# A Smart Handheld Welding Torch Device for Manual Spot Laser Welding
## 3 Results  
### Determination of the Effect of Torch-Surface Angle on Weld Quality in Manual Laser Spot Welding  
The first step of the study was to determine the welding angle required to weld stainless materials so delicately that they do not create visual defects and, at the same time, overcome the loads that will arise over time under working conditions. The primary motivation of this study was to develop an auxiliary system in which the welding operator can perform the welding process in this specified angular range within a specific tolerance range. In manual micro-spot laser welding, the gap between the mating surfaces of sheet materials and the torch grip angle (the angle between the laser beam and the weld surface) are critical variables to achieving sufficient weld strength without creating heat marks on the visible surface. While the absence of weld marks on the visible surface is the essential requirement of laser welding, joint strength is often the critical quality criterion. Therefore, the heat traces on the visible surfaces of the test specimens and the weld cross-section size were examined under a microscope (Celestron Pro, Celestron, LLC., Torrance, CA, USA). The surfaces named with the capital letters A, B, C, and D in Figure 4 represent the invisible outer surface of the 2 mm thick sheet, the joining surface of the 2 mm thick sheet (after breaking it), and the joining surface of the 0.8 mm thick sheet (after breaking it). The latter refers to the visible outer surface of the 0.8 mm sheet metal. Since the melting zone could not reach the outside of the 2 mm sheet at larger angles of 30\({}^{\circ}\), welding was impossible, and tests could not be performed for 30\({}^{\circ}\) angles. There is sufficient weld area for testing in the range of 10\({}^{\circ}\)-30\({}^{\circ}\), and no heat trace is formed on the visible sheet surface. Micro-blisters appear on the 7.5\({}^{\circ}\) visible surface. The images of these surface traces, which are evident due to the light reflection at certain angles, could not be taken because the illumination angle of the microscope was not at the angle to create these light reflections. By comparison, at less than 5\({}^{\circ}\), evident heat traces occur on the visible surface. Microstructure microscope (Nikon Eclipse MA100, Nikon Instruments Inc., Melville, NY, USA) photographs obtained by the metallurgical cutting and etching method at the welding point of the 2 mm thick top sheet are given on the right of Figure 4. As the angle between the torch and the welding  
Figure 3: (**a**) Dimensions of test specimens and welding of 2 mm and 0.8 mm 304 series stainless steel test specimens from two points. (**b**) Laser welding parameters and signal form. (**c**) Photograph of the custom-made benchtop tensile test device with a test specimen. surface changes, it is understood from the microscope images of the welding section that the angular position of the melting zone changes parallel to this. Figure 4: Weld traces and weld sections for different welding torch angles (70.43 Joules). (**a**) \(\theta=30^{\circ}\) (extremely tilted holding angle). (**b**) \(\theta=15^{\circ}\) (appropriate holding angle). (**c**) \(\theta=5^{\circ}\) (extremely steep holding angle). In Figure 5, the effect of the torch holding angle approaching the 0\({}^{\circ}\) perpendicular holding angle in increments from 30\({}^{\circ}\) to 2.5\({}^{\circ}\) on the weld cross-section, and thus on the weld cross-sectional area, is shown with the microscope photographs of the joining surface of the 0.8 mm sheet metal. The tests were cut at 5\({}^{\circ}\) at a 0\({}^{\circ}\) vertical angle so that the laser beam does not reflect and damage the optical system. The microscope photographs show that the welding cross-section increases smoothly as the torch grip angle approaches the surface perpendicular to the surface. Figure 6 shows the variation in the force (\(F\)) carried by a single spot weld with elongation for different torch angles.