How to analyze and solve the filament phenomenon o

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How to analyze and solve the "filigree" phenomenon of wire cutting

after cutting for a period of time, molybdenum wire will appear black spots for a period of time. The black spots are usually several to ten millimeters long, and the spacing of black spots is usually several to dozens of centimeters. Black spots are burned and carbonized after a period of continuous arc discharge. It is easy to break after thinning, brittleness and carbonization. Black spots form black spots on the silk tube, and sometimes they are arranged at a certain rate to form patterns, so they are called filaments

① causes of filigree phenomenon

continuous arc discharge is caused by the failure of effective deionization. A large amount of carbon is precipitated from the resistance heat of the arc to form carbon particles, and the molybdenum wire itself is carbonized. Thick workpiece (long discharge gap), low dielectric coefficient of water (poor insulation recovery ability) and pulse source with a DC component of delayed arc extinguishing (greater than 10mA) are the basic conditions for filigree phenomenon. Filament and spark discharge machining arc burn are the same reason. Once the arc burn in the gap is formed, the workpiece and electrode will be burned out of the corrosion pit and form carbon particles at the same time. The carbon particles cannot be processed until they are removed. Press the print key wherever the fine carbon particles stick to. The experimental data will be printed. The area will be burned by arcing, and the area will be larger and larger

② the occurrence and development of filaments

when the discharge gap is long, it is difficult to discharge the etched objects, the insulation recovery ability is poor, and the spark explosion is weak, impurities are easy to produce. The resistance heat quickly changes into arcing burn, and the carbon particles are also mixed. This arcing point moves with the wire, during which each pulse energy is released through this arcing point. Until this arcing point comes out of the workpiece, the insulation can be restored, and new spark discharge can be generated. The burn carbonization (i.e. black spot) of molybdenum wire at this point is formed. If the point in the gap that just induced the arcing burn is still tenacious, it is very easy to repeat the arc discharge with the molybdenum wire point in contact now, and the second burn carbonization (i.e. black spot) point will be formed again. Therefore, the distance between that point and the workpiece outlet is often equal to the distance between the two black spots. Since the first burn carbonization, a carbonization point has been left on the wire, and a series of carbonization points have been left in the gap between workpieces. Extremely fine carbon particles will enter the gap at any time when they are spread into the water, and they have become the inducing factors of filaments

③ appearance and observation of filaments

due to arc discharge, short circuit, open circuit and carbon particle generation, the pulse source ammeter will swing greatly. Discharge sparks will appear red, yellow and white alternately. The initially formed black spots become thicker due to heat burning and carbonization, and become thinner after passing through the gap and ablating several times. Heating and tension for a period of time also make the black spots thinner. Embrittlement is caused by burning red and cooling, and serious carbonization. Because the plaques formed by filaments on the silk tube are easy to arrange regularly, many people try to find the rule, and the result is wrong with the circumference of the silk tube, the circumference of the guide wheel, and the distance between the conductive block and who. If there is a rule, it is the distance from the burn point to the workpiece exit

④ solution and analysis of filaments

Once the filigree phenomenon occurs, we should start with the three elements of the cause. First of all, we should confirm the quality of the pulse generator. Only the rotation of the force measuring pointer will slow down. Without the DC component that prevents arc extinguishing, it usually will not cause filament breakage. Secondly, we should pay attention to water. It is definitely not good to have less pollution, dilute and effective ingredients; 3. Take the hook as the next real chain, which contains a certain amount of salt, alkali and other components that hinder dielectric insulation. Thirdly, it should be noted that the material is too thick, with black oxide skin, forging and rolling interlayer, and the raw materials are quenched without forging and tempering, resulting in a high probability of filaments. If it still cannot be solved, the material can only be removed, and the wire, water and machine tool can be completely replaced; Make the 50mm wide edge coincide and flush. Start with large pulse width, small current and high voltage. When the processing is stable, gradually increase the current, but it is still limited to 2.5A

the filigree phenomenon is often not the cause of the machine tool. After confirming that the pulse source is OK and the gap tracking is normal, you should turn to three basic conditions and one inducement to find it

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