Analysis of the Part Distortions for Inconel 718 SLM: A Case Study on the NIST Test Artifact

The present paper evaluates the misalignment and geometry distortion of the standard National Institute of Standards and Technology (NIST) test artifact in Inconel 718 alloy, when several layers with and without supports are employed to manufacture it by the Selective Laser Melting (SLM) process. To this end, a coordinate-measuring machine (CMM) is used to measure the geometrical distortion in each manufacturing configuration, following the same measurement protocol. The results show that the laser path strategy favors a thermal gradient which, consequently, induces geometrical distortions in the part. To prove this hypothesis, a numerical simulation is performed to determine the thermal gradient and the pattern of the residual stresses. It was found that the geometrical distortion certainly depends on the position of the feature position and laser strategy, where thermal cycles and residual thermal stresses had an impact in the end-part geometry, especially if a high strength-to-weight ratio commonly used in aeronautics is present.

CEPHALOMETRIC FLOATING NORMS FOR THE MMBP-WITS AND b ANGLE AMONG THE CHENNAI POPULATION

AIM: The purpose of this study was to attain floating norms for the MMBP-Wits and 𝛽 angle in adult Chennai population that can aid in proper diagnosis and treatment planning of different cases. Methods: Lateral cephalograms were acquired from 100 subjects (50 males and 50 females; mean age: 18-25 years) with pleasant profile and well-balanced and a near-ideal occlusion. Land mark identification and tracings were carried out manually on 0.003’ thickness acetate film. The ANB angle, the 𝛽-angle, the MMBP-Wits were measured. Four Other angular cephalometric parameters which included the SN/PP, SN/MP, SNA, and NSB angles were also measured. Multiple regression models were used to quantify the correlation of the ANB angle, MMBP-Wits and 𝛽 angle with each other and also with four other angular cephalometric parameters mentioned above. RESULTS: All the three cephalometric parameters of antero-posterior maxillary-mandibular relationship had considerable association with the explanatory variables with 𝑅2 range from 0.183 to 0.212 for the ANB angle and the MMBP-Wits, respectively. The ANB angle was considerably related with all the explanatory variables. In particular, the NSBa, SNA, and SN/MP angles were certainly associated with the ANB angle, whereas the SN/PP angle was inversely associated. On the contrary, both the 𝛽 angle and MMBP-Wits were considerably associated with SNA and SN/MP angles. These explanatory variables showed positive and inverse association with the MMBP-Wits and the 𝛽 angle. CONCLUSION: (i) The ANB angle is prone to have considerably more geometrical distortion as compared to the MMBP-Wits and the 𝛽 angle. (ii) Floating norms have been given to individualize the reference values for both the MMBP-Wits and 𝛽 angle.