# Adjustment of Wire Vibrations in Order to Improve Geometric Accuracy and Surface Roughness at WEDM
## 2 Geometric Accuracy and Surface Roughness in Electrical Discharge Machining  
The machined surface quality achieved through electrical discharge machining, in terms of roughness parameters (according to ISO 4287) is according to [PERSON] [12], [PERSON] [13], and [PERSON] [14], and is comparable to the surface quality of fine grinding (Figure 1). Grinded surfaces are often characterized by a high gloss of the machined surface.  
However, in many cases, these have higher values of the arithmetic mean deviation of the roughness profile (\(Ra\)), the maximum height of the roughness profile (\(Rz\)), or the root mean square deviation of profile \(Rq\) than matte eroded surfaces.  
The resulting value of the maximum height of roughness profile Rz of the finished surface after WEDM is in the range from 1.5 to 20.0 micrometers. The arithmetic mean deviation of profile Ra is greater than 3 to 5 times.  
According to [PERSON] [15], after WEDM, geometric deviations of the machined surface usually represent shape deviations. Of these, deviations in circularity and cylindricality are particularly important for maintaining the quality of a machined surface after WEDM with a circular shape profile [16]. In the case of circularity deviations, the circular profile can be considered correct if the difference in the radii of two concentric circles, between which is located any point of the actual profile, equals or is less than the tolerance value (\(T\)) (Figure 2a). In the case of cylindrical deviations, the cylindrical profile is suitable only if the difference between the diameters of two concentric cylinders, between which is located any point of the actual profile, equals or is less than the tolerance value (\(T\)) (Figure 2b). In both cases, the center of the concentric circles/cylinders and their radii must be chosen so that their difference is as small as possible.  
If the correct position of the concentric circles is according to Figure 2a, designated as \(A_{2}\), with a center at \(C_{2}\), then the maximum permissible distance (\(\Delta r_{2}\)) of the considered circular profile is represented by two concentric circles. Their maximum radial distance is equal to the maximum permissible value, and is usually given as tolerance (\(T\)). The actual achieved value of the dimension of the machined surface, in any part of the circular profile, must therefore be located between these two concentric circles. The same applies for cylindrical deviations. The maximum radial distance between two concentric cylinders, in general, equals the maximum permissible value given as tolerance (\(T\)) (Figure 2b).  
[PERSON] [17] and [PERSON] [18] argued that the occurrence of geometric deviations from circularity and cylindricality of an actual machined surface from a nominal surface after WEDM depends on several factors. First, these geometric deviations depend on the limit values of the accuracy of the hardware and software guidance of the wire electrode and the workpiece. This was also confirmed by [PERSON] [19]. Other factors entering the process, which result in undesired geometric form deviations, are the properties of the wire electrode and those of the workpiece material. [PERSON] [20], [PERSON] [21], and [PERSON] [22] also declared these facts. According to [PERSON] [23], [PERSON] [24], and [PERSON] [25] the key factors are also technological and process parameters. [PERSON] [26] and [PERSON] [27] also claimed that the final value of the geometric form deviations from circular profiles, made using WEDM, is the result of the complex influence of these factors during the electroerosion process.  
Figure 1: Relief of the material surface after wire electrical discharge machining with a coated electrode (magnification 1000\(\times\)).