## 3 Results
### Visual Appearance and Surface Quality  
Visual inspections were performed on all welded studs to evaluate surface finish, stud alignment, and the presence of visible defects such as spatter, discoloration, or irregular weld collars. Representative photographs of the welded stud collars for each process are presented in Figures 5-7.  
The ARC CF (ceramic ferrule) process generally produced weld collars with slight surface roughness and occasional residue where the ferrule was removed after solidification. Minor ferrule breakage sometimes left small chips or marks on the surrounding area, requiring light post-weld cleaning to achieve a uniform appearance. A few samples displayed hot welds, where excessive heat input caused over-spreading of the molten metal beyond the ferrule boundary, often accompanied by spatter deposition (Figure 5).  
Figure 4: Boxplot of measured weld penetration depths for ARC CF, ARC SG, and ARC SRM processes. Each value represents one welded sample per steel type.  
This phenomenon is typically associated with excessive welding current or extended arc duration; however, as the parameters were pre-validated by bend testing at a 60\({}^{\circ}\) angle, these anomalies were purely visual and did not compromise joint integrity. All ARC CF joints met the acceptance criteria defined in EN ISO 14555.  
Heat input and shielding gas composition must be carefully controlled to maintain stable arc behavior and uniform weld bead formation [28]. Shielding gas composition significantly affects arc stability and weld collar uniformity [29]. Numerical analyses confirm that residual stress patterns and thermal gradients are highly dependent on the welding heat input and process duration [30].  
The ARC SG (shielding gas) method resulted in cleaner weld collars with minimal surface contamination and very low spatter levels. The absence of ceramic ferrules eliminated ferrule residue, simplifying post-veld finishing. However, some samples exhibited _cold welds_ characterized by an irregular or thin weld collar due to insufficient fusion or arc blow effects, as shown in Figure 6. Although the weld bead appeared continuous, variations in thickness around the stud were evident and could affect local fusion quality if not properly controlled. Careful adjustment of heat input and precise positioning of the welding gun are essential to prevent this defect. Irregular collar formation in SG welding can be attributed to unstable arc behavior, which is sensitive to heat input [31].  
Figure 5: Representative photographs of welded stud collars for ARC CF (ceramic ferrule) (**left**); example of a “hot weld” in ARC CF welding, showing over-spread molten metal beyond the ferrule boundary (**right**).  
Figure 6: Example of a “cold weld” in ARC SG welding, displaying irregular collar thickness around the stud.  
The ARC SRM (radially symmetric magnetic field) process produced the most uniform and symmetrical weld collars among the three methods. The enhanced arc stability provided by the magnetic field minimized arc wandering, resulting in smooth, well-centered collars with virtually no spatter or discoloration (Figure 7). This clean appearance and consistent collar shape make the SRM process particularly attractive for automated production lines where minimal post-processing is preferred.  
Overall, all three welding processes produced visually acceptable welds with no surface flaws severe enough to compromise structural performance. However, differences in surface cleanliness, collar uniformity, and post-weld finishing requirements should be considered when selecting a suitable process, especially for applications where final appearance is critical.