# Fabrication and Analysis of a Ti6 Al4V Implant for Cranial Restoration
## 2 Methodology
### Fabrication  
The fabrication of the customized cranial implant and dog bone shaped specimens were carried out in this phase. The dog bone shaped specimens were needed to assess the tensile strength of the tailor-made cranial implant. The custom made cranial implant as a result of its aberrant and unsteady structure could not be analyzed with any standard mechanical testing. Moreover, there was no conclusive standard which could be employed to perform the tensile test on the customized cranial implant. Henceforth, to investigate the tensile strength of Ti6 Al4V ELI material used in cranial implant, dog bone shaped specimens as per ASTM E-8 standards were designed. Certainly, several previous works can be pointed out which have also performed similar studies on titanium specimens to estimate their mechanical properties [33; 36; 37]. There are also shreds of evidence in the literature, where dog bone shaped specimens were analyzed instead of real shapes in order to comprehend the tensile properties of a particular material. For example, [PERSON] et al. [38] recommended a dog bone shaped specimen as the ideal geometry for estimating accurate tensile results of different rock materials. The dog bone shaped specimen used in this study possessed an overall length of 100 mm, a gauge length of 25 mm and a width of 6 mm as depicted in Figure S3. The dog-bone structure was manufactured as per ASTM E-8/E-8M/16a standard [39; 40]. The particle size analysis as shown in Figure 9a revealed that the titanium powder (Ti6 Al4V ELI) with the particle size between 50-100 \(\upmu\)m was utilized for the fabrication of the customized cranial implant and the dog bone specimen in this study. Figure 9b represents the analysis of Ti6 Al4V ELI powder using JOEL's JSM-6610 LV (JOEL, United States) Scanning Electron Microscope (SEM). The formation of the powder particles was primarily spherical in shape with slight variation in geometry. The chemical composition of Ti6 Al4V Extra-low interstitial (ELI) as revealed in Figure 9c was 6.04% Aluminum (Al), 4.05% Vanadium (V), 0.013% Carbon (C), 0.0107% Iron (Fe), and 0.13% Oxygen (O), with the remaining constituent as Titanium (Ti) in weight percent. Figure 9: Ti6 Al4V ELI: **(a)** particle size distribution; **(b)** SEM image; **(c)** material composition. The ARCAM's EBM machine as shown in Figure 10 was employed for the fabrication. The fabrication in the EBM process consisted of three primary stages: (1) preheating of the metal powder, (2) scanning as well as melting of the powder and (3) lowering of the building platform along with the raking of the powder bed. At the outset, the entire Ti powder layer in the powder bed was warmed up (or preheated) through scanning at a high scan speed until the certain intended temperature (730 \({}^{\circ}\)C) was reached. The preheating was carried out at eightty percent of the melting temperature in order to fuse the powder particles. The preheating also aided in reducing the stresses and sintering the unbound powder particles for the retention of the consecutive powder layers. The standard ARCAM parameters, preheat-I and preheat-II were utilized during fabrication. In preheat-I, the complete powder bed was scanned and in preheat-II, the scanning was executed only in the melting region. Subsequently, a high-velocity beam of electrons scanned the metal powder line by line according to the defined CAD geometry through various lenses. The scanning and melting operation consisted of two processes, contouring and infill hatching. First, the contours were melted by using electron beams, depending on the boundary representation (or the cross-section) of the 2D slices. However, the beam current and the scan speed were raised in hatching in contrast to contouring. In order to melt and fill the area between the contours, the powder layers were screened using a snaking melt strategy in the back and forth direction. The metal powder in the contours and the hatching part was melted, leaving the rest of the powder for recycling.