Direct Metal Deposition Process Research Articles

Laser in situ synthesis of gradient aluminides in metal matrix composite during DMD process

The suitability of direct metal deposition process of exothermic powders (Ni-Al, Ti-Al, Fe-Al systems), traditionally used in the self-propagating high-temperature synthesis technology, is described. Owing to the synthesis of new intermetallic phases, the overlapping of laser in situ synthesis and layerwise deposition processes makes it possible both to obtain more durable parts of complex shape, and to enlarge the functional resource of these functional-graded structures. Besides, relationships between the main laser deposition parameters and the intermetallic phase structures of the built-up objects were studied. In our research we applied optical microscopy, X-ray analysis, microhardness measurement and SEM with EDX analysis of the laser-fabricated intermetallics.

Finite Element Modeling of Microstructure in Laser-Deposited Multiple Layer Inconel 718 Parts

Laser direct metal deposition (LDMD) process is becoming a cost-effective and sustainable alternative to the traditional manufacturing process. However, depending on the process conditions, the high cooling rate in LDMD can result in undesirable microstructure, which can affect the performance and functionality of the manufactured component. This article reports an investigation into the microstructure that arises from LDMD of a multilayered Inconel 718 on EN-43 mild steel substrate. Using the finite element analysis package ANSYS, the investigation focused on prediction of the grain size distribution in the deposited component as a consequence of its thermal history. In agreement with results from experimental examination, the results of the investigation predicted an increase in interdendric arm spacing from the bottom towards the top of the deposited wall. This characterizes a finer microstructure at the bottom of the wall, which progressively coarsens towards the top of the wall as more layers are deposited. This variation in grain sizes gradually tapers off to a steady level after a few layers. The present model provides a simple yet effective method to estimate the microstructure in LDMD encompassing wide range of materials.

Tensile strength of functionally graded and wafer layered structures produced by direct metal deposition

Purpose – This paper aims to investigate the changes in tensile properties of novel functionally graded materials (FGMs) and wafer structures created by direct metal deposition (DMD) additive manufacturing (AM) technology. Design/methodology/approach – Laser-assisted DMD was used to create two innovative sets of metallic structures – the functionally graded and wafer-layered structures – using pairs of six different engineering alloys in different combinations. These alloys were selected due to their high popularity within a diverse range of industries and engineering applications. The laser-assisted DMD was selected as a suitable technique to create these complex structures because of its capability to deposit more than one alloy powder at a time. After creation of these structures, their tensile strength was tested in a series of tensile tests and the results were compared with those of single alloy samples. Findings – It was observed that the mechanical properties of FGMs and wafer structure samples were clearly different from those of the single alloy samples, a fact which creates a whole pool of opportunities for development of new materials or structures with desired mechanical properties that cannot be achieved in single alloy parts. Originality/value – The study demonstrates the application of the DMD process to produce unique structures and materials, which would be high in demand in engineering applications, where metallic parts are exposed to high loads and where excessive tensile stresses may adversely affect the performance of such parts.

Effect of Process Parameters on Residual Stress Distribution during Direct Laser Metal Deposition Shaping

In order to improve the quality of sample and decrease the stress during process, it is important to study the residual stress distribution during direct laser metal deposition (LMDS) process. In this paper, according to the “element life and death” technique of finite element method ,with APDL, we simulated the effects of Laser power, scanning velocity, substrate preheat temperature and powder addition speed in top layer of samples residual stress distribution during whole LMDS process are studied. The residual stress distribution under different process parameters is researched in detail. Using the same process parameters, the simulation results show good agreement with the features of sample which fabricated by LMDS.

Strength and Electrical Conductivity Relationships in Al-Mg-Si and Al-Sc Alloys

Aluminium alloys play an important role in overhead power transmission applications. All-aluminium alloy conductor cables require increasingly hard-to-achieve combinations of high tensile strength and high electrical conductivity. The problem is that a high strength is normally associated with a reduced electrical conductivity. Both heat-treatable 6xxx series aluminium alloys and work-hardening 1xxx series aluminium alloys are important contenders for these applications. By contrast, the addition of rare earths and/or transition metals to aluminium may provide further opportunities to achieve improved combinations of precipitation hardening, substructural hardening and elevated temperature stability. In this work, strength and electrical conductivity relationships are investigated for a range of 6xxx series aluminium alloys and an Al-Sc alloy. The Al-Sc alloy was produced by means of a direct laser metal deposition process that allowed more Sc to be placed into solid solution than by conventional casting or solution treatment. The paper explores the relative effects of composition, cold working and age hardening on the balance of strength and electrical conductivity, including examples of how improved combinations of both strength and conductivity can be achieved.

Compressive Properties of Solid and Porous Parts Made from High Strength Steel Alloys by Direct Metal Deposition

The potential of laser assisted Direct Metal Deposition (DMD) process, for creating structures from high strength steel alloys that can be used in engineering applications requiring high strength and greater ductility in combination with high hardness is investigated. Due to increasing interest in metallic honeycomb and sandwiched structures, solid and porous specimens are prepared and examined in similar conditions. Specimen using two different powders of 316L stainless steel and H13 tool steel alloy are generated by DMD cladding on mild steel plates as substrates. The parts are tested under quasi static compressive loading and curves plotted and analysed for stress vs. strain behaviour. The results indicate that at low laser power, solid and porous steel structures with yield strength and ductility comparable to commercial grades can be produced. Porous structures show excellent characteristics suitable for applications in newly developing field of metallic honeycombs and sandwiched structures. Low modulus of elasticity is a matter of concern, but it can be improved by heat treatment.

Improvement of the Laser Direct Metal Deposition Process in 5-axis Configuration

Abstract The implementation of the continuous 5-axis configuration can extend the limits of the Laser Direct Metal Deposition (LDMD) processes, especially when the complexity of the parts to be built is growing. In order to follow the profile of a part, we use the orientation of its growth axis. Although 5-axis machining is well known nowadays, LDMD processes require a specific optimization that depends on many parameters. Unlike conventional machining, it has to be noted that the speed variation tool tip affects the stability of deposition. Thus, we have to smooth trajectories in order to provide fluid movements and also to ensure the stability of deposition. This article describes the method and results in the optimization of trajectories to build metallic parts with freeform. Optical sensors have been implemented in the focusing unit in order to follow the variations of the laser-powder-substrate interaction and also to detect the process instabilities. Thanks to the right use of a new and large 5 axis machine and specific setting trajectories, manufacturing parts in 5-axis, with no concession on the construction rate has been possible.

Predictive Model for Environmental Assessment in Additive Manufacturing Process

Additive Manufacturing is an innovative way to produce parts. However its environmental impact is unknown. To ensure the development of additive manufacturing processes it seems important to develop the concept of DFSAM (Design for Sustainable Additive Manufacturing). In fact, one of the objectives of environmental sustainable manufacturing is to minimize the whole flux consumption (electricity, material and fluids) during manufacturing step. To achieve this goal, it is interesting to get a predictive model of consumptions, integrated in the design step, allowing to evaluate the product's environmental impact during the manufacturing step. This paper presents a new methodology for electric, fluids and raw material consumptions assessment for additive manufacturing processes, in particular for a direct metal deposition process. The methodology will help engineers to design parts optimized for additive manufacturing with an environmental point of view.

Influence of a pulsed laser regime on surface finish induced by the direct metal deposition process on a Ti64 alloy

The direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allows generating a prototype or small series of near net-shape structures. Despite numerous advantages, one of the most critical issues of the technique is that produced pieces have a deleterious surface finish which requires post machining steps. Following recent investigations where the use of laser pulses instead of a continuous regime was successful to obtain smoother DMD structures, this paper relates investigations on the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titanium alloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate a specific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laser heating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsed mode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger and stable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients and Marangoni flow in the external side of the fusion zone were assumed to be the main reasons for surface finish improvement. Additional results indicate that combining the benefits from a pulsed regime and a uniform laser irradiation does not provide further reduction of surface roughness.

Parametric study of development of Inconel-steel functionally graded materials by laser direct metal deposition

Laser direct metal deposition (LDMD) has developed from a prototyping to a single and multiple metals manufacturing technique. It offers an opportunity to produce graded components, with differing elemental composition, phase and microstructure at different locations. In this work, continuously graded Stainless Steel 316L and Inconel 718 thin wall structures made by direct laser metal deposition process have been explored. The paper considers the effects of process parameters including laser power levels and powder mass flow rates of SS316L and Inconel 718 during the deposition of the Steel–Ni graded structures. Microstructure characterisation and phase identification are performed by optical microscopy and X-ray diffraction techniques. Mechanical testing, using methods such as hardness, wear resistance and tensile testing have been carried out on the structures. XRD results show the presence of the NbC and Fe2Nb phases formed during the deposition. The effect of experimental parameters on the microstructure and physical properties are determined and discussed. Work shows that mechanical properties can be controlled by input parameters and generation of carbides provides an opportunity to selectively control the hardness and wear resistance of the functionally graded material.

Influence of various process conditions on surface finishes induced by the direct metal deposition laser technique on a Ti–6Al–4V alloy

The direct metal deposition (DMD) with laser is a free-form metal deposition process for manufacturing dense pieces, which allows generating a prototype or small series of near net-shape structures. One of the most critical issues is that produced pieces have a deleterious surface finish which systematically requires post machining steps. This problem has never been fully addressed before.The present work describes investigations on the DMD process, using an Yb-YAG disk laser, and a widely used titanium alloy (Ti–6Al–4V) to understand the influence of the main process parameters on the surface finish quality. The focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish.In order to understand the physical mechanisms responsible for deleterious surface finishes, we have carried out: (1) a precise characterization of the laser beam and the powder stream; (2) a large number of multi-layered walls using different process parameters (P(W), V(m/min), Dm (g/min), Gaussian or uniform beam distribution); (3) a real time fast camera analysis of melt pool dynamics and melt-pool – powder stream coupling; (4) a characterization of wall morphologies versus process parameters using 2D and 3D profilometry.The results confirm that surface degradation depends on two distinct aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters. Last, a simple analytical model was proposed to correlate melt-pool geometries to resulting surface finishes.

Development of Bio-Compatible Metallic Structures Using Direct Metal Deposition Process

This paper investigates the capabilities of Direct Metal Deposition (DMD) process, which is a novel additive manufacturing technique, for creating structures that can be used as bone implants. Emphasis is on the use of bio-compatible metals, because metals are the most suitable materials in terms of mechanical strength when the requirement arises for supporting and replacing the load bearing bones and joints such as hip and knee. Specimens using two different metal powders, 41C stainless steel and Ti6Al4V titanium alloy, are generated by DMD process on mild steel and titanium plates as substrates respectively. Metallographic samples were made from the cladding, and tested for surface roughness and micro-hardness. The results indicate that at low laser power, hard and strong structures with good porosity can be successfully created using the DMD system.

Numerical study of thermal history in laser aided direct metal deposition process

Temperature evolution in the laser aided direct metal deposition (LADMD) process has considerable influence on the microstructure and properties of the final part. A 3D transient finite element model was developed to study the temperature evolution during the multilayer LADMD process. To make the property analysis from thermal history easier, a critical temperature specific to thermal history was defined and the distribution of it in the part was also discussed. The simulation results indicated that the critical temperature can make the property analysis from thermal history easier. Thermal history of all the deposited materials was similar. It was also concluded that process parameters needed to be time-varying according to the real-time temperature field during the process.

Texture control during laser deposition of nickel-based superalloy

A nickel-based superalloy was deposited on a nickel-based superalloy substrate by a laser-aided direct metal deposition process. The age-hardening behavior of the as-deposited clad was studied. The effect of laser beam scanning pattern on dendrite growth morphology was investigated using electron backscatter diffraction. Unidirectional laser beam scanning pattern developed a fiber texture; conversely, a backward and forward scanning pattern developed a rotated cube texture in the deposit. This paper reports a route to produce texture-controlled laser clad on a polycrystalline substrate.

2D longitudinal modeling of heat transfer and fluid flow during multilayered direct laser metal deposition process

Derived from laser cladding, the direct laser metal deposition (DLMD) process is based upon a laser beam–powder–melt pool interaction and enables the manufacturing of complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DLMD parts usually necessitate postmachining steps. Within this context, the focus of our work is to improve the understanding of the phenomena responsible for deleterious surface finish by using numerical simulation. Mass, momentum, and energy conservation equations are solved using comsol multiphysics® in a 2D transient model including filler material with surface tension and thermocapillary effects at the free surface. The dynamic shape of the molten zone is explicitly described by a moving mesh based on an arbitrary Lagrangian–Eulerian method (ALE). This model is used to analyze the influence of the process parameters, such as laser power, scanning speed, and powder feed rate on the melt pool behavior. The simulations of a single layer and multilayer claddings are presented. The numerical results are compared with experimental data, in terms of layer height, melt pool length, and depth of penetration, obtained from high speed camera. The experiments are carried out on a widely used aeronautical alloy (Ti–6Al–4 V) using a Nd:YAG laser. The results show that the dilution ratio increases with increasing the laser power and the scanning velocity or with decreasing the powder feed rate. The final surface finish is then improved.

Effect of Scanning Methods on Residual Stress Distribution during Direct Laser Metal Deposition Shaping

In order to improve that quality of sample and decrease the stress during process, it is of great importance to study the residual stress distribution during direct laser metal deposition (LMDS) process. In this paper, according to the “element life and death” technique of finite element method ,with APDL, we simulated the effects of long edge reciprocating scanning method, short edge reciprocating scanning method and direction orthogonal changing in different layers reciprocating scanning method to residual stress distribution during whole LMDS process are studied. The residual stress distribution under different scanning methods is researched in detail. Using the same process parameters, the simulation result show good agreement with the features of sample which fabricated by LMDS

Investigation on the Process Characteristics of Laser Cladding Fabrication Using 45 Carbon Steel Wire

This study investigates the effect of wire feeding direction, angle, wire feeding speed, laser scanning speed and laser power in a high power Nd:YAG laser direct metal deposition process for single and multilayered clad/parts. The lap cladding experiment using 500 W Nd:YAG laser is designed to study the best lap rate of 45 carbon steel. The microstructure and micro hardness of the melting track shows that dense metal microstructure can be obtained using laser cladding.

An anisotropic enhanced thermal conductivity approach for modelling laser melt pools for Ni-base super alloys

Ni-base super alloys are extensively used in high temperature gas turbine engines and energy industries. Due to the high replacement costs of these components, there are huge economic benefits of repairing these components. Laser direct metal deposition processes (LDMD) based on laser cladding, laser fusion welding, and laser surface melting are some of the processes which are used to repair these high value components. Precise control of these processes is important to achieve the desired microstructure, stress distribution, distortions due to thermal stresses and other important output variables. Modelling of these processes is therefore an extremely important activity for achieving any degree of control/optimisation. However, modelling of these processes is not straight-forward due to melt pool flows dominated by Marangoni and buoyancy driven convection. Detailed CFD models are required for accurate prediction of melt pool geometry. But these models are computationally expensive and require greater expertise. To simplify and speed up the modelling process, many researchers have used the isotropic enhanced thermal conductivity approach to account for melt pool convection. A recent study on mild steel has highlighted that isotropic enhanced thermal conductivity approach is not able to accurately predict the melt pool geometry. Based on these findings a new approach namely anisotropic enhanced thermal conductivity approach has been developed. This paper presents an analysis on the effectiveness of the isotropic and anisotropic enhanced thermal conductivity approaches for laser melting of Inconel 718 using numerical technique. Experimental melt pool geometry has been compared with modelling results. It has been found that the isotropic enhanced thermal conductivity approach is not able to accurately predict the melt pool geometry, whereas anisotropic enhanced thermal conductivity approach gives good agreement with the experimental results.

Evolution of microstructure in laser deposited Al–11.28%Si alloy

Laser melting of Al–Si alloys has been investigated extensively, however, little work on the microstructural evolution of laser deposited Al–Si alloys has been reported to date. This paper presents a detailed microstructural investigation of laser deposited Al–11.28Si alloy. Laser aided direct metal deposition (DMD) process has been used to build up solid thin wall samples using Al 4047 prealloyed powder. The evolution of macro- and microstructures of laser deposited Al–Si samples was investigated using X-ray diffraction, optical microscopy, scanning electron microscopy and electron backscattered diffraction techniques. Microstructural observation revealed that the morphology and the length scale of the microstructures are different at different locations of the sample. A periodic transition of microstructural morphology from columnar dendrite to microcellular structure was observed in each layer. The observed difference in the microstructure was correlated with the thermal history of the deposit.

Numerical and experimental investigation of multilayer SS410 thin wall built by laser direct metal deposition

The influence of thermal history on the microstructures and properties of a multilayer stainless steel 410 (SS410) thin wall built by laser direct metal deposition (LDMD) process was investigated experimentally and numerically. Thermal history at two specified points in the substrate was measured by thermocouples during the process. A three-dimensional (3D) finite element model was developed to study the thermal history of the deposited material for the laser direct metal deposition of multilayer thin wall. The simulated and measured thermal history indicated that the absorption and loss of heat tended to be close to equilibrium when the deposited material reached a certain height during the LDMD process. Different microstructure regions were formed due to the different thermal history the material experienced. The hardness distribution along the height centerline of the thin wall was measured. The results indicated that thermal history had an important effect on the microstructure, and consequently on the final properties.