Key Takeaways & Executive Findings
- •• • In-situ active modulation directly intervenes during defect nucleation, offering superior effectiveness over post-printing repairs and avoiding performance degradation risks; this is critical for industrial adoption where defect control is paramount. • • Process and path parameter optimization is the simplest and preferred control method, with widespread attention on its effects on microstructure and mechanical properties; it serves as the baseline for quality improvement in MAM. • • Laser beam shaping addresses edge over-melting and localized energy deficiency caused by non-uniform energy distribution, which are common issues in high-power laser processes; this is essential for achieving uniform material properties. • • Additional physical field modulation is considered when optimal process parameters fail to achieve desired microstructure and mechanical properties; the review summarizes effects on various metallic base materials, providing a decision framework for engineers.
Abstract
Metal additive manufacturing (MAM) enables integrated one-piece fabrication of parts, high material utilization efficiency, and unparalleled design freedom. However, problems such as low production efficiency, difficulties in ensuring quality stability and defect control limit the large-scale industrial application of AM. In-situ active modulation for AM enables dynamic regulation of parts during the fabrication process, thereby enhancing the quality of the final fabricated parts without introducing extra processing steps. In-situ active regulation enables direct intervention during defect nucleation, providing better effectiveness than post-printing repairs while avoiding performance degradation risks associated with post-processing. Based on the difference of core factors directly affected during regulation, in-situ active regulation is categorized into the following. (1) Process and path parameter optimization, where regulation directly impacts manufacturing-related procedural rules. It is the simplest method of control and the preferred approach, with widespread attention focused on its effects on microstructure and mechanical properties. (2) Laser beam shaping, where regulation directly influences the energy carrier morphology. To address issues such as edge over-melting and localized energy deficiency caused by non-uniform energy distribution, laser beam shaping should be employed. (3) Additional physical field modulation achieved by superimposing supplementary physical fields. When optimal process and path parameters still fail to obtain the desired microstructure and mechanical properties, additional physical field control may be considered. Meanwhile, this work summarized the effects of different additional physical fields on the mechanical properties of various metallic base materials. The future trends of in-situ modulation in additive manufacturing are also discussed.
1. Introduction
Metal additive manufacturing (MAM) has revolutionized industrial production by enabling the fabrication of complex geometries with high material utilization, yet its large-scale adoption is hindered by persistent challenges: low production efficiency, inconsistent quality, and defect formation. Traditional post-processing methods are reactive, often introducing performance degradation risks and additional costs. The bottleneck lies in the inability to control defect nucleation and microstructure evolution in real-time during the build process, leading to variability in mechanical properties that fails to meet stringent aerospace, automotive, and biomedical standards.
In-situ active modulation emerges as a paradigm shift, allowing dynamic regulation of the manufacturing process itself. By categorizing modulation strategies into process/path parameter optimization, laser beam shaping, and additional physical field assistance, this review provides a systematic framework to address the root causes of defects. This approach not only enhances final part quality but also eliminates the need for separate post-processing steps, thereby improving efficiency and cost-effectiveness. The synthesis of current research and future trends positions in-situ modulation as a cornerstone for the next generation of intelligent additive manufacturing systems.
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Ziyun Long, Yinghao Zhang, Ce Jiang, Puxiang Wang, Jinzhao Zhao, Yangyang Huang, Zhanwei Liu, Wei Feng, Huimin Xie (2026). Review on in-situ active modulation technology in metal additive manufacturing processes. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3963-5
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Frequently Asked Questions
What are the primary defect mechanisms that in-situ active modulation targets, and how does it intervene during defect nucleation?
In-situ active modulation targets defects such as porosity, lack of fusion, and cracking by directly adjusting process parameters, beam shaping, or applying external physical fields during the build. For instance, beam oscillation in laser-arc hybrid welding has been shown to stabilize keyholes and reduce porosity in aluminum alloys, as evidenced by studies like Liu et al. (2026) which resolved the conflict between forming precision and keyhole-induced porosity.
How does laser beam shaping quantitatively improve energy distribution and what are the measurable outcomes on part quality?
Laser beam shaping modifies the spatial energy profile to eliminate edge over-melting and localized energy deficiency. This results in more uniform melt pools and reduced thermal gradients. For example, in dual-laser powder bed fusion, overlap scanning strategies have been optimized to improve micro-characteristics and mechanical properties of AlSi10Mg, as reported by Shi et al. (2025).
What are the comparative benefits of additional physical field modulation (e.g., ultrasonic, magnetic) versus process parameter optimization in achieving desired microstructures?
Additional physical fields, such as ultrasonic impact treatment (UIT), can refine grain structure and improve fatigue properties. For instance, UIT on LPBF-manufactured Inconel 718 enhanced fatigue performance (Mazruee Sebdani et al., 2024). Process parameter optimization is simpler but may not fully control microstructure; physical fields provide an extra degree of freedom when parameter tuning alone is insufficient.
What are the scalability challenges of implementing in-situ active modulation in industrial-scale MAM systems, particularly for large parts?
Scalability challenges include integrating sensors and control systems into large-format printers, ensuring uniform modulation across the build area, and managing increased complexity. Multi-laser systems, such as quad-laser large-scale powder bed fusion, require careful coordination of beam overlap and scanning strategies to maintain quality, as demonstrated by Liu et al. (2023) for SS316L.
How does in-situ active modulation affect the cost-effectiveness of MAM compared to traditional post-processing routes?
By reducing the need for post-processing steps and minimizing defects, in-situ modulation can lower overall production costs and lead times. For example, achieving strength-plasticity breakthroughs in Mg alloys via laser-cold metal transfer hybrid processes (Zhu et al., 2026) indicates that in-situ control can produce high-performance parts directly, eliminating expensive heat treatments or mechanical post-processing.
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