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Laser directed energy deposition (DED-LB) technology is currently facing challenges in controlling geometry accuracy of metal components. There is an urgent need to develop a numerical model that is more efficient and accurate compared to existing models and to analyze the dynamic behavior of the melt pool under the interaction of process parameters during DED-LB process to optimize parameters with fewer experimental studies to reduce costs. Therefore, a three-dimensional powder-scale multi-physics model is proposed during the single-track DED-LB process in this study. The powder particles are added by a Lagrangian particle model in this model without the need for assuming that the powder particles entering the molten pool are added by the mass source term, which improves model accuracy and efficiency. The effects of energy per unit mass (EUM, J g−1), mass per unit length (MUL, g mm−1), and standoff distance (SD, mm) intensities on transient molten pool motion and flow field are comprehensively investigated. It is discovered that the proposed model is able to predict the single-track height, width, depth, and dilution rate, or less than 9% relative error from experimentation, providing a useful tool for track geometry to predict. Furthermore, the flow velocity, width, and depth of melt pool also gradually are improved with higher EUM, MUL, and SD intensity and fluctuate within a small range. However, the height is improved and then decreases with higher SD intensity, and is improved with higher EUM or MUL. Overall, this study contributes to developing an optimizing process approach to improve formation accuracy for DED-LB manufacturing. [ABSTRACT FROM AUTHOR]

At present, in the directed energy deposition (DED) of metals, the heat transfer of the melt pool and microstructural evolution are not fully understood. This study investigates the thermal effect on the microstructure and the mechanical properties of DED AISI 316L, using in situ optical monitoring. Five thin-wall samples were tested to determine the effect on microstructural evolution and mechanical properties with variable laser powers and scanning speeds. A comprehensive optical monitoring system with a CMOS (coaxial complementary metal oxide semiconductor) visual module and an infrared camera was adopted in analyzing the temperature gradient and the solidification rate. The emissivity of the melt pool was calibrated, using the melt pool length, extracted from the coaxial visual image. The results showed that microstructures mainly consist of the coarse columnar grain and the equiaxed grain at the top layer of AISI 316L samples. The direction of epitaxial growth of columnar grains is affected by the compromise between directional heat flux and crystallographic direction. High numerical temperature gradient and high solidification rate are beneficial to obtaining fine grain size and high yield stress. A modified microstructure map for DED AISI316L was established, which correlates the solidification parameters with a solidification microstructure. This research study, combining temperature distribution, solidification parameter, microstructure, and tensile property, provides an experimental identification of solidification parameters and the model on the solidification theory for precision control of DED process. [ABSTRACT FROM AUTHOR]

As an advanced metal additive manufacturing technology, laser-directed energy deposition (DED-LB) has attracted a lot of attention in recent years, and is increasingly used in aerospace, automotive, marine, and biomedical applications. However, as industry application standards continue to improve, the challenges of part quality, process stability, and molding efficiency faced by DED-LB are becoming more and more prominent. On-line monitoring and real-time quality regulation can effectively avoid quality defects in processing, which is an effective measure to solve the problem. This paper summarizes the current research status of on-line monitoring means and closed-loop quality regulation technology for DED-LB. The on-line monitoring signals and related sensing devices mainly based on image signals, temperature signals, spectral signals, acoustic emission signals, and X-ray imaging, as well as the closed-loop control strategies and intelligent optimization methods in the process are discussed. Finally, a view on the future direction of on-line monitoring-control system for DED-LB is presented. [ABSTRACT FROM AUTHOR]

In the direct laser deposition (DLD) process, it is common to employ constant processing parameters. The utilization of the constant parameters may lead to fluctuations in the dynamic evolution of the molten pool, primarily due to the intricate thermal effects involved, which will significantly impact the processing quality. To address this issue, this study proposed a closed-loop control approach that effectively modifies processing parameters in real time by targeting on the molten pool transient area. The type of the laser used in this study is a flat-top beam. Laser power, powder feeder rate, and scanning speed are the input variables of the study to control molten pool, considering the manufacturing system. The most suitable processing parameter to control the molten pool area was found to be the laser power by a set of orthogonal experiments, with a correlation coefficient of 0.706, and significance level of 0.002. Then, the dynamic response relationship between laser power and the molten pool area was mathematically characterized by a third-order transfer function model to simplify the complex physical model of the DLD process. Subsequently, a PID controller with a filtering coefficient and anti-windup compensation was chosen compared with the other controller. In the validation experiments, it was observed that the closed-loop processing group demonstrated improved stability in maintaining the molten pool transient area, with a notable decrease of 33.7% in variability compared to the open-loop processing group. As a result, the deposited layer of the closed-loop processing group exhibited a much more satisfying surface quality and heat affect zone than the open-loop group. This study established a third-order mathematical model of the dynamic molten pool and realized the optimization of deposition quality by controlling the molten pool transient area with an enhanced PID controller, providing a fundamental basis for improving the consistency of the direct laser deposition processing quality through the implementation of real-time feedback control of molten pool physics. [ABSTRACT FROM AUTHOR]

This paper mainly deals with the current status and development trends of research on the microstructure and properties of additive manufacturing formed parts. According to the laser processes and powder processing, the microstructure of the parts including morphologies, phase composition, and grain orientation is analyzed; the forming quality of the parts including hardness, wear resistance, corrosion resistance, strength, fracture toughness, residual stresses, and fatigue properties is analyzed in many ways. At the same time, we expect to find the research directions that conform to the future development trends for LAM. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the current research status and development trend of on-line monitoring technology for laser additive manufacturing. We have analyzed various on-line monitoring techniques for laser additive manufacturing based on visual imaging, temperature field, spectral analysis, and acoustic principles. Numerous analyses are performed on the monitored objects, the melt pool, including melt pool temperature and morphology dimensions, and the formed parts, including microstructure and properties. The analysis of on-line monitoring techniques for laser additive manufacturing is expected to find the research directions that meet future development trends. [ABSTRACT FROM AUTHOR]