# Effect of Process Parameters on Distortions Based on the Quantitative Model in the SLM Process
## 3 Results
### Stiffness of Support Structures and Scanning Strategy  
Residual stress distributions of different components fabricated on support structures with column gaps ranging from 150 \(\upmu\)m to 750 \(\upmu\)m are shown in Figure 9. As the column gap increases, which decreases the stiffness of the support structures, the residual stress in each layer decreases. According to Equation (12), reducing the stiffness of the support structures is equivalent to reducing the value of \(E_{s}A_{s}\), which increases the absolute value of the displacement. Then, the residual stress will be reduced correspondingly (refer to Equation (13)). However, the distortion degree continuously increases from 13.4 m\({}^{-1}\) to 18.3 m\({}^{-1}\) as the stiffness of the support structures decreases (shown in Figure 10). This is because the residual stress gradient in the building direction increases as the stiffness decreases. The simulated distortions, shown in Figure 11, present the same trend. It can be concluded that increasing the stiffness of the support structures is beneficial to reducing the distortion of the component.  
Figure 11: The distortion of the component with different support structures stiffness.  
Figure 10: The distortion degree of the component with different support structures stiffness.  
Figure 9: Residual stress distributions along the vertical direction of components with different column gaps in support structures.  
Figure 12 shows the maximum and average distortion for different scanning strategies, and Figure 13 shows the distribution of distortions with different scanning strategies. Case (a) has the minimum distortion. This is because the scanning directions are consistent in Case (a). In addition, residual stress distributions in the \(x\)-direction and the \(y\)-direction are nearly the same among layers. This leads to a low residual stress gradient in the building direction. However, the distortion significantly increases when changing the scanning direction, such as Case (b). As shown in Figure 13b, the distortion is mainly distributed in the \(y\)-direction. Since the residual stress in the scan direction is relatively high [14], the residual stresses in the \(y\)-direction (along the scanning path) are much higher in the upper layers than in the lower layers, where the scanning direction is along the \(x\)-direction.  
Conversely, the residual stress in the \(x\)-direction is less in the upper layers than in the lower layers. Thus, the distortion distribution along the \(x\)-direction is high in the  
Figure 12: The maximum distortions and average distortions of components fabricated with different scanning strategies.  
Figure 13: The distribution of distortions with different scanning strategies. Case (**a**) is the unidirectional scanning; Case (**b**) has 90\({}^{\circ}\) rotation angles; Case (**c**) is the 45\({}^{\circ}\) inclined scanning with 90\({}^{\circ}\) rotation angles; Case (**d**) has 45\({}^{\circ}\) rotation angles; Case (**e**) is the out–in scanning; Case (**f**) is the in–out scanning.  
middle and down at the ends. Distortions in Case (c) and Case (d) are higher than in other cases. This is because the residual stress rises as the scan length increases. Therefore, the maximum distortion is located in the 45\({}^{\circ}\) direction. In addition, the distortion in Case (d) is less than that in Case (c) due to the relatively small change in the scanning direction. The distortion distributions of Case (e) and Case (f) are similar, which are low in the center and high at the edges.