Wire electrical discharge machining (WEDM) is a specialised thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This practical technology of the WEDM process is based on the conventional EDM sparking phenomenon utilising the widely accepted non-contact technique of material removal. Since the introduction of the process, WEDM has evolved from a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degree of dimensional accuracy and surface finish quality. Over the years, the WEDM process has remained as a competitive and economical machining option fulfilling the demanding machining requirements imposed by the short product development cycles and the growing cost pressures. However, the risk of wire breakage and bending has undermined the full potential of the process drastically reducing the efficiency and accuracy of the WEDM operation. A significant amount of research has explored the different methodologies of achieving the ultimate WEDM goals of optimising the numerous process parameters analytically with the total elimination of the wire breakages thereby also improving the overall machining reliability. This paper reviews the vast array of research work carried out from the spin-off from the EDM process to the development of the WEDM. It reports on the WEDM research involving the optimisation of the process parameters surveying the influence of the various factors affecting the machining performance and productivity. The paper also highlights the adaptive monitoring and control of the process investigating the feasibility of the different control strategies of obtaining the optimal machining conditions. A wide range of WEDM industrial applications are reported together with the development of the hybrid machining processes. The final part of the paper discusses these developments and outlines the possible trends for future WEDM research.

State of the art in wire electrical discharge machining (wedm)

Because of its excellent anodic bonding property and surface integrity, borosilicate glass is usually used as the substrate for micro-electro mechanical systems (MEMS) For building the communication interface, micro-holes need to be drilled on this substrate However, a micro-hole with diameter below 200 μm is difficult to manufacture using traditional machining processes To solve this problem, a machining method that combines micro electrical-discharge machining (MEDM) and micro ultrasonic vibration machining (MUSM) is proposed herein for producing precise micro-holes with high aspect ratios in borosilicate glass In the investigations described in this paper, a circular micro-tool was produced using the MEDM process This tool was then used to drill a hole in glass using the MUSM process The experiments showed that using appropriate machining parameters; the diameter variations between the entrances and exits (DVEE) could reach a value of about 2 μm in micro-holes with diameters of about 150 μm and depths of 500 μm DVEE could be improved if an appropriate slurry concentration; ultrasonic amplitude or rotational speed was utilized In the roundness investigations, the machining tool rotation speed had a close relationship to the degree of micro-hole roundness Micro-holes with a roundness value of about 2 μm (the max radius minus the min radius) could be obtained if the appropriate rotational speed was employed

Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining

A study on the characterization of high nickel alloy micro-holes using micro-EDM and their applications

Results of applying the wire Electrical Discharge Machining (EDM) process to generate precise cylindrical forms on hard, difficult-to-machine materials are presented. The design of a precise, flexible, and corrosion-resistant underwater rotary spindle is first introduced. A detailed spindle error analysis identifies the major sources of error at different frequency spectrum. The spindle has been added to a conventional two-axis wire EDM machine to enable the generation of free-form cylindrical geometries. The mathematical model for material removal rate of the free-form cylindrical wire EDM process is derived. Experiments were conducted to explore the maximum material removal rate for cylindrical and 2D wire EDM of carbide and brass work-materials. Compared to the conventional 2D wire EDM of the same work-material, higher maximum material removal rates may be achieved in the cylindrical wire EDM, possibly due to better debris flushing condition.

Development of the Cylindrical Wire Electrical Discharge Machining Process

Development of the Cylindrical Wire Electrical Discharge Machining Process, Part 1: Concept, Design, and Material Removal Rate

A combined machining method, micro ultrasonic machining (micro-USM), is proposed here for the fabrication of three-dimensional (3D) microstructures with high aspect ratios. Wire electro-discharge grinding (WEDG) and electro-discharge machining (EDM) are combined onto the USM machine to provide a capability of making co-axial microtools for USM and, thereafter, microholes as small as 15 μm in diameter and a variety of high-aspect-ratio microstructures on brittle materials have been achieved for the first time by optimizing the ultrasonic machining processes. The combination of WEDG, EDM and USM on a micro-USM machine also makes possible the construction of complete 3D micromachines within one total manufacturing process. With this method, a 3D micro center-pin bearing air turbine has been successfully developed. The design, fabrication and testing issues are described in this paper.

M. Fujino

Papers

Micro ultrasonic machining and its applications in MEMS