High-speed reciprocating hot wire WEDM cutting

High Speed ​​Wire-cut Electrical Discharge Machine (HSWEDM) has entered the market since the 1970s and is accepted by the mold processing market with its high cost performance. Currently, the annual sales volume has reached 50,000. Around Taiwan, it has become an irreplaceable processing method in the field of mechanical processing, and its application areas are constantly expanding, and the level of technology is constantly improving. The HSWEDM with China's independent intellectual property rights is also gradually being accepted by all countries in the world.

Due to the characteristics of HSWEDM's self-propelled traversing, it is impossible for the cutting accuracy of the HSWEDM to contend with the low speed Wire-cut Electrical Discharge Machine (LSWEDM). Therefore, an important manifestation of its good price/performance ratio is its ability to perform. Efficient and long-term stable cutting process, especially in high-thickness cutting.

Let's briefly talk about HSWEDM's high-thickness cutting.

A significant difference between HSWEDM and LSWEDM is its ability to perform stable high-thickness (thickness >500mm) cutting. For LSWEDM, the inter-electrode cooling is based on high-pressure injection of deionized water into the discharge gap. Therefore, when the cutting thickness exceeds 200 mm, the difficulty of deionized water entering the slit increases, cutting efficiency is significantly reduced, and the probability of broken filaments is greatly reduced. improve. Since HSWEDM mainly relies on electrode ribbons for the working media between the electrodes, the problems of cooling, washing and deionization are no longer a hindrance to high-thickness cutting after using a good-cleaning compound working solution. Currently, the highest cutting thickness of commercialized HSWEDM has exceeded 1200mm, and customized products with cutting thickness of 1500mm or more have been marketed.

Of course, the ability to perform high-thickness cutting of more than 500 mm does not only solve the problem of stable inter-electrode cooling. Since the length of the electrode wire in the slit increases, the electrode wire has a throw-off effect after passing through the guide wheel, and the distance δ and the amount of bouncing off the theoretical tangent of the upper and lower guide wheels after throw-off are related to the span of the upper and lower arm.

Therefore, first, the kerf must have enough clearance for the electrode wire to jump, so it is required that the pulse power source has enough explosive force to obtain a large discharge gap.

Secondly, the distance from the theoretical tangent of the upper and lower guide wheels after the electrode wire is thrown off is related to the span and the wire tension (T), so the wire tension and its stability must be controlled.

Third, due to the increase in working length of the working fluid between the poles and the working fluid having a certain conductivity, it will inevitably generate a high leakage current between the poles, and the leakage current will become unstable due to the non-uniform medium between the poles, which will result in Affects the stability of the sampling voltage between the electrodes, so the selection of low-conductivity working medium and the sampling method and sampling point improvement are also problems to be faced.

Fourth, due to the increase in the time for the electrode wire to stay between the poles, the distance between the poles and the distance between the poles, etc., it is easy to cause the possibility of abnormal discharge between the poles, and the probability of wire breakage of the wire is increased. The normal discharge state is judged in time, and once the abnormal discharge occurs, the discharge pulse should be cut off in time. After solving the above problems, the stability of high-thickness cutting will be greatly improved.

Fifth, the latest research by China Southern Airlines’ Liu Zhidong's group has proved that high-speed reciprocating walking is asymmetrical cutting, which results in inconsistencies in forward and reverse cutting, resulting in a unilateral loosening problem. This phenomenon is particularly evident in high-thickness cutting. obvious. The unilateral loose wire will make the high-thickness cutting not last too long. To solve this problem, the purpose of balancing the resistance of the electrode wire is basically achieved by adjusting the wire take-off speed of the forward and the reverse electrode wire, thereby reducing or eliminating the unilateral loose wire. The problem is that the high-thickness cutting can be carried out lastingly and steadily, and the fine work fluid with low conductivity can achieve a good processing index.