Electrochemical milling of deep-narrow slots with a pulsating electrolyte flow field

Abstract

Deep-narrow slots (DNSs) (width<4 mm and depth/width>2 mm) are inherent features in die-casting molds as heat-dissipating slots and turbomachinery components for seal slots. Electrochemical milling (EC-milling) is a flexible method to machine variety of structures by controlling the tool path. The process employs a tubular tool with a flat end face through which the electrolyte is supplied coaxially. However, owing to the small inter-electrode gap (IEG), the quantity and velocity of electrolyte flowing into the IEG are weakened during machining of DNSs. This reduces the machining quality and efficiency. Therefore, this paper proposes a method of EC-milling of DNSs with a pulsating flow field. A tubular tool with a wedge-shaped end face (WS-tube) is designed, and both the quantity and velocity of electrolyte flowing into the IEG will be changed with the rotation of WS-tube. Thus, a pulsating flow field is generated which can enhance the mass transport in the IEG. Consequently, both the machining efficiency and quality are improved. Flow-field simulation results indicate that as compared with the traditional flat end face tube (F-tube), WS-tube can generate a periodic pulsating flow field in both front and side IEG, and the peak electrolyte flowing velocity is also increased. The experiment results reveal that compared to that of 0.24 mm/min with F-tube, the maximum feeding speed reaches to 0.42 mm/min with WS-tube, and both the surface quality and taper are improved at the same time. Increasing the rotation speed of tube tool and pulse frequency further enhances the transport of electrolytic by-products, and the machining quality is improved. With the optimized parameters, a 5 mm deep DNS with width of 1.48 mm ± 0.02 mm, taper of 1.44° ± 0.27° and the surface roughness (Ra) of 0.7 µm has been successfully fabricated. • Pulsating flow field was proposed for electrochemical milling of deep-narrow slot. • A tube tool with wedge-shaped end face was designed to generate pulsating flow field. • With the rotation of wedge-shaped tube tool, pulsating flow field was generated in both front and side inter-electrode gap. • Both the machining quality and feeding speed of DNS were improved with pulsating flow field.