Micro/nano milling applications are needed due to the miniaturization tendency of components used in medical devices and aerospace equipments. Accordingly, micro end mills are needed. However, there are no special purpose machine tools designed for the fabrication of such tools made of ultra hard materials and with complicated three-dimensional geometries. In this paper, a six-axis wire electrical discharge machine (WEDM) designed for the fabrication of micro end mills is developed. Direct drive linear motors and rotary motors are used for linear and rotary axes respectively to realize direct drive instead of ball screws or gearboxes. A special cooling system for all motors makes the thermal effect minimum on the mechanical structures. After the introduction of the developed WEDM, its kinematics model is built. The error analysis for the key axis directly supporting the wire is introduced and the corresponding results are used to guide the mechanical design of the six-axis WEDM and to compensate for position errors during machining. Based on these techniques, high machining accuracy is achieved. Finally, the fabrications of a cutter with complicated geometry and a cutter made of ultra hard material are successfully demonstrated on the developed machine tool.

Micro end mills play a key role in micro/nano milling applications for intricate three-dimensional die/molds or sensors for micro-electro-mechanical systems (MEMS). In order to achieve higher machining accuracy and longer tool life, micro end mills are usually made of ultra-hard materials such as polycrystalline diamond (PCD) or cubic boron nitride (CBN). One of the best choices for their fabrication is the wire electrical discharge machining (WEDM) method. There are two basic categories of micro end mills, namely the ball end mill for 3D freeform surface machining and straight/round edge end mills for non-freeform surface machining. This paper focuses on the design and development of the micro ball end mill for hard and brittle materials. Firstly, the available typical ball end mill is analyzed. Secondly, a micro ball end mill with uniform axial rake and clearance angles is designed and analyzed by the finite element method (FEM). The designed micro ball end mill only needs simultaneously three linear and one index rotational WEDM axes instead of simultaneously five WEDM axes for traditional ball end mills. Then, micro PCD ball end mills are fabricated and the radius variation follows in ±2.0 μm, which is more accurate than commercially available ones. Finally, the 3D freeform geometry milling on tungsten carbide (WC) and silicon wafer successfully demonstrated the possibility of micro-mechanical freeform machining by the developed micro ball end mill.