Welding in the World最新文献

This study addresses the effects of alloying elements and radius curvature of the electrode on the degradation behavior during resistance spot welding (RSW) of A6451-T4. The importance of electrode characteristics is emphasised according to changes in hardness and electrical conductivity by electrode composition and radius curvature. The electrodes that were alloyed with Ag, Cr, and Be with varied radii were used in this study. The endurance limit of electrode was investigated by producing 100 welds with the optimised welding parameters. In addition to mechanical characterisation of the weld samples, comprehensive analyses of the electrode surfaces were carried out by carbon imprint, 3D digital microscope profiling, and electron microscopy. A computational analysis using the commercialised SORPAS software was also conducted to analyse heat generation according to the electrode characteristics. The results demonstrate that the electrode degradation proceeds by four discrete stages: aluminum pick-up and alloying, contact area increase, pitting, and cavitation. It was confirmed that load-bearing capacity and nugget diameter also change in proportion to the generated heat between the electrode and welded sheet. Among the physical properties of the electrode, the hardness and electrical conductivity most influence the electrode wearing behavior.

Proper parameter selection is crucial for obtaining the required shape of the beads and reducing defects like uneven welds, cracks, porosity, and irregularities while creating wire arc additive manufacturing (WAAM) samples. This study aims to investigate the impact of three input process parameters (current, welding speed, and gas flow rate) at three different levels on the properties (weld bead width, bead height, and dilution) of samples made from aluminum 4047 using the CMT-WAAM process. The study will analyze the data using response surface methodology (RSM). A central composite design (CCD) matrix was employed to develop a design of experiment incorporating three process factors. The appropriateness of the design was assessed by ANOVA analysis. The upper limits for the height and penetration of the weld bead were 2.83 mm and 3.12 mm, respectively. The lowest level of width measured was 9.44 mm. The forecasted ideal input parameters were a current of 150 A, a welding speed of 50 cm/min, and a shielding gas flow rate of 15 l/min. The findings demonstrated that the current exerted the most significant impact on determining the various responses, with welding speed and gas flow rate being the subsequent influential factors. The microstructures were analyzed using optical microscopy, revealing that the microstructure of the wall region comprised columnar and equiaxed grains. This study has considerable potential for manufacturing aluminum items utilizing a CMT-based arc welding technique.

Graphical Abstract

In this paper, the results of microstructural analyses, including optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analysis, of the Ni-based self-fluxing alloys NiCrBSi, NiCrBSi–WC, and NiBSi–WC deposited on a previously quenched and tempered (QT) steel substrate 42CrMo4 by flame spraying with simultaneous fusing and plasma transferred arc (PTA) process are presented. The aforementioned microstructural analysis was carried out to determine the microstructural characteristics of the investigated coatings, especially at the coating/substrate interface, and the influences of the spraying and welding technology on the steel substrate. The analysis revealed a change in the microstructure of the coating/substrate interface. Specifically, the diffusion characteristics of certain chemical elements (carbon and iron) from the coating to the substrate and from the substrate to the coating were observed. Additionally, the analysis established the existence of new phases within the coating that arose as a result of the aforementioned diffusion and reaction with chemical elements from the coating. The diffusion of chemical elements was most pronounced in the area of the coating/substrate interface, while it decreased away from this area.

Friction Stir Processing (FSP) is an innovative and promising technique for microstructure refinement, material property enhancement, and surface composite production. The current study describes the fabrication of AA8090/boron carbide surface composites (SCs) by FSP. Experimental studies were conducted by varying the FSP parameters, specifically the rotational speed (800–1400 rpm), traverse speed (25–75 mm/min), and groove width (1–1.8 mm). Ultimate Tensile Strength (UTS), Surface Roughness (SR), and Percentage Elongation (El) were used as response measures. Experiments were planned based on the central composite design (CCD) of Response Surface Methodology (RSM) and a mathematical relationship between the input parameters and UTS, SR and El, and were obtained by RSM. The model adequacy was tested using analysis of variance (ANOVA). The models enabled the examination of individual and interaction effects of input parameters on the UTS, SR, and El of the produced SCs. AA8090/boron carbide SC strength was optimal of 366 MPa at 800 rpm, 75 mm/min, and 1.8 mm and optimal 21.13% elongation at 1400 rpm, 25 mm/min, and 1 mm. A smoother surface with 0.82-μm roughness was optimal at 1400 rpm, 25 mm/min, and 1.2 mm. The present study uses the FSP method to synthesize near-net-shaped SCs without further machining by systematically selecting process parameters. The study shows that the increase in rotational speed during AA8090/boron carbide SC fabrication produces composites with a good surface finish, lower UTS, and good ductility. However, the increase in the other two parameters, namely, traverse speed and groove width, produces low ductile composites with rougher surfaces and higher strengths.

Graphical abstract

This paper examines the issue of wire deflection in wire and arc additive manufacturing (WAAM) and robotic welding, which leads to process instability and defects in printed geometry. The study focuses on the deflection of alloy 625, alloy 718, and 3Si1 welding wires during the deposition process. Measurements were taken to determine the relationship between wire deflection and the amount of wire used. Regression models were developed for each material to predict initial wire deflection and changes in deflection due to contact tip wear. The results showed that the deflection of alloy 625 and alloy 718 wires followed a nonlinear pattern for the first 500 m of wire, while the deflection of 3Si1 wire followed a nearly linear trend. The intensity of the contact tip wear is dependent on the normal contact load, which decreases as the wear increases. A generalized regression model of wire deflection was constructed based on the obtained regressions and the study of the wire’s deformed state. Based on these models, an algorithm was developed to correct the wire deflection by adjusting the tool center point coordinates. The effectiveness of the developed algorithm was verified in practice.

The weld of resistance projection welded joints is not visible from outside. Therefore, visual evaluation is restricted, and visual inspection is not possible at all. So far, the parameters of the welding process are monitored and controlled. In addition, the welds are periodically tested destructively to determine the quality of the welds. No industrial standard has yet been established in the field of non-destructive testing (NDT) for projection welded joints. This study focuses on NDT of projection welds using two different ultrasonic imaging inspection systems and the passive magnetic ux density testing (pMFT) method. The ultrasonic inspection systems commercially available and established in the field of NDT of spot welds. Both systems are originally designed for the NDT of spot welds and not for projection welds. Unlike the ultrasonic systems, the pMFT is still in laboratory status. The method has originally been developed to evaluate spot welds and is also used in this study to evaluate projection welds. The applicability of the investigated systems to projection welding is investigated in order to derive mandatory development steps to achieve reliable results. The pMFT method shows also good results for NDT of spot welds In this contribution, the measurement and evaluation concept of the three NDT systems for projection welded joints is presented. The NDT results are discussed in the context of the corresponding destructive results in terms of tensile forces and fracture areas. Advises for further development of all investigated systems are given.

A three-dimensional transient model of gas metal arc welding (GMAW) process including the arc plasma and droplet transfer was established to investigate the complex coupling mechanism of mass transfer, heat transfer, electromagnetism, and hydrodynamics. The arc shape, current density, temperature field, electromagnetic force, arc pressure and droplet behavior were analyzed. The results showed that the iron vapor generated on the droplet surface and diffused in the arc, which changed the plasma thermal-pressure distribution. The upward surface tension maintained the forming droplet at the wire tip. The electromagnetic force promoted necking, resulting in a decrease in surface tension. Gravity and plasma drag force accelerated the droplet. The behaviors of the inner arc layer varied periodically with the droplet transfer, while the arc periphery remained stable. Droplet transfer was the result of periodic changes in the resultant of all external forces over time, which also led to periodic changes in arc behavior. This study laid the foundation for further research on the influence of arc and droplet behaviors on the weld pool.

Graphical Abstract