It is very important to pay attention to the pulse interval and discharge time when the dies are processed by electric pulse.
Pulse width, which is the duration of voltage pulse applied to both ends of discharge gap on tools and workpieces, is usually referred to as pulse width in open-die processing of pulse injection moulding. In order to prevent arc burns, EDM can only be processed by intermittent pulse voltage waves. Rough processing can be carried out with a larger pulse width, while fine processing can only be done with a smaller pulse width.
Pulse interval is also referred to as pulse interval or interval. It can also be called pulse pause time. It means the interval between two voltage pulses. If the interval time is too short, the discharge gap can not eliminate ionization and restore insulation. It is easy to produce arc discharge and burn tools and workpieces. If the interval time is too long, it is easy to reduce the processing productivity.
Pulse period of injection mould usually refers to the time between the beginning of one pulse voltage and the next adjacent pulse voltage, which is called pulse period. It is equal to the sum of pulse width and pulse interval.
Discharge time refers to the current duration from the gap after dielectric breakdown through to the end of current pulse, which is called discharge time.
The pause time is the time interval between two adjacent discharges called the pause time. Pulse frequency is the number of voltage pulses generated by the power supply in a unit time, which is called pulse frequency. Peak current is the maximum value (instantaneous) of pulse current in gap spark discharge, which has a great influence on surface roughness and processing efficiency.
When we process dies by EDM, both positive and negative electrodes will be corroded to different degrees. Even if the two electrodes of the same material are corroded differently, we will find that one of the electrodes is more corroded than the other. This phenomenon is usually called polarity effect. If the two electrode materials are different, the effect of polarity will be more obvious. Generally, the process of connecting the workpiece to the positive pole of the pulse power supply is called "positive polarity" processing; conversely, the process of connecting the workpiece to the negative pole of the pulse power supply is called "negative polarity" processing. Making full use of polarity effect in practice can improve processing speed and reduce tool electrode loss.
In the process of electric pulse processing, we decompose the free carbon particles with negative polarity in the oil medium. Under the suitable pulse width and pulse-to-pulse conditions, the carbon particles will be covered on the positive electrode of the discharge, which is called the covering effect. At the same time, the electrode wear can be reduced by using a certain covering effect, but the tool electrode must be connected with the positive electrode, and the workpiece is connected with the negative electrode, that is, the workpiece is processed by the negative polarity processing method.
The energy released by pulsed discharge in injection moulding is mainly absorbed by tool electrodes and workpieces, and is usually corroded by melting or vaporization. It is obvious that the higher the melting point, boiling point, thermal conductivity, melting latent heat and vaporization latent heat of tool electrode or processed metal, the less the erosion amount will be. For tool electrode, it is easy to guarantee the processing accuracy; for processing workpiece, it is slow and ineffective.