Laser Direct Metal Deposition Process Research Articles

Experimental study of SS316L, Inconel 625, and SS316L-IN625 functionally graded material produced by direct laser metal deposition process

Three types of walls were produced by the direct laser metal deposition (DLMD) process; SS316L, Inconel 625 (IN625), and SS316L-Inconel 625 FGM. The thin walls were deposited on an AISI 4130 austenitic steel substrate in five layers with a length of 2 cm. The solidification behavior, secondary dendrite arm spacing (SADS) value, chemical composition, and hardness of samples were studied. Microstructures were evaluated using optical microscopy (OM) images, scanning electron microscopy (SEM), EDS Line, EDAX, and Map analyses. OM and SEM images showed an acceptable bonding between the layers in all samples. The main solidification was equiaxed dendritic and columnar dendritic in most parts. The growth of dendrites was perpendicular to the substrate. Some dendrites grew epitaxially at the interface of two sequential layers. The standard deviation of SDAS value for SS316L, IN625, and SS316L-IN625 FGM was 0.63, 0.71, and 0.73, respectively. The lowest value of SDAS was obtained in layer one, while the highest value was obtained in layer five of the thin walls. The average SDAS values for SS316L, IN625, and SS316L-IN625 FGM were 4.40, 4.53, and 4.76 µm, respectively. Therefore, the difference between the SDAS values was not significant. EDAX and Map analyses showed that the segregation of Nb and Mo to the dendritic boundary and the formation of eutectic, secondary phases, and brittle Laves phases have occurred. Additionally, the segregation of Nb and Mo to the dendritic boundary in the SS316L-IN625 FGM sample was higher than SS316L and IN625 samples. The microhardness values oscillated significantly and decreased by moving away from the substrate (in the build direction). The microhardness values of different points of the SS316L-IN625 FGM walls were in the range of 218–278 HV. EDS line scan, microstructure, and microhardness analyses indicated the successful fabrication of the SS316L-IN625 FGM by the DLMD process.

The dynamic carbon footprint modeling for laser direct metal deposition based on processing states

The Laser Direct Metal Deposition (LDMD) process offers notable advantages and obtains wide application in aerospace, defence equipment and other industrial sectors. However, the characteristics of multiple-inputs and low-efficiency in the process will bring about high carbon footprint. Additionally, the carbon footprint fluctuates with processing states and equipment systems owing to the discontinuous process in LDMD involving the layer-by-layer deposition and the laser-powder coupling. This paper investigated dynamic carbon footprint based on the resource and energy consumption from the process-oriented standpoint in LDMD process, which quantified the processing time, power distribution and material consumption of each processing state for every sub-system. In this research, the discontinuous process was divided into effective processing state, rapid moving state and transformed delay state and the processing time of each state were estimated with process parameters. Besides, the operating state time and power distribution of five sub-systems were estimated combining the equipment triggering mechanism and the processing state time. The orthogonal experiment was carried out to deposit the 316L stainless steel powder into parts with the size of 15 mm*15 mm*10 mm under the given process parameter conditions (Vf ∈ [8,12] g/min, P ∈ [600,1000] w, Vs ∈ [500,900] mm/min). The results show that carbon footprint of deposited parts fluctuates in the range of 3624.68–15759.08 g under parameter combinations and the low carbon footprint parameter-interval is obtained. The average carbon footprint of effective processing state, the transformed delay state and the rapid moving state account for 55%, 40% and 5% respectively, while the carbon footprint of powder supply sub-system contributes to 68% among the five sub-systems. This research revealed and qualified the dynamicity of carbon footprint at the levels of processing states, process parameters and sub-systems, offering potential for carbon footprint reduction in advanced manufacturing processes.

Effect of laser direct metal deposition process on the microstructure and mechanical properties and temperature and stress fields of 24CrNiMo

Effect of laser direct metal deposition process on the microstructure and mechanical properties and temperature and stress fields of 24CrNiMo

Online monitoring of direct laser metal deposition process by means of infrared thermography

AbstractDirect laser metal deposition (LMD–DED) is an additive manufacturing (AM) process that is used to build up and repair high-quality metal components. It works by overlapping layers of powder material and melting them with a laser. To get a stable process without defects and to reach, at the same time, high mechanical properties, a robust assessment and control of the process parameters, and above all of their combination, is required. The ideal goal is to assure the online control, to stop or correct the process in case of unexpected anomalies. In this work, a robust online monitoring of the laser metal deposition (LMD–DED) process based on the use of infrared thermography was developed and proposed. After choosing the suitable process parameters, a customized design of experiments (DOE) was set, and the statistical analysis of different thermal features was carried out to develop the most robust models that correlate them with the input process parameters (laser power, scanning speed, and powder flow rate). The proposed procedure was based on the extraction of different thermal features from suited regions of interest (ROI), performing statistical analyses by means of analysis of variance (ANOVA) and building regression models to correlate the process parameters with the thermal behavior. The obtained results demonstrated the possibility to control the process by means of the chosen thermal features, independent of the position of the ROI. Moreover, the possibility to use the models to detect typical AM defects, and anomalies, online directly during the process, has been proved and verified by destructive macrographs carried out on the manufactured coupons.

Functionally Graded Additive Manufacturing of Thin-Walled 316L Stainless Steel-Inconel 625 by Direct Laser Metal Deposition Process: Characterization and Evaluation

Direct Laser Metal Deposition (DLMD) is a state-of-the-art manufacturing technology used to fabricate 316L stainless steel/Inconel 625 functionally graded material (FGMs) in this research. For the practical application of these materials in the industry, the effects of process parameters on the geometric characteristics and surface roughness require more investigation. This FGM was additively manufactured in five layers by changing the 316L stainless steel/Inconel 625 ratio in each layer. The effects of laser power on geometric characteristics, height stability, and surface roughness were investigated. The microstructural analysis and microhardness profiles were studied. The results show that despite the high solidification rate, the segregation of alloying elements into dendritic areas occurred. It was also found that increasing the laser power will increase the height, width, height stability, and surface roughness of the gradient walls. The maximum width and height of the deposited layers were 1.615 and 6.42 mm, respectively, at the highest laser power (280 W). At the laser power of 220 W, the least surface roughness (Ra = 105 µm) and the best height stability (0.461 mm) will be obtained. The microhardness values will differ in various sections of the gradient walls in a range of 225–277 HV.

Coupling Characteristics of Powder and Laser of Coaxial Cone Nozzle for Laser Direct Metal Deposition: Numerical Simulation and Experimental Study.

Laser direct metal deposition (LDMD) enables not only the preparation of high-performance coatings on the surfaces of low-property materials but also the three-dimensional direct manufacturing and re-manufacturing of parts. In the LDMD process, the spatial coupling characteristics of the powder flow and the laser beam are the key factors affecting the forming quality of the cladding layer. Based on the gas-solid two-phase flow theory, a numerical model of coaxial powder feeding was established by CFD. The powder flow characteristics of the lower part of the nozzle, the powder particle motion trajectory, and the optical-powder spatial coupling morphology and law were studied, and the relationship between the powder flow morphology, laser beam, and powder utilization was explored. On this basis, the law between the optical-powder coupling characteristics and the geometric characteristics of the cladding layer is discussed in conjunction with LDMD experiments. The results show that the powder concentration scalar located in the focal plane of the laser beam can be used to visualize the optical-powder coupling morphology. When the powder feeding speed exceeds the loading capacity of the carrier gas flow, the powder concentration in the center of the spot and the powder utilization rate decrease. When the carrier gas flow rate is 4.0 L/min and the powder feeding rate is 4.0 g/min, the best utilization rate achieved is 81.4%. In addition, the H (height) of the cladding layer is more sensitive to changes in the powder concentration than the W (width). These findings provide new ideas for nozzle structure design and the optimization of LDMD parameters.

Direct laser metal deposition (DLMD) additive manufacturing (AM) of Inconel 718 superalloy: Elemental, microstructural and physical properties evaluation

In this study, Direct Laser Metal Deposition (DLMD) technique is adopted for the additive manufacturing (AM) of Inconel 718 Superalloy. A 1 kW fiber laser with a coaxial nozzle head is used. The effects of scanning speed (2.5 and 5 mm/s) as well as powder feed rate (17.94 and 28.52 g/min) on the process were investigated. Characteristics of the 3D printed wall specimens such as the geometrical dimensions (width and height), microstructure observations, and the microhardness were obtained. To study the stability of the 3D manufactured walls, the height stability was considered for the investigation. Optical microscopy (OM), field emission electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and mapping analysis were performed to derive the microstructural features of the additively manufactured parts (AMP). Vickers microhardness test is used to evaluate the hardness distributions of AMP. Catchment concept of the powder in DLMD process is used for explaining different trends of the process. Results indicated that, by decreasing the scanning speed, the width and height of the deposited layer increase. The average width of AMP directly depends on scanning speed and the powder feed rate. Scanning speed has a reverse effect on the height stability; that is, the lower the scanning speed, the larger the stability. Microstructural results showed that because of the solidification process, the alloying elements will be accumulated in the grain boundaries. The non-uniform cooling rate and non-steady solidification rates of molten area in additive manufacturing process, the microhardness values of the AMP following a fluctuated trend.

Modeling of laser aided direct metal deposition of stainless steel using supervised deep learning algorithms

Laser Direct Metal Deposition (LDMD) is a very promising additive manufacturing methodology which provides metal cladding layer over the substrate with good corrosion resistance, desired surface finish and very accurate geometry. In this work, an attempt has been made to develop a forward and reverse model of laser aided direct metal deposition utilizing deep learning algorithms. Forward model aims at predicting the deposited bead height and width from the known set of LDMD process parameters such as laser power, scanning velocity, and powder flow rate. Reverse modelling shows the effectiveness of each input parameter over the chosen response factors. Therefore, in the reverse modelling, the optimized input parameters values have been tried to predict to get the desired deposition characteristics during experimentation. Three different neural networks based deep learning architectures, namely, Multi-Layer Feed Forward Neural Network (MLFFNN), Recurrent Neural Networks (RNN) and Radial Basis Function Neural Network (RBFNN), have been put forward to develop the said predictive models. The supervised learning algorithms are used to train the neural networks. The performances of MLFFNN, RNN and RBFNN models are compared among themselves. The results show that all the models are capable of making better predictions and the models can be effectively used in shop floor in optimal selection of most influential parameters for the desired outputs.

A monitoring framework based on exergetic analysis for sustainability assessment of direct laser metal deposition process

With the constant increase of energy costs and environmental impacts, improving the process efficiency is considered a priority issue for the manufacturing field. A wide knowledge about materials, energy, machinery, and auxiliary equipment is required in order to optimize the overall performance of manufacturing processes. Sustainability needs to be assessed in order to find an optimal compromise between technical quality of products and environmental compatibility of processes. In this new Industry 4.0 era, innovative manufacturing technologies, as the additive manufacturing, are taking a predominant role. The aim of this work is to give an insight into how thermodynamic laws contribute at the same time to improve energy efficiency of manufacturing resources and to provide a methodological support to move towards a smart and sustainable additive process. In this context, a fundamental step is the proper design of a sensing and real-time monitoring framework of an additive manufacturing process. This framework should be based on an accurate modelling of the physical phenomena and technological aspects of the considered process, taking into account all the sustainability requirements. To this end, a thermodynamic model for the direct laser metal deposition (DLMD) process was proposed as a test case. Finally, an exergetic analysis was conducted on a prototype DLMD system to validate the effectiveness of an ad-hoc monitoring system and highlight the limitations of this process. What emerged is that the proposed framework provided significant advantages, since it represents a valuable approach for finding suitable process management strategies to identify sustainable solutions for innovative manufacturing procedures.

A comparison of the microstructures and hardness values of non-equiatomic (FeNiCo)-(AlCrSiTi) high entropy alloys having thermal histories related to laser direct metal deposition or vacuum remelting

Compared with conventional casting process, laser direct metal deposition (LDMD) can effectively reduce component segregation in non-equiatomic high entropy alloys (HEAs). However, the non-equilibrium thermal history imparted by this method has a significant effect on the microstructure and mechanical properties of the HEA. The present work prepared non-equiatomic (FeNiCo)-(AlCrSiTi) HEAs using the LDMD process, after which some samples were subjected to a subsequent vacuum remelting (VRM) treatment. The variations in phase composition, microstructure and hardness between the HEAs processed using the LDMD or VRM methods were investigated. Differences in phase composition increased with increases in the proportion of the Al, Cr, Si and Ti components. Compared with the HEA samples processed using the VRM method, the LDMD specimens possessed much finer and simpler microstructures mainly comprising solid solution phases. At relatively high concentrations of the Al, Cr, Si and Ti components (32 at% and 40 at% in total), the HEAs processed under LDMD conditions had similar grain morphologies, intermetallic phases and microhardness values, while the VRM specimens presented completely different microstructures and properties.

An accurate and real-time melt pool dimension measurement method for laser direct metal deposition

Laser direct metal deposition (LDMD), as a type of additive manufacturing (AM) technology, has gained broad applications across many industries. However, producing high-quality and accurate geometric workpieces remains a challenge without controlling the fabrication process. A visual-based process monitoring system provides information about melt pool dimensions as vital process parameters for controlling the LDMD process. As the result, the accuracy of the measurement determines the performance of the control system. This paper proposes a method that includes an efficient approach for obtaining the melt pool dimensions in real time and a novel melt pool boundary calibration for finding a suitable threshold to achieve high measurement accuracy. The proposed method is verified on an LDMD system, and the experimental results show that the proposed approach has provided accurate measurements of the melt pool widths that can be used for process quality control.

Prediction of Thermal Residual Stress and Microstructure in Direct Laser Metal Deposition via a Coupled Finite Element and Multiphase Field Framework

Direct laser metal deposition (DLMD) is a modern powder-fed additive manufacturing process, which builds up complex objects layer by layer, providing a potential capacity to produce key structural components specifically for the aerospace industry. The printing process is of a multidisciplinary nature, and has gained increasing attention in the areas of engineering mechanics, material science, control engineering and many other related fields. The quality control of the printed part depends on a large number of process parameters. The aim of this work, therefore, is to develop a coupled finite element and multiphase field framework, that provides an effective way to understand the quantitative relationship between the process parameters, temperature history, thermally-induced residual stresses and microstructures in the DLMD process. More specifically, the established multiscale framework is able to sequentially couple the heat transfer, metal melting/solidification, and stress analysis to simulate the macroscopic temperature distribution, thermal residual stresses and dendrite growth and solute segregation in a thin wall structure made of a binary nickel-copper alloy. The latest simulation technologies are used to model the process of progressive material deposition as well as the movement of the laser beam. It has been found that the high intensity laser introduced in DLMD can produce a complex thermal history and a significant level of thermal residual stresses and distortion. Microstructure predictions demonstrate the location-dependent morphology evolution, e.g., the dendrite spacing and the degree of solute segregation, attributed to the spatially variant temperature history.

Measurement of Thermal Cycle at Multi-Pass Layer Build-Up with Different Travel Path Strategies during DLMD Process

The shape of the parts, created by the technology of direct laser metal deposition (DLMD), is influenced by various parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser affects the temperature distribution in the formed layers. The changing temperature in the working area entails a change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An infrared camera was used to measure thermal cycles. The correspondence table between the intensity of thermal radiation of the material and the absolute temperature was developed. The experiments are carried out with the filler material 316L. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers for different filling strategies are presented.

Uncertainty quantification of grain morphology in laser direct metal deposition

Uncertainty quantification (UQ) has an important role to play in the quality control of additively manufactured products. With a focus on laser direct metal deposition (LDMD), this work presents a systematic UQ framework to quantify the uncertainty of grain morphology due to various sources of uncertainty in the LDMD simulation process. The LDMD process is simulated by a coupled analysis consisting of a macroscale finite element model for the melt pool and a microscale cellular automata model for solidification to predict the microstructure. UQ is carried out using singular value decomposition-based Kriging surrogate of the expensive simulation model. The effectiveness of the proposed approach is demonstrated by identifying several major sources of uncertainty and studying their contributions to the uncertainty in the grain size distribution using a variance-based sensitivity analysis method.

Laser Direct Metal Deposition of 2024 Al Alloy: Trace Geometry Prediction via Machine Learning.

Laser direct metal deposition is an advanced additive manufacturing technology suitably applicable in maintenance, repair, and overhaul of high-cost products, allowing for minimal distortion of the workpiece, reduced heat affected zones, and superior surface quality. Special interest is growing for the repair and coating of 2024 aluminum alloy parts, extensively utilized for a wide range of applications in the automotive, military, and aerospace sectors due to its excellent plasticity, corrosion resistance, electric conductivity, and strength-to-weight ratio. A critical issue in the laser direct metal deposition process is related to the geometrical parameters of the cross-section of the deposited metal trace that should be controlled to meet the part specifications. In this research, a machine learning approach based on artificial neural networks is developed to find the correlation between the laser metal deposition process parameters and the output geometrical parameters of the deposited metal trace produced by laser direct metal deposition on 5-mm-thick 2024 aluminum alloy plates. The results show that the neural network-based machine learning paradigm is able to accurately estimate the appropriate process parameters required to obtain a specified geometry for the deposited metal trace.

Simulation of thermal behaviours and powder flow for direct laser metal deposition process

Laser engineering net-shaping (LENS), based on directed energy deposition (DED), is one of the popular AM technologies for producing fully dense complex metal structural components directly from laser metal deposition without using dies or tooling and hence greatly reduces the lead-time and production cost. However, many factors, such as powder-related and laser-related manufacturing parameters, will affect the final quality of components produced by LENS process, especially the powder flow distribution and thermal history at the substrate. The powder concentration normally determines the density and strength of deposited components; while the thermal behaviours of melt pool mainly determines the cooling rate, residual stress and consequent cracks in deposited components. Trial and errors method is obviously too expensive to afford for diverse applications of different metal materials and various manufacturing input parameters. Numerical simulation of the LENS process will be an effective means to identify reasonable manufacturing parameter sets for producing high quality crack-free components. In this paper, the laser metal powder deposition process of LENS is reported. The gas-powder flow distribution below the deposition nozzle is obtained via CFD simulation. The thermal behaviours of substrate and as-deposited layer/track during the LENS process are investigated by using FEM analysis. Temperature field distributions caused by the moving laser beam and the resultant melt pool on the substrate, are simulated and compared. The research offers a more accurate and practical thermal behaviour model for LENS process, which could be applied to further investigation of the interactions between laser, melt pool and powder particles; it will be particularly useful for manufacturing key components which has more demanding requirement on the components’ functional performance.

Study on direct laser metal deposition

In the current economic situation with worldwide trend for developing new products, the importance of time and cost reduction increases day-by-day. To achieve this goal the man-machine-material interaction should be maximized. Direct laser metal deposition (DLMD) is one of the most famous approaches for this. DLMD is one kind of 3D printing technology (Additive Manufacturing) together with laser cladding process. In DLMD, it is possible to fabricate fully functional metallic parts directly from CAD data, which involves a feeding of metal powders through a nozzle into a high power laser beam and creates a melt pool on the surface of the solid substrate upon which a metallic powder is injected. DLMD process are now acknowledged worldwide and is also known to all by several other names such as Laser metal deposition (LMD), Direct laser deposition (DLD), Laser engineered net shaping (LENS), Direct light fabrication (DLF), Laser deposition welding (LDW) and powder fusion welding (PFW). The role of nozzle in this process is as important as the heart of a human being. There are verity of nozzle configurations namely off-axis, continuous coaxial and discontinuous coaxial powder injection. Comparison of these types towards specific applications revels very interesting observations which are subsequently reproduced in this article. In DLMD, laser beam and powder metals are fed through the nozzle onto a metallic substrate. Then, powder melts by the laser heat and creates a metal pool on the solid substrate by fusion bonding. Once the feedback control sensor gives feedback of completion of deposition of a layer, the laser head, along with the powder delivery nozzle, move up. The whole process is carried out until final near-net-shape of the metal part or component is achieved with a variety of material applicability area and high quality clad track deposition with good mechanical properties. After development of this process in 1995, lot of researchers for several years work on various aspects of high quality deposition with dimensional accuracy such as good clad geometry, clad height, and microstructure study of the mechanical properties. Through this paper on the basis of literature survey an attempt has been made to focus on proper selection of the set up configuration for direct laser metal deposition to fulfill the requirement and helps to achieve high quality deposition.

Laser direct metal deposition process of thin-walled parts using variable spot by inside-beam powder feeding

PurposeThe purpose of this paper is to improve the forming efficiency and quality of unequal-width parts fabricated by laser direct metal deposition technology, some experiments were designed.Design/methodology/approachA new method by varying laser spot was adopted to fabricate unequal-width single track using one scanning rather than multi-track overlapping in the way of the inside-beam powder feeding, and the thin-walled parts were fabricated layer by layer. The theoretical model among layer thickness of z-axis, height of single track and the section curve order of single track was established.FindingsThe top surface unevenness of the thin-walled parts could be compensated automatically within the laser defocusing ranges from −2.5 to −5 mm and from 0.5 to 2.5 mm. The growth rate with the large width/height ratio was more than the small ratio, while the set height of the single track was uniform. The problem of non-uniform growth rate could be solved based on a stepped single-track method. The thin-walled parts with the smooth top surface was fabricated layer by layer which had a continuously variable width from 1 to 3 mm by splicing the laser defocusing range.Practical implicationsThe shapes of the to-be-fabricated parts affect variable laser spot process in practical applications. For example, it will be difficult to apply variable laser spot process on the parts with the hole features.Originality/valueThis paper provided a guidance for forming unequal-width parts by laser direct metal deposition based on the inside-beam powder feeding.

Numerical modelling of pulsed and continuous wave direct laser deposition of Ti-6Al-4V and Inconel 718

Effect of varying laser pulse parameters in laser direct metal deposition (LDMD) of Inconel 718 and Ti-6Al-4V have been shown to be quite complex and results in generation of two brittle phases Ti2Ni and TiNi3. Previous experimental study carried out by the authors discussed by Shah et al. (Sci World J 2014:6, 2014) the LDMD of Inconel 718 and Ti-6Al-4V, where all the sample developed cracks except with ones at low powder feed rate. In order to understand the effect of thermal and structural history on development of stresses during LDMD process, an extensive numerical modelling study has been carried out in the work. Thermal and structural analysis results are verified using the available experimental data. Residual stresses are calculated using numerical modelling in the clad region and at the interface of clad and substrate. Experimental and modelling results show that powder mass flow rate plays an important role in crack development during deposition of Inconel 718 and Ti-6Al-4V and it should be kept at minimum level in order to deposit crack-free samples.

Fabrication of Al-11.2Si Components by Direct Laser Metal Deposition for Automotive Applications

Recently, Al-Si alloys samples have been manufactured at lab scale using various additive manufacturing processes, but so far there is no literature available to investigate the feasibility of fabricating Al-Si alloy component for automotive component applications using Direct Laser Metal Deposition (LMD) technique. This paper deals with the practical challenges of building single wall and block deposition (cuboid shapes) of eutectic Al-Si alloy using direct laser metal deposition process for developing automotive applications. Two scanning pattern, hatch pattern and single wall pattern were chosen to study the effect of scanning direction on mechanical properties as well as microstructural evolution. Microstructural investigation of single wall and block deposition using optical and scanning electron microscopy revealed a 99.9% dense component with very fine hypoeutectic microstructure. Tensile test sample extracted from block deposition showed an impressive elongation of 9% with an ultimate tensile strength of 225 MPa and tensile test sample of single wall showed an average elongation of 9.4% with an ultimate tensile strength of 225 MPa. This investigation revealed that direct laser metal deposition could successfully print the eutectic Al-Si alloy bracket on shock tower hood without any distortion or bending. Key words: Al-Si alloy, Laser cladding, Microstructure, Additive manufacturing, Laser metal deposition