Journal of Advanced Joining Processes最新文献

Transmission Laser Welding (TLW) is a promising technique for joining thermoplastic and composite components, especially those produced through additive manufacturing or 3D printing processes. However, achieving optimal welding quality and efficiency in TLW of 3D printed parts is challenging due to the presence of highly heterogeneous and anisotropic materials, which introduce light scattering and absorption issues. Light scattering is caused by the refraction phenomenon. These phenomena significantly impact the laser intensity profile within the materials and at the welding interface, thereby affecting the energy required for successful welding and the mechanical strength of the final assembly. In this paper, we present an in-depth investigation into the laser intensity profile and the effects of laser-matter interaction on the welding of 3D-printed parts. Our approach combines experimental measurements using a heat flux sensor and an analytical inverse model to measure the laser intensity distribution within the materials at the welding interface. The results obtained from the experimental measurements and numerical identification are compared and analyzed, providing insights into the laser intensity profile in TLW of 3D printed parts.

Modern vehicles as well as structures consist more and more often of a multi material mix. In addition to the use of light materials (e. g. aluminium) to optimise lightweight construction potential, higher strength alloys are being used more and more frequently. With the different material combinations, the requirements for the joining technology also increase. Thus (due to restrictions in the area of thermal joining processes) the joining of different material combinations is often realised by mechanical joining technology. Even though different joining tasks (dissimilar material or sheet thicknesses) can be solved by mechanical joining technology in general, it is often required to switch between appropriate auxiliary joining elements and even joining technique. To adapt the auxiliary elements to the individual requirements of each joint an innovative manufacturing process of customisable auxiliary joining elements has been developed. The use of the incremental, thermomechanical manufacturing process called friction-spinning for the manufacturing of adaptive auxiliary joining elements enables to individualise each element for the subsequent joining process. However, this advantage comes at the cost of a high mechanical and thermal loads on the forming tools. These loads also depend on the process design (trajectory, feed, rotational speed) and have to be controlled in order to improve the tool life. For a more profound process knowledge and to better understand the corellation of the individual process variables, a series of tests with varying process parameters were carried out in a partial factorial design of experiments. The results show not only an possible improvement in the tool life, but also the required process design for a higher reproducibility of the auxiliary joining element geometry and the possibility of positively influencing the geometry to achieve a force-closure of the joint.

This paper introduces a novel joining process for producing hybrid metal-polymer joints. The process, called hole hemming, involves deforming the metal sheet to establish a mechanical interlock with the polymer sheet, requiring neither heating nor auxiliary elements. The applicability of this process is tested for joining aluminum and polycarbonate (PC) sheets. Initially, an analytical design method is presented to achieve a connection without failure and with a mechanical interlock. Subsequently, the accuracy of the predictions is assessed through experiments and finite element simulations, employing the modified Mohr-Coulomb criterion for the prediction of ductile damage. Additionally, a new design for hole-hemmed joints, involving the incorporation of branches in the hole of the outer sheet, is introduced to expand the process window of this novel joining technology. Finally, the mechanical behavior of four different types of hybrid hole-hemmed joints (HHH joints) are evaluated through single-lap shear tests. The results show that the hole hemming process can successfully join AA6082-T4 and PC sheets, validating the proposed designs and ideas. The new hybrid joints demonstrate a maximum force and displacement of 1.6 kN and 12.9 mm, respectively, in the shear test, indicating significant potential of the proposed technology for joining metal and polymer sheets.

Utilizing pulsed lasers in favor of a continuous wave in laser beam welding is a well-established method to achieve higher process efficiency and reduce heat input into the workpiece, which is especially useful for thin-walled workpieces (Steen, 2005). In addition, pulsed processes have shown to lead to smaller grain sizes due to higher cooling rates, which can lead to a reduction in hot cracks in some aluminum alloys (Beiranvand et al., 2019). Since an electron beam can also be pulsed, a technique industrially utilized in electron beam drilling, the same principles apply (Schultz, 2000). However, pulsed electron beam welding is rarely used in industrial welding applications due to the risk of pores, spiking and sputtering resulting from the pulsed process dynamic, especially in the deep welding regime (Kautz, 1991). This study aims to develop a pulsed electron beam welding process for AW 6061 sheet metal, which is susceptible to hot cracking. The influence of the welding and pulse parameters, as well as the combination of a pulsed beam with high frequency beam oscillation is discussed. Furthermore, suitable welding parameters for pulsed electron beam welding of AW 6061 are developed, and the increased efficiency of pulsed welding is shown by comparison to continuous welds.

The objective of this research is to assess the influence of in-situ localised electron beam post-weld heat treatment (LEB-PWHT) on the microstructure and mechanical properties of high-strength S690QL steel welded joints utilising highly sophisticated electron beam welding (EBW) technology. Although EBW is well-known for creating high-quality welds, the addition of the novel LEB-PWHT technique may significantly improve the characteristics of the welded joints. To systematically analyse the impacts of PWHT on the welded joints, the study employs microstructural analysis like optical microscopy and mechanical properties like microhardness testing, bending, tensile, and impact tests. Furthermore, tensile fractography analysed by scanning electron microscopy (SEM) to provide detailed insights into the fracture behaviour of the welded joints. The results show that the in-situ PWHT approach improves the microstructure and mechanical characteristics of the welded joints, such as a lower hardness peak in the heat affected zone (HAZ), increased tensile strength (5%), and improved toughness by 7 times. LEB-PWHT fractured surface revealed smaller, more sharply defined dimples and micro-voids. These results suggest that in-situ PWHT is an attractive option for improving the quality and performance of welds in a wide range of applications incorporating S690QL steel.

Resource-efficient electrochemical polymerization of acrylic acid (AA) on steel (DC04), from mildly acid Zn²⁺/ AA-containing aqueous solutions, is presented as an effective and sustainable thin film technology which allows for a precise control of the polymer thickness and morphology. The steel substrates were potentiostatically polarized to -1.4 V (vs. Ag/AgCl) or cycled between +0.1 to -1.4 V (vs. Ag/AgCl) in a degassed 2.0 M AA and 0.2 M ZnCl₂-containing aqueous electrolyte solution at pH 6. FE-SEM, AFM, FT-IRRAS, XPS, and electrochemical measurements shed light on the structural and chemical features exhibited by the as-prepared polyacrylic acid (PAA) thin films. When PAA-modified DC04 plates are joined to Al EN AW-1050A H24 specimens by plastic deformation using cold pressure welding (CPW), tensile strength testing unveiled the macroscopic interfacial adhesion-promoting capabilities exhibited by PAA layers to the opposing aluminum oxide surfaces. Carboxylate moieties present in the PAA are shown to form stable chemical bonds with metal oxide surfaces and with amine-epoxy-based resins. Interestingly, higher maximum shear force values are obtained for the PAA films when Zn metallic deposits are not present in the organic layer, but, when these welded specimens are heated up to 200 °C in a N₂ atmosphere, it occurred exactly the opposite: Zn particle-containing PAA films showed the highest maximum shear force values for the same deposition time.

The use of a hemispherical tool tilted towards the retreating side for friction stir welding 6061-T6 aluminum alloy is investigated. Joints with smooth surfaces and without internal voids are obtained. Under the same welding and rotational speeds, adapting the tilt angle makes it possible to weld various thicknesses up to 3.5 mm. Plunge depth and tilt angle are demonstrated to be key geometrical parameters driving material flow when using the hemispherical tool. Microstructural features in the weld are equiaxed and refined grains below 5 µm in the stirred zone and narrow thermo-mechanical affected zones. The through-thickness thermomechanical gradient developing beneath the hemispherical tool leads to different extents of dynamic recrystallization and recovery in the stirred zone. The tool orientation towards the retreating side and the division of the tool-workpiece interaction in continuous and intermittent contact leads to an asymmetrical thermal field around the stirred zone. Hence, the new derivative friction stir welding solution allows the welding of multiple aluminum alloy blank thicknesses using the same tool.

A novel solid-state joining method, called cold spot joining (CSJ), has been successfully developed. In this method, the material near the joining interface undergoes plastic deformation under high pressure, forming a joining interface, while oxide layers at the interface are fragmented and expelled to the exterior. High-strength steel sheets (HSS) with strengths of 780 MPa were joined under various conditions. The joining temperature can be adjusted by applying pressure during CSJ. Applying suitable pressure results in solid-state joining, and microstructural observations, alongside fracture morphology, indicate that the formation of a brittle structure was effectively prevented. Furthermore, cross-tensile strength measurements were conducted on steel sheets of varying strength grades, ranging from 270 to 1180 MPa and exhibited that the cross-tensile strength increased with increasing tensile strength.

This study presents a non-destructive testing (NDT) thermographic procedure for assessing the quality and mechanical strength of Resistance Projection Welded (RPW) joints with rectangular embossments. We analysed twelve RPW joints by systematically varying process parameters based on a factorial design. These joints underwent flash thermography followed by mechanical tests to evaluate the maximum breaking force (F_max). Significant statistical correlations between process parameters (time and force) and F_max were established. Furthermore, we found a correlation (p-value 0.86) between the optically measured fused region and F_max. Subsequently, we developed a pulsed phase thermography-based procedure for non-destructively measuring the fused region, resulting in an average difference of approximately 4 % compared to optical measurements. An empirical linear relationship was derived to correlate the welded area obtained by thermal data with F_max, enabling the estimation of mechanical joint strength through non-destructive pulsed thermography. This research offers a promising approach for assessing the mechanical integrity of RPW joints using thermal imaging techniques.

Due to the distinct differences in physical and metallurgical properties, it is hard to join titanium alloys to stainless steels directly via conventional welding processes. In this research, the grade 5 titanium alloy was subjected to brazing with austenitic stainless steel through the vacuum furnace, and the process was conducted above the β transition temperature (BTT). In order to reduce brittle intermetallic formation, a nickel base filler metal (Ni-6.6Cr-4.5Si-3B) was employed under a vacuum condition, and the effect of time on the microstructure and mechanical properties of the joints was investigated. The brazing temperature led to the thickening of the interface to 400 µm, toward the titanium alloy, and the FeTi formed adjacent to the diffusion affected zone (DAZ). Moreover, the isothermal solidified zone (ISZ) widened during the whole process, which, led to higher dissolution of the titanium base metal in the ISZ. Because of the widening of the interfaces, there were no Ni-rich compounds or residual filler metal in this region. SEM result showed that TiB strengthening borides, which were distributed after 45 min, and this evolution caused an increase in the shear strength of the joint up to 67 MPa. Fractography analyses and XRD results of the fractured surfaces revealed that the Ti₂Ni phase, which formed in the athermaly solidified zone (ASZ) during a two-step solidification reaction, caused the brittle fracture in all joints.