# Adjustment of Wire Vibrations in Order to Improve Geometric Accuracy and Surface Roughness at WEDM
## 4 Results of Experiments
### Measurement of Wire Tool Electrode Vibrations during Electrical Discharge Machining
Figure 11: _Cont._  
Proposal of Solution for Adjustment of Wire Tool Electrode Vibration during Electrical Discharge Machining  
For a more detailed examination of the possible causes of the increased value of the geometric deviations of circularity in the middle of the profile compared to the edge lines, we came to the conclusion that this phenomenon is caused by the vibrations of the wire tool electrode. Despite tensioning of the wire electrode, with tension force close to the maximum values for the given strength of the wire electrode material, it was not possible to completely eliminate the vibrations caused by discharges between the electrode and the machined material. This was also confirmed by research by [PERSON] [29], [PERSON] [30], and [PERSON] [31]. These vibrations reach a maximum amplitude approximately in the middle of the machined surface profile, which is also confirmed by the particular recorded values of the maximum geometric deviations from circularity (\(y_{Cmax}\)). Based on a detailed analysis of the results of the experimental measurements of geometric deviations of circularity (\(y_{Cmax}\)) and cylindricity (\(z_{Cmax}\)) of the surface after WEDM, it can be concluded that the main cause of the deviations are vibrations of the wire tool electrode. The size of the deviations depends, to a large extent, on the tensioning force of the wire and also on the actual settings of the technological parameters of the electric discharge. Their range is defined by the frequency of the generated electric discharges. It was discovered that the maximum value of the amplitude vibrations of the wire tool electrode is reached when applying the critical frequency of the generated electric discharges. However, in addition to the electric discharge parameters, the critical frequency  
Figure 11: Vibration amplitude values of wire tool electrode during WEDM on an Agiecut Classic 3S electroerosion machine. of the generated electric discharges also depends on other parameters, such as the thickness of the machined material, the diameter of the wire tool electrode, its tensile force (\(Fw\)) and a number of other parameters. Therefore, the critical frequency of generated electric discharges during WEDM cannot be implicitly determined. One possibility for their identification is the application of on-line monitoring. A suitable method for their identification during the electroerosion process appears to be the indirect measurement method, by means of acoustic emissions propagating in the tool wire electrode. However, there is a problem with the location of acoustic emission sensors. A proper solution seems to be their dual placement, on the upper and lower parts, of the wire tool electrode guide. If only one sensor is applied, there is a risk of distorting the recorded values. With the given method of indirect vibration measurement, there is a partial risk of electromagnetic interference (EMI) overlapping with the sensed acoustic emission signals. However, in this case, it was not a disturbing element, because, in both cases, it was essentially a noise. When unwanted vibrations of the wire tool electrode occur, the acoustic emission sensors capture the unwanted vibrations and send the signal regarding the acoustic emission to the transducer, and subsequently to the control unit, which controls the electroerosion process. The control unit processes these values and sends a signal to the electric pulse generator to adjust the parameters of electroerosion process and thus prevents unwanted vibrations of the tool electrode. In addition, the adjustment of the discharge energy can be performed in two phases. In the first phase, there is only a short-term change in the generated pulse frequencies; this change will disturb the increasing oscillation amplitude of the wire tool electrode. If the required change in vibration of the wire tool electrode is not achieved, the system will proceed to the overall adjustment of the values of the main technological parameters.