Laser directed energy deposition (LDED) is one of the most important parts of metal additive manufacturing, which can provide fast building speed, allows for large building volumes, and is suitable for part repair. LDED can manufacture components layer by layer through processes of rapid heating, melting, solidification, and cooling with the laser beam as a heat source. However, deposition quality and repeatability of components produced by LDED are poor because of the complex thermal cycle and processing environment, hindering the spread of this technique. Adaptive control technology (ACT) is consistently considered an effective and potential way to solve the problem. Many studies have focused on LDED and established the relations of process parameters, process signatures, and product qualities, which promote the rapid development of ACT, with the development of monitoring devices and data processing technology. We review and discuss the problems existing in the ACT of LDED.

Laser-based additive manufacturing (LBAM) is a group of advanced manufacturing processes used to produce metal components and functionally graded products. Production in LBAM is either limited to the formation of thin or thick coatings on a substrate by laser metal deposition or the production of a fully functional metallic product by selective laser melting. In every case, LBAM fabricated components require optimization for the process parameters to avoid defects, such as porosity, crack holes, thermal deformation, and mechanical strength. As a key link in the laser additive manufacturing (LAM) process, laser scanning path planning is an effective strategy for balancing the temperature field of the formed part, avoiding stress concentration, and preventing deformation and cracking. Efficient, accurate, and reasonable planning of the laser scanning path is of great significance for improving the processing efficiency of the process data, prolonging the life of the laser scanning system, and improving the forming quality of the specimen. Through many studies, it was found that the scanning pattern of the lasers has a significant impact on the mechanical properties and deformations caused by a thermal mismatch during the process. Therefore, it is essential to have indepth knowledge about path planning in LBAM. Our review mainly focuses on the influence of scanning patterns on deformation, temperature, and mechanical properties in LBAM. Finally, our paper discusses the current study limitations and some future studies in LAM technology.

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The quality of parts manufactured using laser metal deposition (LMD), similar to other additive manufacturing methods, is influenced by processing parameters. Such parameters determine geometric stability, favorable microstructures, and good mechanical properties. This study aimed to investigate the effects of pulsed laser parameters (duty cycle and pulse frequency) and scanning patterns (unidirectional and bidirectional patterns) on the properties of parts fabricated using LMD. Results show that the properties of the LMD-fabricated parts are obviously influenced by pulsed laser parameters and scanning patterns. Using the unidirectional scanning pattern in both pulsed laser parameters enhances the properties of the thin-walled parts prepared using LMD. An increase in duty cycle can improve geometric stability, increase grain size, and reduce microhardness. Furthermore, the geometric stability does not vary considerably with the use of different frequencies, but the microstructure of fabricated parts shows various grain sizes with different pulse frequencies. In addition, the microhardness increases as the frequency increases from 13.33 to 50 Hz. In general, the influence of the duty cycle on geometric properties is greater than that of frequency. Meanwhile, the impact of frequency on microhardness is greater than that of the duty cycle.