Moreover, these low and high spots affect the nozzle-to-workpiece distance, with excessive distance leading to inadequate shielding of the pool and shorter distance causing the spatter phenomenon, where droplets adhere to the nozzle or collide with the upper layer's surface. The deposited substrate exhibits unevenness in the additive manufacturing method based on GMAW, creating significant differences in the substrate's geometry at the beginning and end of welding paths. Additionally, the intersection of deposition paths may result in partial protrusions, leading to a substantial change in the layer's height. Furthermore, the connecting surface is not smooth at the junction of welding paths. Overall, the persistence of unevenness throughout the process poses challenges in completing the production process or results in a finished piece with very low dimensional accuracy [17; 21; 22]. Figure 2 illustrates two uneven and smooth paths in the GMAW process. One of the challenges in GMAW welding is the inconsistency of weld geometry along the weld line and the significant variation in weld bead height. Consequently, [PERSON] et al. [23] have developed a new method to enhance components' surface quality and dimensional accuracy by combining plasma arc deposition and milling techniques. The precision of components produced in the combined CNC process, which eliminates the steps resulting from layer-wise additive manufacturing, is ensured, resulting in parts that closely resemble the original component. Using the optimized set of process parameters obtained, a group of metal components, such as hollow metal containers, has been manufactured. [PERSON] et al. [24] have also presented a combined layer-wise additive manufacturing process using milling techniques to enhance dimensional accuracy and surface quality. [PERSON] and [PERSON] [21] have developed an auxiliary visual sensor system to monitor the distance between the nozzle and the upper surface for adaptive control of deposition height in layer-wise additive manufacturing of GMAW-based materials. Deviations in the nozzle-to-upper-surface distance are compensated for by adjusting the working flat displacement and deposition rate in the next layer. After simplifying the controlled process into a linear system, they implemented an adaptive control system to maintain a constant nozzle-to-upper-surface distance. The effectiveness of the controller has been evaluated through the deposition of single-bead multi layer walls, and experimental results have confirmed that the developed controller can improve process stability when applied. [PERSON] et al. [25] have presented a single-layer neural network-based self-regulating controller for layer width adjustment. In this method, the input parameter is the nozzle velocity, and the output parameter is the layer width. The controller's performance is valid under deposition conditions, interlayer temperature variations, and layer width changes. The proposed controller significantly enhances process stability. Another study investigated control strategies for arc striking and extinguishing areas in constructing additive manufacturing materials based on multi layer single-pass GMAW. The arc striking and extinguishing areas  
Figure 2: Two uneven and smooth paths in the GMAW process. are placed within the same layer to compensate for height differences in deposited parts. A control strategy for alternate deposition in adjacent layers is employed for open-path parts. Parameter adjustment within the arc striking and extinguishing area uses the same deposition direction [26]. In another investigation, [PERSON] et al. [27] recommended using GMAW in additive manufacturing for constructing thin-walled parts. The nozzle is oriented perpendicular to the work surface during additive manufacturing. They examined the effects of nozzle-to-workpiece distance, wire transfer speed, and nozzle traverse speed on the produced sloped surface.