A special process of 3D servo scanning micro electro discharge machining for machining pierced micro structures of NiTi alloy tube

Although nickel-titanium (NiTi) alloys have many excellent material properties, micro structures of NiTi alloys are rarely machined by conventional mechanical machining due to its high elasticity and severe tool wear. A micro tube as an active catheter with typical driving structures made from a NiTi shape memory alloy (SMA) is a key part in an interventional micro robot system. The driving structures, as complex 3D micro structures pierced through the thin-walled micro tube, are mainly fabricated by a lithography-based process at present. However, not only is the process inefficient and costly, but its etching depth is also limited. In this research, a novel process of 3D servo scanning micro electro discharge machining (EDM) with the movement of two-axis linkage and one-axis servo is proposed for efficiently machining 3D micro structures. The processing procedures are presented, including 3D model design, scanning paths planning, 3D NC codes generation and 3D micro EDM. The emphasis is focused on the methods for planning the scanning paths and generating the CNC codes considering the special 3D micro structures. By using the planned complementary scanning paths, the processing stability is improved for successfully machining the typical driving structures within 5 h. The machining experiments verify the feasibility of the proposed process and related methods.