1. Tightness level of molybdenum wire
If the molybdenum wire is loosely installed, the strong vibration of the molybdenum wire will not only lead to wire breakage, but also immediately damage the surface roughness of the workpiece because of the vibration of the molybdenum wire. However, the molybdenum wire can not be installed too tightly. If it is too tight, the thermal stress will expand, which will also lead to wire breakage. Therefore, in the whole process of laser cutting, the tightness level of molybdenum wire should be appropriate. The newly installed molybdenum wire should be tightened before production and processing, and the tightening force need not be great. After a period of production and processing, the molybdenum wire is sagged due to its own stretching. When the stretching amount is large, the vibration of molybdenum wire will be aggravated or the molybdenum wire will overlap on the wire storage cylinder. The wire is unstable and broken. The tightness level of molybdenum wire should be checked frequently. If there is looseness, tighten it immediately.
Molybdenum wire installation. Molybdenum wire shall be wound on the wire storage cylinder according to the specified direction, and both sides shall be fixed at the same time. During wire winding, 10mm shall be reserved on both sides of the wire storage barrel, and the middle part shall be fully wound without overlapping. The total width shall not be less than half of the length of the wire storage barrel, in order to prevent the parts from being damaged quickly due to frequent motor phase change, and also to prevent molybdenum wire from being broken due to frequent participation in laser cutting.
The molybdenum wire on the CNC lathe is led out with a wire stopper. The wire stopper is a guiding upright made of two emeralds. The wire stopper does not do the turning exercise like the guide wheel. They immediately touch the molybdenum wire for rolling friction. As a result, the damage is rapid, and the area where the cylinder and molybdenum wire touch will produce grooves soon after application. It is necessary to immediately check, rotate and replace them, otherwise the stacked wire and broken wire will occur.
2. Silk conveying organization
The wire transporting organization of the medium wire walking WEDM machine is mainly composed of a wire storage cylinder, a wire rack and a guide wheel. When the precision of the silk conveying structure decreases (mainly the rotating bearing), the axial and radial vibrations of the silk storage drum will be caused. The axial vibration of the wire storage cylinder will reduce the supporting force of the electrode wire, resulting in wire looseness. In serious cases, the molybdenum wire will slip from the guide pulley groove and break. The radial shaking of the wire storage cylinder will cause uneven wire arrangement and wire stacking. The shaft, rolling bearing and other parts of the wire storage cylinder are often damaged to cause clearance, which is also very easy to cause the wire to vibrate and break. Therefore, the damaged shaft, rolling bearing and other parts must be removed and replaced immediately. If the high-voltage power supply is not cut off during the phase change of the wire storage cylinder, the molybdenum wire will be burned out due to excessive temperature in a short period of time. Therefore, it is necessary to check whether the limit switch behind the wire storage cylinder is invalid. It is necessary to maintain the flexible rotation of the wire storage cylinder and guide wheel, otherwise the wire will be broken due to the vibration of the wire conveying system during the back and forth exercise. After the wire is wound, fully load the wire to detect whether the molybdenum wire vibrates. If it does, analyze the cause. The stopper of the limit switch at the rear end of the filament storage cylinder must be adjusted properly to prevent the filament storage cylinder from breaking through the travel arrangement of the limit switch. The contact and friction between the stopper and the rapidly moving molybdenum wire in the wire stopper device will easily cause pipe trench and lead to the breakage of the wire clamp, so it needs to be removed and replaced immediately. The wear of the roller bearing of the guide wheel will immediately endanger the precision of the cook guide wire. In addition, when the v-groove of the guide wheel, the crystal limit switch block, and the conductive block are damaged, the pipe trench will also cause excessive sliding friction of the electrode wire, which is easy to break the molybdenum wire. This kind of situation generally occurs when the CNC lathe has been used for a long time, the production and processing workpieces are too thick, and the silk transportation organization is not easy to remove. Therefore, in the application of numerical control lathe, the precision of wire conveying organization should be maintained regularly, and the vulnerable parts should be replaced immediately.
Workpiece raw materials: for raw materials that are not forged or heat treated, ultra-low temperature quenching is used to remove the internal force before online cutting. If the thermal stress of the workpiece is not removed, some workpieces will crack and break the molybdenum wire during laser cutting; Some of them will deform the gap and break the molybdenum wire. For example, t8 steel after heat treatment shall be used as little as possible in the process of wire cutting and easy to cause wire breakage. When laser cutting thick aluminum raw materials, due to the difficulty of milling, the conductive block is seriously damaged. Pay attention to the immediate replacement.
Workpiece clamping: Although the workpiece bears little force in the whole process of wire cutting, it is still necessary to firmly clamp the workpiece to avoid wire breakage due to the change of workpiece position in the whole process of production and processing. At the same time, it is necessary to prevent wire breakage caused by the weight of the workpiece itself and the elastic deformation of the raw materials of the workpiece. During the production and processing of thick workpieces, when the production and processing are about to be completed, the falling workpieces can be sucked up with magnets, or the falling workpieces can be manually maintained, so that their parallel surfaces fall slowly to avoid wire breakage. 4 Main electrical parameters The unreasonable selection of main electrical parameters is also a key reason for wire breakage. Therefore, effective main electrical parameters should be selected according to the thickness of the workpiece, and the single pulse interval should be opened a little, which is beneficial to the discharge of molten metal material particles. At the same time, the highest electric flow rate and full load working voltage should not be too high, otherwise, the single pulse energy will increase, and the laser cutting speed will accelerate, It is very easy to cause centralized charging and discharging and arcing, resulting in wire breakage. Generally, the full load working voltage is about 100v. In WEDM, arc charge and discharge are the key factors leading to negative etching damage. In addition, the gap is not suitable, so it is very easy for a single pulse to generate arc charge and discharge. As long as the arc charge and discharge are concentrated in a certain section, wire breakage will occur.