## 4 Results Analysis and Discussion
### Double-Channel Overlapping Deposition
#### 4.3.1 Calculation and Comparison of Double-Channel Overlapping Deposition Shapes
In order to describe and analyze the influence of the overlapping channel temperature on the temperature of the first deposition channel more precisely, the temperature variation along the symmetry line (along the x-axis) on the surface of the first deposition channel is depicted in Figure 16 with the moment of the start of the second overlapping channel as the zero moment. The place shown by the dashed line in the picture is the beginning point of the laser scan, which is located at 0.005 m along the x-coordinate of the scanning direction in the model's 3D coordinate system. Depending on the x-coordinate location, the figure's curve may be subdivided into many feature sections according to the x-coordinate position: (1) The region located to the left of the dashed line. This portion of the specimen is not scanned by the laser, so the temperature profile begins slightly above room temperature at the specimen's edge and rises slowly and then rapidly as it approaches the scan's beginning point, indicating that the temperature gradient on the specimen near the spot is significantly greater than that further away. (2) The far right portion of the graph, corresponding to x-coordinate 0.010 m. The majority of the curves are arranged in time order from top to bottom, with the exception of the final two. This suggests that the end of the first channel remains in a cooling condition for the majority of the time after the spot leaves the first channel and enters the overlapping channel, and that rewarming does not begin until 0.31 s after the spot enters the overlapping channel. (3) On the dashed line. This place represents the beginning of the two scans. Once the spot reaches the second channel (0.01 s), the first channel has been cooled for a considerable amount of time, and the temperature is relatively low. Following this, the temperature of the first channel begins to increase from 0.01 s to 0.16 s as a result of the second channel's energy input. As a consequence of the second scan spot's movement away from this place, the temperature at this location from 0.21 s onwards begins to be lower than the temperature at 0.16 s and continues to fall. (4) The right side of the dotted line. For analysis, the location with x-coordinate 0.008 m is utilized as an example. At the 0.01 s mark of the overlapping channel scan, the laser beam just reaches the overlapping deposition channel, at which moment the first scan influences the location and the temperature rises to 1597.73 K. The laser point location on the overlapping channel was distant from this position at 0.06 s, 0.11 s, and 0.16 s since the overlap had just begun, this position was still in the cooling condition, and the temperature  
Figure 15: Temperature distribution at different moments from the beginning of overlapping. (**a**) 0.05 s; (**b**) 0.15 s; (**c**) 0.30 s; (**d**) 0.40 s.  
had been falling to 1351.62 K with the passage of time. As the laser point approaches this area, the temperature increases to 1436.13 K at 0.21 s and begins to warm up. At 0.31 s, the temperature reached a high of 1535.88 K. At this moment, the temperature recovery was 184.26 K. Other places in this area also had comparable findings. According to Figure 16, the rewarming phenomenon caused by the energy input of the overlapping channel on the temperature of the first channel has been present since the position of x-coordinate 0.005 m (the starting position of the first channel), causing the temperature of the first deposition channel as a whole to increase, decrease, increase, and decrease again. The affected temperature of the first pass deposition re-rises in the range of 1000-1600 K and the amplitude is 100-300 K. During one-way parallel overlapping deposition, the rewarming of the first deposition channel modifies its residence duration, cooling rate, and temperature gradient in this temperature interval.