新興的積層製造除能夠減少原料浪費及製造時間，更能提高製造產品的自由度，其中選擇性雷射熔融(Selective Laser Melting, SLM)為目前最主流的技術，其產品密度可達99%以上。SLM工件的緻密性取決於是否獲得足夠的熱能與周圍的粉體形成緊密的接合，透過調整加工參數來提升工件品質，雖已有能模擬最佳參數區域的系統，但仍不是完全準確，因此工件完成後之品質檢測亦相當重要，而非破壞性檢測為最普遍及方便的方式。本研究致力於使用高頻超音波系統對材料Inconel 718之SLM工件進行品質檢測，利用20 MHz及40 MHz探頭，分別量測超音波聲速及積體逆散射(Integrated Backscatter, IB)與Nakagami-m，進而評估工件內部的異質性，同時量測工件的孔隙率及表面粗糙度確認模擬出最佳區域的準確性。結果顯示，最佳區域中製造的工件品質確實優異，多數的孔隙率皆低於1%，表面粗糙度低於4 μm，並且從孔隙率的結果可推得最佳加工參數落在雷射功率252 W與掃描速率850 mm/s且能量密度為165 J/mm3時。而在超音波檢測結果中，聲速在最佳加工參數前會與能量密度呈現正相關，並且與孔隙率呈現高度正相關(R2 = 0.79)，因此可以表徵工件的異質性。而Nakagami-m可以呈現金屬內部散射子的分布情形，在孔隙率較高時Nakagami-m值較大，表明了較多孔隙散射子分布其中，而其與孔隙率的高相關性(R2 = 0.72)也能推論出Nakagami-m能有效地評估內部品質。當工件密度較接近時，IB與孔隙率的相關性較低(R2 = 0.15)，因此當工件內部差異較小時用來分析超音波逆散射強度的IB可能較不適合評估。

The emerging additive manufacturing (AM) can not only reduce the waste of raw materials and manufacturing time, but also increase the geometric freedom of manufacturing products. Selective laser melting (SLM) is currently the most mainstream AM technology, and density of components fabricated by SLM can reach more than 99%. The compactness of the SLM components depends on whether it obtains sufficient heat energy to tightly bond with the surrounding powder and improve components quality by adjusting processing parameters. Although there are systems that can simulate the optimal parameter region, they are still not completely accurate. Therefore, quality inspection after manufacturing is also very important, and non-destructive testing is the most common and convenient way to assess the components. This study is devoted to evaluating the quality of Inconel 718 SLM components using a high-frequency ultrasonic system with 20 MHz and 40 MHz transducers. Speed of sound, Integrated Backscatter (IB) and Nakagami-m are measured to evaluate the internal heterogeneity of components. At the same time, the porosity and surface roughness of the components are used to confirm the accuracy of the simulated optimal region. The results showed that the quality of the components manufactured from the optimal region is indeed excellent, most of the porosity is less than 1%, the surface roughness is less than 4 μm. From the results of porosity, it can be deduced that the best processing parameters are when the laser power is 252 W, the scanning speed is 850 mm/s, and the energy density is 165 J/mm3. In the ultrasonic testing results, the speed of sound has a positive correlation with the energy density before the best processing parameters, and it has a high positive correlation with the porosity (R2 = 0.79), so it can characterize the heterogeneity of SLM components. Nakagami-m can present the distribution of scatterers inside the metal. Higher Nakagami-m can be obtained in high porosity SLM components with more pore scatterers. Nakagami-m and porosity have high correlation (R2 = 0.72) that can also be inferred that Nakagami-m can effectively evaluate the internal quality of components. When the density of the component is close, IB and porosity have low correlation (R2 = 0.15). Therefore, when the internal difference of the components is small makes the IB less suitable for evaluation.

[1] H. Kodama, "Automatic method for fabricating a three‐dimensional plastic model with photo‐hardening polymer," Review of scientific instruments, vol. 52, no. 11, pp. 1770-1773, 1981.
[2] H. Kodama, "A scheme for three-dimensional display by automatic fabrication of three-dimensional model," IEICE Trans. on Electronics, pp. 237-241, 1981.
[3] D. H. Freedman, "Layer by layer," Technology Review, vol. 115, no. 1, pp. 50-53, 2012.
[4] S. S. Crump, "Apparatus and method for creating three-dimensional objects," ed: Google Patents, 1992.
[5] W. Meiners, K. Wissenbach, and A. Gasser, "Shaped body especially prototype or replacement part production," DE Patent, vol. 19, 1998.
[6] B. Wu, C. Myant, and S. Weider, "The value of additive manufacturing: future opportunities," Imperial College London, Briefing Paper, no. 2, 2017.
[7] I. Astm, "ASTM52900-15 standard terminology for additive manufacturing—general principles—terminology," ASTM International, West Conshohocken, PA, vol. 3, no. 4, p. 5, 2015.
[8] L. Jiao, Z. Y. Chua, S. K. Moon, J. Song, G. Bi, and H. Zheng, "Femtosecond laser produced hydrophobic hierarchical structures on additive manufacturing parts," Nanomaterials, vol. 8, no. 8, p. 601, 2018.
[9] C. Y. Yap et al., "Review of selective laser melting: Materials and applications," Applied physics reviews, vol. 2, no. 4, p. 041101, 2015.
[10] G. X. Chen, X. Y. Zeng, Z. M. Wang, K. Guan, and C. W. Peng, "Fabrication of removable partial denture framework by selective laser melting," in Advanced materials research, 2011, vol. 317: Trans Tech Publications, pp. 174-178.
[11] V. Panchenko, A. Larichev, and G. Zheltov, "International Conference on Lasers, Applications, and Technologies 2007: Laser Technologies for Medicine," in International Conference on Lasers, Applications, and Technologies 2007: Laser Technologies for Medicine, 2007, vol. 6734.
[12] R. Bibb, D. Eggbeer, P. Evans, A. Bocca, and A. Sugar, "Rapid manufacture of custom‐fitting surgical guides," Rapid Prototyping Journal, 2009.
[13] T. Laoui et al., "Properties of titanium dental implant models made by laser processing," Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, vol. 220, no. 6, pp. 857-863, 2006.
[14] I. Yadroitsev, I. Shishkovsky, P. Bertrand, and I. Smurov, "Manufacturing of fine-structured 3D porous filter elements by selective laser melting," Applied Surface Science, vol. 255, no. 10, pp. 5523-5527, 2009.
[15] J. Sun, Y. Yang, and D. Wang, "Mechanical properties of a Ti6Al4V porous structure produced by selective laser melting," Materials & Design, vol. 49, pp. 545-552, 2013.
[16] K. Amato et al., "Microstructures and mechanical behavior of Inconel 718 fabricated by selective laser melting," Acta Materialia, vol. 60, no. 5, pp. 2229-2239, 2012.
[17] Z. Wang, K. Guan, M. Gao, X. Li, X. Chen, and X. Zeng, "The microstructure and mechanical properties of deposited-IN718 by selective laser melting," Journal of alloys and compounds, vol. 513, pp. 518-523, 2012.
[18] N. T. Aboulkhair, N. M. Everitt, I. Ashcroft, and C. Tuck, "Reducing porosity in AlSi10Mg parts processed by selective laser melting," Additive manufacturing, vol. 1, pp. 77-86, 2014.
[19] D. Buchbinder, H. Schleifenbaum, S. Heidrich, W. Meiners, and J. Bültmann, "High power selective laser melting (HP SLM) of aluminum parts," Physics Procedia, vol. 12, pp. 271-278, 2011.
[20] E. Louvis, P. Fox, and C. J. Sutcliffe, "Selective laser melting of aluminium components," Journal of Materials Processing Technology, vol. 211, no. 2, pp. 275-284, 2011.
[21] K. Kempen, L. Thijs, E. Yasa, M. Badrossamay, W. Verheecke, and J. Kruth, "Process optimization and microstructural analysis for selective laser melting of AlSi10Mg," in Solid Freeform Fabrication Symposium, 2011, vol. 22, no. 2011, pp. 484-495.
[22] E. Olakanmi, "Selective laser sintering/melting (SLS/SLM) of pure Al, Al–Mg, and Al–Si powders: Effect of processing conditions and powder properties," Journal of Materials Processing Technology, vol. 213, no. 8, pp. 1387-1405, 2013.
[23] H. Gu, H. Gong, D. Pal, K. Rafi, T. Starr, and B. Stucker, "Influences of energy density on porosity and microstructure of selective laser melted 17-4PH stainless steel," in 2013 Solid Freeform Fabrication Symposium, 2013, vol. 474.
[24] L. Thijs, F. Verhaeghe, T. Craeghs, J. Van Humbeeck, and J.-P. Kruth, "A study of the microstructural evolution during selective laser melting of Ti–6Al–4V," Acta materialia, vol. 58, no. 9, pp. 3303-3312, 2010.
[25] R. Li, J. Liu, Y. Shi, L. Wang, and W. Jiang, "Balling behavior of stainless steel and nickel powder during selective laser melting process," The International Journal of Advanced Manufacturing Technology, vol. 59, no. 9, pp. 1025-1035, 2012.
[26] I. Koutiri, E. Pessard, P. Peyre, O. Amlou, and T. De Terris, "Influence of SLM process parameters on the surface finish, porosity rate and fatigue behavior of as-built Inconel 625 parts," Journal of Materials Processing Technology, vol. 255, pp. 536-546, 2018.
[27] T. Peng and C. Chen, "Influence of energy density on energy demand and porosity of 316L stainless steel fabricated by selective laser melting," International Journal of Precision Engineering and Manufacturing-Green Technology, vol. 5, no. 1, pp. 55-62, 2018.
[28] U. S. Bertoli, A. J. Wolfer, M. J. Matthews, J.-P. R. Delplanque, and J. M. Schoenung, "On the limitations of volumetric energy density as a design parameter for selective laser melting," Materials & Design, vol. 113, pp. 331-340, 2017.
[29] J. Yi et al., "Effect of laser energy density on the microstructure, mechanical properties, and deformation of Inconel 718 samples fabricated by selective laser melting," Journal of Alloys and Compounds, vol. 786, pp. 481-488, 2019.
[30] S. Liu, H. Li, C. Qin, R. Zong, and X. Fang, "The effect of energy density on texture and mechanical anisotropy in selective laser melted Inconel 718," Materials & Design, vol. 191, p. 108642, 2020.
[31] H.-C. Tran and Y.-L. Lo, "Systematic approach for determining optimal processing parameters to produce parts with high density in selective laser melting process," The International Journal of Advanced Manufacturing Technology, vol. 105, no. 10, pp. 4443-4460, 2019.
[32] H. Kim, Y. Lin, and T.-L. B. Tseng, "A review on quality control in additive manufacturing," Rapid Prototyping Journal, 2018.
[33] C. J. Hellier, Handbook of nondestructive evaluation. McGraw-Hill Education, 2013.
[34] D. Chauveau, "Review of NDT and process monitoring techniques usable to produce high-quality parts by welding or additive manufacturing," Welding in the World, vol. 62, no. 5, pp. 1097-1118, 2018.
[35] F. Honarvar and A. Varvani-Farahani, "A review of ultrasonic testing applications in additive manufacturing: Defect evaluation, material characterization, and process control," Ultrasonics, p. 106227, 2020.
[36] K. K. Shung, Diagnostic ultrasound: Imaging and blood flow measurements. CRC press, 2005.
[37] E. Gadelmawla, M. M. Koura, T. M. Maksoud, I. M. Elewa, and H. Soliman, "Roughness parameters," Journal of materials processing Technology, vol. 123, no. 1, pp. 133-145, 2002.
[38] Geometrical Product Specifications (GPS)—surface texture: profile method—terms, definitions and surface texture parameters, ISO 4287, 1997.
[39] A. Charles, A. Elkaseer, L. Thijs, V. Hagenmeyer, and S. Scholz, "Effect of process parameters on the generated surface roughness of down-facing surfaces in selective laser melting," Applied Sciences, vol. 9, no. 6, p. 1256, 2019.
[40] A. Sola and A. Nouri, "Microstructural porosity in additive manufacturing: The formation and detection of pores in metal parts fabricated by powder bed fusion," Journal of Advanced Manufacturing and Processing, vol. 1, no. 3, p. e10021, 2019.
[41] K. Walton and M. Skliar, "Ultrasonic Characterization of Spatially Varying Material Properties in Metal Components Fabricated by Additive Manufacturing," in 2019 IEEE International Ultrasonics Symposium, 2019: IEEE, pp. 1260-1263.
[42] J. A. Slotwinski, E. J. Garboczi, and K. M. Hebenstreit, "Porosity measurements and analysis for metal additive manufacturing process control," Journal of research of the National Institute of Standards and Technology, vol. 119, p. 494, 2014.
[43] A. B. Spierings, M. Schneider, and R. Eggenberger, "Comparison of density measurement techniques for additive manufactured metallic parts," Rapid Prototyping Journal, 2011.
[44] M. O'Donnell, D. Bauwens, J. Mimbs, and J. Miller, "Broadband integrated backscatter: An approach to spatially localized tissue characterization in vivo," in 1979 Ultrasonics Symposium, 1979: IEEE, pp. 175-178.
[45] P.-H. Tsui and S.-H. Wang, "The effect of transducer characteristics on the estimation of Nakagami paramater as a function of scatterer concentration," Ultrasound in medicine & biology, vol. 30, no. 10, pp. 1345-1353, 2004.
[46] Y.-H. Lin, C.-C. Huang, and S.-H. Wang, "Quantitative assessment on the orientation and distribution of carbon fibers in a conductive polymer composite using high-frequency ultrasound," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 59, no. 5, pp. 970-980, 2012.
[47] Y.-H. Lin, K.-L. Tung, S.-H. Wang, Q. Zhou, and K. K. Shung, "Distribution and deposition of organic fouling on the microfiltration membrane evaluated by high-frequency ultrasound," Journal of membrane science, vol. 433, pp. 100-111, 2013.
[48] P.-H. Tsui, H.-Y. Ma, Z. Zhou, M.-C. Ho, and Y.-H. Lee, "Window-modulated compounding Nakagami imaging for ultrasound tissue characterization," Ultrasonics, vol. 54, no. 6, pp. 1448-1459, 2014.
[49] C. Qiu, C. Panwisawas, M. Ward, H. C. Basoalto, J. W. Brooks, and M. M. Attallah, "On the role of melt flow into the surface structure and porosity development during selective laser melting," Acta Materialia, vol. 96, pp. 72-79, 2015.
[50] G. Hamada and V. Joseph, "Developed correlations between sound wave velocity and porosity, permeability and mechanical properties of sandstone core samples," Petroleum Research, vol. 5, no. 4, pp. 326-338, 2020.
[51] H. Gong, K. Rafi, H. Gu, T. Starr, and B. Stucker, "Analysis of defect generation in Ti–6Al–4V parts made using powder bed fusion additive manufacturing processes," Additive Manufacturing, vol. 1, pp. 87-98, 2014.