# Influence of Welding Parameters on the Weld Pool Dimensions and Shape in a TIG Configuration
## 4 Discussion
### Effect of the Cathode Tip Angle  
To study the effect of the cathode tip angle, Arcal.37 gas: Cases n\({}^{\circ}\) 1 and n\({}^{\circ}\)5, n\({}^{\circ}\)3 and n\({}^{\circ}\)6 and helium gas: Cases n\({}^{\circ}\)4 and n\({}^{\circ}\)7 are considered. Figure 6 displays the weld pool width evolution for L = 5 mm in Arcal.37 plasma (Figure 6a), L = 3 mm in Arcal.37 plasma (Figure 6b) and L = 3 mm in helium plasma (Figure 6c) for \(\theta\) = 30\({}^{\circ}\) and \(\theta\) = 60\({}^{\circ}\) cathode tip angle from 1 to 20 s.  
Figure 5: (**a**) Effect of the shielding gas on the evolution of the weld pool width; (**b**) Effect of the shielding gas on the evolution of the weld pool shapes; (**c**) Effect of the shielding gas on the depth-to-width ratio; (**d**) Effect of the shielding gas on the ratio between the energy used to fuse the metal and the energy applied to the system. Figure 6: **(a)** Effect of the tip angle on the evolution of the weld pool width Arcal.37, 100 A, 5 mm; **(b)** Effect of the tip angle on the evolution of the weld pool width Arcal.37, 100 A, 3 mm; **(c)** Effect of the tip angle on the evolution of the weld pool width Helium, 100 A, 3 mm. In the case of Arcal.37, the mean values of the weld pool width, estimated with the three methods, are little impacted with the changes of the cathode tip angle, as a difference of 0.23 mm (respectively 0.35 mm) is noticed for an arc length of five millimeters (respectively three millimeters) after 20 s of interaction when the cathode tip is reduced. These differences are in the range of the uncertainties so it is difficult to conclude that this parameter has a significant influence. For the helium plasma, values are more impacted as a difference of almost one millimeter is observed between the two cathode tip angle values. Using a smaller angle value of the cathode tip leads to a wider weld pool. The mathematical models [17; 22] proposed by [PERSON] et al. deal with this point. The authors indicate [17; 22] that by decreasing the electrode tip angle the anode spot at the weld pool surface tended to be flatter, leading to a smaller heat flux and anode current density, that the gas shear stress increased due to gas flow, and that the two effects led to a wider weld pool. The study was made for an interaction time of two seconds and for cathode tip angles in the range 9.18\({}^{\circ}\) to 131.41\({}^{\circ}\). The theoretical shapes presented by the authors for 28.36\({}^{\circ}\) and 60\({}^{\circ}\) in case of an arc length of five millimeters differed by only 0.2 mm when applying a current intensity of I = 200 A. Only this interaction time was presented in the paper [22]. The main differences in our cases are from 2 s up to 20 s. Our experimental width evolutions during the first second for the two angles are included in the error bars and weak differences appear. Nevertheless, from 2 s up to 20 s our conclusion is consistent with the behaviour found by [PERSON] et al. Other theoretical results exist on the influence of the value of the cathode tip angles, such as for instance the paper presented by [PERSON] et al. [23], however in those cases the torch position is not vertical (70\({}^{\circ}\)) and the model is stationary. Figure 7a presents the depth-to-width ratio for two cathode tip angles. The ratio decreases when the tip angle increases in helium and L = 5 mm in Arcal.37 plasma. In reality, if we observe Figure 7b the weld pool shapes after t = 20 s of interaction, the widths are weakly modified, the changes having been in the weld pool areas and in the depths. Due to the decrease of the cathode tip angle, the depth-to-width ratio increases as the depths increase. Theoretical study [20] has shown, adapting the intensity to assume the same power for a given distance between the electrodes, that the heat flux transferred to the material was greater using helium. Changing the distance from L = 3 mm to L = 5 mm in Arcal.37 does not allow compensation of the energy transferred in the helium case for the same value of the current intensity.