Micro-wire EDM (MW250)

MW250 is a high-precision micro wire EDM machine with a highly flexible wire management system. Utilizing open V-groove wire guides and a takeup spool for the used wire, EDM wires ranging from 0.01 to 0.1 mm (0.0004 - 0.004”) can be used without changes to the machine. The wire is set up in a vertical arrangement that facilitates vibration-free self-flushing induced by the heat of the EDM process. The X- and Y-axes with a travel of 250 mm (9.84”) have a linear resolution of 0.0001 mm (0.000004 in) to allow the precise servoing required for micro-EDM.
The machine uses a RC-based discharge generator that was specifically designed for wire-EDM with extremely small wire diameters. EDM parameters that can be adjusted include the ionization voltage (24 - 200 V), the work voltage (12 - 100 V), the on-time (0.6 - 3 usec), the off-time (4 - 35 usec) as well as any combination of 5 ionization and 8 work capacitors. Grounding of the work piece is achieved through the tank plate, which remains at earth ground regardless of whether positive or negative EDM polarity is used.

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Wire System

The upper and lower wire guides are mounted to micro-flexure stages that allow precise alignment of the wire to the machine axes. The position and length of the cutting section is adjusted by varying the vertical position of both wire guides. This highly flexible wire guide system yields a wide range of cutting lengths (4 - 102 mm = 0.16 - 4.01”) as well as cutting heights. The depth of cut is limited by the geometry of the lower wire guide assembly and cannot exceed 75 mm (3.0”). The MW250 wire system requires manual threading, and as such is primarily intended for work pieces with external features. The machining of internal features requires pre-machined starter holes through which the wire needs to be threaded manually. The control software includes G-Code commands for threading and cutting of the EDM wire.

Dielectric System The dielectric system is based on synthetic EDM oil whose extremely low viscosity paired with high dielectric strength is a major factor in achieving very fine surface finishes. The oil, which requires no maintenance besides filtering, is stored below the machine in a separate tank. Before machining, the oil is pumped through a filter into the work tank, thereby cleaning the oil of particulates.

Controls

The user interface (MicroPEC 5) was specifically created for touchscreens. On the left 1/2 of the screen, critical information about machine status such as axis position, EDM status, etc. is provided. The right 1/2 of the screen are tabbed according to individual machine function. Shown in the picture is the “Work Piece Setup” tab, which provides controls and information that are relevant to setting up the work piece offsets (G54 - G59). In the case of the MW250, the work piece can be setup by touching two surfaces with the EDM wire or optically using the optical system and its live video stream. A second tab provides controls and information related to machining, which is based on line-by-line instructions provided as G-Code. A separate tab is provided that allows the machine to be used as a coordinate measuring machine (CMM) by sampling work piece data points optically or by touch with the EDM wire.

MicroPEC 5 performs machining by executing G-Code that includes the full set of EDM parameters. A unique feature is Auto Tuning, whereby the control software optimizes the axis feed rates to maximize the machining rate. When Auto Tuning is disabled, the axes move at the rate as set by the G-Code, which can be overwritten manually using the the feed rate override buttons. Another feature of MicroPEC is that setting up work piece offsets is supported by a graphical interface that offers various options (finding corners vs. center of work piece). The setup is performed by automatically taking into consideration the probe size (radius of EDM wire) as well as the approach direction, thereby eliminating the need for manual modifications.