# Optimization of Pin Type Single Screw Mixer for Fabrication of Functionally Graded Materials
## 3 Results and Discussion
### Comparison of Transition Delay Distances  
It is evident that utilizing image processing methods offers a cost-effective approach for detecting gradient variations in extrusion filament. Firstly, the printed output displayed in Figure 15 was processed through the MATLAB platform and transformed into a grayscale representation to obtain the grayscale value for each individual pixel. Secondly, pixel coordinates were determined based on the locations of sampling points in the grayscale map presented in Figure 16, and the normalized values were characterized as the composition ratio at each of these sampling points. A total of 113 sampling points were acquired, employing a uniform sampling strategy aligned with the length of the extruded filaments, which resulted in a cumulative printing duration of 373 s. Finally, a comparative analysis was conducted between the experimental results and the CFD results, as illustrated in the coordinate system of Figure 16. Additionally, the commencement and conclusion points of the transition delay time for three mixers, as determined using the CFD results, are denoted in Figure 16.  
Figure 16: Digital image processing of three print filaments.  
From the findings presented in Figure 16, it is evident that all three mixers have the capability to change the gradient of material components in an extruded filament spanning 1120 mm, ranging from a ratio of 9:1 to 1:9. The complete transformation of material components is readily observable through digital image processing methods. Moreover, when comparing the experimental results with those derived from CFD simulations, it is apparent that the simulation results exhibit acceptable deviations, thereby establishing the validity and reasonable accuracy of the FEM model in the context of the mixing process.  
In Figure 16a, the analysis results depict the extruded filaments produced by the screw mixer devoid of any pins. The grey values of the sampled points in the transition delay interval are evenly distributed on either side of the CFD results, signifying a considerable delay in the transition process. In Figure 16b, a comparison with the CFD results reveals that the presence of pins in actual printing only marginally enhances the effects of chaotic mixing convection, resulting in a tendency to delay the transformation of material components during practical use. In Figure 16c, the grey scale values of the sampled points from the experiment surpass the CFD results, indicating that in practice, the screw with the optimized pin shape significantly promotes chaotic mixing, leading to shorter transition distances for material gradient changes. This smooth transition of material components in functional gradient materials can substantially reduce interlayer stresses induced by abrupt shifts in material properties, thus enhancing the overall structural integrity and durability of the component. The reduced transition distance allows for more complex and accurate material gradient adjustments between layers in confined dimensions, thereby enhancing printing flexibility and enabling the design of FGM parts that transcend dimensional limitations. This not only maximizes the unique advantages of individual component materials but also offers a wider range of performance combinations.