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

2. Poor chip removal

A. The influence of processing depth

The smaller the discharge cross-sectional area and the deeper the processing depth, the more difficult it is to remove chips. It is the key to treat the processing of this type of cavity and improve the quality of chip removal. Referring to the discharge of cuttings by electric discharge, there are 

two conventional methods at present, one is the flushing method, the other is the immersion method, and the immersion processing at the same time with the flushing method auxiliary, in order to improve the liquidity of the liquid to strengthen the effect of the discharge of chips. In terms of processing accuracy and chip removal effect, the immersion method is much better than the simple flushing method (see figure). The chip removal mechanism of the immersion processing method is that the high-speed movement of the spindle causes the cavity to be in a state of high pressure or vacuum, causing a strong disturbance of the liquid to achieve the purpose of chip removal. Imported equipment, because the spindle running acceleration is very high, very suitable for this method of chip removal, and the effect is very good. Punching processing method, because of the fluid flow direction and pressure is not uniform, chip removal may not be complete, where the debris is gathered, easy to form two discharge, affecting the accuracy of the cavity; Secondly, it is also easy to cause carbon accumulation, so under the condition of permit, we should try to use immersion processing method for processing.

B. The influence of processing position

The discharge position of electric discharge is related to whether it is easy to form carbon accumulation. It is not necessarily that the discharge stability of open discharge machining is higher than that of blind hole machining. The processing stability of only one surface is sometimes worse than that of all peripheral surface machining at the same time. The reasons are as follows, the discharge of EDM chips mainly depends on the disturbance of the processing liquid, or scouring, or extrusion, the stronger the liquid fluidity, the more thoroughly the discharge of chips. And in the 

case of processing only one surface, due to the up and down movement of the electrode can not cause the strong disturbance of the processing fluid, and if the spindle up and down pulsation distance is relatively small, the electrical corrosion products can not be separated from the discharge gap, easy to cause processing stability and even carbon accumulation. As shown in the picture.

In this case, if the machine tool performance is good, can realize the three-axis machining, it is best to adopt the side servo machining, so that the electrode in the rollback slightly away from the machining surface a distance, so that the electrical corrosion products can be washed away smoothly. If there are no conditions, try to increase the amplitude of spindle motion, so that the processing surface as far as possible exposed to the processing fluid, in order to eliminate electrical corrosion.

C. Influence of liquid flow treatment

In discharge machining, liquid flow treatment is very important. The direction of liquid flow should follow the direction of electrical corrosion products. In the above example, if the direction of liquid flow is not parallel to the discharge gap but perpendicular to the discharge gap, then the discharge state may become worse. Like the processing of the above items, but by immersion processing may not be very good, it is best to assist with the flushing method.

D. Influence of electrode material quality

Electrode material quality, of course, is also the main reason for processing abnormalities. Generally speaking, the probability of quality problems of graphite materials is higher than that of copper. The 

reason is that graphite manufacturing process is complex, and after all, it is a non-metallic material with many characteristics that are different from metal materials. The quality of graphite is generally reflected in the material is relatively loose, easy to drop slag, uneven discharge roughness, but all these phenomena is not equal to the quality of graphite, the processing state is not good, processing conditions used improperly will also cause these problems, only after the exclusion of these possibilities to consider whether the material problem. Toyang Carbon provides pure daily graphite with stable product quality and guaranteed service. Customers can rest assured to use various brands of graphite products provided by our company.