## 4 Conclusions  
In this article, a 3D FE model was developed to analyze the influence of the number of forming layers and the overhanging length on the warping and dress formation in the forming process of an overhang structure. Meanwhile, 30 groups of experiments with different parameters were carried out. Combined with the simulation results, the main conclusions are as follows:  
1. The different thermal conductivity between the powder and solid support zone leads to the difference in the molten pool size, which is the main reason for the appearance of dorsal formation. The simulation result showed that when the laser scanned the powder support zone, the temperature difference between the two regions reached  
Figure 13: Illustration of overhang structure warping deformation process.  
approximately 900 \({}^{\circ}\)C, causing the size of molten pool to increase significantly. The molten pool sank due to the actions of gravity and the capillary force, leading to the droplet\(-\)like dress formation on the lower surface beyond the designed shape area. With the increase in the number of forming layers, each formed layer plays a role in heat conduction; therefore, the difference becomes smaller and smaller;
2. The main reason for warping deformation is that when manufacturing commences, the overhang structure has no constraint; therefore, plastic deformation occurs when the residual stress exceeds the strength of the material. This leads to a low residual stress zone at the edge of overhang area. This deformation affects the subsequent powder spreading process, which makes the warping area exist in a state of remelting. As the number of forming layers increases, the stiffness of the overhang structure increases as well, and the warping deformation gradually decreases;
3. In the forming process, the warpage at the top of the parts that can be formed will continue to decrease. The results of the experiment showed that the top warpage reduced to zero for groups 1-6 (2 mm length) with a 1.2 mm (40 layers) height, groups 7-12 (2.5 mm length) with a 1.8 mm (60 layers) height, and groups 13-18 (3 mm length) with a 2.4 mm (80 layers) height. During the simulation process, as the number of forming layers increased, the deformation of the top area decreased from 28.5 mm to 9.18 mm, and the warpage of the parts increased from 2.44 um to 56.1 um. These values indicate that with the increase in the number of manufacturing layers, the overall warping of the parts also increased, while the top warping gradually decreased.  
This study is helpful for understanding the generation and change of defects and can provide some ideas for subsequent process parameter optimization. For example, from the simulation results, it seems that different scanning methods will have a greater impact. At the same time, improving the thermal conductivity of the powder support area is a key problem to be solved. Future work can continue from the above aspects to study the optimization of the overhanging structure.  
Conceptualization: C.S. and Y.Y.; investigation, C.S., P.L. and M.W.; methodology, M.W. and V.A.T.; validation, P.L.; writing\(-\)original draft, P.L.; writing\(-\)review and editing, M.W., C.S. and Y.Y. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Guangdong Basic and Applied Basic Research Foundation (2020B1515120013, 2022B1515120066), National Natural Science Foundation of China (No. U2001218), Key-Area Research and Development Program of Guangdong Province (2020B090923001). Special Support Foundation of Guangdong Province (No. 2019 TQ05Z110).  
Not applicable.  
The authors declare no conflict of interest.