Electrodes Are Prone To Carbon Accumulation For Several Reasons
Electrodes are prone to carbon accumulation for several reasons
1. Improper use of processing regulations, exceeding the current density bearing capacity of discharge section and too small between pulses
The application of discharge energy is not random, want to process a little faster to apply a little more current, discharge processing specifications generally refer to the peak current, that is, the pulse in the conduction when the current flows through the discharge channel, current action time is very short, depending on the pulse conduction time, that is, pulse width. The current value displayed by the ammeter or analog ammeter on the machining equipment is the average value of the pulse current because the pulse is interstitial discharge. Generally speaking, the peak current is determined by the number of power amplifier components put into the discharge circuit and the voltage applied by the circuit, and has nothing to do with pulse width and pulse; The machining current is not only related to the peak current but also can be changed by adjusting the pulse width and interpulse. As shown in the picture.
The discharge current density of graphite electrode is about 6 ~ 8 (A) /cm2. If the current density exceeds this value, the probability of abnormal discharge increases and the probability of carbon accumulation increases.
The correct method is to estimate the discharge area correctly and select the machining parameters according to the discharge area.
For example, there is a square electrode whose discharge area is 3×3 (mm). When selecting discharge parameters, first select the model number condition of 3, and then select a suitable initial processing condition according to the electrode reduction.
It must be noted that the discharge current should be estimated according to the discharge area. The normal value of the current of this area should be controlled at about 1/9 of the current density value, which can be appropriately increased to a larger number, not more than 2.5A is appropriate. If too large, it is easy to produce carbon accumulation. Therefore, with some small electrodes, it is not necessary to make the electrode reduction too large. For the above example, the reduction of 0.1 electrode on one side is basically sufficient.
The processing parameters of the imported discharge equipment are set relatively complete and scientific, generally as long as the need to choose, but some Taiwan machine or domestic low-gear spark discharge motor, its processing parameters are generally not as detailed as the imported machine, even without expert database for automatic selection, can only choose their own processing conditions according to the experience of the operating staff. The principle of selecting the processing conditions is the same, first estimate the processing area, determine the discharge current, because the discharge current is related to the pulse width and pulse, so also must consider the matching relationship between the two, especially pay attention to is set reasonable or enough pulse, not enough pulse time will make the discharge channel too late to deionization, discharge process has been in the on-state, Form an arc discharge (i.e. carbon deposit). In the case of uncertainty, it is better to set the pulse gap larger to improve the machining stability