Laser Directed Energy Deposition Process Research Articles

Achieving high strength 316L stainless steel by laser directed energy deposition-ultrasonic rolling hybrid process

Laser directed energy deposition (LDED) has attracted as a progressive additive manufacturing technique in fabricating the stainless steel components. The rapid melting and solidification velocity under LDED process induces the appearance of pores and the columnar dendritic, which degrades the strength of alloys. Here, a self-developed LDED-UR (ultrasonic rolling) synchronous manufacturing equipment is developed to fabricate the 316L stainless steel, and the characterization of microstructure and mechanical properties are studied. Results show that the size and fraction of pores are significantly reduced by LDED-UR processing, and fine equiaxed grains are obtained under the combined effects of ultrasonic vibration and roller pressure. With the severe plastic deformation, the average grain size of LDED-UR sample is decreased from 76.10 μm to 26.23 μm (LDED sample), and high angle grain boundaries transforms to low angle grain boundaries. Meanwhile, the dislocation density in LDED-UR sample is increased compared to the LDED sample. Owing to the grain refinement and dislocation strengthening, the average microhardness, yield strength, ultimate tensile strength and elongation of the LDED-UR sample reach 268.18 ± 13.90 HV0.2, 442 MPa, 771.2 MPa, and 49.8 %, respectively, which are larger than those of LDED sample (214.13 ± 13.76 HV0.2, 396 MPa, 682 MPa, and 45.5 %). This implies that the superior mechanical properties are obtained by employing in-situ ultrasonic rolling under LDED process. The insight of the influence of microstructure on mechanical properties extends a new approach for enhancing the mechanical properties of LDED alloys.

Microstructure, microhardness, tensile and fatigue investigation on laser shock peened Ti6Al4V manufactured by high layer thickness directed energy deposition additive manufacturing

Thin layer thickness in additive manufacturing (AM) has always been a hindering factor leading to long completion times. Increasing layer thickness is accompanied by a higher tendency of surface cracks and inferior mechanical properties. These can be improved with laser shock peening (LSP). Emphasizing on the high layer thickness, this paper elucidates the high-layer thickness laser directed energy deposition (LDED) AM and the effects of LSP on the fabricated parts. Primary focus was given to the investigation of surface microcracks, microstructures, tensile and fatigue properties. Ti6Al4V bulk sample was prepared using the LDED process. Tensile, fatigue, and other samples were extracted to investigate the above-mentioned properties using different characterization tools such as optical microscope, scanning electron microscope, Vickers microhardness tester, and universal testing machine. Results showed proper depositions without major defects despite the high-layer thickness. Micro-cracks were limited to the surface only, and typical Widmanstätten patterns with parallel α lath and mixed α+β microstructures are observed. Yield strength (YS) varied from 730 MPa to 940 MPa, while ultimate tensile strength (UTS) ranged from 799.5 MPa to 953.75 MPa. Even though laser peening significantly improved micro-hardness by 49.81 % on average, not all fatigue samples observed enhanced fatigue life. A maximum improvement of 40.34 % in fatigue performance was observed in the LDED+LSPed samples. The strain hardening, plastic deformation, and grain refinement during the LSP process contributed to the enhanced mechanical properties. Some samples’ reduced fatigue life may be due to the anisotropic nature of additively manufactured parts, internal defects, and surface cracks on the specific samples. Considering high layer thickness, vertical orientation of samples, and as-prepared samples, our research shows a promising high layer thickness additive manufacturing process. The current research can be used as a base for further study on other properties and characteristics.

On the control of epitaxial growth and stray grains during laser-directed energy deposited Ni-based single crystal superalloy

Laser-directed energy deposition (L-DED) is considered as an effective repair method for damaged single-crystal (SX) superalloy turbine blades. However, controlling stray grains (SGs) and epitaxial growth is still the major problem. This study investigated the influences of pre-solution treatment and intrinsic heat treatment (IHT) on the formation of SGs and epitaxial growth of L-DED René N5 SX superalloy. The γ/γ’ eutectics and coarse γ’ precipitates at the inter-dendrite region can be eliminated after pre-solution treatment procedures before the L-DED experiment. A lower temperature in pre-solution treatment resulted in the retention of residual γ/γ’ eutectics and coarse γ’ precipitates. Thus, the aggravated element segregation within the local melt pool and interface collapse during the L-DED process can result in stray grains (SGs) formation. Improved pre-solution treatment procedures can help reduce SGs caused by the residual carbides at the bottom of the molten pool. Besides, the SG formation in the deposited layers can be attributed to the recrystallization as a result of high thermal stress during the IHT in thermal cycles. The optimized pre-solution treatment procedure reduced the elemental segregation of the substrates, resulting in a larger primary dendrite arm spacing (PDAS) from the bottom of the deposited layers. Due to IHT during thermal cycles in the deposited layers, the partial aging treatment promoted the re-precipitation and growth of γ’ phase. Meanwhile, the optimized pre-solution treatment procedure decreased the size of the heat-affected zone (HAZ) caused by thermal cycles. In summary, by optimizing the substrates' pre-solution treatment procedures to eliminate the γ/γ’ eutectics, the formation of SGs resulting from substrate segregation can be controlled. This work provides the potential guidance of substrate pre-treatment for L-DED repair of SX superalloys.

Hybrid Analytical-Numerical Modeling of Surface Geometry Evolution and Deposition Integrity in a Multi-Track Laser-Directed Energy Deposition Process

Abstract Modeling multitrack laser-directed energy deposition (LDED) is different from single-track deposition. There is a temporal variation in the deposition geometry and integrity in a multitrack deposition, which is not well understood. This article employs an analytical model for power attenuation and powder catchment in the melt pool in conjunction with a robust fully coupled metallurgical-thermomechanical finite element (FE) model iteratively to simulate the multitrack deposition. The novel hybrid analytical–numerical approach incorporates the effect of preexisting tracks on melt pool formation, powder catchment, geometry evolution, dilution, residual stress, and defect generation. CPM 9V steel powder was deposited on the H13 tool steel substrate for validating the model. The deposition height is found to be a function of the track sequence but reaches a steady-state height after a finite number of tracks. The height variation determines the waviness of the deposited surface and, therefore, the effective layer height. The inter-track spacing (I) plays a vital role in steady-state height evolution. A larger value of I facilitates faster convergence to the steady-state height but increases the surface waviness. The FE model incorporates the effects of differential thermal contraction, volume dilation, and transformation-induced plasticity. It predicts the deposition geometry and integrity as a function of inter-track spacing and powder feed rate. The insufficient remelting of the substrate or the preceding track can induce defects. A method to predict and mitigate these defects has also been presented in this article.

Laser-Directed Energy Deposition of Ti-Mo Biomaterials: Influencing Mechanisms of Molybdenum on Microstructure and Performance

Ti-Mo alloys with variable molybdenum (Mo) contents were fabricated by the laser-directed energy deposition process. The in-depth influencing mechanisms of the Mo element on microstructure and performance were quantitatively analyzed by experiment and first-principal calculation. Increasing Mo content decreased the formation and cohesive energies and stabilized the 𝛽 phase. The grain refining efficiency was increased, and the relative grain size was decreased by increasing the Mo content. The MS temperature decreased, and the acicular martensite formed with increasing Mo content. Both the solid-solution hardening and fine grain strengthening effects had positive influences, while the 𝛽 phase softening effect had a negative influence on the hardness and wear performance with increasing Mo content.

Effect of oblique angle on the formability, crystal growth behavior and microstructure in laser direct energy deposited thin-wall structure of single-crystal superalloy

Laser directed energy deposition process shows a tremendous potential to additively repair and manufacture single-crystal components in a near-net shape. For the specific non-vertical structure such as the tilted and torsional sidewalls of single-crystal components, achieving complete monocrystalline nature in the manufactured zone is still a great challenge and hazy. In this study, oblique thin-wall structures of single-crystal superalloy were fabricated by coaxial laser directed energy deposition process. The effect of oblique angle on the formability, crystal growth behavior and microstructure formation in thin-wall structures of single-crystal superalloy was discussed. The results showed that the critical oblique angle for good formability of thin-wall structure is 30°. A poor-quality and shapeless deposited bead forms once the oblique angle researches 40°. The thin-wall structure inherits the [001]/<100> crystalline orientation from parent single-crystal substrate through the continuous epitaxial growth of ultrafine columnar dendrites. The competition and alternate development of primary trunks-secondary arms-tertiary arms achieve the multiplication and reproduction of ideal columnar dendrites along the [001]/<100> crystalline orientation in the overhanging region of the thin-wall structure. Periodic segregation forms among the columnar dendrites. Epitaxial-growth continuity of the columnar dendrites with consistent crystalline orientation of substrate can be successfully achieved in large-scale tilted and torsional thin-wall structures of single-crystal superalloy with proper processing parameters. These findings are of great importance in the microstructure control for additively manufacturing complex single-crystal components by laser directed energy deposition process.

Energy and mass assessment of the laser Directed Energy Deposition process (DED-LB) for reduced environmental impact

ABSTRACT Additive Manufacturing (AM) processes have the capability to promote a more rational use of resources, reduce generated waste, as well as repair damaged components to extend their lifespan. With the aim of contributing to a more efficient and environmentally friendlier manufacturing process, this research work investigates the energy consumption of the Laser Directed Energy Deposition process (DED-LB) through the introduction of new parameters in its characterisation, which are energy and mass efficiency. First, the energy efficiency of the laser generator itself has been characterised. Based on the results obtained, it was possible to conclude that pulsed laser operation strategies allow a reduction in consumption of up to 9% compared to a continuous laser operation mode. Second, a design of experiments was carried out to relate the energy and mass efficiency of the deposition process to the input parameters: laser power, feed rate, and mass rate. The parameter that most influences the energy efficiency of the process is the mass rate, where high rates are advisable to maximise its value. On the other hand, it is concluded that an increase in the mass rate or a reduction in the feed rate results in an increase in the mass efficiency

In-situ synthesis of high-performance TiN/TC4 sandwich structures via nitrogen-controlled laser directed energy deposition

Laser Directed Energy Deposition (LDED) additive manufacturing offers a versatile approach for fabricating composite materials, encompassing a wide range of heterogeneous and transition materials, known for their exceptional mechanical properties. In this study, we focus on the synthesis of TiN/TC4 sandwich structural materials in atmospheres characterized by varying nitrogen-to-argon ratios. This study includes the in-situ synthesis, microstructural evolution, and mechanical characteristics of these TiN/TC4 sandwich structures during the LDED process. Through this process, TiN was formed in-situ by the interaction of Ti and N atoms, exhibiting in robust metallurgical bonding with the TC4 matrix. Notably, the microhardness of the TiN/TC4 sandwich structures exhibits periodic variations along the deposition direction, ranging between 314.4 HV0.2 and 661.5 HV0.2. The tensile strength of the TiN/TC4 sandwich structures experiences significant enhancement, while maintaining toughness due to the laminate structure and reinforced with ceramic particles inside. The resulting sandwich composites demonstrate outstanding ultimate tensile strength, which can achieve 1123.3 ± 29.7 MPa. This represents a notable improvement of 20.3% over the TC4 deposited in a pure Ar environment, with a corresponding plastic strain of 2.5 ± 1.7%. This study demonstrates that layered heterogeneous materials with superior mechanical strength can be synthesized in-situ through flexible integration of LDED process and reaction atmospheres.

Powder degradation as a consequence of laser interaction: A study of SS 316L powder reuse on the laser directed energy deposition process

The feedstock capture efficiency on powder laser directed energy deposition (L-DED) is becoming a big challenge in the industrial use of the L-DED process for the manufacturing of large-scale AM parts. The powder capture efficiency is dependent on process optimization and the toolpath. The current literature presents a vast range of usual powder efficiency, between 3% and 32% and in some specific cases exceeding 90%. In L-DED, the powder-gas jet stream interacts with the laser beam adding material locally onto the substrate. Part of this material is captured by the melt pool. The not captured material that is affected by the laser beam suffers degradation. In the literature, there is a lack of studies related to powder reuse in the L-DED process. This paper presents a comprehensive study on the consequence of laser interaction with SS 316L metal powder particles during the L-DED process using a range of different powder characterization techniques to assess the powder morphology, size distribution, chemical composition, followability, and density. The study was conducted within eight powder reuse cycles, without adding virgin material to the powder batch. Reduction of particle size distribution range, increase in circularity, and improvement in the powder flowability were identified as consequences of powder reuse. The result of laser interaction with particles was further explored by scanning electron microscopy, presenting the continuous modification of the particles across the eight reuse cycles. The oxygen content on the particles was also measured to access the O2 pick-up as a consequence of particle heating.

Hybrid directed energy deposition process coupled with plastic deformation

Laser directed energy deposition (LDED) process has unique advantage in rapid forming of large-sized metal components, gradient material/structural components, or repairing/remanufacturing worn parts. However, the high residual stress and strong anisotropy in mechanical properties of the as-deposit components limit the application of LDED technology in the manufacturing of key structural components. To overcome these problems, various hybrid additive manufacturing (HAM) technologies have been developed, such as plastic deformation, ultrasonic or magnetic field assisted LDED processes to improve the quality and the mechanical properties, where these coupled processes are carried out either simultaneously or cyclically with the LDED process. The hybrid additive manufacturing, while retaining the advantages of individual forming process, avoids the mutual interference between each process and reducing the adverse effects generated if used separately. Hybrid additive manufacturing processes fundamentally change the underlying physical mechanisms of molten pool dynamics, microstructural evolution, temperature and thermal stress gradient in additive manufacturing, thereby optimizing the microstructure and performance of the manufactured components. In this paper, the key technical features of the hybrid additive manufacturing process coupled with plastic deformation were described in details, and the resulting differences in microstructure, residual stress, and mechanical properties of the prepared samples were systematically analyzed. The developing trend of hybrid additive manufacturing processes in coupling mechanisms, parameter optimization, and equipment have been discussed.

Prediction of crystal nucleation and growth behavior of Fe/Ni-based multi-materials deposited by laser directed energy deposition using a multi-area, multi-layer, and multi-scale phase field calculation (M3-PFC)

Laser directed energy deposition (LDED), based on the powder feeding technology, possesses the capability to fabricate complex structures within hollow structures. The arbitrary Lagrangian-Eulerian (ALE) method was innovatively applied to derive temporal interpolation functions for the free surface contour F (x, y, t) and the temperature distribution T (x, y, t) of the melt pool from a mesoscopic computational fluid dynamics (CFD) thermal model. These interpolation functions were not simply integrated but specifically designed to impart a quantified impetus for the growth of crystalline solidification within the microstructural phase field, effecting real-time adjustments to the computational domain of the phase field model. The multi-area, multi-layer and multi-scale phase field calculation (M3-PFC), which takes into account the bi-directional coupling of Marangoni flow and the phase field, was established to incorporate the transportation of elements within the multi-layer deposition and previously solidified material. Thermodynamics of multi-layer deposition was integrated into M3-PFC, enabling the prediction of multi-layer dendritic evolution using LDED process. Influence of Marangoni flow on microstructure evolution of multi-layer C276 deposited on 316 L-substrate utilizing M3-PFC was investigated during LDED process. It was observed that the nucleation of equiaxed and columnar crystals occurred at the top and bottom-middle of the melt pool. Both columnar and equiaxed crystals were preferentially produced along the opposite direction of Marangoni flow, impeding the apparent dendrite-growth in the counter direction. Partial remelting of the (N + 1)th layer was induced by the thermodynamics generated in the (N + 2)th deposition layer, promoting re-solidification of the liquid phase in the (N + 1)th layer. However, no liquid-solid transformation occurred in the Nth layer subjected to periodic heating. The partially remelted tissue in the (N + 1)th layer was shown in wider columnar crystals generated through the competitive growth, which were transformed into planar crystals and identified as the initial solidification conditions for the nucleation of the (N + 2)th layer. The columnar crystal growth, nucleated at the planar crystals of the (N + 1)th layer, was dominated in the (N + 2)th layer. Micropillar compression tests revealed that the columnar crystal had a compressive strength of 1102.78 MPa, while the equiaxed crystals displayed a higher compressive strength of 1464.34 MPa.

Investigation on the evolution of deposition layer grain structure and its effect on mechanical properties in aluminum alloy fabricated by laser directed energy deposition

In recent years, aluminum alloy additive manufacturing has played a significant role in promoting lightweight applications in aerospace and automotive industries due to its efficiency and cost advantages. In order to study the evolution of grain structure in the deposition layer, single-variable single-pass deposition experiments was conducted to optimize the process parameters of laser directed energy deposition (LDED). Subsequently, multi-layer multi-pass depositions were performed to fabricate the components. The deposition layer was divided into three distinct regions: Top coarse grain zone (TCZ), Central equiaxed grain zone (CEZ), and Bottom columnar grain zone (BCZ). It was observed that subsequent depositions led to recrystallization, resulting in the refinement of the original equiaxed grain region and the coarsening of the grain structure in the deposition layer, leading to the formation of the latter two characteristic grain regions. Interestingly, within the TCZ and BCZ, we observed the presence of aluminum alloy twins that are difficult to form. This observation may be attributed to a significant reduction in the required twin shear stress within the coarse grains. The stress concentration at the grain boundaries of the coarse grains and the rapid strain rate during the LDED process could also be contributing factors to the formation of aluminum alloy twins. In terms of mechanical properties, the tensile strength of the samples parallel to the deposition direction is 268.25 MPa, while the tensile strength of the samples perpendicular to the deposition direction is 276.68 MPa. The fracture surfaces exhibit numerous equiaxed dimples, displaying characteristics of ductile fracture. There is almost no anisotropy observed in the mechanical properties, this is attributed to the alternating arrangement of different crystal regions within the deposition layer and the role of twins in suppressing dislocation motion.

Development of Fe–Cr–Si deposited layer manufactured by laser directed energy deposition process

In this study, the mechanical and corrosion characteristics of a corrosion-resistant layer made of stainless steel (STS) 316 L and Fe–Cr–Si alloy powder were investigated using laser-directed energy deposition (DED). In the STS 316 L deposited specimen, both the substrate and deposited layer were face-centred cubic (FCC). The deposited Fe–Cr–Si layer was clearly separated from the substrate because it was composed of body-centred cubic (BCC). Despite the phase differences, the surface of the Fe–Cr–Si-deposited layer showed a lower corrosion rate than that of the STS 316 L. All the deposited specimens exhibited typical high-temperature tensile behavior. However, the Fe–Cr–Si deposited layer at 600 °C showed a notable reduction in strength and increased elongation compared to the room temperature (RT) and 300 °C test results owing to the carbide concentration and phase transformation in the deposited layer. Because nuclear facilities mainly operate at temperatures below 600 °C, Fe–Cr–Si materials can also be used as nuclear piping coating materials. This study provides a mechanism for the high-temperature properties and corrosion resistance of the Fe–Cr–Si deposited layer and makes it competitive for application in fourth generation nuclear power systems.

Thermo-fluid dynamics and morphology evolution of nickel-based superalloy in a multilayer laser directed energy deposition process

The complex thermo-fluid dynamics of the molten pool determine the dimension accuracy and mechanical properties of laser directed energy deposition (L-DED) components. In this work, a three-dimensional (3D) multiphase computational fluid dynamics (CFD) model based on the Volume of Fluid (VOF) method was proposed to establish the relationship between the thermo-fluid dynamics and the molten pool morphology evolution of René N5 nickel-based superalloy in L-DED. The single-track and ten-layer deposition processes under unidirectional and bidirectional scanning strategies were studied. Results show that the predicted deposition morphology and dimensions are in good agreement with the experimental samples. The heat accumulation in the multilayer deposition process increases the size of the molten pool, thereby increasing the width of the deposit. Different from the single-layer deposition driven by the Marangoni force, gravity is the key factor in the multilayer deposition process without the side support. The hump structure at the starting position under unidirectional scanning is attributed to the backward flow of the melt of the molten pool, while the decline structure at the end position is enhanced by the forward flow of the melt. At the starting position of each layer under bidirectional scanning, the expansion of the molten pool resulted from the heat accumulation and mass addition increases the width of the two ends and compensates for the deposition height. This work can provide a theoretical basis for understanding the uneven morphology characteristics and the dimensional accuracy control in L-DED.

Multisensor fusion-based digital twin for localized quality prediction in robotic laser-directed energy deposition

Early detection of defects, such as keyhole pores and cracks is crucial in laser-directed energy deposition (L-DED) additive manufacturing (AM) to prevent build failures. However, the complex melt pool behaviour cannot be adequately captured by conventional single-modal process monitoring approaches. This study introduces a multisensor fusion-based digital twin (MFDT) for localized quality prediction in the robotic L-DED process. The data used in multisensor fusion includes features extracted from a coaxial melt pool vision camera, a microphone, and an off-axis short wavelength infrared thermal camera. The key novelty of this work is a spatiotemporal data fusion method that synchronizes multisensor features with the real-time robot motion data to achieve localized quality prediction. Optical microscope (OM) images of the printed part are used to locate defect-free and defective regions (i.e., cracks and keyhole pores), which serve as ground truth labels for training supervised machine learning (ML) models for quality prediction. The trained ML model is then used to generate a virtual quality map that registers quality prediction outcomes within the 3D volume of the printed part, thus eliminating the need of physical inspections by destructive methods. Experiments show that the virtual quality map closely matches the actual quality observed by OM. Compared to traditional single-sensor-based quality prediction, the MFDT has achieved a significantly higher quality prediction accuracy (96%), a higher ROC-AUC score (99%), and a lower false alarm rate (4.4%). As a result, the MFDT is a more reliable method for defect prediction. The proposed MFDT also lays the groundwork for our future development of a self-adaptive hybrid processing strategy that combines machining with AM for defect removal and quality improvement.

Melt pool dynamics on different substrate materials in high-speed laser directed energy deposition process

High-speed laser directed energy deposition (HSL-DED) is a variant of the laser directed energy deposition process where a defocused metal powder stream is used, and it typically involves processing speeds exceeding 5 m/min. However, the interactions between the laser beam, powder stream, and substrate surface in HSL-DED have not been extensively studied. This study used a specialized XIRIS XVC-1000 welding camera with a narrow bandpass filter to record the interaction phenomenon. These observations were first carried out without powder delivery, using laser surface melting techniques, and involved processing speeds of up to 20 m/min and laser powers of up to 3 kW. HSL-DED with powder delivery was then conducted with the same parameter combinations for comparative analysis. The in situ observations in laser surface melting and HSL-DED identified a physical separation between the laser spot and the melt pool boundary, referred to as melt pool lag. Different substrates’ chemical compositions and the resulting thermophysical properties significantly impact melt pool dynamics during the high-speed laser-material interactions for a given process condition. The findings from this work have enabled a better understanding and control of melt pool dynamics in HSL-DED.

Influence of post-processing heat-treatment on the mechanical performance of AISI 410L stainless steel manufactured by the L-DED process

Additively manufactured martensitic stainless steel components can combine complex geometry with superior mechanical and corrosion performance. In this work, the mechanical performance of AISI 410L processed by laser directed energy deposition (L-DED) additive manufacturing using previously optimized parameters is assessed. Microstructure, hardness, tensile strength, and Charpy impact toughness are evaluated in the as-built and heat-treated conditions. Four heat-treatment routes are investigated: (I) austenitization and water quenched, and austenitization, water quenched, and tempered at (II) 300, (III) 450, and (IV) 600 °C, followed by air cooling. The results show that, for tempering temperatures up to 450 °C, the hardness, yield strength, and ultimate tensile strength show an increasing trend when compared with the as-built condition and reference commercial standard (annealed AISI 410) because of microstructure refinement induced by recrystallization. Tempering at 600 °C, on the other hand, enhances the ductility of the specimens, accounting for an increased deformation until fracture and superior Charpy impact toughness. In summary, this work demonstrates that, for all tested conditions, the tensile strength of the AISI 410L additively manufactured by L-DED outperforms that of the standardized commercial AISI 410 martensitic stainless steel, and that post-processing heat-treatments can be used to further enhance toughness and ductility, making it even more competitive.

Porosity Reduction in 15CDV6 Steel Manufactured by L-DED

The Laser Directed Energy Deposition (L-DED) is an Additive Manufacturing process based on the direct injection of the filler material into the desired areas of a substrate. Damaged components can be repaired or coated in order to enhance their properties and increase their lifespan. However, this process is highly material dependent and to assure the quality of the deposited material, the process parameters need to be optimised. In the present work, a novel material for the L-DED is developed, the 15CDV6 aeronautical steel. The material was atomized ad hoc and the obtained powder was characterized (particle shape, size distribution, and chemical composition) in order to ensure its quality. Once the powder was analysed, the suitability of the 15CDV6 steel for the L-DED process was studied through a methodology consisting of three sequential steps: single clad tests, layer deposition and wall construction. The main process parameters (laser power, feed rate and powder feed rate) were controlled during these tests. Nevertheless, the initial tests showed high levels of porosity, which required considering additional process parameters to reduce them, such as the carrier and shielding gas flows, preheating, or the laser beam diameter. Consequently, the porosity formation mechanisms were identified and the most relevant process parameters established, which for the 15CDV6 steel were the gas flows. The effect of the shielding gas flow in the powder distribution below the nozzle was studied experimentally by digital image analysis to better interpret the obtained results and determine the optimum process parameters for achieving defect free parts. The quality of the deposited material was studied through metallographic analysis and an Acicular Ferrite structure was observed, ensuring good mechanical properties. To summarise, this research work proves the viability of employing 15CDV6 steel in the L-DED process and has determined the main process parameters to obtain porosity-free parts.

Offline planning optimization and formation prediction of laser directed energy deposition process

Offline planning optimization and formation prediction of laser directed energy deposition process

A Deep Learning Approach to Classify and Detect Defects in the Components Manufactured by Laser Directed Energy Deposition Process

This paper presents a deep learning approach to identify and classify various defects in the laser-directed energy manufactured components. It mainly focuses on the Convolutional Neural Network (CNN) architectures, such as VGG16, AlexNet, GoogLeNet and ResNet to perform the automated classification of defects. The main objectives of this research are to manufacture components using the laser-directed energy deposition process, prepare a dataset of horizontal wall structure, vertical wall structure and cuboid structure with three defective classes such as voids, flash formation, and rough textures, and one non-defective class, use this dataset with a deep learning algorithm to classify the defect and use the efficient algorithm to detect defects. The next objective is to compare the performance parameters of VGG16, AlexNet, GoogLeNet and ResNet used for classifying defects. It has been observed that the best results were obtained when the VGG16 architecture was applied to an augmented dataset. With augmentation, the VGG16 architecture gave a test accuracy of 94.7% and a precision of 80.0%. The recall value is 89.3% and an F1-Score is 89.5%. The VGG16 architecture with augmentation is highly reliable for automating the defect detection process and classifying defects in the laser additive manufactured components.