(1) Open circuit
There is no breakdown of the discharge gap, and there is a voltage greater than 50V on the gap, but no current flows in the gap, which is a no-load state.
(2) Spark discharge
The insulation performance in the gap is good, and the metal can be effectively thrown out and corroded after the breakdown of the working fluid medium. The waveform characteristics are: there are td on the voltage, small sawtooth waveforms with high frequency oscillation on the te and Ie waveforms.
(3) Short circuit
The discharge gap is directly short-circuited, which is due to the excessive instantaneous feed of the servo feed system or the overlap of electrical corrosion products in the discharge gap. When the gap of the wire EDM machine is short-circuited, the current is large, but the voltage across the gap is very small, and there is no erosion and processing effect.
(4) Arc discharge
Due to poor chip removal, the discharge point is concentrated in a certain part but not dispersed, local heat accumulation, temperature rise, vicious cycle, at this time spark discharge becomes arc discharge, because the discharge point is fixed at a certain point or a certain part, so called Stable arc often causes carbon formation and burns on the electrode surface.
(5) Transition arc discharge
Transition arc discharge is a transition state between normal spark discharge and stable arc discharge, and is a precursor to stable arc discharge. The characteristic of the waveform is that the breakdown time delay td is very small or close to zero, and it only becomes a spike, and the high frequency component on the voltage and current wave becomes low and becomes sparse and sawtooth.
Because the high-speed wire EDM machine adopts the method of high-speed reciprocating wire feeding by the wire electrode, the loss of the wire electrode is evenly distributed on the electrode wire of nearly 300 meters. There are many factors for the surface quality of the workpiece, and it is necessary to reasonably select the relevant processing parameters to ensure the surface quality of the workpiece. In order to improve the surface quality of the machined workpiece, the control method and improvement method of the machining quality can be considered from the three aspects of the most influential human factors, machine tool factors and material factors.
In CNC wire EDM machining, the loss or wire breakage of the electrode wire seriously affects its continuous automatic operation, especially in high-speed wire EDM wire cutting, due to the repeated use of the electrode wire in processing, with the The increase of wire loss and the narrowing of the slit will not only increase the dimensional error of the machined surface; but also once the wire breaks during processing, the processing must be restarted, which not only takes more man-hours, but also affects the surface quality of the machined surface. . Causes and measures of electrode wire loss or wire breakage include:
(1) When the electrode wire moves rapidly, friction occurs with the guide wheel and the conductive block, causing wear of the guide wheel and the conductive block. When used for a long time, the bottom of the V-shaped groove of the guide wheel is pulled out of the groove by the electrode wire. When the conductive block is used for a long time, the side that contacts the electrode wire is also pulled out of the groove. As a result, the frictional resistance of the guide wire part increases, and the electrode wire is broken due to the blockage of movement.
(2) When the material to be cut is offset and the weight of the material to be cut is heavy, deflection and displacement are likely to occur when the WEDM machining is about to end, resulting in the electrode wire being stuck. To this end, a ground plane permanent magnet can be added to the plane of the workpiece and the material to be removed to help the material to be removed in a fixed position during the cutting process.
(3) When the electrode wire is used for a long time, the wire diameter becomes thinner and full of micro-discharge pits, the tensile strength decreases, and finally breaks. Generally speaking, when the measured wire diameter is 0.03-0.05mm less than the new wire, the new wire should be replaced in time.
(4) The electrode wire should be wound evenly and neatly on the wire storage drum. When the inner and outer circles of the wire storage cylinder are not coaxial, an unbalanced inertia will be generated, and it is easy to generate overlapping wires during rotation, resulting in the breakage of the electrode wire. Therefore, the wire accumulator must be dynamically balanced.