Wire Arc Additive Manufacturing Research Articles

Fabrication and characterization of a new high-strength alloy via WAAM using GMAW+cold wire feeding

The demand for high-strength steels has continued to increase in various fields of industry due to the advancement in technology. The wire arc additive manufacturing (WAAM) enables the fabrication of high-strength structures from different materials by controlling the raw wire in layers. This study focuses on the fabrication of high-strength steel by WAAM using the gas metal arc welding + cold wire feeding (GMAW + CWF) technique. A new alloy was formed by simultaneously adding 316LSi stainless steel from the CWF to the low alloyed ER70S-6 steel from the GMAW torch. In this way, three different new alloyed structures were produced with varied 316LSi ratios ranging from 10 %, 20 % and 25 % respectively. Besides, their metallurgical and mechanical properties were compared with each other and with single material WAAMed structures. In the macrostructure examinations, no defects due to the mixture of both materials were found and both materials melted properly to create the new alloy. Due to the alloying elements transferred from 316LSi, the microstructure of the new material parts were completely changed compared to the single material WAAMed components and bainite and martensite phases were found in the new alloys. The hardness increased significantly compared to the single-material WAAMed structures and increased up to 139 % and 84 % compared to the single-material WAAMed ER70S-6 and 316LSi, respectively. The tensile strength showed a great improvement and reached almost 1200 MPa, increased by 142 % compared to the single-material WAAMed structure. The fabricated new alloys have the potential to be a candidate material for industries that use high-strength steel.

Parametric optimization of weld bead of aluminium 6061 fabricated through wire arc additive manufacturing

Parametric optimization of weld bead of aluminium 6061 fabricated through wire arc additive manufacturing

Effect of heat treatment on the microstructure and mechanical properties of AZ91D magnesium alloy fabricated via GTA wire arc additive manufacturing

This study aims to address elemental segregation and poor mechanical properties in as-deposited AZ91D magnesium alloy fabricated via wire arc additive manufacturing through heat treatment. Three distinct heat treatments are investigated: solution treatment (T4), artificial aging treatment (T5), and a combination of solution and aging treatment (T6). Microstructural analysis reveals equiaxed grains in all samples. In the T4 state, the eutectic phase along grain boundaries dissolvs into the matrix, reducing elemental segregation but increasing grain size. In the T5 state, elemental segregation is further reduced; however, due to the relatively low aging temperature, the microstructural features of the as-deposited state are largely retained. In the T6 state, solution treatment increases grain sizes, and the uneven distribution of the reprecipitated β phase leads variations in mechanical properties between vertical and horizontal directions. Compared to the as-deposited state, the T6 treatment achieves a synergistic improvement in both strength and ductility. The ultimate tensile strength increases to 262.3 MPa, and the elongation rises to 13.8%, representing improvements of 12.5% and 32.7%, respectively, compared to the as-deposited values of 233.2 MPa and 10.4%.

Fabricating complex parts through optimizing weld bead geometry in WAAM: A comparative study of surface tension transfer and cold metal transfer

Wire arc additive manufacturing (WAAM) technology is being employed in industries such as aerospace, maritime and automotive to produce high-valued metallic parts. With a growing demand for products with complex structures, it is crucial to develop an effective and reliable method for fabricating such parts to meet the demand. Currently, cold metal transfer (CMT), is one of the waveform-controlled short circuit transfer processes, commonly adopted in the WAAM process to fabricate medium to large-scale parts due to its perceived low heat input. However, the approach of using synergic control of wire feed speed and torch travel speed to control weld bead geometry in CMT may not be applicable for fabricating parts with complex structures. In these circumstances, surface tension transfer (STT), a waveform controlled short circuit transfer process, or one of the alternative variants of controlled short circuit transfer with low heat input, may provide more options to control weld bead geometry. There appear to have been few systematic investigations of alternative controlled short circuiting variants for use in WAAM. This paper provides a comparative study to explore the potential of the STT process for fabricating parts with complex geometries in WAAM. Firstly, the working principles of the STT and CMT processes are reviewed. Then, the impacts of welding parameters in the STT and CMT on weld bead geometry are analysed based on experiment results. Finally, a comparison between these two welding processes with regard to flexibility in welding parameter adjustment, heat input and overlapping performance is conducted. Finally, a comparison between these two welding processes is conducted from three critical aspects: (i) Flexibility in parameter adjustment: STT has 333 % and 174 % larger average width and height variation ranges than CMT; (ii) Heat input: STT's heat input is 74.66 % higher than CMT's at TS = 300 mm/min; (iii) Overlapping performance: the average surface roughness of the tested CMT and STT groups is 0.1312 and 0.1823, respectively. Suggestions for using STT and CMT to fabricate parts with complex geometries are provided accordingly.

Mechanical and microstructural investigation of multi-layered Inconel 825 wall fabricated using CMT-based WAAM

In this research, a multi-layered wall was produced using the Wire-Arc Additive Manufacturing (WAAM) technique, specifically employing the Cold Metal Transfer (CMT) method with Inconel 825 wire. The optimized CMT-WAAM parameters were identified using multivariate regression analysis. The mechanical and microstructural properties of the wall were assessed in its lower, middle, and upper sections. The tensile properties showed that the ultimate tensile strength (UTS) ranged from 505 MPa to 514 MPa, closely matching that of conventionally wrought Inconel 825 (505–514 MPa). The yield strength (YS) varied from 199 MPa to 207 MPa, while elongation values ranged from 49.7 % to 57.5 %, depending on the section of the wall. A gradual decrease in hardness was observed from the bottom (246.16 Hv) to the top (221.75 Hv) of the wall. Microscopy identified continuous and discontinuous cellular-dendritic microstructures across the sections. Tensile and impact test fractographs revealed a fibrous ductile fracture mode, with SEM images highlighting the presence of Laves phases and micro-voids, particularly in the upper sections. Despite the formation of Laves phases, which can act as crack initiation sites, the mechanical properties of the WAAM-fabricated wall were comparable to those of wrought Inconel 825.

Development of ferritic–austenitic functionally graded structure via twin wire arc additive manufacturing route

Development of ferritic–austenitic functionally graded structure via twin wire arc additive manufacturing route

Performance Evaluation of Cold Metal Transfer-Based Wire Arc Additive Manufacturing of SS316L: An Effect of Weld Thermal Cycles and Heat Inputs

Performance Evaluation of Cold Metal Transfer-Based Wire Arc Additive Manufacturing of SS316L: An Effect of Weld Thermal Cycles and Heat Inputs

Origins and optimization mechanisms of periodic microstructures in Al-Cu alloys fabricated by wire arc additive manufacturing combined with Interlayer Friction Stir Processing

Inter-layer Friction Stir Processing on Arc Additive Manufactured Components offers significant potential for performance enhancement, yet the homogenization of microstructures has become a challenge for industrial application. To address this, 2319 Al-Cu alloy components were fabricated through the Wire Arc Additive Manufacturing + Interlayer Friction Stir Processing (WAAM-IFSP)1 technique, and a systematic study was conducted on the effects of deformation degree, deformation temperature, and strain rate changes on the microstructural evolution, revealing three distinct periodic microstructures. An increase in deformation degree resulted in a uniform periodic microstructure, attributed to the more uniform internal deformation caused by the increased deformation degree. At a deformation degree of 24.1 %, higher strength and ductility were achieved, along with a notable bimodal grain structure (BGS). Further research indicated that this structure would distribute more widely within the matrix with increasing strain rate, aiding in further performance breakthroughs, ultimately reaching an ultimate tensile strength (UTS) of 404 MPa and an elongation (EL) of 32 %. However, imperfections in the process led to inhomogeneity in the structure. Focusing on the dynamic recrystallization (DRX) mechanisms during stirring can improve this phenomenon. The research revealed that the fine grains in the BGS were controlled by a synergy of dominant discontinuous dynamic recrystallization (DDRX) and auxiliary continuous dynamic recrystallization (CDRX) nucleation mechanisms. The findings are expected to provide a theoretical basis for the optimization of WAAM-IFSP processes and microstructural and performance regulation, which is crucial for enhancing the industrial application prospects of aluminum alloys.

Too hot to print, too slow to handle; finding optimal path characteristics for WAAM

Wire + Arc Additive Manufacturing (WAAM) is recognized as a highly capable metal additive process. However, the quality of manufactured parts is often compromised by defects stemming from process-induced temperature fields and transient weld-bead shapes, largely due to suboptimal path planning. Recent efforts have predominantly focused on optimizing either the thermal aspects or the productivity of WAAM, but the interplay between these factors and the final geometric accuracy of the parts has not been thoroughly investigated. This study introduces an automated framework for path planning optimization in WAAM, effectively bridging the gap between temperature control, geometric accuracy, and productivity. The approach utilizes a reinforcement learning agent to generate paths that minimize deposition time. These paths are subsequently segmented and optimized for their temperature response using a Monte Carlo tree search algorithm, with the thermal effects efficiently approximated through a reduced-order model. The paper presents a comparative analysis of various deposition strategies, offering insights and recommendations to enhance both productivity and part quality in WAAM path planning.

An experimental study on wire arc additive manufacturing (WAAM) of 308L stainless steel and its chemical dissolution

Wire arc additive manufacturing (WAAM) is a potential method of producing complicated metal parts directly from computer-aided design (CAD) models. In this experiment, stainless steel 308 L alloy was deposited with a GMAW-interfaced three-axis special purpose Cartesian robot. The major goal was to understand the behaviour of deposited material and, later, its dissolution in specific concentrations of chemical combinations. The deposited samples were investigated for better understanding of the impact of welding current on bead properties, surface roughness, and microstructure. Furthermore, the dissolving behaviour of deposited samples was investigated in various acidic bath mixes to better understand the rate of dissolution. The results reveal that WAAM parameters, particularly current, have a considerable impact on bead properties, roughness, and microstructure. On the other hand, dissolution experiments demonstrated that the faster breakdown of WAAM deposited stainless steel occurs when a 1:1 ratio mixture of acids is used.

Mechanical and Metallurgical Characteristics of Wire-Arc Additive Manufactured HSLA Steel Component Using Cold Metal Transfer Technique

Recently, the application of wire-arc additive manufacturing (WAAM) for the production of metallic products is gaining traction. WAAM is associated with the direct energy deposition technique and therefore has a higher deposition rate (approximately 4 kg/h). For this reason, it is of greater interest than powder-based additive manufacturing techniques. Industrial applications such as marine and offshore structures and pressure vessels for space programs commonly utilize high-strength low-alloy (HSLA) steel. HSLA steel components produced by casting methods exhibit defects due to oxidation. Therefore, cold metal transfer (CMT)-WAAM was adopted in this study to fabricate HSLA steel components. The metallurgical properties were analyzed using microscopic and diffraction techniques. The effects of the evolved microstructures on mechanical properties, such as strength, microhardness, and elongation to fracture, were evaluated. To analyze and test the structure, two regions were selected, namely, top and bottom. Microstructural analyses revealed that both regions were primarily composed of acicular ferrite, polygonal ferrite, and bainitic structures. The bottom region exhibited superior mechanical properties compared with the top region. The improved strength at the bottom region can be ascribed to the formation of a high density of dislocations and finer grains.

Weighted average algorithm: a novel meta-heuristic optimization algorithm based on the weighted average position concept

To address the ever-increasing complexity of real-world engineering challenges, meta-heuristic algorithms have been extensively studied and applied. However, balancing exploration and exploitation remains a significant challenge. In this paper, a novel meta-heuristic optimization algorithm based on the weighted average position concept, and named weighted average algorithm (WAA), is proposed and implemented. In this algorithm, the weighted average position for the whole population is first established at each iteration. Subsequently, WAA applies one of two movement strategies to balance exploration and exploitation, determined by a parameter function that depends on random constants and iteration numbers. To validate the effectiveness and reliability of WAA, it is applied to various optimization challenges, amongst which unconstrained benchmark functions and constrained engineering challenges. Based on the Friedman and Wilcoxon analyses, it can be concluded that the proposed algorithm obtained the best performance for the considered benchmark functions and engineering problems. The WAA is applied to prediction and optimization of surface waviness in Wire Arc Additive Manufacturing (WAAM) components. First, two prediction models relating WAAM process parameters and surface waviness are established based on an Artificial Neural Network (ANN) optimized by WAA, and Particle Swarm Optimization (PSO), respectively. The WAA optimized ANN (WAA/ANN) model outperforms both the standard ANN models and those optimized by PSO. Finally, leveraging the developed WAA/ANN prediction model, WAA and other optimization algorithms are applied to minimize waviness of a WAAM component, with WAA exhibiting promising performance.

A Bibliometric Analysis of the Global Trend of Residual Stress Induced by WAAM Process and Stress Relief Heat Treatment

Gathering data from previous research and incorporating it into a scientometrics investigation can provide valuable insights into a particular area of study. Wire Arc Additive Manufacturing (WAAM) is currently popular for producing customized metal products quickly. Despite this, there have been lack of studies on implementing stress relief heat treatment after the manufacturing process to reduce residual stress in the resulting parts potentially. This paper represents the first bibliometric analysis study focusing on the application of stress-relief heat treatment as a post-processing method for wire arc additive manufacturing (WAAM). Given the exploratory nature of this research, it is expected that future investigations will continue to delve into these areas, ultimately contributing to a better understanding of the effects of stress-relief heat treatment on the additively manufactured materials.

Interpass temperature impact on bead geometry of mild steel in wire-arc additive manufacturing

In wire-arc additive manufacturing (WAAM), melt pool dynamics produce variations in bead geometry that create undesired part geometries and can also lead to material defects. In the current state of the art, reducing melt pool and bead variation is still an aspect of WAAM that is underdeveloped. Several factors influence the bead geometry including the type of material that is being deposited and process inputs. In this study, ER70S-3 mild steel was deposited onto steel build plates using a cold metal transfer (CMT) deposition process. Varying plate preheat surface temperatures were used from ambient temperature to 300 °C using different welding travel speeds. To control build plate surface temperature, a preheat stage was designed and implemented to simulate different interpass temperatures. Beads were deposited and subsequently measured to determine their geometric properties such as bead height and bead width. Initial results indicate that as the preheat temperature increases, resulting bead height decreases, bead height variation decreases, and bead width increases. Initial microstructural data also indicates that as preheat temperature increases, the microstructure becomes more equiaxed with decreasing grain sizes.

Machine tool cross beam design, fabrication, and testing using metal big area additive manufacturing

This paper describes the application of metal Big Area Additive Manufacturing (mBAAM) to the fabrication of a machine tool cross beam. The replacement of a traditional box design weldment with a new design printed by wire arc additive manufacturing using the MedUSA system at Oak Ridge National Laboratory (ORNL) is detailed. This requires a new design strategy based on the unique mBAAM capabilities. The intent of the new design is to reduce mass, while maintaining the dynamic stiffness. To compare the two designs, the natural frequencies and mode shapes are measured using impact testing and predicted using finite element analysis. It is confirmed that the printed structure dynamics agreed with the numerical model predictions, which demonstrates that it is feasible to model a large-scale mBAAM part and understand its behavior prior to printing. Another notable outcome of this study is that the significant residual stress and distortion in the print indicate that knowledge gaps remain for widespread implementation of mBAAM.

The role of coherent nano precipitates on stacking fault and deformation twin formation during tensile deformation of wire arc additive manufactured nickel-aluminum-bronze

The strain hardening mechanisms and dislocation interactions of a wire arc additively manufactured (WAAM) nickel-aluminum-bronze (NAB) alloy was investigated using multi-scale characterization approach cross-correlating scanning electron microscopy (SEM), SEM-based electron back-scatter diffraction (EBSD), site- and crystallographic orientation-specific focused ion beam (FIB) nanofabrication, scanning transmission electron microscopy (STEM) and STEM-based energy dispersive X-ray spectroscopy (EDS). Flat, rectangular dog bone specimens were strained under uniaxial tension conditions. To understand the micro- and nanometer scale deformation mechanisms throughout the microstructure, tensile test specimens were interrupted near the yield strength and ultimate tensile strength. STEM microstructural characterization revealed that tensile deformation occurs by planar slip and multiple slip bands interacting on different {111} planes as well as the nucleation of dislocations from the interfaces associated with grains and secondary phase particles. To the authors knowledge for the first time the Center of symmetry (COS) analysis revealed that in both samples the shearing of nanoscale precipitates led to the formation of extended stacking faults including a combination of intrinsic stacking faults and 2-layer extrinsic stacking faults. At high strain levels more dislocations and stacking faults were nucleated, as well as intersecting slip bands further facilitating the activation of the stair-rod cross-slip mechanism and thickening of an ESF to create a 3-layer nano-twin. Activated mechanisms of plastic deformation and associated role of the precipitates are discussed with respect to the microscopic strength-plasticity characteristics as well as macroscopic mechanical properties of WAAM NAB alloy.

Robot path planning for metrology in hybrid manufacturing

The objective of the wire arc additive manufacturing (WAAM) hybrid cell is to significantly reduce lead time associated with large scale parts. The WAAM process utilizes a 6 degree-of-freedom (DOF) robot manipulator in addition to a 2 DOF part positioner. After printing, the part is translated into position for scanning to inform the subtractive manufacturing process. Scanning in a manual setting can be a long and arduous process to generate scans of sufficient quality for the basis of informed machining. Effective path planning for scanning with the intent to reduce scanning time, increase quality of scans, and move toward a full automation of the hybrid manufacturing cell is investigated in this paper. Simulation software is used to create and verify path plans prior to importing and implementing on a 6 DOF robotic manipulator to which a GOM ATOS Q 3D scanner is mounted. The quality, amount of time necessary to produce, and number of scans required to produce a sufficient representation for machining are compared using three methods. The first method is a manual scanning configuration, the second is using a generalized path plan, and the third is using a geometry-based path plan.

Effect of welding gas mixtures on weld material and bead geometry

Abstract Shielding gas is an essential parameter in welding processes, serves to shield the molten material from the atmosphere and external contaminations while providing a stable electric-arc pathway during the process, thus influencing the quality of the weld bead and several other aspects of the process. Therefore, any welding-based process, such as wire-arc additive manufacturing, could benefit from shielding gas mixture optimisation to selectively improve the processing and possibly the final mechanical properties of the welded material. In this study welding of EN AW 5183 aluminium (single weld bead and wire-arc additive manufacturing build-up) was conducted using several gas mixtures and their influence on final geometry defects, and microstructure measured. The gas mixtures used were a combination of varying amounts of carbon dioxide, nitrogen, and oxygen. These were added to commercially available argon gas. It was observed that: CO2 additions led to an unfavourable bonding defect and increased mean grain size; nitrogen additions caused a decrease in mean grain size, decreased pore count while maintaining a similar pore volume fraction to the reference argon mixture samples; oxygen additions showed slight reduction of mean grain size, decreased pore count and decreased pore volume fraction. These results further showcase that varying shielding gas mixtures influence the final material properties and should be considered as an additional improvement route for conventional welding and additive manufacturing.

Study of Residual Stress Using Phased Array Ultrasonics in Ti-6AL-4V Wire-Arc Additively Manufactured Components

This paper presents a study on residual stress measurement in wire-arc additively manufactured (WAAM) titanium samples using the non-destructive method of phased array ultrasonics. The contour method (CM) was used for the verification of the phased array ultrasonic results. This allowed for a comparison of measurement methods to understand the effects on the distribution of residual stress (RS) within Ti-6Al-4V samples and the effectiveness of measurement of residual stress using phased array ultrasonics. From the results of the experiments, the phased array ultrasonic data were found to be in good agreement with the CM results and displayed similar residual stress distributions in the samples. The results of the individual elements of the phased array were also compared and an improvement in accuracy was found. From per-element results, anomalies were found and could be mitigated with the ability to average the results by using phased array ultrasonics. Therefore, based on these results, there is a strong case for the benefits of using phased array ultrasonics as a method of residual stress measurement for WAAM Ti-6Al-4V components over other existing residual stress measurement techniques.

Numerical simulation for microstructure control in wire arc additive manufacturing of thin-walled structures

The difference of cooling rates on the surface and the interior of thin-walled structures leads to significant differences of microstructures in additive manufacturing (AM). To reveal the microstructure control in wire arc additive manufacturing of thin-walled structures, a gas-heat coupling model with experimental validation is proposed. The computational accuracy can reach 96% in prediction of temperatures and microstructures. Increasing the preheating or scanning speed leads to a higher probability of heterogeneous nucleation on the surface of thin-walled structures. When the pre-heating is increased from 550 K to 750 K, the proportion of equiaxed grains increases by 20.8%. When the gas flow rate of super cooling is increased from 20 L/min to 30 L/min, the size of equiaxed grains is decreased from 0.33 mm to 0.23 mm on the surface, and the width of columnar grains is decreased from 0.53 mm to 0.42 mm in the interior. This is due to the significant differences in cooling rates in thin-walled structures.