Wire And Arc Additive Manufacturing Research Articles

Realization of synergistic enhancement for fracture strength and ductility by adding TiC particles in wire and arc additive manufacturing 2219 aluminium alloy

TiC reinforced Al-matrix composites were fabricated by wire and arc additive manufacturing (WAAM) method. The effects of TiC content on the evolution of grain boundary structure, phase transformation, grains distribution, interface mismatch, and mechanical properties of the WAAM-deposited 2219 Al–Cu alloys were investigated. The columnar grains in the inner-layer zone were transformed to equiaxed grains by the addition of TiC particles, which eventually induced the decrease of free energy for the Al-matrix, promoting an opportunity for nuclei to grow on the TiC substrate. TiC particles played an important role in generating the nucleation supercooling (ΔTns, 3.8 °C), multi-site heterogeneous nucleation with a lower value of ΔTns inhibited the constitutional supercooling (ΔTcs) caused by segregation of Cu. The degree of grain boundary segregation was greatly weakened, and the α-Al+θ-CuAl2 phase was semi-coherent with the matrix at the grain boundary, i.e. [1–31]Al2Cu//[0–11]Al, (211)Al2Cu//(100)Al. The fine spot-like phase possessed a strong interfacial bonding with the Al-matrix. The Al2Cu and TiC possessed a coherent interface with crystal orientation relations, i.e. [00–1]TiC//[01-1]Al2Cu, (110)TiC//(100)Al2Cu. Besides that, the fine spot-like phases and the well-dispersed TiC particles within the grains promoted the formation of dislocations. Therefore, the strength and toughness of the deposited 2219 alloy were improved synergistically. Eventually, the deposited sample exhibited a tensile strength around 384 MPa, and the elongation was up to 18.3%.

Wire and Arc Additive Manufacturing of High-Strength Al–Zn–Mg Aluminum Alloy

High-strength 7xxx series aluminum alloys are of great importance for the aerospace industries. However, this type of aluminum alloys has poor processability for most additive manufacturing techniques. In this paper, a newly designed Al–Zn–Mg alloy was used as a feeding wire to fabricate thin wall-shaped samples using the wire and arc additive manufacturing (WAAM) technique. These samples were fabricated based on the cold metal transfer (CMT) process with four different types of arc modes, that is, CMT, CMT-incorporated pulse (CMT + P), CMT-incorporated polarity (CMT + A), CMT-incorporated pulse and polarity (CMT + PA). The optical microscopy, x-ray computed tomography, and scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) were employed to characterize the microstructure and phase constitution. The results clearly reveal that the porosity varies with the arc modes, and the densest sample with porosity of 0.97% was obtained using the CMT + P mode. The mechanical properties of the fabricated samples are also dependent on the arc modes. The tensile strength and yield strength of the sample manufactured by the CMT + PA arc mode are the highest. In terms of anisotropy, the strength differences in horizontal and vertical direction of the samples made by CMT + PA, CMT + A, and CMT modes are all large, which is mainly ascribed to the pores distributed at the interlayer region.

Automatic calibration of work coordinates for robotic wire and arc additive re-manufacturing with a single camera

Industrial robots are increasingly applied in the automatic die repair welding via the prevalent wire and arc additive manufacturing (WAAM) technology. However, the precise calibration of work coordinates is indispensable for the off-line programming of robotic welding paths, which often results in positioning error, path deviation, or even tool collisions. The die is pre-heated at about 500 °C before the robotic WAAM processes. Thus, it is challenging to calibrate work coordinates by touch sensing because those points on the X-axis and the Y-axis to determine the location of the part need to be caught by human eyes. In this paper, a camera vision calibration (CVC) method based on stereo vision is developed. Image feature points are extracted by a multi-saliency fusion algorithm based on the human visual attention mechanism. Through stereo vision, 3D information of the feature points is obtained, and the workpiece coordinate system (WCS) is finely calibrated. Compared with the random error of human vision calibration (HVC), the proposed method could improve the workpiece’s calibration accuracy, reduce the unexpected collisions in limited space, and improve the dimensional precision of the welding layer.

A probabilistic approach for high cycle fatigue of Wire and Arc Additive Manufactured parts taking into account process-induced pores

Wire and Arc Additive Manufacturing (WAAM) is a direct-energy deposition technique (unlike SLM or EBM) that builds up a part in a layer-by-layer fashion, each layer being constituted of interlaced weld beads. It is the best suited Additive Manufacturing (AM) technique for large structures thanks to its high deposition rate (5 kg/h). The resulting material shows a rough surface, strong residual stress induced by its complex thermal history, a heterogeneous microstructure marked by the different weld passes as well as defects formed by gas pockets. Despite their rarity, pores are found to have a first-order influence on the fatigue life of machined specimens. The discrepancy in their size (> 100 μm) and position is responsible for a considerable scatter that makes classical fatigue tests ineffective. The aim of this study is to propose a novel approach to take into account the effect of rare WAAM-induced defects in high cycle fatigue. To achieve this, numerical porous structures are generated from the knowledge of the real pore population determined by tomography. Their fatigue performances are predicted via a two-scale probabilistic model identified on experimental self-heating results, on which pores have no influence. In that sense, the probabilistic model describes the behavior of a virtually healthy material. Then, by computing a database of representative pore cases, the whole bundle of Wöhler curves for each numerical porous structure is determined. Finally, the numerical fatigue scatter is in close agreement with experimental data, and it is shown that the ranking in pore criticality according to the model matches the fractography observations.

Simulation of precipitates evolution driven by non-isothermal cyclic thermal history during wire and arc additive manufacturing of IN718 superalloy

For wire and arc additive manufacturing (WAAM) of IN718 superalloy, predicting the evolution of precipitates driven by non-isothermal cyclic thermal history has been guiding significance for tailoring the manufacturing process to obtain satisfactory microstructure and properties. Based on the thermodynamic calculation for IN718 superalloy and the thermal simulation for multi-layers & multi-passes WAAM process, the simultaneous transformation kinetics (STK) model derived from the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory was used to simulate the evolution of precipitates in the WAAM process. The evolution and final spatial distribution characteristics of different precipitates in the WAAM sample were investigated. When the time subdivision increment of thermal history is between 0.1∼0.4 s, the phase fraction calculated by the STK model tends to be stable. The macro distribution of constituent phases on the middle section of the 8-layers & 10-passes WAAM sample is inhomogeneous. In particular, the strengthening phases γ’/γ” precipitate more in the middle and upper region than that in other regions of the WAAM sample, and this result is indirectly evaluated by the distribution of micro-hardness. Moreover, in the last one or two passes of the WAAM sample, the NbC is depleted and the brittle Laves phase is enriched, which means that the regions where WAAM processing ended are likely to become the performance weak region of the whole part.

Residual stress in wire and arc additively manufactured aluminum components

In this study, a number of numerical simulations have been performed to analyze the distribution characteristics of residual stress (RS) in the wire and arc additive manufacturing (WAAM) components made of aluminum alloys. Experiments have been performed to measure temperature results (thermal cycles, etc.), residual stresses, and deformation for verification. The results show that the variation in the height of beam can affect the magnitude and distribution of longitudinal RS in both the substrate and the beam, while that can only influence the transverse RS in the substrate but not in the beam nearly. The longitudinal RS on the top surface of the last layer in the WAAM parts changes from tension to compression if the height of beam is above a certain value (about 20 mm here), which is obviously different from that in the multi-pass weldments and the selective laser melting (SLM) components. The restraint condition of the substrate can apparently affect the magnitude and distribution of longitudinal RS in the beam, while that almost has no influence on transverse RS in the beam. In terms of numerical results, the generation mechanism and distribution of RS in WAAM components have been systematically illuminated in the current work, which is quite useful to guide the mitigation of the generated high RS.

Influence of Duty Ratio and Current Mode on Robot 316L Stainless Steel Arc Additive Manufacturing

Wire and arc additive manufacturing (WAAM) is usually for fabricating components due to its low equipment cost, high material utilization rate and cladding efficiency. However, its applications are limited by the large heat input decided by process parameters. Here, four 50-layer stainless steel parts with double-pulse and single-pulse metal inert gas (MIG) welding modes were deposited, and the effect of different duty ratios and current modes on morphology, microstructure, and performance was analyzed. The results demonstrate that the low frequency of the double-pulse had the effect of stirring the molten pool; therefore, the double-pulse mode parts presented a bigger width and smaller height, finer microstructure and better properties than the single-pulse mode. Furthermore, increasing the duty ratio from 35% to 65% enlarged the heat input, which then decreased the specimen height, increased the width, and decreased the hardness and the tensile strength.

In Situ Monitoring of Additive Manufacturing Using Digital Image Correlation: A Review.

This paper is a critical review of in situ full-field measurements provided by digital image correlation (DIC) for inspecting and enhancing additive manufacturing (AM) processes. The principle of DIC is firstly recalled and its applicability during different AM processes systematically addressed. Relevant customisations of DIC in AM processes are highlighted regarding optical system, lighting and speckled pattern procedures. A perspective is given in view of the impact of in situ monitoring regarding AM processes based on target subjects concerning defect characterisation, evaluation of residual stresses, geometric distortions, strain measurements, numerical modelling validation and material characterisation. Finally, a case study on in situ measurements with DIC for wire and arc additive manufacturing (WAAM) is presented emphasizing opportunities, challenges and solutions.

System study of the formability, nitrogen behaviour and microstructure features of the CMT wire and arc additively manufactured high nitrogen Cr-Mn stainless steel

Large-scale high nitrogen steel (HNS) components with complex facade promote the application of Wire and Arc Additive Manufacturing (WAAM) technology in this area. However, the lack of fundamental research restricts its development. In this study, a self-made HNS wire with 0.99 wt.% nitrogen content (N%) was systematically studied in the aspects of the additive seam formability, nitrogen behaviour, along with microstructure characterizations. A designed Tanguich experiment with three factors (cold metal transfer (CMT) models, wire feeding speed and oxygen content in shielding gas) and four levels were used to reveal the suitable parameters for AM and the rule of nitrogen behaviour in the molten pool. For the semi-quantitative calculation of the N%, a modified kinetic model was proposed with the prediction accurate less than 12 %. Besides, the nitrogen pore and microstructure characterizations under different CMT models were studied. Results showed that for fewer pores in a smaller size, the molten pool volume should be in the range of 200 ∼ 300mm3. The austenite cell substructures in the microstructure were mainly found in the low heat input additive seams with a diameter around 9 μm. The microhardness test showed that for the AM of HNS, the first few layers can also be used with no need to remove. When the N% is lower than 0.8 %, positive relativity between N% and microhardness can be expected. Besides, the fluctuation of microhardness was found to be connected with the irregular columnar grains, Mn Oxides and Cr nitrides in the additive seams.

Decision-based process planning for wire and arc additively manufactured and machined parts

The conventional manufacturing of aircraft components is based on the machining from bulk material and the buy-to-fly ratio is high. This, in combination with the often low machinability of the materials in use, leads to high manufacturing costs. To reduce the production costs for these components, a process chain was developed, which consists of an additive manufacturing process and a machining process. To fully utilize the process chain’s capabilities, an integrated process planning approach is necessary. As a result, the work sequence can be optimized to achieve the economically most suitable sequence. In this paper, a method for a joint manufacturing cost calculation and subsequent decision-based cost minimization is proposed for the wire and arc additive manufacturing (WAAM) & milling process chain. Furthermore, the parameters’ influence on the results and the magnitude of their influence are determined. These results make it possible to design an economically optimal work sequence and to automate the process planning for this process chain.

Wire and arc additive manufacturing of 308L stainless steel components: Optimization of processing parameters and material properties

In the current study, wire and arc additive manufacturing (WAAM) of thin-walled 308L stainless steel components was reported. Firstly, the influence of the welding current, the voltage, and the travel speed in the WAAM process on the geometry of single weld beads was investigated. These parameters were also optimized for the deposition of 308L steel walls. Secondly, the microstructure and the mechanical characteristic of WAAM 308L steel walls have been explored. The obtained results reveal the optimized that parameters giving the desirable geometry of single weld beads for building 308L walls by the WAAM process. The microstructure of WAAM 308L steel walls mainly features the dendrites of austenite growing vertically and residual ferrite existing in grain boundaries of the austenite matrix. The microhardness of the built material is about 163 HV0.1. The UTS, YS and elongation of WAAM 308L walls are 532–553 MPa, 344–353 MPa, and 40–54%, respectively, which are relatively similar to those of wrought 308L stainless steel (UTS: 530–650 MPa, YS: 360–480 MPa, and elongation: 35–45%). Thus, the mechanical properties of WAAM 308L steel walls are considered to be adequate for industrial applications.

Model of weld beads geometry produced on surface temperatures by Wire and Arc Additive Manufacturing (WAAM)

Wire and Arc Additive Manufacturing (WAAM) is an Additive Manufacturing (AM) technology that knows a strong interest in recent years. With this technology, the combination of an electrical arc welding and a metallic wire feedstock is used to manufacture parts layer by layer. As part geometry depends strongly on deposition conditions, this study is focused on the characterization of single bead walls and their geometrical evolutions according to welding parameters and surface temperatures. Our experiment has consisted of the production of walls manufactured with a 5083Al wire and built from 1 layer up to 10 layers with several surface temperatures (Tsur fixed at 100, 200, 300 and 400°C). Before the deposition of each new layer, we ensure that the substrate is at the correct temperature using a thermometer in order to guarantee constant welding conditions. Those welding parameters have been kept constant with a Wire Feed Speed (WFS) at 5 m/min and a Travel Speed (TS) at 0.6 m/min. Wall bead geometry and dimensions, width (w) and height (h), have been then measured using a 3D scanner. Results are used to feed a predictive model developed with a circular model curve fitting each top layer cross-section of walls. Data form this study, coupled with thermal simulation, will allow us to predict faithfully parts shapes and to control their dimensions.

Wire and arc additive manufacturing: Opportunities and challenges to control the quality and accuracy of manufactured parts

Wire and arc additive manufacturing (WAAM) has proven that it can produce medium to large components because of its high-rate deposition and potentially unlimited build size. Like all additive manufacturing (AM) technologies, however, an optimized process planning that provides uniform, defect-free deposition is key for the production of parts. Moreover, AM, particularly WAAM, is no longer just a prototyping technology, and most of today's attention is on its transformation to a viable and cost-effective production. With this transformation, a number of issues need to be addressed, including the accuracy and effectiveness of the manufactured components. Therefore, the emphasis should be on dimensional precision and surface finish in WAAM. This paper covers heat input and management concept, related to the resulting shrinkage, deformation, and residual stresses, which is particularly critical. In addition, we focus on process planning including build orientation, slicing, and path planning, as well as the definition of process parameter selection from a single track to multi-track and multilayer, and finally geometric features from a thin-wall to lattice structures with several case studies. Central to addressing component quality and accuracy, we summarize guiding designs and future needs through numerous WAAM-specific issues, which require for manufacturing of complex components.

Realization of structural evolution in grain boundary, solute redistribution and improved mechanical properties by adding TiCnps in wire and arc additive manufacturing 2219 aluminium alloy

Non-equilibrium solidification and experienced thermal conditions of deposited 2219 aluminium alloy during wire and arc additive manufacturing (WAAM) result in the grain boundary segregation, which makes it difficult to avoid the appearance of columnar grain. In this work, columnar crystal defects and grain boundary segregation were eliminated by adding TiC nanoparticles (TiCnps) to WAAM-deposited 2219 aluminium alloy. The effects of TiCnps addition on the solidification dynamics, particles distribution, grain boundary structure, solute redistribution, and mechanical properties were investigated. The solidification dynamics of the droplet induced by mesoscopic TiC particles was assessed and the result showed that the addition of c. 80 nm TiCnps could reduce the solid–liquid growth rate (R), besides, the critical movement rate (Rc) of 80 nm TiCnps was much lower than that of R, i.e. TiCnps were inclined to be distributed inside the grains as effective nucleation particles. Micro-pools with multi-site nucleation inhibited grain boundary segregation and increased Cu concentration in Al-matrix. Such a variation in Cu atom concentration promoted the precipitation of the fine spot-like θ′-CuAl2 phase with a diameter of c. 500 nm, besides, the dendritic θ-CuAl2 phase along the grain boundary was all transformed into α-Al+θ-CuAl2 phases with a semi-coherent state. The fine spot-like phase and TiCnps possessed a strong interfacial bonding with the Al-matrix, thereby the mechanical properties of the deposited 2219 aluminium alloy were strengthened. Eventually, the deposited 2219 aluminium alloy with the addition of TiCnps exhibited excellent mechanical properties, i.e. the tensile strength of the samples were around 380 MPa, and the elongation could be up to 21.4%.

Effects of Heat Input on Morphology of Thin‐Wall Components Fabricated by Wire and Arc Additive Manufacturing

In the process of wire and arc additive manufacturing (WAAM), it is crucial to improve the surface quality and maintain a uniform building morphology. Unacceptable morphology of components influences the surface roughness and deposition efficiency, limiting the application of WAAM in the fabrication of complex‐shaped components. Herein, linear energy density is used to estimate the applied heat input. The single‐pass single‐layer bead morphology is analyzed to establish the relationship between linear energy density and the bead width ratio to bead height. In addition, four four‐layer components under different heat inputs are deposited to reveal the process of multilayer deposition. According to the morphology and surface appearance, heat input effects on surface roughness, straightness, and deposition efficiency are investigated. Then, a relationship is established to predict the outcomes of heat input on deposition quality. It is inferred that good deposition performance can be obtained when the linear energy density lies around 600 J mm−1. A simulation based on the Simufact welding software is made on temperature field distribution and thermal cycles to illustrate the relationship, confirmed by 3D scanning results. At last, based on the investigations, a uniform and well‐formed thin‐wall component is fabricated, and its deposition efficiency can reach 80%.

Defect-correlated fatigue resistance of additively manufactured Al-Mg4.5Mn alloy with in situ micro-rolling

Hybrid in situ rolled wire + arc additive manufacturing (HRAM) is a potential 3D printing method that combines traditional wire and arc additive manufacturing (WAAM) with in situ micro-rolling. Here, the manufacturing defects and mechanical and fatigue strength were explored for an HRAM- and WAAM-processed Al-Mg4.5 Mn alloy. The results show that advanced HRAM can result in significant grain refinement and enhance the material failure resistance compared with standard WAAM. High-resolution X-ray tomography was adopted to identify the defect density, morphology, distribution, and size, which showed that the defect population and size produced by HRAM were considerably lower than those produced by WAAM. Based on high-cycle fatigue tests, fatigue failure was observed entirely from metallurgical defects. Finite element simulations of the defect images based on computed tomography scans showed that lack-of-fusion defects are more dangerous than gas porosity in terms of increasing the local stress. Finally, the defect-controlled fatigue lifetime was predicted by combining the peaks-over-threshold method with a modified NASGRO model.

An automatic compensation method for improving forming precision of multi-layer multi-bead component

Wire and arc additive manufacturing (WAAM) is a promising technology for manufacturing large-sized metal components. However, the material shortage region (MSR) at the edge of each slicing layer can influence the forming precision and surface flatness of components. To solve these problems, this paper proposes a shape follow-up edge cycle compensation (SECC) method and model for predicting the weld width and weld height to improve the efficiency of the WAAM process. First, the prediction model was used to determine the weld width and weld height for various welding parameters. The predicted width was then used to obtain the optimal overlap distance, and the filling path of each layer was generated. The same weld height was used for slicing of the 3D model and the tool path compensation cycle was generated. Second, the influence of the MSR on the morphology of multi-layer multi-bead (MLMB) components was analyzed. The MSR results in a height difference between the edge height and the middle height of every deposited layer, and the height difference increases as more layers are added and the height of the component increases. Furthermore, the influence of the MSR gradually extends from the edge to the middle, such that the upper surface presents a parabolic shape. Finally, a mathematical model was established to determine the height difference based on the area of the MSR. When the height difference reaches the weld height, an edge compensation weld is added to eliminate the height difference. Our experimental results show that the proposed forming control strategy improves forming precision and surface flatness. The method is highly feasible and can be applied to a wide range of WAAM applications.

On the influence of the geometrical irregularities in the mechanical response of Wire-and-Arc Additively Manufactured planar elements

The use of Additive Manufacturing (AM) technologies in the construction industry is still at its pioneering stage. The first investigations indicate that, among actually available metal 3D-printing strategies, Wire-and-Arc Additive Manufacturing (WAAM) process appears to be the most suitable for realizing large-scale steel structures. Nonetheless, the limited knowledge of the mechanical response of WAAM-produced alloys requires further experimental work for a reliable evaluation of the structural behavior of WAAM structural members. One specific issue which still needs to be fully investigated is the peculiar geometrical irregularity resulting from WAAM process that could have non-negligible effects on the mechanical behavior, such as anisotropy and non-homogeneous stress-strain fields.The present work explores the influence of the inherent geometrical irregularities of planar 308LSi stainless steel WAAM specimens on the tensile response. For this purpose, detailed geometrical characterization of the external surface of WAAM specimens was carried out with 3D scanning techniques and random field theory. Different sets of specimens were subjected to tensile tests to evaluate the influence of surface finishing (machined vs. as-built), orientation (with respect to the printing layers) and cooling strategy on the key mechanical parameters. The whole strain field was then studied in detail through Digital Image Correlation (DIC) monitoring technique. Key findings are given in terms of geometrical characterization of surface roughness and thickness variability, as well as a quantitative assessment of the influence of geometrical irregularities on the main mechanical parameters. The material response reveals a significant anisotropy related to a marked crystallographic micro-texture. The geometrical irregularities negatively impact some of the mechanical parameters of the as-built material, suggesting further considerations for practical structural design applications.

A novel method of bead modeling and control for wire and arc additive manufacturing

Purpose Modeling and control of bead geometry in wire and arc additive manufacturing is significant as it affects the whole manufacturing process. The purpose of this paper is to establish an efficient model to control the bead geometry with fewer experiments in wire and arc additive manufacturing (WAAM). Design/methodology/approach A multi-sensor system is established to monitor the process parameters and measure the bead geometry information. A dynamic parameters experimental method is proposed for rapid modeling without dozens of experiments. A deep learning method is used for bead modeling and control. To adaptively control the bead geometry in real-time, a closed-loop control system was developed based on the bead model and in situ monitoring. Findings A series of experiments were conducted to train, test and verify the feasibility of the method and system, and the results showed that the proposed method can build the bead model rapidly with high precision, and the closed-loop system can control the forming geometry adaptively. Originality/value The proposed modeling method is novel as the experiment number is reduced. The dynamic parameters experimental method is effective with high precision. The closed-loop control system can control the bead geometry in real-time. The forming accuracy is elevated.

Process Planning for the Machining of Ti-6Al-4V Near-net Shaped Components

In order to decrease mass, and thus fulfill the targets set for airplane traffic emission reduction, the amount of lightweight materials used for structural components, such as Ti-6Al-4V, is rising. With the conventional milling process, low material utilization and short tool life span lead to high manufacturing costs. Therefore, a process chain consisting of wire and arc additive manufacturing (WAAM) and machining is developed. To exploit its full potential, the process planning needs to be adapted to the near-net shaped WAAM components. In this paper a method for the process planning is explained and virtually validated for the manufacture of Ti-6Al-4V parts.