Laser induced arc dynamics destabilization in laser-arc hybrid welding

The 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

Influence of low-pulsed frequency on arc profile and weld formation characteristics in double-pulsed VPTIG welding of aluminium alloys

AA2219 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 alloy

Influence of early use of sodium-glucose transport protein 2 inhibitors, glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors on the legacy effect of hyperglycemia

BackgroundA phenomenon known as legacy effect was observed that poor glycemic control at early stage of patients with newly-diagnosed type 2 diabetes (T2D) increases the risk of subsequent cardiovascular diseases (CVD). Early use of some novel anti-hyperglycemic agents, such as sodium-glucose transport protein 2 inhibitors (SGLT-2i), may attenuate this effect, but the evidence is limited.MethodsTwo retrospective cohorts of newly diagnosed T2D patients from 2010–2023 were assembled using the Yinzhou Regional Health Care Database (YRHCD) with different definitions of the early exposure period - the 1-year exposure cohort and 2-year exposure cohort, which were comprised of subjects who had HbA1c measurement data within 1 year and 2 years after their T2D diagnosis, respectively. Using Cox proportional hazards models, we examined the association between high HbA1c level (HbA1c>7%) during the early exposure period and the risk of subsequent CVD. This analysis was performed in the overall cohort and three subpopulations with different treatments during the early exposure period, including patients initiating SGLT-2i or glucagon-like peptide-1 receptor agonists (GLP-1RA), patients using dipeptidyl peptidase-4 inhibitors (DPP-4i), and patients without using SGLT-2i, GLP-1RA, and DPP-4i. Besides, subgroup analyses were performed by stratifying patients into age <55 and ≥55 years.ResultsA total of 21,477 and 22,493 patients with newly diagnosed T2D were included in the two final cohorts. Compared with patients with mean HbA1c ≤ 7% during the early exposure period, those with HbA1c>7% had higher risks of incident CVD, with a HR of 1.165 (95%CI, 1.056–1.285) and 1.143 (95%CI, 1.044–1.252) in 1-year and 2-year exposure period cohort. Compared to non-users, in patients initiating SGLT-2i/GLP-1RA within 1 or 2 years after T2D diagnosis, higher HbA1c level at baseline was not associated with CVD in both two cohorts. In subgroup analyses, results were generally consistent with the main analysis.ConclusionsPoor glycemic control in the early stage of T2D increased later CVD risk in Chinese adults with newly diagnosed T2D. Compared to non-users, this association was smaller and non-significant in patients receiving SGLT-2i/GLP-1RA during the early stage of T2D, indicating early use of these drugs may have the potential to mitigate legacy effects of hyperglycemia

Molten Pool Behaviors in Double-Sided Pulsed GMAW of T-Joint: A Numerical Study

The T-joint is one of the essential types of joints in aluminum welded structures. Double-sided welding is a preferable solution to maintain high efficiency and avoid significant distortion during T-joint welding. However, interactions between double-sided molten pools make flow behaviors complicated during welding. Numerical simulations regarding molten pool behaviors were conducted in this research to understand the complex flow phenomenon. The influences of wire feed rates and torch distances were simulated and discussed. The results show that droplet impinging drives the fluid to flow down to the root and form a frontward vortex. Marangoni stress forces the fluid to form an outward vortex near the molten pool boundary and flatten the concave-shaped molten pool surface. With an increased wire feed speed, the volume of the molten pool increases, and the root fusion is improved. With an increased torch distance, the width of the front molten pool decreases while the length increases, and the rear molten pool size decreases slightly. Both wire feed speeds and the torch distances have limited influences on the basic flow characteristics

Effect of process modes on microstructure and mechanical properties of CMT wire arc additive manufactured WE43 magnesium alloy

The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %

The Effect of Martensitic Phase Transformation Dilation on Microstructure, Strain–Stress and Mechanical Properties for Welding of High-Strength Steel

The application of low transformation temperature (LTT) wire can effectively reduce residual stress, without the need for preheating before welding and heat treatment after welding. The mechanism reduces the martensitic transformation temperature, allowing the martensite volume expansion to offset some or all of the heat-shrinking, resulting in reduced residual stress during the welding process. In this paper, commercial ER110S-G welding wire and LTT wire with chemical composition Cr10Ni8MnMoCuTiVB were developed to solve the problem of stress concentration. The microstructure of the LTT joint is mainly composed of martensite and a small amount of residual austenite, while the microstructure of the ER110S-G joint is mainly composed of ferrite and a small amount of granular bainite. The micro-hardness and tensile strength of the LTT joint is higher than that of ER110S-G joint; however, the impact toughness of the LTT joint is not as good as that of the ER110S-G joint. The martensitic phase transformation of LTT starts at 212 °C and finishes at around 50 °C, and the expansion caused by phase transition is about 0.48%, which is much higher than that of the base metal (0.15%) and ER110S-G (0.18%). The residual tensile stress at the weld zone of the ER110S-G joint is 175.5 MPa, while the residual compressive stress at the weld zone of LTT joint is −257.6 MPa

Ride comfort optimization of a multi-axle heavy motorized wheel dump truck based on virtual and real prototype experiment integrated Kriging model

The optimization of hydro-pneumatic suspension parameters of a multi-axle heavy motorized wheel dump truck is carried out based on virtual and real prototype experiment integrated Kriging model in this article. The root mean square of vertical vibration acceleration, in the center of sprung mass, is assigned as the optimization objective. The constraints are the natural frequency, the working stroke, and the dynamic load of wheels. The suspension structure for the truck is the adjustable hydro-pneumatic suspension with ideal vehicle nonlinear characteristics, integrated with elastic and damping elements. Also, the hydraulic systems of two adjacent hydro-pneumatic suspension are interconnected. Considering the high complexity of the engineering model, a novel kind of meta-model called virtual and real prototype experiment integrated Kriging is proposed in this article. The interpolation principle and the construction of virtual and real prototype experiment integrated Kriging model were elucidated. Being different from traditional Kriging, virtual and real prototype experiment integrated Kriging combines the respective advantages of actual test and Computer Aided Engineering simulation. Based on the virtual and real prototype experiment integrated Kriging model, the optimization results, obtained by experimental verification, showed significant improvement in the ride comfort by 12.48% for front suspension and 11.79% for rear suspension. Compared with traditional Kriging, the optimization effect was improved by 3.05% and 3.38% respectively. Virtual and real prototype experiment integrated Kriging provides an effective way to approach the optimal solution for the optimization of high-complexity engineering problems

Effect of External Magnetic Field on the Forming, Microstructure and Property of TC4 Titanium Alloy during the Directed Energy Deposition Arc Additive Manufacturing

In this work, the thin wall components of TC4 titanium alloy were produced by using external magnetic field hybrid gas metal welding (EM-GMAW). The effect of the external magnetic field on the forming, microstructure, and property of wire arc additively manufactured TC4 titanium alloy was studied in detail. The results showed that the height of the average deposition layer of EM-GMAW was less than that of GMAW and decreased with the increase of magnetic excitation current, and the width of the average deposition layer of EM-GMAW was greater than that of GMAW. The microstructure of the deposition layer consisted of fine α phase and coarse β grains. Compared with the traditional GMAW, the coarse β grain size in the EM-GMAW was reduced obviously. The maximum size of β grain was decreased by 100μm when the magnetic excitation current of 3A was used. In addition, the EM-GMAW tensile strength in the transverse and horizontal was increased by around 20 MPa and 100 MPa, respectively, compared with that of GMAW

Characteristics of Periodic Ultrasonic Assisted TIG Welding for 2219 Aluminum Alloys

Tungsten inert gas (TIG) arc welding of 2219 aluminum alloy was assisted with a trailing periodic ultrasonic vibration, which was output from a trailing roller behind the welding torch. It was found that the weld appearance was periodically convex due to the periodic input of ultrasonic vibration. With the addition of ultrasonic vibration, the columnar grains in the weld zone transformed to equiaxed grains, so along the longitudinal direction, the equiaxed grains and the columnar grains were alternately distributed due to the periodic ultrasonic vibration. The effects of different ultrasonic powers were investigated. The penetration depth and the amount of the melting metal both increased as the ultrasonic power increased. The coarse precipitated phases in the weld zone tended to disperse uniformly under ultrasonic vibration. Compared with conventional TIG welded joints, the hardness of the weld zone of the ultrasonic assisted TIG welding increased by 8.43%, and the tensile strength increased by 29.02%. The ultrasonic cavitation could decrease the nucleation radius and break the dendrites, which led to the grains’ refinement and the final mechanical properties’ improvement