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Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

The influence of clinching tool design in joining metal sheets by the clinching process with extensible dies is investigated. The material flow during the clinching process was examined experimentally and numerically. The geometrical and mechanical characteristics of joints produced under different processing conditions, that is, forming loads, were used to calibrate and validate a 3D finite element model of the clinching process. Then, the model was utilized to evaluate the influence of clinching tool design parameters, namely the punch diameter, the punch corner radius, the fixed die depth, the fixed die diameter, and the die corner radius. The effects of design parameters on the cross section of a clinched joint, the required forming load and the joint strength were analysed and the appropriate processing window was determined. According to the achieved results, the main benefits and drawbacks of each configuration are discussed.

This study delves into the crucial aspect of sample preparation methodology and its profound impact on characterizing the physical and mechanical properties of components fabricated through the material extrusion (fused deposition modeling—FDM) process. Two distinct manufacturing approaches, direct printing and sample extraction from a plate, were employed to produce samples. To assess the influence of artifacts introduced by direct printing, compression tests were conducted under various loading directions. The investigation extends to density measurements and comprehensive morphological analysis, which plays a pivotal role in understanding the ramifications of different manufacturing approaches and principal sample directions. Notably, the research findings reveal that direct printing inflicts significant artifacts within the samples, fundamentally altering the properties obtained during testing. These artifacts substantially affect density measurements and mechanical behavior, indicating a potential avenue for future research and applications. Besides, the printing direction also significantly influenced the extent of the artifacts and differences in mechanical behavior. The maximum difference in density measurement was − 5.3%, while Young’s modulus reached − 29%, and yield strength ranged between − 12% (for vertical samples) and + 18% for horizontal samples with filaments arranged along the loading path. These findings underscore the necessity for meticulously crafted quality assessment protocols when utilizing functional parts manufactured through the material extrusion process. Such protocols should also consider the influence of sample dimensions on the mechanical characteristics of the components.

The present study investigates the compression behavior of components made by material extrusion, also known as fused filament fabrication (FFF) or fused deposition modeling (FDM). An experimental plan was conducted by adopting a high-density fulfillment and varying the material flow. Additional tests were performed by thermomechanical compaction to produce full-density samples. Compression tests were performed at various strain rates ranging between 5 × 10−4 and 5 × 10−1 s−1. Yielding and post-yielding behaviors were analyzed. Morphological analysis was carried out to determine the mesostructural features (interlayer neck and void sizes) and how they behave during the compression test. The results indicated that the principal dimension of the voids ranged between 65 mm and 170 mm depending on the adopted value of the extrusion multiplier. On the other hand, thermomechanical compaction enabled the restriction of the voids of printed samples to 10 mm. The cross-sectioning of samples at different strains indicated the formation of shear banding strain localization. In addition, printed samples behaved like porous media during the compression tests and showed different characteristic regions with different void dimensions. The samples printed at the higher material extrusion showed similar behavior to compacted samples. Post-yielding analysis indicated that strain softening observed on compacted samples was more severe as compared to that observed on printed samples. This behavior is dramatically reduced by decreasing the extrusion multiplier.

This paper investigates the influence of the main process parameters on the geometry of the bead deposited during WAAM using MIG welding technology. A campaign of experimental tests was conducted using a design of experiments approach. The campaign was conducted under a wide range of processing conditions up to a deposition rate of 22 kg/h. Geometrical characterization of the weld bead was performed by optical microscopy and 3D reconstruction techniques. The key geometrical features of the beads and suitable processing windows were identified. The experimental measurements of the cross-sectional profile of the weld bead were compared with common approximation models. A new model based on a circular approximation was proposed. The results demonstrated that the circular approximation showed better agreement with the experimentally measured profiles than the commonly adopted parabolic approximation. This commonly adopted model was fully unable to describe the weld bead profile under medium–large deposition rates. Under these conditions, the parabolic approximation predicted taller and larger weld bead profiles as compared to the experimental measurements. On the other hand, the circular profile showed much better agreement with the experimental profiles within the entire experimental window. A semi-empirical model capable of predicting the bead cross section given the deposition parameters was developed. The model showed good reliability and agreement with the experimental measurement. Consequently, this model would represent a compelling tool to select the process parameters to achieve more precise geometries during WAAM processes.

The present work introduces an expert system that automatically selects and designs rolling sequences for the production of square and round wires. The design strategy is aimed at reducing the overall number of passes assuming a series of process constraints, e.g., available roll cage power and torque, rolls groove filling behaviors, etc. The method is carried out into two steps: first a genetic algorithm is used to select the proper rolling sequence allowing to achieve a desired finished product; then, an optimization roll pass design tool is utilized for proper design of roll passes. Indeed, an artificial neural network (ANN) is utilized to predict the main geometrical characteristics of the rolled semi-finished product and technological requirements. The ANN was trained with a non-linear finite element (FE) model. The proposed methodology was applied to some industrial cases to show the validity of the proposed approach in terms of reduction of number of passes and search robustness.

Evaluating local mechanical properties of parts made by additive manufacturing processes can improve the deposition conditions. This study proposes a non-destructive characterization test to determine the mechanical behavior of fused deposition modeling (FDM) components. Indentation and compression tests were conducted on samples produced by the FDM process, which were created by varying the material flow during the deposition. An empirical relationship was determined between yield strength determined through compression and indentation tests. R2 = 0.92 characterized the correlation between the compression and indentation test. The results indicated that both the yield strength measured through compression tests and that measured by the indentation tests increased linearly with the density of the components. Indentation tests provided more insights concerning the tested surface’s local characteristics than the compression test.

The hole-clinching process is one of the mechanical methods for joining dissimilar materials, such as aluminum alloy with advanced high-strength steel, hot-pressed steel, and carbon fiber reinforced plastics, employing forming technology-based methods. In joint design, the analysis of the failure-mode dependent joint strength is a crucial step in achieving structural performance for practical applications. In this study, the influence of the geometrical interlocking parameters on the failure-mode dependent joint strength was investigated in order to design the geometrical interlocking shape of the hole-clinched joint to achieve a target joint strength. Moreover, the failure process of the hole-clinched joint under pullout loading condition was studied to determine the geometrical interlocking parameters that affect joint strength. Based on the results of the finite element analysis, an analytical approach for the failure-mode dependent joint strength was proposed to predict the strength of the hole-clinched joint. In addition, the proposed analytical approach was applied to the hole-clinching process with dissimilar materials. Its effectiveness was then verified using the cross-tension test. Accordingly, it was found that it was possible to predict the failure modes and joint strength with a maximum error of 7.8%.

The present study is aimed at determining the local density of components made by fused deposition modeling (FDM) through non-destructive indentation tests. An experimental campaign was performed to assess such a relationship. Specimens were made varying the amount of material flow and the direction of deposition. The specimen’s dimension and weight were measured to determine the average density. The internal porosity due to uncomplete filling produced due to the deposition process was also assessed through cross-sectioning. Instrumented indentation tests were conducted on the samples to determine a relationship between the density and the slopes during the loading and unloading phases. The tests were performed using flat cylindrical indenters of different diameters. The results indicated that the density of the specimens was strongly influenced by the adopted material flow and the orientation during deposition. An empirical relationship was determined between the slopes measured during indentation tests and the density. Such a relationship is independent of the deposition orientation. The optimized procedure represents a valuable tool to determine the local density of components made by fused deposition modeling through non-destructive indentation tests.

In this study, an analytical model is developed to evaluate the bending angle in laser forming of metal sheets. The model is based on the assumption of elastic-bending theory without taking into account plastic deformation during heating and cooling phases. A thermal field is first established, then the thermal component of deformation is calculated and it is used in the strain balance to evaluate the bending angle. The basic idea is that it is possible to use a two-layer model whereas the heated layer thickness depends on the effective temperature distribution along the sheet thickness. A comprehensive experimental study is carried out and the main process parameters, i.e., laser power, scanning speed, sheet thickness, were varied among several levels to evaluate the accuracy of the developed model. Model predictions were confirmed by experimental measurements especially on materials with low conductivity. The established analytical model has demonstrated to provide a great insight into the process parameters effects onto the deformation mechanism within pure temperature gradient mechanism and bucking to temperature gradient transition conditions.