*3.2. SPF Process Investigation and Outcomes*

The FE simulation of the SPF process allowed to calculate the thickness distributions useful to check the presence of any critical region and to define the gas pressure profile to be used in the manufacturing process. In addition, it was possible to assess the key role played by the die geometry, which resulted to have a significant effect not only on the profile but also on the total forming time, as shown in Figure 15.

**Figure 15.** Gas pressure profiles obtained from the simulations of the SPF process when using the two investigated types of tools.

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ The maps showing the distribution of the COPEN output variable are reported for both the investigated types of tools: in fact, such an output variable describes the capability of the blank to fill the die cavity (the blue regions refer to a complete contact between the die and the blank, whereas the white ones indicate that the points are still not adjacent). A consideration that could be drawn from the presented plot is that with both the tools the part corresponding to the final prosthesis geometry was successfully copied; furthermore, by looking at the two pressure profiles, the concave geometry led to a satisfactory filling of the die cavity in a sensibly lower period of time than the other solution. Numerical results were also analysed in terms of final thickness distributions. The curves plotted in Figure 16 suggest that, within the blank portion of the final prosthesis geometry (highlighted by the grey box on each plot), both the investigated tools led to an almost uniform final distribution of thickness along the considered paths, about equal to 0.85 mm.

**Figure 16.** Thickness distributions along: (**a**) the longitudinal and (**b**) transversal symmetry paths.

‐ Due to the large forming time reduction that it allows, the concave die was thus used for the manufacturing of all prostheses. In Figure 17 the customized ceramic insert positioned in the steel frame is shown.

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**Figure 17.** Die adopted during the prostheses manufacturing via SPF.

In Figure 18a the geometry of the prosthesis obtained by means of the SPF process is shown, whereas Figure 18b shows the custom prosthesis to be implanted extracted from the formed sheet by wire EDM.

**Figure 18.** (**a**) Prostheses manufactured via SPF; (**b**) final geometry obtained after EDM cutting.

‐ ‐ ‐ Finally, Figure 19 shows the thickness distribution mapped on the prosthesis obtained via SPF and the corresponding frequency of the thickness values on the whole surface. It is worthy of notice that the prosthesis was characterized by a homogeneous thickness distribution, ranging between 0.91 mm and 0.95 mm. ‐ ‐ ‐

**Figure 19.** (**a**) Thickness map of the prosthesis produced by SPF; (**b**) frequency of thickness values.
