# A Smart Handheld Welding Torch Device for Manual Spot Laser Welding
## 2 Materials and Methods  
A Turcvel LP300 series, Nd: Yag type laser welding machine was used together with the manual hand torch shown in Figure 1a for individual micro-laser welding of stainless test specimens. In this system, the graphite inserts were specially designed for the weld piece, and the operation is very economical as it does not require fixtures. With its ergonomic design, it facilitates welding in hard-to-reach areas. The standard laser welding torch shown in Figure 1d was developed with the angular positioning assistant device as shown in Figure 1c. The circuit diagram of the device created using an Arduino pro micro-board and MPU6050 angular position sensor is given in Figure 1d. The angular position of the welding torch is continuously measured with the help of the angle sensor placed on the top of the torch. It warns the operator at specified intervals with the use of an RGB LED.  
Stainless steel sheets (304 series) are widely used in the production of industrial kitchen equipment due to their beautiful appearance, corrosion resistance, and anti-fingerprint properties. Manual micro-point laser welding is frequently used for fixing the visible surfaces of industrial kitchen equipment. An industrial application example of visual micro-laser spot welding is shown in Figure 2a,b. This application provides sufficient welding area on the invisible surface of the 0.8 mm thick, thin sheet. This welding process is expected to be performed with a sensitivity that will not create a heat trace on the visible front surface of the sheet, due to a very short-term temperature increase.  
Weld test samples of 2 mm and 0.8 mm 304 series stainless steel sheets, the mechanical and chemical properties of which are given in Table 1, were fixed on top of each other from two points (Figure 3a) with the laser signal and parameters shown in Figure 3b. The size of each of the samples, which are joined at a single point to each other, is 80 mm long and 14 mm wide. The length of the welded pieces to be subjected to the tensile test after joining is 110 mm. Each weld sample was fixed with the same compressive force for gap-free contact of the weld surfaces of the two sheets. In order to measure the weld strength of the lap weld samples, the samples were subjected to tensile tests using a 0.4 N precision micro tensile device produced in Bursa Uludag University Laboratories (Figure 3c). Weld joints are torn under shear stress. During the tests, the head speed was set to 10 mm/min, and the tensile-shear force was slowly increased until the specimen broke from the welding points.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Grade**} & \multicolumn{8}{c}{**Chemical Composition (\%)**} & \multicolumn{8}{c}{**Shear Stress**} & **Yield Stress** & **Hardness** \\ \cline{2-10}  & **C** & **Si** & **Mn** & **P** & **S** & **Ni** & **Cr** & **N** & **(N/mm2)** & **(N/mm2)** & **(HV)** \\ \hline
304/304L/1.4301/1.4307 & 0.022 & 0.34 & 1.38 & 0.028 & 0.002 & 8.01 & 18.15 & 0.065 & 632 & 274 & 164 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Material properties of test sample stainless steel sheets. (Guangdong Yongjin Metal Technology Co., Ltd. Test Certificate, Certificate No: YJ2021122336, Date of Survey: 12 December 2021).  
Figure 1: (**a**) Standard hand laser welding torch. (**b**) Smart hand torch with angular positioning assistant device. (**c**) Circuit diagram of angular positioning assist device.  
Figure 2: Visual micro-laser spot welding application on thin inox material. (**a**) Visible surface (0.8 mm thick 304 stainless steel sheet on “Cold well with fan”). It is expected that there will be no heat trace or deformation due to welding on this inox surface of the device. (**b**) Invisible surface (2 mm thick 304 stainless steel sheet “well support, hook sheet”). Laser marks on this surface, located on the hidden interior of the device, are an acceptable error.