During processing of the wire cut EDM machines, it often occurs such cases like rough finish surface, groove marks on the workpieces, poor accuracy and whatnot.

The reasons for this situation are usually as follows：

• The molybdenum wire is too loose and trembling.
• The working fluid is too dirty.
• Improper selection of pulse parameters are used.
• The molybdenum wire groove of the guide wheel is too large.
• The reel is not concentric and whatnot.

The solution for this kind of problem can be checked here. It is nothing more than tightening the electrode wire, changing the working fluid, selecting the best pulse parameters, and replacing the guide wheel or bearing. In addition to the above reasons, during the repair of EDM machines, we also find that the keyway between the coiled wire spool DC motor shaft and the friction coupling due to long-term repeated operation is deformed and increased, and the machined surface was caused by the large gap wire barrel vibration during commutation.

How to achieve a better finish surface of workpieces?

Two factors influences the finish surface of workpieces during wire cutting：

One is the size of the pits removed by a single discharge. Its RZ is usually between 0.05μand 1.5μ, which is secondary to the cutting finish. 

The second is the convex and concave stripes caused by commutation. Its RZ is usually between 1μ and 50μ, and it is possible to be as large as 0.1mm or more. This is the most important factor in the finish of wire cutting. At the same time, it is accompanied by reversing black and white stripes, which gives a strong visual impact.

It is easier to control the size of the pit caused by a single discharge, and only the energy of a single pulse needs to be reduced. Only a single pulse energy is small enough to cause thick workpieces to not move, or even a non-sparking state with only short circuit and no discharge. This is similar to the fine regulations in EDM, resulting in extremely low efficiency and poor chip removal ability. The unstable processing. Moreover, the RZ caused by the discharge pits and the RZ caused by the commutation fringes are not within the same order of magnitude, so controlling the RZ accompanying the commutation fringes is the most important. The precision of the guide wheel and the bearing, the constancy of the tension during the up and down movement, etc., cause the inconsistent movement trajectory of the wire up and down. This mechanical factor is the main reason for the commutation convexity.

The following measures will improve the finish to a certain extent:

1. Appropriately reduce the pulse width and peak current, that is, reduce the size of the pits.
2. The guide wheels and bearings maintain good accuracy and stable operation, reduce wire jitter and wire jump, and minimize the displacement of the wire movement track.
3. Maintain the proper tension of the wire, and adjust the guide wheel and power feed contact so that the tension of the working area remains unchanged when the wire goes up and down.
4. The wire should not be too tight, and the processing fluid should not be too new. The new processing fluid is definitely beneficial to the cutting efficiency, but the cutting finish is not the best for the new processing fluid.
5. Add a splint on the upper and lower sides of the too thin workpiece to buffer the reversing stripes within the splint.
6. X and Y axis movement is stable, accurate, follow-up fidelity is good, and crawling without blocking is also extremely important.

1.  Maintain stable and loose frequency conversion tracking.
2. Re-cutting or multiple cuts with appropriate allowance. Scanning the cutting surface when the amount of cutting is small will have a beneficial effect on dimensional accuracy and smoothness. Scanning three times will basically remove the commutation stripes. As long as the machine has high repeat positioning accuracy and multiple processing with proper allowance, the smoothness of the cutting surface will be improved by one to two orders of magnitude. The effect is similar to that of slow wire walking, and it does not take too much time. This is fast wire cutting. One of the machine’s strengths.
3. Short wire can be used appropriately for thicker workpieces, and the reversing feed at a time is less than half the wire diameter, which also covers the reversing stripes. Of course it's just a cover up.