In conventional laser powder bed fusion (PBF-LB/M) processes, three-dimensional (3D) printed parts are typically secured to a baseplate using support structures to prevent their movement and thermal deformation. However, removing these supports can often be challenging or even impossible, which results in decreased printing efficiency and limited design freedom. In this study, a novel approach was developed for printing metal parts without the use of conventional support by employing focused infrared (IR) heating in conjunction with conventional PBF-LB/M process. The effectiveness of the proposed approach was validated by successfully printing 3D structures (an unprecedented 18-mm-long 0-degree overhang beam) using Ti-6Al-4 V powder without using support structures. An IR-heated powder with loose consolidation functions as both a reinforcing structure and a heat sink, providing not only structural support to the part but also withstanding the internal thermal stresses and external impacts attributed to the moving blade. Further, the loosely fused powder can be easily removed from the printed part and reused, thereby saving material. Thus, this proposed approach promises to be a significant step towards the additive manufacturing of intricate metal parts without requiring conventional support structures.

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Despite the intense research attention on the three-dimensional printing of metal structures via selective laser melting, a unified understanding of thermal conditions, and more specifically the input energy levels, necessary for minimizing macroscopic-defect generation is still lacking. Although simple and widely used parameters, such as linear or volumetric energy density, can be utilized to represent the characteristic energy level of the process, notable differences in printed morphologies and microstructures are observed in structures fabricated at the same energy density. Consequently, designing a process in terms of laser power and scan speed is largely based on trial-and-error approaches. In this work, based on the dimensional analysis of reported experimental data and nu-merical computation, the process windows suitable for the fabrication of single tracks were examined for various metals. In addition to the normalized enthalpy that quantifies the input energy level, another dimensionless parameter which measures the thermal penetration depth relative to the thickness of powder layer was found to be critical in defining the process window that resulted in acceptable single-track structure formation. To confirm the validity of the analysis, via the elimination of uncertainties and ambiguities inherent to the empirical data, numerical computations were conducted for single-track fabrications using Ti-6Al-4 V and 316L stainless steel alloys. The results of the numerical simulations showed good agreement with the findings obtained from the empirical data.

최근 다양한 분야에서 NP-hard에 속하는 그래프 문제를 효율적으로 해결하는 것이 점차 중요해지고 있다. 그래프 분석에서 가장 핵심적인 문제 중 하나는 부분 그래프 동형(subgraph isomorphism)문제이다. 부분 그래프 동형 문제란 데이터 그래프와 쿼리 그래프가 주어졌을 때, 데이터 그래프에서 쿼리그래프의 모든 임베딩(embedding)을 찾는 문제이다. 이 문제를 해결하는 최신 알고리즘인 DAF에서는 후보 수 순서(candidate-size order)와 경로 수 순서(path-size order)라는 두 가지 동적 매칭 순서를 제시하였다. 하지만 구체적으로 어떤 경우에 두 가지 동적 매칭 순서의 성능 차이가 일어나는지는 언급되지 않았다. 본 논문에서는 다양한 그래프에서 두 가지 동적 매칭 순서의 성능을 비교하여 쿼리 그래프의 트리 형태 경로(tree-like path)의 평균 길이가 길어지거나 데이터 그래프의 레이블(label) 개수가 줄어들수록 경로 수 순서의 효율성이 높아지는 것을 밝혔다.