# Optimization of Pin Type Single Screw Mixer for Fabrication of Functionally Graded Materials
## 3 Results and Discussion
### Functionally Graded Materials Part Print Specim  
We printed a 35 \(\times\) 35 \(\times\) 3.2 mm\({}^{3}\) cube with a gradient variation to verify the printing performance of the optimized pin screw mixer, as illustrated in Figure 17. Each layer was set to a height of 0.8 mm, and a consistent gradient change was maintained in each layer. The printing path followed an offset printing sequence, progressing from the outermost to the innermost regions, and was accompanied by a 100% fill rate. Figure 17a illustrates the gradient variation of the pre-designed printed sample, where the region denoted as 6:4 measures 2 mm in width, the 9:1 region spans 3 mm in width, and the central region accounts for a component ratio of 1.5:8.5. To account for the delay in material component transformation once the printing system receives the G-Code, the mixing chamber was initially purged with a mixture of pastes in a 6:4 ratio before commencing printing. Printing commenced with G-Code specifying a material ratio of 9:1 and continued until the next ratio change point, i.e., (30, 5). From that point onward, the ratio was adjusted to 1.5:8.5 until the completion of the layer. Figure 17b displays the specimen that was printed following the predefined G-Codes and the associated process parameters from the aforementioned experiment. The print results indicate that the specimen exhibits satisfactory surface quality.  
Figure 17: Illustration of: **(a)** pre-designed gradient change, and **(b)** print specimen.  
Similarly, digital image processing was employed to analyze the gradient variations of the printed sample in a targeted manner. Sampling components along the designated arrow paths in the greyscale diagram presented in Figure 18 and subsequently comparing them with the expected gradient changes revealed that the transitional region between the ratios of 6:4 and 9:1 spanned approximately 2 mm. In addition, the width of this transition region measured approximately 5 mm after the material feed transition point, set at a ratio of 1.5:8.5. In summary, the optimized pin screw mixer demonstrates a significant capability to achieve the distribution of components as pre-designed.  
Direct ink writing, a sophisticated additive manufacturing method, offers remarkable flexibility and adaptability. This method excels in accurately depositing materials at predetermined locations to create complex geometries and complex structures. However, a significant challenge encountered when preparing FGMs parts with the DIW process is the unavoidable formation of transition delay regions. While these regions may not be functionally critical, they can exert a significant effect on the overall performance of the manufactured parts. Further research should focus on the development of more efficient path planning strategies, along with accurate characterization of the transition delay distances between varying gradient variations. By strategically placing these transition delay regions in non-core functional areas of the part, it is possible to enhance overall part performance and quality without compromising critical functionality.  
In this study, we have successfully determined a pin shape for single-screw mixer by virtue of chaotic mixing, combined with several digital optimization techniques. Experimental validation shows that the optimized active screw mixer can effectively shorten the transition delay distance, as well as achieve sufficient distribution mixing capacity, when the material components are transformed. Finally, we successfully prepared printed samples with gradient changes with the optimized screw, which will help the application development in the field of functional gradient materials.