To improve the quality and efficiency of surface coating with the GTAW (Gas Tungsten Arc Welding) method a semi-automatic welding machine was designed based on PLC (Programmable Logic Controller) control. The control program using ladder logic can accomplish system management and control functions. This system could control welding travel speed up to 560 mm/min, measure and saves the current status of the surface temperature at the welding zone via infrared thermometer up to 1600 °C in real-time, has complete automatic fault diagnosis, modify the welding travel speed and save the inputted welding parameters. To evaluate the performance of the designed welding machine, several experiments have been conducted. Optical microscope (OM) and scanning electron microscope (SEM) methods were used for microstructure examinations. In addition, mechanical tests were carried out with the microhardness method. An average of 377.5 HV0.2 microhardness was obtained from the surface of SAE (AISI) 1040 materials used in the experiments to a depth of 1 mm via the coating powders containing 64 wt% FeCrC + 16 wt% FeTi and 20 wt% Ni. The results from the experiments have shown that the designed PLC-based semi-automatic welding machine could be effective in determining the optimum conditions for surface coating and different welding processes.