# Adjustment of Wire Vibrations in Order to Improve Geometric Accuracy and Surface Roughness at WEDM
## 4 Results of Experiments  
### Circularity Deviations vs. Roughness of Eroded Surface after Electrical Discharge Machining  
The identification of geometric deviations of circularity \(y_{Cmax}\) of the experimental samples profile from EN40 CrMnMoS8-6 tool steel was performed. Individual values of circularity deviations were successively measured from the upper edge downwards, as shown in Figure 4.  
Through the complex identification of maximum geometric deviations from circularity \(y_{Cmax}\) of experimental samples (circular cross-section with nominal diameters of \(\mathrm{\SI{e}}_{C}\) = 5.0, 20.0, 40.0, 80.0, and 120.0 mm, made using WEDM technology from EN 40 CrMnMoS8-6 tool steel using a wire electrode (Bedra Megacut pro(r) TWO/250) with a diameter \(\mathrm{\SI{e}}_{TE}\) = 0.25 mm) the courses of the deviations (Figure 5) were determined for individual material thicknesses of \(H_{w}\) = 10.0, 50.0, and 100.0 mm.  
Based on the identified values of the maximum geometric deviations of circularity \(y_{Cmax}\) in the individual lines of the profiles of the machined surfaces after WEDM using a Ms wire electrode of \(\mathrm{\SI{e}}_{TE}\) = 0.25 mm, several significant facts were determined. First of all, it was found that the smallest deviations in circularity \(y_{Cmax}\) were recorded in the upper and lower profiles of the eroded area. The lowest value of \(y_{Cmax}\) = 29.5 \(\mathrm{\SI{e}}\)m was recorded in the lower  
edge of the eroded profile with a thickness \(H_{w}\) = 100.0 mm and a diameter \(\alpha_{Ci}\) = 120.0 mm. These circularity deviations increased significantly in the direction of the middle of the profile, reaching a maximum value at approximately the middle of the profile. The highest value of \(y_{Cmax}\) = 175.2 \(\mu\)m was achieved in the middle of the erosion profile with a thickness \(H_{w}\) = 10.0 mm and diameter \(\alpha_{Ci}\) = 5.0 mm. In some cases, the increase was up to two-fold.  
At the same time, experimental measurements of the roughness parameters of the eroded surface were performed on the experimental samples made using tool steel after WEDM. The roughness of the machined surface was measured in several lines of the eroded area, from the upper edge of the sample towards the lower edge, as shown in Figure 6.  
Even though several sources in the literature report that parameter \(Rz\) shows more reliable results for surfaces machined via electroerosion, from a practical point of view, roughness parameter \(Ra\) was considered when evaluating the results of the experimental measurements. The graphical dependences in Figure 7 document the course of deviations of circularity (\(y_{Cmax}\)) vs. roughness of the machined surface (\(Ra\)) of experimental samples after WEDM at individual parameters of \(\alpha_{Ci}\) and \(H_{w}\).  
Figure 4: Measurement of geometric deviations of the circular profile, \(\alpha_{Ci}\) = 40.0 mm, on the measuring device Mitutoyo Roundtest RA-120 (Mitutoyo, Kawasaki, Japan).  
Figure 5: \(Cont.\)  
\(H_{w}\) = 100.0 mm, and a diameter of \(\upomega_{Ci}\) = 5.0 mm, the maximum deviation of circularity, \(y_{Cmax}\) = 140.5 \(\upmu\)m, was recorded. This represented a significant decrease. At the same time, the course of the surface roughness parameter (\(Ra\)) was identified based on the performed experimental measurements. It was found that with an increasing diameter (\(\upomega_{Ci}\)) the roughness of the machined surface also increased. It was also found that higher values of surface roughness (\(Ra\)) were recorded at smaller thicknesses (\(H_{w}\)) of the machined material. The highest value of the surface roughness, \(Ra\) = 2.2 \(\upmu\)m, was recorded at \(H_{w}\) = 10.0 mm and \(\upomega_{Ci}\) = 120.0 mm. On the contrary, the lowest value of the machined surface roughness, \(Ra\) = 1.1 \(\upmu\)m, was recorded at \(H_{w}\) = 100.0 mm and \(\upomega_{Ci}\) = 5.0 mm.