18-07-2012, 02:35 PM
Wire Electric Discharge Machining (WEDM)
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INTRODUCTION
Wire Electric Discharge Machining (WEDM) is a non-traditional process of material removal from electrically conductive materials to produce parts with intricate shapes and profiles. This process is done by using a series of spark erosion. These sparks are produced between the work piece and a wire electrode (usually less than 0.30 mm diameter) separated by a dielectric fluid and erodes the work piece to produce complex two and three dimensional shapes according to a numerically controlled pre-programmed path. The sparks produce heating and melt work piece surface to form debris which is then flushed away by dielectric pressure. During the cutting process there is no direct contact between the work piece and the wire electrode. The wire electrical discharge machining (WEDM) has become an important non-traditional machining process because it can machine the difficult-to-machine materials like titanium alloys and zirconium which cannot be machined by conventional machining processes.
PRINCIPLE OF WEDM
WEDM is a process of repetitive sparking cycles. A series of electrical pulses generated by pulse generator unit is applied between the work-piece and travelling wire electrode. During spark discharge, there is flow of current across the wire electrode-work piece gap. Energy contained in tiny spark discharge removes a fraction of work material. Duration of each spark is very short. Large number of such time spaced tiny discharges between the work piece and wire electrode cause the electro-erosion of work piece material. The entire cycle time is usually few micro-seconds.
WORKING OF WEDM
WEDM is a specialized thermal machining process capable of accurately machining parts which have varying hardness, complex shapes and sharp edges that are very difficult to be machined by traditional machining methods. The practical technology of WEDM process is based on the conventional EDM sparking phenomenon utilizing the widely accepted non-contact technique of material removal. In WEDM material is eroded from the work piece by a series of discrete sparks occurring between work piece and wire electrode separated by a stream of dielectric fluid, which is continuously fed to the machining zone with the help of nozzle.
WIRE-CUT EDM MACHINE
There are four basic elements of WEDM machine tool, the power supply system, the positioning system, the drive system and the dielectric system. All the four basic sub systems are distinct from conventional EDM.
Positioning System
Usually positioning system is a CNC two axes table. However, it operates in adaptive control mode so that in case wire approaches very near to the work piece, or the gap is bridged by debris and causes short circuit, the positioning system should be capable to sense it. Instantaneously, it should move back to re-establish proper cutting conditions in the gap.
Dielectric System
The dielectric system consists of dielectric fluid, reservoir, filters, pump and delivery devices. While the machining is continued, the machining zone is continuously flushed with water passing through nozzles on both sides of the work piece. The spark discharge across the work piece and wire electrode causes ionization of the water which is used as dielectric medium.