Investigation of thermal deformation and surface microstructure of wire electrical discharge machining for thin-walled rare-earth gadolinium

Abstract

Rare-earth gadolinium (Gd) has excellent magnetocaloric properties. High-aspect-ratio arrays of thin-walled parts processed with rare-earth Gd are typical structures for regenerators, which are the core components of magnetic refrigeration. Wire electrical discharge machining (WEDM) offers significant advantages for manufacturing micro-structured parts. However, in WEDM, materials are thermally ablated, which leads to compromised surface quality and significant thermal deformation in thin-walled structures with low stiffness. In this study, the effects of different process parameters on the thermal deformation and surface microstructure of rare-earth Gd thin-walled parts were studied by single-factor experiments. It was found that the pulse-on time, open voltage, and water pressure had prominent effects on thermal deformation. Lowering the pulse energy can effectively reduce the thermal deformation and oxidation of the samples and improve the machined surface quality. Through the SNR analysis of the thermal deformation and surface roughness results for the optimized experimental sample, the optimal processing parameter combination of rare-earth Gd thin-walled structure regenerator with high-aspect-ratio of 38 was determined. It was proved that the thermal deformation of thin-walled parts can be controlled within 20 μm by using the combination of optimal thermal deformation parameters, including a pulse-on time of 0.5 μs, pulse-off time of 25 μs, peak current of 12 A, open voltage of 95 V, and a water pressure of 0.22 MPa.