

Abstract: Complex internal channels enable optimization of thermal and fluid transfer efficiency, weight reduction, and minimization of material waste in the tooling and aerospace industries [1]. As examples shown in Fig. 1, conformal cooling channels for injection molds (Fig. 1a), fabricated by metal additive manufacturing (MAM), may reduce cooling time by up to 70% [2]; MAM tapered fuel channels within jet engine nozzles (Fig. 1b) can increase fuel delivery efficiency by 15% [3]; internal cooling channels within gas power turbine blades, manufactured by loose-wax casting or shaped tube electrochemical machining (Fig. 1c), allow elevated inlet temperature for enhanced engine efficiency [4].These complex internal channels often need improvement in surface finishing and geometric tolerance. As-built MAM channels have average surface roughness (Sa) ranging from 10 to 30 μm with maximum peak to valley heights (Sz) of more than 150 μm [5]. This high surface roughness negatively affects the fatigue life, corrosion resistance, and dimensional tolerance [6]. The turbine blade cooling channel needs surface finishing before aluminide coating for heat resistance. Polishing these complex channels, characterized by small internal diameters (ID) (1-5 mm), high aspect ratios (>20:1), high tortuosity, and varied diameters and geometries is challenging. Existing internal polishing methods for complex channels include abrasive flow machining [7], magnetic abrasive finishing [8], chemical polishing [9], and electrochemical polishing [10]. • Abrasive flow machining (AFM) [7], shown in Fig. 2(a), is a loose abrasive process that forces a slurry with 50- 80% abrasives in volume through the channel with a pressure up to 7.0 MPa. The flowing abrasives scratch the channel wall for material removal and surface finishing. For complex channels with an internal diameter less than 5 mm, an aspect ratio greater than 40:1, or tapered or curved geometry, however, this process may suffer from a fluid pressure drop of nearly 50%, leading to low efficiency and poor uniformity. • Magnetic abrasive polishing (MAF) [8], shown in Fig. 2(c), drives abrasives through internal channels via a controlled magnetic field. It requires precise positioning of magnetic poles at a set distance from the internal surface of the workpiece to achieve controllable and uniform surface finishing, which is often not feasible in large onepiece constructions like turbine blades. Chemical polishing (CP) [9], shown in Fig. 2(d), etches and levels the channel inner surface via chemical reaction with a specific solution. It is not limited by channel geometries and can achieve high material removal rate. However, the control of chemical etching for uniform, precise material removal is challenging. • Electrochemical (ECP) [10], shown in Fig. 2(e), polishing applies direct current to the workpiece immersed in the electrolyte to produce selective anodic dissolution to reduce the microroughness of the metal surface. It is not suitable for non-metallic materials and challenged by electrode positioning through complex channels. As summarized in Table 1, none of the existing internal polishing methods can efficiently polish complex channels with uniform surface finishing improvement while maintaining dimensional integrity. Based this review, we identify the following key requirements for uniform, adaptable and controllable, internal polishing of these complex internal channels:

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