Browsing by Author "Chen, Xin"
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Item Open Access Achieving a columnar-to-equiaxed transition through dendrite twinning in high deposition rate additively manufactured titanium alloys(Springer, 2024-04-09) Davis, A. E.; Wainwright, J.; Sahu, V. K.; Dreelan, D.; Chen, Xin; Ding, Jialuo; Flint, T.; Williams, Stewart; Prangnell, Philip B.The coarse β-grain structures typically found in titanium alloys like Ti–6Al–4V (wt pct, Ti64) and Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242), produced by high deposition rate additive manufacturing (AM) processes, are detrimental to mechanical performance. Certain modified processing conditions have been shown to lead to a more refined grain structure, which has generally been attributed to a change in the solidification conditions with respect to the experimental Hunt diagram proposed by Semiatin and Kobryn. It is shown that with Wire Arc AM (WAAM) increasing the wire feed speed (WFS) is effective in promoting a columnar-equiaxed transition (CET). Conversely, estimates of the dendrite-tip undercooling using the KGT model suggest that this will be too small for free nucleation without the addition of artificial nucleants, due to the very low solute partitioning in Ti alloys. It is also shown that it is difficult to promote a CET with plasma transferred arc WAAM as computational fluid dynamics (CFD) melt-pool simulations indicate that the solidification parameters remain within the columnar region on the Semiatin-Kobryn Hunt map, within the constraints of a stable process. However, a high fraction of twin boundaries was observed in the refined β-grain structures seen at high WFS. This has been attributed to departure of {001}β alignment from the direction of maximum thermal gradient, caused by the curvature of the fusion boundary, stimulating dendrite twinning during solidification. In addition, it is shown that increasing the WFS leads to a change in melt-pool geometry and a reduction of remelt depth, which promoted dendrite twinning and grain refinement.Item Open Access Comparative analysis of cold and warm rolling on tensile properties and microstructure of additive manufactured Inconel 718(Springer, 2022-01-14) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, Xin; Zhang, XiaoyongDespite the high efficiency and low cost of wire + arc additive manufacture (WAAM), the epitaxial grown columnar dendrites of WAAM deposited Inconel 718 cause inferior properties and severe anisotropy compared to the wrought components. Fundamental studies on the influence of one-pass cold and warm rolling on hardness and microstructure were investigated. Then the interpass cold and warm rolling on tensile properties were also analyzed. The results show that the one-pass rolling increases the hardness and displays a heterogeneous hardness distribution compared to the as-deposited material, and the warm rolling exhibits a larger and deeper strain compared to cold rolling. The columnar dendrites gradually change to cell dendrites under the rolling process and then change to equiaxed grains with the subsequent new layer deposition. The average grain size is 16.8 μm and 23.5 μm for the warm and cold rolling, respectively. The strongly textured columnar dendrites with preferred < 001 > orientation transform to equiaxed grains with random orientation after rolling process. The grain refinement contributes to the dispersive distributed strengthening phases and the increase in its fraction with heat treatment. The as-deposited samples show superior tensile properties compared to the cast material but inferior compared to the wrought components, while the warm-rolled samples show superior tensile properties to wrought material. Isotropic tensile properties are obtained in warm rolling compared to cold rolling. The rolling process and heat treatment both decrease the elongation and lead to a transgranular ductile fracture mode. Finally, the rolling-induced strengthening mechanism was discussed.Item Open Access Control of meltpool shape in laser welding(Springer, 2024-03-05) Suder, Wojciech; Chen, Xin; Rico Sierra, David; Chen, Guangyu; Wainwright, James; Rajamudili, Kuladeep; Rodrigues Pardal, Goncalo; Williams, StewartIn laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.Item Open Access Data Supporting "Managing Assumption-Driven Design Change via Margin Allocation and Trade-offs"(Cranfield University, 2023-10-24 15:45) Chen, Xin; El Fassi, Soufiane; Riaz, Atif; Guenov, Marin; van Heerden, Albert S. J.; Jimeno Altelarrea, SergioResults of design of experiment study produced in "Managing Assumption-Driven Design Change via Margin Allocation and Trade-offs". Presented as Figures 16, 17, and 18 in the paper.Item Open Access Data supporting "Set Based Design Techniques for Evolvability Exploration During Conceptual Aircraft Design”(Cranfield University, 2024-09-19) Jimeno Altelarrea, Sergio; Riaz, Atif; van Heerden, Albert S. J.; Chen, XinItem Open Access Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures(Elsevier, 2021-07-03) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, XinInferior mechanical properties and severe anisotropy behavior of wire + arc additive manufactured (WAAM) Inconel 718 due to the large epitaxial grown columnar dendrites restrict the industrial application of WAAM deposition. Cold rolling was integrated into the WAAM deposition process and the effect of rolling force on microstructure, precipitatation distribution and tensile properties at ambient and elevated temperatures were investigated. The results show that the hardness of cold-rolled samples is much larger than that of the as-deposited and it increases with the increase in the rolling force. The columnar dendrites of the as-deposited sample changed to finer equiaxed grains of 26.5 and 14.7 μm after cold rolling with the force of 50 kN and 75 kN, respectively. Meanwhile, more uniformly distributed grains and less δ phase appear for 75 kN rolled sample. The stress-strain curves are smooth for the tensile tests at ambient temperature, while there are serrations at elevated temperature due to the dynamic strain aging behavior. The as-deposited sample shows inferior tensile properties to the wrought material at ambient and elevated temperatures. The cold-rolled samples both exceed the wrought material at ambient temperature; however, they show higher strength but lower elongation compared to the wrought material. The 75 kN cold rolled sample shows much higher strength and similar elongation to the wrought material for the test at elevated temperature. The grain morphology and recrystallization, as well as the strengthening mechanism of hybrid deposition and cold rolling process were discussed.Item Open Access Effect of shielding conditions on bead profile and melting behaviour in laser powder bed fusion additive manufacturing(Elsevier, 2020-05-26) Caballero, Armando; Suder, Wojciech; Chen, Xin; Pardal, Goncalo; Williams, Stewart W.A series of experiments were performed using a 500 W continuous wave fibre laser on a single powder bed layer using different processing variables. The aim was to investigate the effect of different shielding conditions on melting behaviour and bead profile in laser powder bed fusion (PBF). Through high-speed imaging, it was found that under an argon atmosphere a strong plasma plume is generated from the meltpool. Laser beam-plasma plume interactions caused strong instabilities during melting, including laser wandering, track instability and continuous fluctuations between melting regimes (conduction and keyhole). Hence, it was not possible to control the profile of the melted tracks under this condition. By using a helium atmosphere, a smaller plasma was obtained, reducing the disruptions caused by laser-plasma interactions. This led to a stable melting regime that allowed control of the melt bead profile. This condition was used to study the effect of laser-material fundamental interaction parameters on the bead geometry in powder bed melting. It was found that during melting of single tracks, the dominant regime of melting is conduction for the range of parameters tested. Penetration and melt width were found to increase with increasing energy density. For longer interaction times, melt widths were found to be up to ten times the size of the beam diameter used. Fluid flow modelling showed that this is due to strong melt flow as consequence of surface tension gradients generated by very high temperature gradientsItem Embargo Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy(Springer , 2024-07) Zhang, Tao; Qin, Zhen-yang; Gong, Hai; Wu, Yun-xin; Chen, XinWire-arc additive manufacture (WAAM) has great potential for manufacturing of Al-Cu components. However, inferior mechanical properties of WAAM deposited material restrict its industrial application. Inter-layer cold rolling and thermo-mechanical heat treatment (T8) with pre-stretching deformation between solution and aging treatment were adopted in this study. Their effects on hardness, mechanical properties and microstructure were analyzed and compared to the conventional heat treatment (T6). The results show that cold rolling increases the hardness and strengths, which further increase with T8 treatment. The ultimate tensile strength (UTS) of 513 MPa and yield stress (YS) of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment, which is much higher than that in the as-deposited samples. The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling; while both the T6 and T8 treatments decrease the elongation. The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitated θ′ phases, which inhibits the dislocation movement and enhances the strengths; as a result, T8 treatment shows better strengthening effect than the T6 treatment. The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.Item Open Access Efficient method for variance-based sensitivity analysis(Elsevier, 2018-07-05) Chen, Xin; Molina-Cristobal, Arturo; Guenov, Marin D.; Riaz, AtifPresented is an efficient method for variance-based sensitivity analysis. It provides a general approach to transforming a sensitivity problem into one uncertainty propagation process, so that various existing approximation techniques (for uncertainty propagation) can be applied to speed up the computation. In this paper, formulations are deduced to implement the proposed approach with one specific technique named Univariate Reduced Quadrature (URQ). This implementation was evaluated with a number of numerical test-cases. Comparison with the traditional (benchmark) Monte Carlo approach demonstrated the accuracy and efficiency of the proposed method, which performs particularly well on the linear models, and reasonably well on most non-linear models. The current limitations with regard to non-linearity are mainly due to the limitations of the URQ method used.Item Open Access Efficient reduced-order thermal modelling of scanning laser melting for additive manufacturing(Elsevier, 2023-10-02) Chen, Guangyu; Ding, Jialuo; Sun, Yongle; Chen, Xin; Wang, Chong; Rodrigues Pardal, Goncalo; Williams, StewartAdditive manufacturing (AM) with a scanning laser (SL) to independently control melt pool shape has the potential to achieve part building with high geometric accuracy and complexity. An innovative dynamic convection boundary (DCB) method is proposed to develop a reduced-order finite element (FE) model to accelerate the thermal analysis of a SL process for AM. The DCB method approximates the thermal conduction of the adjacent material around the bead region by using a convection boundary condition that can be dynamically adjusted during the numerical solution. Thereby, a smaller problem domain and fewer elements are involved in the reduced-order FE modelling. A non-oscillating equivalent bar-shaped heat source was also introduced as a simplified substitution for a high oscillation frequency SL heat source. The DCB-based reduced-order thermal model achieved over 99% accuracy compared to the full-scale model but reduced the element amount by 73% and the computational time by 58%. The use of the bar-shaped equivalent heat source can further enhance computational efficiency without compromising the prediction accuracy of a high oscillation frequency SL process. The DCB-based reduced-order thermal modelling method and equivalent heat source could be adopted to boost extensive parametric analysis and optimisation for novel AM processes. Study on large structures AM could also be facilitated by simplifying the computation at critical regions. This study can also enable efficient thermal analyses of different manufacturing processes, such as welding, cladding, and marking.Item Open Access Efficient reduced-order thermal modelling of scanning laser melting for additive manufacturing.(Cranfield University, 2023-09-25 16:20) Chen, Guangyu; Ding, Jialuo; Sun, Yongle; Chen, Xin; Wang, Chong; Rodrigues Pardal, Goncalo; Williams, StewartThermal videos show the dynamic changing of the scanning laser melt pools with different oscillation frequenciesItem Open Access Enablers for uncertainty quantification and management in early stage computational design. An aircraft perspective(2017-10) Chen, Xin; Guenov, Marin D.; Molina-Cristobal, ArturoPresented in this thesis are novel methods for uncertainty quantification and management (UQ&M) in computational engineering design. The research has been motivated by the industrial need for improved UQ&M techniques, particularly in response to the rapid development of the model-based approach and its application to the (early) design of complex products such as aircraft. Existing work has already addressed a number of theoretical and computational challenges, especially regarding uncertainty propagation. In this research, the contributions to knowledge are within the wider UQ&M area. The first contribution is related to requirements for an improved margin management policy, extracted from the FP7 European project, TOICA (Thermal Overall Integrated Conception of Aircraft). Margins are traditional means to mitigate the effect of uncertainty. They are relatively better understood and less intrusive in current design practice, compared with statistical approaches. The challenge tackled in this research has been to integrate uncertainty analysis with deterministic margin allocations, and to provide a method for exploration and trade-off studies. The proposed method incorporates sensitivity analysis, uncertainty propagation, and the set-based design paradigm. The resulting framework enables the designer to conduct systematic and interactive trade-offs between margins, performances and risks. Design case studies have been used to demonstrate the proposed method, which was partially evaluated in the TOICA project. The second contribution addresses the industrial need to properly ‘allocate’ uncertainty during the design process. The problem is to estimate how much uncertainty could be tolerated from different sources, given the acceptable level of uncertainty associated with the system outputs. Accordingly, a method for inverse uncertainty propagation has been developed. It is enabled by a fast forward propagation technique and a workflow reversal capability. This part of the research also forms a contribution to the TOICA project, where the proposed method was applied on several test-cases. Its usefulness was evaluated and confirmed through the project review process. The third contribution relates to the reduction of UQ&M computational cost, which has always been a burden in practice. To address this problem, an efficient sensitivity analysis method is proposed. It is based on the reformulation and approximation of Sobol’s indices with a quadrature technique. The objective is to reduce the number of model evaluations. The usefulness of the proposed method has been demonstrated by means of analytical and practical test-cases. Despite some limitations for several specific highly non-linear cases, the tests confirmed significant improvement in computational efficiency for high dimensional problems, compared with traditional methods. In conclusion, this research has led to novel UQ&M tools and techniques, for improved decision making in computational engineering design. The usefulness of these methods with regard to efficiency and interactivity has been demonstrated through relevant test-cases and qualitative evaluation by (industrial) experts. Finally, it is argued that future work in this field should involve research and development of a comprehensive framework, which is able to accommodate uncertainty, not only with regard to computation, but also from the perspective of (expert) knowledge and assumptions.Item Open Access Enhancing microstructural and mechanical characteristics of laser welded NiTi SMA/304 SS lap joints with medium and high entropy alloy fillers(Springer, 2024-01-03) Wang, Yipeng; Zhang, Dongni; Li, Hong; Li, Zhuoxin; Yang, Zijia; Chen, Xin; Cong, BaoqiangThe demand for high-quality nickel-titanium (NiTi) shape memory alloy (SMA) and stainless steel (SS) welded structures has led to significant challenges in fusion welding technology, which is largely influenced by filler materials. This study explores the application of CoCrNi medium entropy alloy and CoCrNiFe high entropy alloy as filler materials for laser lap welding of NiTi SMA and 304 SS. A self-fusing joint was produced for comparison. The results demonstrate that the interface zone on the NiTi side was the weakest area regarding cracking defects in NiTi/304 SS lap joints. However, using CoCrNi and CoCrNiFe fillers effectively eliminated cracking defects by considerably suppressing the formation of brittle FeTi and Fe2Ti intermetallic compounds (IMCs). The average microhardness value of the weld zone without filler was higher than with CoCrNi and CoCrNiFe. Furthermore, the addition of CoCrNi and CoCrNiFe fillers to NiTi/304 SS lap joints resulted in a substantial increase in tensile properties, with tensile strength reaching 196 ± 39 MPa without filler, 319 ± 25 MPa with CoCrNi, and 377 ± 33 MPa with CoCrNiFe, respectively.Item Open Access Evaluation of a collaborative and distributed aircraft design environment, enabled by microservices and cloud computing(AIAA, 2023-01-19) Chen, Xin; Isoldi, Adriano; Riaz, Atif; Mourouzidis, Christos; Keskin, Akin; Smith, Dale; Guenov, Marin D.; Pachidis, VassiliosPresented in this paper are the outcomes from the evaluation of a distributed aircraft design environment, based on microservices and cloud computing. The evaluation was performed on a representative airframe-engine optimization case study, including the engine, wing aero-structural geometry, and high-lift devices. The (computational) design process involved multiple distributed design teams and design tools. The latter were implemented with different programming languages and deployed on the Azure cloud service. As a benchmark, the same case study was performed using the traditional email/document-based approach to design collaboration. Compared with the traditional collaboration, the cloud-based approach substantially reduced the time for design iterations between the design teams. This was mainly due to the fast remote access of models/tools on the cloud and automation of data exchange. Also, the exercise indicated that the cloud-based approach is more flexible with regard to orchestrating the computational workflows and optimization studies, while protecting the Intellectual Property (IP) of the collaborating partners.Item Open Access Framework for multi-fidelity assessment of open rotor propeller aeroacoustics(AIAA, 2024-05-30) Huang, Guangyuan; Sharma, Ankit; Chen, Xin; Riaz, Atif; Jefferson-Loveday, RichardAerodynamically generated noise from open rotor aircraft has received immense research interests. Multi-fidelity numerical approaches are in demand for evaluating open rotor propeller noise without compromising computational accuracy and reducing cost. In this paper, propeller noise modelling methods at different fidelity levels are assessed by application to an aircraft propeller configuration at an advance ratio of 0.485 together with tip Reynolds and Mach numbers of 3.7×10^5 and 0.231, respectively. The flow solution of the propeller is obtained using coarse-grid Large Eddy Simulation and then inputted into three acoustic solvers. At higher-fidelity level, Ffowcs-Williams and Hawkings analogy method is employed. Hanson’s method and Gutin’s method are applied at the medium- and lower -fidelity levels, respectively. Results from the three models are compared correlatively, as well as against existing experimental measurement data. Through the assessment, insight is given into future development of a multi-fidelity model for low-emission open rotor aircraft design. The presented multi-fidelity framework is being developed as part of the Innovate UK, Aerospace Technology Institute (ATI) funded research project – ONEheart (Out of Cycle NExt generation highly efficient air transport).Item Unknown Framework for multi-fidelity simulations of flow interaction and noise of an open rotor(American Institute of Aeronautics and Astronautics (AIAA), 2025-01-06) Huang, Guangyuan; Sharma, Ankit; Chen, Xin; Jimeno, Sergio; Riaz, AtifFlow-induced noise from open rotor aircraft has received immense research interests as the flow interactions of the components of open rotors lead to significant non-linear features and the flow-induced noise is complicated. Numerical approaches for predicting open rotor flow interactions and the induced noise are in demand without compromising computational accuracy and reducing cost. In this paper, an existing multi-fidelity framework for propeller noise modelling is extended to open rotor configuration. A generic contra-rotating open rotor (CROR) configuration is developed to assess the capability of this multi-fidelity framework. The flow and noise of this configuration are modelled separately in hybrid manner. The flow solution is computed using two methods, which employ unsteady Reynolds average Navier-Stokes (URANS) equations and lattice-vortex method (VLM) at respectively higher- and lower-fidelity levels. Then, the acoustic solution is computed based on the flow solution using Gutin’s method. Results show that transonic features over the rotor blades and significant tip vortices in the wake characterise the CROR flow. Multi-rotor interactions are observed. The aerodynamic loadings are investigated in terms of their mean and fluctuating components. In addition, the far-field noise from the two rotors are compared. The present multi-fidelity framework will be used in future aircraft design which involves open rotor engines. This work is being administered as part of the Innovate UK, Aerospace Technology Institute (ATI) funded research project - ONEheart (Out of Cycle NExt generation highly efficient air transport).Item Unknown Grain refinement and mechanical properties improvement of additively manufactured Al-Cu alloy through pre-deformation in thermo-mechanical treatment(Elsevier, 2024-11) Zhang, Tao; Chen, Junwen; Gong, Hai; Wu, Yunxin; Chen, XinInferior mechanical properties induced by porosity and coarse grains of wire-arc additively manufactured Al-Cu alloy restrict its industrial application. The inter-layer cold rolling, conventional heat treatment (T6) and thermo-mechanical heat treatment (T8) was applied to Al-Cu alloy, and the effect of pre-stretched strain in T8 treatment was investigated. The pre-stretched strain induces equal increments of hardness and YS for both the as-deposited and cold-rolled conditions before aging treatment, while the increments for cold-rolled samples are larger after aging treatment. The cold-rolled sample shows better tensile properties than the as-deposited sample with the same pre-stretched strain in T8 treatment, proving that T8 treatment further increased the strengths compared to the T6 treatment. It shows the best tensile properties with the pre-stretched strain of 5 %, exceeding the properties of 2219-T87 plate. With the increased pre-stretched strain, the density of the θ′ phases significantly increases; while further increase to 10 % pre-stretched strain induces severe coarsening of θ′ phases. Therefore, an optimized pre-stretched strain leads to high-density and tiny dispersed θ′ phases, thus resulting in the best tensile properties. Grain refinement induced by inter-layer cold rolling and uniformly precipitated phases resulted from proper pre-stretched strain both contribute to the strengths enhancement. The strengthening mechanism of hybrid additive manufacturing and inter-layer cold rolling followed by T8 treatment was discussed.Item Unknown Influence of low-pulsed frequency on arc profile and weld formation characteristics in double-pulsed VPTIG welding of aluminium alloys(Elsevier, 2020-09-21) Wang, Yipeng; Cong, Baoqiang; Qi, Bojin; Chen, Xin; Yin, Yuhuan; Lin, SanbaoAA2219 aluminium alloy plates were processed by double pulsed variable polarity tungsten inert gas (DP-VPTIG) welding, and the influence of low-pulsed frequency on arc profile, weld appearance and penetration characteristics were investigated. An image processing algorithm was proposed for arc edge extraction and arc feature sizes acquisition. The arc energy equations in low-frequency pulse peak stage (tp) and base stage (tb) were established based on the electrical parameters. The arc profile periodically expanded in tp and shrunk in tb, resulted from the difference in arc energy of the two stages. The pulsation effects in arc profile, weld appearance and penetration, caused by the pulsed arc were observed to exhibit a decreasing trend with the increase of low-pulsed frequency (fL). The pulsation effects were obvious when fL was 0.5 Hz, then became weak and tended to disappear as fL increased above 3 Hz. The empirical correlations between fL and the pulsation effects of arc profile, weld appearance and penetration were respectively developed. It is recommended to use fL in the range of 1–2 Hz to properly exert the low-frequency pulsation effect. The results provide a valuable basis for controlling and optimizing the DP-VPTIG process in the high efficiency welding of aluminum alloysItem Unknown Interactive uncertainty allocation and tradeoff for early-stage design of complex systems(AIAA, 2019-11-20) Molina-Cristobal, Arturo; Chen, Xin; Guenov, Marin D.; Riaz, Atif; van Heerden, Albert S. J.A common probabilistic approach to perform uncertainty allocation is to assign acceptable variability in the sources of uncertainty, such that prespecified probabilities of meeting performance constraints are satisfied. However, the computational cost of obtaining the associated tradeoffs increases significantly when more sources of uncertainty and more outputs are considered. Consequently, visualizing and exploring the decision (trade) space becomes increasingly difficult, which, in turn, makes the decision-making process cumbersome for practicing designers. To address this problem, proposed is a parameterization of the input probability distribution functions, to account for several statistical moments. This, combined with efficient uncertainty propagation and inverse computation techniques, results in a computational system that performs order(s) of magnitude faster than a state-of-the-art optimization technique. The approach is demonstrated by means of an illustrative example and a representative aircraft thermal system integration example.Item Unknown Laser induced arc dynamics destabilization in laser-arc hybrid welding(IOP, 2019-12-05) Mu, Zhongyan; Chen, Xin; Hu, Renzhi; Lin, Sanbao; Pang, ShengyongThe interaction between laser and arc plasma is a central issue in laser-arc hybrid welding. We report a new interaction phenomenon called laser destabilizing arc dynamics in kilowatt fiber laser-TIG hybrid welding of 316L stainless steel. We found the laser action significantly oscillates the arc tail with a 1–3 kHz high frequency. Direct numerical simulation demonstrates that the destabilization mechanism is due to the high-speed oscillated metal vapor ejecting from the mesoscopic keyhole. More interestingly, the high-speed metal vapor could contrict the arc plasma by physical shielding. This provides a fundamentally different explanation from the generally adopted metal vapor ionization theory for laser constrict arc plasma phenomenon. Also, the results substantiate that the arc plasma cannot easily enter into the keyhole because of the violent metal vapor.