A comparative study of additive manufacturing techniques: Residual stress and microstructural analysis of CLAD and WAAM printed Ti-6Al-4V components

Nowadays, there is a great manufacturing trend in producing higher quality net-shape components of challenging geometries. One of the major challenges faced by additive manufacturing (AM) is the residual stresses generated during AM part fabrication often leading to unacceptable distortions and degradation of mechanical properties. Therefore, gaining insight into residual strain/stress distribution is essential for ensuring acceptable quality and performance of high-tech AM parts. This research is aimed at comparing microstructure and residual stress built-up in Ti–6Al–4V AM components produced by Wire + Arc Additive Manufacturing (WAAM) and by laser cladding process (CLAD)

Numerical modeling for large-scale parts fabricated by Directed Energy Deposition

International audienceThe possibility of large-scale part fabrication is the biggest novelty factor associated with Directed Energy Deposition (DED) Additive Manufacturing (AM) technology. However, issues like deformation and residual stresses in the fabricated part originated from DED process physics are still hindering the possibility of large-scale part fabrication. To overcome these bottlenecks, a DED process simulation that predicts the thermo-mechanical response of the material/workpiece can be a useful tool. There are some conventional simulation techniques that are employed commonly for other technologies like welding or Powder Bed Fusion (PBF). But using the same simulation methodologies for the DED process will lead to impractical computation time or inaccurate results. Hence, in the present work, an efficient simulation methodology dedicated to DED is proposed. The proposed model reduces the computation time drastically and also keeps the desired computation accuracy levels. An equivalent heat source is employed that efficiently models the material deposition along with the programmed deposition strategy. The inclusion of deposition strategy in the efficient model is very important for model accuracy, as deposition strategy plays a critical role in the thermo-mechanical response of the deposited material. The proposed model is developed and implemented in COMSOL Multiphysics. With a cantilever tooling, multiple Stainless Steel 316L (SS 316L) thin wall builds of 50- and 100-layers high is fabricated. Numerical results predicted with the efficient model are successfully compared with experimental data such as thermocouple's in-situ temperature recordings and Laser Displacement Sensor's in-situ distortion recordings at the substrate during the fabrication of 50- and 100-layers wall. The efficient model successfully captures the thermo-mechanical response of the sample. It also correctly predicts the effect of the number of layers on the accumulation of distortion during and after the material deposition

Conventional Meso-Scale and Time-Efficient Sub-Track-Scale Thermomechanical Model for Directed Energy Deposition

Thermally-induced distortion and residual stresses in parts fabricated by the additive manufacturing (AM) process can lead to part rejection and failure. Still, the understanding of thermo–mechanical behavior induced due to the process physics in AM process is a complex task that depends upon process and material parameters. In this work, a 3D thermo-elasto-plastic model is proposed to predict the thermo–mechanical behavior (thermal and distortion field) in the laser-directed energy deposition (LDED) process using the finite element method (FEM). The predicted thermo–mechanical responses are compared to stainless steel 316L (SS 316L) deposition, with single and double bead 42-layer wall samples subject to different inter-layer dwell times, which govern the thermal response of deposited parts in LDED. In this work, the inter-layer dwell times used in experiments vary from 0 to 10 s. Based on past research into the LDED process, it is assumed that fusion and thermal cycle-induced annealing leads to stress relaxation in the material, and is accounted for in the model by instantaneously removing stresses beyond an inversely calibrated relaxation temperature. The model predicts that, for SS 316L, an increase in dwell time leads to a decrease in in situ and post-process distortion values. Moreover, increasing the number of beads leads to an increase in in situ and post-process distortion values. The calibrated numerical model’s predictions are accurate when compared with in situ and post-process experimental measurements. Finally, an elongated ellipsoid heat source model is proposed to speed up the simulation

Conventional Meso-Scale and Time-Efficient Sub-Track-Scale Thermomechanical Model for Directed Energy Deposition

International audienceThermally-induced distortion and residual stresses in parts fabricated by the additive manufacturing (AM) process can lead to part rejection and failure. Still, the understanding of thermo–mechanical behavior induced due to the process physics in AM process is a complex task that depends upon process and material parameters. In this work, a 3D thermo-elasto-plastic model is proposed to predict the thermo–mechanical behavior (thermal and distortion field) in the laser-directed energy deposition (LDED) process using the finite element method (FEM). The predicted thermo–mechanical responses are compared to stainless steel 316L (SS 316L) deposition, with single and double bead 42-layer wall samples subject to different inter-layer dwell times, which govern the thermal response of deposited parts in LDED. In this work, the inter-layer dwell times used in experiments vary from 0 to 10 s. Based on past research into the LDED process, it is assumed that fusion and thermal cycle-induced annealing leads to stress relaxation in the material, and is accounted for in the model by instantaneously removing stresses beyond an inversely calibrated relaxation temperature. The model predicts that, for SS 316L, an increase in dwell time leads to a decrease in in situ and post-process distortion values. Moreover, increasing the number of beads leads to an increase in in situ and post-process distortion values. The calibrated numerical model’s predictions are accurate when compared with in situ and post-process experimental measurements. Finally, an elongated ellipsoid heat source model is proposed to speed up the simulation

Conventional Meso-Scale and Time-Efficient Sub-Track-Scale Thermomechanical Model for Directed Energy Deposition

Thermally-induced distortion and residual stresses in parts fabricated by the additive manufacturing (AM) process can lead to part rejection and failure. Still, the understanding of thermo–mechanical behavior induced due to the process physics in AM process is a complex task that depends upon process and material parameters. In this work, a 3D thermo-elasto-plastic model is proposed to predict the thermo–mechanical behavior (thermal and distortion field) in the laser-directed energy deposition (LDED) process using the finite element method (FEM). The predicted thermo–mechanical responses are compared to stainless steel 316L (SS 316L) deposition, with single and double bead 42-layer wall samples subject to different inter-layer dwell times, which govern the thermal response of deposited parts in LDED. In this work, the inter-layer dwell times used in experiments vary from 0 to 10 s. Based on past research into the LDED process, it is assumed that fusion and thermal cycle-induced annealing leads to stress relaxation in the material, and is accounted for in the model by instantaneously removing stresses beyond an inversely calibrated relaxation temperature. The model predicts that, for SS 316L, an increase in dwell time leads to a decrease in in situ and post-process distortion values. Moreover, increasing the number of beads leads to an increase in in situ and post-process distortion values. The calibrated numerical model’s predictions are accurate when compared with in situ and post-process experimental measurements. Finally, an elongated ellipsoid heat source model is proposed to speed up the simulation

Direct Laser Additive Manufacturing of TiAl Intermetallic Compound by Powder Directed Energy Deposition (DED)

Directed Energy Deposition of the commercial intermetallic Ti-48Al-2Cr-2Nb alloy was investigated. The CLAD® process is dependent on multiple parameters, which were successfully optimised through several experiments, including series of beads, small blocks, and massive blocks, under argon atmosphere. The use of adapted temperature management leads to massive blocks manufacturing that bear no apparent macroscopic defects, such as cracks, which are generally observed in this brittle material due to strong temperature cycling during the manufacturing. The microstructure and geometrical parameters were characterised by scanning electron microscopy (SEM). This process generates an ultra-fine and anisotropic microstructure, which is restored to a homogeneous duplex microstructure by a subsequent heat-treatment. Mechanical characterisation is in progress and will be used to validate the soundness of the materials produced in these conditions

Development of an Elongated Ellipsoid Heat Source Model to Reduce Computation Time for Directed Energy Deposition Process

Directed Energy Deposition (DED) Additive Manufacturing process for metallic parts are becoming increasingly popular and widely accepted due to their potential of fabricating parts of large dimensions. The complex thermal cycles obtained due to the process physics results in accumulation of residual stress and distortion. However, to accurately model metal deposition heat transfer for large parts, numerical model leads to impracticalcomputation time. In this work, a 3D transient finite element model with Quiet/Active element activation is developed for modeling metal deposition heat transfer analysis of DED process. To accurately model moving heat source, Goldak’s double ellipsoid model is implemented with small enough simulation time increment such that laser moves a distance of its radius over the course of each increment. Considering thin build-wall of Stainless Steel 316L fabricated with different process parameters, numerical results obtained with COMSOL 5.6 Multi-Physics software are successfully validated with experiment temperature data recorded at the substrate during the fabrication of 20 layers. To reduce the computation time, elongated ellipsoid heat input model that averages the heat source over its entire path is implemented. It has been found that by taking such large time increments, numerical model gives inaccurate results. Therefore, the track is divided into several sub-tracks, each of which is applied in one simulation increment. In this work, an investigation is done to find out the correct simulation time increment or sub-track size that leads to reduction in computation time (5–10 times) but still yields sufficiently accurate results (below 10% of relative error on temperature). Also, a Correction factor is introduced that further reduces computation error of elongated heat source. Finally, a new correlation is also established in finding out the correct time increment size and correction factor value to reduce the computation time yielding accurate results

Crystallographic analysis of functionally graded titanium-molybdenum alloys with DED-CLAD® process

International audienceIn today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach

Functionally graded Ti6Al4V-Mo alloy manufactured with DED-CLAD ® process

International audienceThis paper presents the results of functionally graded Ti6Al4V-Mo alloy manufactured with directed energy deposition called CLAD ® (Construction Laser Additive Direct) process. Single track width sample with five gradients of composition, from 0 to 100 wt.% Mo, was manufactured using a coaxial nozzle. Both Ti6Al4V and Mo ratios were modified with a 25 wt.% increase or decrease in the chemical composition of each gradient. A two-powder feeder was used to input the correct ratio of each powder, so as to obtain the desired chemical composition. XRD analysis allowed to define the phases present in each deposition, as well as the lattice parameter. SEM observations showed microstructural evolution from 25 wt% Mo on, namely where the ␤-phase becomes dominant. Moreover, dendrites appear from 50 wt.% Mo on. Microhardness analysis revealed variation along the deposition depending on the chemical composition. The homogeneity of the powder mixture under laser beam was highlighted thanks to tomography on the manufactured samples, which validates the processability of functionally graded material (FGM) by CLAD ® process