• • 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.