In addition, there are many other reasons that can cause molybdenum wire breakage, such as differences in materials and other factors.

Relating to the materials

It is generally considered that it is fragile and easily to break if the metal has not been forged, quenched or tempered. This is due to the uneven distribution of carbides in the steel, which causes unstable electrical machining performance and causes arc discharge and wire breakage. The carbide particles contained in the steel are large and aggregated into clusters, but the distribution is not uniform. In the processing of such materials, it is easy to crack, deform and clamp the steel wire, causing moly wire breakage. Especially for quenched parts, after quenching, there are about 500-800MP in carbon-free alloys. The internal stress of high carbon steel can reachc1600MPa. If the internal stress of 1600MPa is ground, it can cause 70-80MP internal stress of electrical discharge machining. The electrical discharge machining will form a white electrical discharge machining deterioration layer on the processed surface, and produce a tensile stress of about 800MPa. The stress concentration caused by the interaction of quenching stress, grinding stress, and electrical discharge machining stress is the direct cause of the cracking of the quenched parts in the online cutting process and the wire breakage. Therefore, in order to reduce wire breakage caused by materials, good forging performance and good harden ability should be selected. Materials with small heat treatment deformation promote uniform distribution of carbides contained in steel, thereby enhancing processing stability. For example, cold-punching dies with wire cutting as the main process; try to choose alloy tool steels such as CrWMn, Cr12Mo, and GCr15, and correctly select hot processing methods and strictly implement heat treatment specifications.

Other factors

When unwrapping the molybdenum wire, the old wire on the wire storage tube is often cut with scissors to form a lot of short ends. In electrical parts or caught in the wire feeding device, it will cause a short circuit and cause wire breakage.

After the processing is completed, the processing power should be turned off first. Then the working fluid should be turned off, and the wire should run for a period of time before stopping.

If the working fluid is turned off first, it will cause electric discharge in the air and cause burning of the filament; if the thread is turned off first, the thread speed will be too slow or even stop running, the filament will be poorly cooled, and the lack of working fluid will also cause burning.

When you need to cut manually (referring to the hand-cranked cross slide) at certain times, you should pay attention to the current meter and not exceed the frequency conversion speed during normal cutting, otherwise the wire will be easily broken.

In practice, there is a phenomenon of molybdenum wire breakage caused by dirt, which often occurs after the workpiece is processed. During the inspection, a multi-meter was used to measure a resistance of about 30kg between the steel wire and the machine shell, and the pen was charged and discharged. Further inspection found that there was a lot of liquid slag and dirt between the molybdenum wire stop screw and the wire frame, and between the broken wire detection block and the screw fixed on the wire frame.

After the stopper and detection block are removed, the charging and discharging phenomenon disappears and the resistance value increases. This is due to the liquid slag dirt forming a resistance capacitor between the steel wire and the machine shell, which is connected in parallel to the output end of the power amplifier tube (because the shell and the power amplifier tube have the same potential), which makes the bottom of the output waveform wider and the DC component increases. When the workpiece is about to be processed, the gap between the molybdenum wire and the workpiece is enlarged to increase the sampling potential and the feed speed is increased, which makes the molybdenum wire easy to break after processing. After cleaning the dirt, the machine tool returns to normal.