Welding in the World最新文献

The present study deals with the adhesive selection for extrusion-based 3D-printed parts. The compatibility of acrylate (AC), polyurethane (PU), methyl methacrylate (MM) and epoxy (EP) adhesives with polylactic acid (PLA), polyethylene terephthalate glycol (PETG), acrylonitrile butadiene styrene (ABS), and acrylonitrile styrene acrylate (ASA) adherends was investigated. Tensile tests were conducted to provide enhanced knowledge on the failure behavior of these joints. Taguchi L16 orthogonal array and analysis of variance (ANOVA) were used to the design of experiment (DOE) and to identify the contribution of each parameter on the response, respectively. In addition, a closed-form solution of critical stress (peel and shear stresses) distributions along the bondline was used to gain a better insight into the failure mechanism of joints considered in this study. The ANOVA results showed that the effect of adhesive type is clearly the most important factor influencing the joint strength, followed by the adherend type. Statistically, the contribution of the adherend type (5.28%) is also important, but it is smaller than the contribution of the adhesive type (91.60%). The highest joint strength was obtained for PETG bonded with MM adhesive. In the case of PU, EP, and AC adhesives, the maximum load-carrying capacity was reached using PLA adherends. ASA showed the lowest joint strength for all adhesive types. This research provides comprehensive knowledge, allowing designers to select an appropriate adhesive for custom or industrial bonding applications without time-consuming surface treatments.

High-strength steel welds are typically not known to be susceptible to Solidification Cracking (SC). However, modern light-weight constructions may force welding in highly restrained conditions, which are known to increase the probability of Solidification Crack (SC) emergence. In this article, the Modified Varestraint-Transvarestraint (MVT) test was used to evaluate the hot cracking susceptibility of welds made from high-strength, low-alloyed filler material. The materials tested include solid wires and a metal-cored wire. All wires are typically used in the Gas Metal Arc Welding (GMAW) process. Susceptibility to SC was measured over a wide range of welding parameters and bending speeds. Results show little affinity of the tested materials to SC. However, crack length increases in most cases with arc energy ((text{U}bullet text{I}/text{welding speed})) and welding speed. The length of the longest crack in one test specimen follows a similar trend until high welding speeds, where stagnation of crack length with changing arc energy was observed.

NiTi shape memory alloys exhibit pseudoelasticity, allowing them to fully recover from prior deformations under varying thermal or mechanical loads. Unlike conventional materials like steels, these alloys can endure elastic strain rates up to ten times higher, owing to a diffusion-free transformation between the austenite and martensite phases in their crystal lattice induced by temperature or stress. Given their material properties, NiTi shape memory alloys find applications as actuators, implants, and stents, demanding high reliability and biocompatibility standards. To maintain maximum pseudoelasticity when joining NiTi components, any microstructural changes have to be kept to a minimum. In this regard, vacuum brazing is a promising joining technique, as it is capable to produce joints at comparatively low joining temperatures without melting the base material. Hence, this paper is aimed at evaluating the influence of different holding times and brazing temperatures on the deformation behavior of NiTi alloys in vacuum brazing applying AgCuTi braze alloy. For this purpose, microstructural analyses by means of SEM and EDS as well as tensile tests were conducted. Furthermore, the fracture surfaces were analyzed by SEM. It could be observed that a stress plateau was present in the brazed samples leading to the assumption that brazing with AgCuTi is a suitable joining technique to preserve the properties of NiTi. Nevertheless, the brazed samples fractured in the stress plateau. 

In V groove butt welding with a ceramic backing material, the molten pool should penetrate well. Regardless of the gap fluctuations, the molten pool must maintain a good penetration shape. For this purpose, the molten pool state is detected using ResNet50 as one of the deep learning. The molten pool using a CMOS camera is taken. Fundamental experiments are performed, and images are collected for learning of ResNet50. Good estimation results are obtained for untraining data. The gap and its center are detected processing the molten pool images. The seam tracking is carried out using PI controller, with inputs being the difference between the wire tip and the gap center, and the output is Y axis position. The weaving width is adjusted to fit the gap. The molten pool state is controlled adjusting the travel speed of the welding torch, to keep constant the arc position, because the state of the molten pool depends on the arc position. If there is gap fluctuation as the disturbance and the reference of the arc position is same, it is difficult to get the same penetration of the molten pool. Therefore, the reference according to the output of ResNet50 is adjusted. Molten pool control is based on PI controller with the input is the difference between the arc position and its reference, and the output is the travel speed. The control performance is verified in a case where the gap varies from 7 to 3 mm, and good results are obtained.

Welding of dissimilar alloys is challenging due to differences in their physical and chemical properties. The main problem while joining dissimilar alloys is intermetallic compound (IMC) formation, which affects the weld quality. Controlling the heat input is necessary to minimize the formation of IMC. This work uses cold metal transfer (CMT) welding with low heat input. However, the application of CMT welding is limited to thin sheets due to low depth of penetration (DOP). Activated flux can improve the performance of CMT welding, thus improving the DOP and minimizing the weld width (WW) by arc constrict mechanism. In this investigation, the SiO₂ was used as an activated flux. The process parameters used in this study are welding current and welding speed, which were used to optimize tensile strength, hardness, DOP/WW ratio, and heat input. Numerous experiments were conducted as per the design of experiment using response surface methodology. The optimal input parameters from various experiments are a welding current of 150 A and a welding speed of 8.295 mm/s. The scanning electron microscope was used to analyze the microstructure of weld specimens. Energy dispersive spectroscopy and X-ray diffraction were used for elements and phase analysis.

The local geometry of the weld toe or the weld seam has a high influence on the fatigue strength of welded joints. Two main parameters for the geometrical description of the weld toe are the weld toe radius and the weld toe angle. Currently, there is no uniform definition or standardized measurement approach for the assessment of these parameters. For this reason, the presented extensive round-robin (RR) study focusses on the influence of different evaluation techniques and measurement systems regarding the mentioned parameters based on 3D surface scans. In total, 20 participants take part in this two stage RR (19 participants in the second part). In this work, the results of the second part (part B) of the RR, namely the evaluation of weld toe radius and weld toe angle on real welded joints, are presented, where the actual weld toe geometry is not known a priori. For this, 22 data sets were evaluated. The data sets consist of measured values for the radius and angle of the weld toe in relation to the position along the weld seam. In general, significant variations are determined for the evaluated weld geometry parameters, especially for the weld toe radius. It is also shown that the condition of the weld toe transition has a high influence on the parameter. Particularly for weld seams with a low weld toe angle, the measurement results for the radius of the individual participants show high variations. For small weld toe radii, the results are quite comparable between the participants. The results for the weld toe angle are comparable for flat welds, but a wide range of results is observed for sharp weld toes. The degree of automation of the measurement method also has a high influence on the results. The most accurate results are expected from manual measurements, while the fully automatic and semi-automatic methods show larger deviations.

The paper presents the results of research on artwork joints of considerable thickness (10 mm). Butt welds in artworks are always difficult to perform because access to the joint is often one-sided. Traditional arc welding technologies are of limited use for such one-off production tasks, as full access to the joint is required and after welding the bulge must be cleaned from all sides of the bar, which is often unacceptable. Existing brazing technologies require a controlled gap between the joining surfaces, which is impossible to achieve for a wide variety of joints in art designs. Increasing the gap results in a decrease in the mechanical properties of the structure. A synergistic combination of welding and brazing using TIG technology can ensure a high-quality joint for thick bars of art structures. For such joints and conditions, the technology of high-temperature arc (TIG) brazing with partial melting of the parts to be joined and subsequent introduction of brazing alloy (CuSi3) into the metal pools of the parts to mix the liquid metal of the parts and the brazing alloy was developed. The developed technology makes it possible to fill the gap between the surfaces of bar-type parts with one-way access in the flat position, with minimal need to clean up solder that has protruded beyond the part.

In hybrid additive manufacturing, components or semi-finished products manufactured by conventional primary forming are enhanced or modified by additive manufactured structures. However, systematic investigations focusing on the critical transition area between the specific properties of the substrate (like high-strength) and the additively manufactured component, made of specific filler material, are still lacking. The focus of the present study was to determine the influence of heat control on the ∆t_8/5 cooling time, the distortion, the mechanical properties, and the residual stresses in the transition area of hybrid-additive components. This contributed to the knowledge regarding the safe avoidance of cold cracking, excessive distortion, a reduction in yield stress, and the implementation of hybrid DED-arc manufacturing. The heat control was varied by means of heat input and working temperature such that the ∆t_8/5 cooling times corresponded to the recommended processing range. The heat input has a greater influence on the cooling time in the transition area than the working temperature. Working temperature and the total energy applied per layer have a significant effect on component distortion. The lowest working temperature of 100 °C in combination with the highest total energy per layer leads to significantly greater distortion compared to manufacturing with a high working temperature of 300 °C and low total energy per layer. In addition, the longitudinal residual compressive stresses in the sensitive transition area are reduced from − 500 MPa to approx. − 200 MPa by adjusting the working temperature from 100 to 300 °C. Such complex interactions must be clarified comprehensively to provide users with easily applicable processing recommendations and standard specifications for an economical hybrid additive manufacturing of components made, for example, of high-strength steels in the transition area.

Joining of dissimilar AZ31 Mg alloy and Cu- 8Zn alloy by using zinc interlayer through Friction Stir Welding (FSW) has been studied for the first time. The process parameters include 1200 rpm rotational speed and 20 mm/min traverse speed. Microstructural characterizations were performed to study material flow behavior, grain refinement and IMCs formation whereas, mechanical characterization includes hardness and tensile tests. SEM EDS and XRD were used for identification of phases and fracture behavior. The study revealed that for direct joining of Mg/Cu, the stir zone (SZ) mainly consisted of two-phase region containing δ-Mg and Mg₂Cu along with fragments of Cu particles. Small amount of MgCu₂ was also observed in the form of intercalated layer along with Cu. Voids and tunnelling defects were also observed. On the other hand, the application of Zn interlayer has completely modified the structure of SZ which contains well distributed mixture of δ-Mg and MgZn. A very thin layer of MgZn₂ and MgO was observed in the SZ. Average tensile strength of Mg/Cu with Zn interlayer has improved to 93 MPa which is the highest joint strength as compared to the previously reported joint strength of Mg/Cu weld.