There are many factors that affect the machining accuracy of wire cut machine tools, such as process (programming skills, cutting path, etc.), machining environment, workpiece material and whatnot, which can influence machining accuracy. The quality of the machine tool itself is an important factor.

Accuracy of machine tool movement

According to the standard of ‘Wire EDM Accuracy’, the geometric accuracy and motion accuracy of the machine tool are 10 items, among which three factors are important, and the impact on machining accuracy is significant.

(1) Loss of momentum of the worktable movement, which mainly reflects the error caused by the gap between the drive screw and the nut when the worktable is moving forward and backward. The standard stipulates that this error value is 0.005 mm.

(2) The repeated positioning accuracy of the worktable movement, which mainly reflects whether the dynamic and static friction and resistance are the same when the worktable is moving, and whether the assembly pre-tightening force is appropriate, but has little relationship with the lead screw gap and pitch error. The standard error value is 0.002 mm. 

(3) The positioning accuracy of the worktable movement mainly reflects the pitch error of the worktable screw, but it also has a certain relationship with the repeat positioning accuracy. The standard error value is 0.03 mm.

The spatial position and movement stability of molybdenum wire

The electric discharge gap and electric discharge machining force of wire cutting are relatively small, but there is always a big gap between the machining accuracy of the workpiece and the static accuracy of the machine tool. The reason for this phenomenon is that the dynamic stability of the molybdenum wire is very poor (regardless of whether it is in a discharged state), and the molybdenum wire cannot always be kept in the same position during operation, such as wire speed, tension, etc., cannot be kept in a constant state. . The fluctuation of the "string line" between the fulcrums of the upper and lower guide wheels, as well as mechanical wear, tension changes, and the vibration of the wire frame and guide wheels, all affect the accuracy of the WEDM machining. If the vibration of the molybdenum wire cannot be greatly improved, the machining accuracy of the wire cutting is difficult to be significantly improved. We have done the experiment of adding a molybdenum wire limiter mechanism. Under the condition of other processing conditions unchanged, compared with the machining accuracy of the original machine tool, the longitudinal section size difference of the workpiece is reduced from the original 9 microns to 3 microns, and the cross section size difference From the original 11 microns to 1 micron. This test strongly shows that the machining error caused by the vibration of the molybdenum wire is quite large.

Thermal deformation of the wire cut EDM machine tool

Both theoretical analysis and actual testing have proved that the deformation of the machine tool caused by the temperature rise cannot be ignored. If the machine tool electrical appliances, pulse power supply and working fluid tank are all installed inside the machine bed, and the ventilation conditions are not good, when the machine is turned on for a period of time, due to the thermal deformation of the machine tool components due to the increase in temperature, the position of the wire frame will be displaced , Thus affecting the machining accuracy.