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Sheet metal forming (SMF) is one of the most popular technologies for obtaining finished products in almost every sector of industrial production, especially in the aircraft, automotive, food and home appliance industries. Parallel to the development of new forming techniques, numerical and empirical approaches are being developed to improve existing and develop new methods of sheet metal forming. Many innovative numerical algorithms, experimental methods and theoretical contributions have recently been proposed for SMF by researchers and business research centers. These methods are mainly focused on the improvement of the formability of materials, production of complex-shaped parts with good surface quality, speeding up of the production cycle, reduction in the number of operations and the environmental performance of manufacturing. This study is intended to summarize recent development trends in both the numerical and experimental fields of conventional deep-drawing, spinning, flexible-die forming, electromagnetic forming and computer-controlled forming methods like incremental sheet forming. The review is limited to the considerable changes that have occurred in the SMF sector in the last decade, with special attention given to the 2015–2020 period. The progress observed in the last decade in the area of SMF mainly concerns the development nonconventional methods of forming difficult-to-form lightweight materials for automotive and aircraft applications. In evaluating the ecological convenience of SMF processes, the tribological aspects have also become the subject of great attention.

Incremental sheet metal forming in general and Single Point Incremental Forming (SPIF) specifically have gone through a period of intensive development with growing attention from research institutes worldwide. The result of these efforts is significant progress in the understanding of the underlying forming mechanisms and opportunities as well as limitations associated with this category of flexible forming processes. Furthermore, creative process design efforts have enhanced the process capabilities and process planning methods. Also, simulation capabilities have evolved substantially. This review paper aims to provide an overview of the body of knowledge with respect to Single Point Incremental Forming. Without claiming to be exhaustive, each section aims for an up-to-date state-of-the-art review with corresponding conclusions on scientific progress and outlook on expected further developments.

Abstract Sheet metal channels with variable sections or local features have been widely used in automobile and construction industries, and novel forming techniques, such as flexible roll forming process, flexibly reconfigurable roll forming process, Deakin’s flexible forming facility, and chain-die forming recently have been developed to manufacture those channels. In this paper, the feasibility of chain-die forming technique to manufacture channels with variable sections is systematically investigated through experiment and finite element simulation by taking 6 types of channel products as demonstration, including three variable-width and three variable-depth profiles. The forming process of the channels shows a combination of roll forming and stamping, and this roll-stamp mode has great potential in manufacturing a wide variety of channels with variable cross-sections. The formability for roll-stamp forming variable-depth channels is evaluated through finite element simulation and forming limit diagram. The roll-stamp mode can be discomposed into roll forming longitudinally and stamping vertically, and can achieve a reduction in forming load by the maximum of 33.9% compared with the conventional stamping in forming the flange step product. The forming direction sensitivity of the variable-width feature is discussed from the aspect of web arch height development.

Shear spinning is an incremental metal forming technique with several advantages when compared with traditional sheet metal forming technologies, including low force requirements, simpler tools, and the capability to produce complex geometries. In this process, a large deformation can be applied due to the localized compressive and shear stresses, which enhance the ductility more than conventional forming processes. Therefore, the final part improves considerably its mechanical properties due to the associated work hardening. Nevertheless, the shear spinning technology involves a complex material flow that is highly dependent on the process parameters. In consequence, it is essential to study the effect of the different parameters on the formability of any material in the shear spinning process, but more importantly, to develop a method to predict the forming limit in terms of such parameters to get most of the process. In this work, a novel approach to study the formability in terms of the radial force was introduced. In this sense, shear spinning experiments on mild steel (DC-04) and martensitic stainless steel (AISI 420) were carried out, to derive forming limit maps as a function of the mandrel wall angle (30–7°), the spindle speed (400–1000 rpm), the feed rate (0.01–1.2 mm/rev), and the roller attack angle (0–30°). It was found that the maximum thickness reduction that the materials can withstand was 84% and 80% for the DC-04 and AISI 420, respectively. The results showed that the spindle speed presents a minor effect while the feed rate and radial force greatly affect the formability; therefore, a parametric equation was proposed to describe the boundary between the safe and failure zones in terms of the maximum thickness reduction. Regarding the mechanical properties, the maximum hardness increment regarding the as-received materials was 73% and 42% for the DC-04 and AISI 420, respectively.

Key Points Pore-forming toxins (PFTs), which are expressed as virulence factors by many pathogenic bacteria, and pore-forming proteins (PFPs) have been found in all kingdoms of life PFTs and PFPs undergo a structural and functional metamorphosis from soluble, inactive monomers to active, complex multimeric transmembrane pores that insert into the membranes of target cells Based on their structure and mechanism of pore formation, six families of PFTs and PFPs have been described, each of which has a distinct structure and mechanism of pore formation. These families can be grouped into two larger classes, α-PFTs and β-PFTs (or PFPs), based on the secondary structures of their transmembrane pore domains Owing to substantial recent advances in the structural biology of PFTs, we are beginning to understand the pore architecture and the mechanism of pore formation for all six families The specificity of PFTs and PFPs is determined by their interactions with lipids, sugars and/or protein receptors present in, or on, the target cell membrane Structural modularity enables toxins with the same pore-forming mechanism to target different host cell types by binding to different receptors For PFTs that contribute to infection, examining their structures, dynamics and interactions with host cells at molecular resolution provides cues for the development of therapeutics that could be highly effective in fighting disease Pore-forming toxins (PFTs) are produced as virulence factors by many pathogenic bacteria. In this Review, Dal Peraro and van der Goot describe new mechanistic insights into the assembly of these toxins and their target specificity, and discuss recent therapeutic developments. Pore-forming toxins (PFTs) are virulence factors produced by many pathogenic bacteria and have long fascinated structural biologists, microbiologists and immunologists. Interestingly, pore-forming proteins with remarkably similar structures to PFTs are found in vertebrates and constitute part of their immune system. Recently, structural studies of several PFTs have provided important mechanistic insights into the metamorphosis of PFTs from soluble inactive monomers to cytolytic transmembrane assemblies. In this Review, we discuss the diverse pore architectures and membrane insertion mechanisms that have been revealed by these studies, and we consider how these features contribute to binding specificity for different membrane targets. Finally, we explore the potential of these structural insights to enable the development of novel therapeutic strategies that would prevent both the establishment of bacterial resistance and an excessive immune response.

Cytotoxic lymphocyte-derived granzyme A (GZMA) cleaves GSDMB, a gasdermin-family pore-forming protein 1 , 2 , to trigger target cell pyroptosis 3 . GSDMB and the charter gasdermin family member GSDMD 4 , 5 have been inconsistently reported to be degraded by the Shigella flexneri ubiquitin-ligase virulence factor IpaH7.8 (refs. 6 , 7 ). Whether and how IpaH7.8 targets both gasdermins is undefined, and the pyroptosis function of GSDMB has even been questioned recently 6 , 8 . Here we report the crystal structure of the IpaH7.8–GSDMB complex, which shows how IpaH7.8 recognizes the GSDMB pore-forming domain. We clarify that IpaH7.8 targets human (but not mouse) GSDMD through a similar mechanism. The structure of full-length GSDMB suggests stronger autoinhibition than in other gasdermins 9 , 10 . GSDMB has multiple splicing isoforms that are equally targeted by IpaH7.8 but exhibit contrasting pyroptotic activities. Presence of exon 6 in the isoforms dictates the pore-forming, pyroptotic activity in GSDMB. We determine the cryo-electron microscopy structure of the 27-fold-symmetric GSDMB pore and depict conformational changes that drive pore formation. The structure uncovers an essential role for exon-6-derived elements in pore assembly, explaining pyroptosis deficiency in the non-canonical splicing isoform used in recent studies 6 , 8 . Different cancer cell lines have markedly different isoform compositions, correlating with the onset and extent of pyroptosis following GZMA stimulation. Our study illustrates fine regulation of GSDMB pore-forming activity by pathogenic bacteria and mRNA splicing and defines the underlying structural mechanisms. The cryo-EM structure of the GSDMB pore reveals mechanisms by which GSDMB pore-forming activity is regulated by pathogenic bacteria and mRNA splicing.

Antimicrobial peptides (AMPs) play a key role in the innate immunity, the first line of defense against bacteria, fungi, and viruses. AMPs are small molecules, ranging from 10 to 100 amino acid residues produced by all living organisms. Because of their wide biodiversity, insects are among the richest and most innovative sources for AMPs. In particular, the insect Hermetia illucens (Diptera: Stratiomyidae) shows an extraordinary ability to live in hostile environments, as it feeds on decaying substrates, which are rich in microbial colonies, and is one of the most promising sources for AMPs. The larvae and the combined adult male and female H. illucens transcriptomes were examined, and all the sequences, putatively encoding AMPs, were analysed with different machine learning-algorithms, such as the Support Vector Machine, the Discriminant Analysis, the Artificial Neural Network, and the Random Forest available on the CAMP database, in order to predict their antimicrobial activity. Moreover, the iACP tool, the AVPpred, and the Antifp servers were used to predict the anticancer, the antiviral, and the antifungal activities, respectively. The related physicochemical properties were evaluated with the Antimicrobial Peptide Database Calculator and Predictor. These analyses allowed to identify 57 putatively active peptides suitable for subsequent experimental validation studies.

Incremental sheet forming (ISF) significantly exempts use of expensive dies and reduces tooling cost for manufacturing complex parts in the field of sheet metal forming which makes it suitable for manufacturing prototypes and low volume production as compared to other traditional sheet metal forming processes. ISF also finds suitability for producing components of old machinery, which are otherwise very difficult to form due to the unavailability of forming dies. Moreover, the incremental nature of the process and local deformation of the sheet ensures higher formability and lower required forming force. To take advantages of lower required forming force, it is important to minimize and estimate forming force through the manipulation of the parameters for the safe utilization of hardware. In this review article, a literature survey was carried out quantitatively to study different aspects of ISF, especially to show different process parameters and techniques that affect the forming forces significantly. The current state of the art of the ISF process has been discussed with detailed analysis of process capabilities and limitations in terms of forming forces. Influences of different process parameters and forming techniques have also been studied on forming forces. Some parameters have shown their significance to control the forming force in order to preserve forming machinery. A lack of focus was found on effects of some important forming process parameters and methods, which could have been crucial for safe utilization of forming hardware. A number of guidelines have been recommended for future research work. Appropriate guidelines have also been suggested regarding the relationship between process parameters and forming forces developed during the process in order to ensure the applicability of the ISF process on the industrial scale.

Gasdermins (GSDMs) are pore-forming proteins that play critical roles in host defence through pyroptosis 1 , 2 . Among GSDMs, GSDMB is unique owing to its distinct lipid-binding profile and a lack of consensus on its pyroptotic potential 3 – 7 . Recently, GSDMB was shown to exhibit direct bactericidal activity through its pore-forming activity 4 . Shigella , an intracellular, human-adapted enteropathogen, evades this GSDMB-mediated host defence by secreting IpaH7.8, a virulence effector that triggers ubiquitination-dependent proteasomal degradation of GSDMB 4 . Here, we report the cryogenic electron microscopy structures of human GSDMB in complex with Shigella IpaH7.8 and the GSDMB pore. The structure of the GSDMB–IpaH7.8 complex identifies a motif of three negatively charged residues in GSDMB as the structural determinant recognized by IpaH7.8. Human, but not mouse, GSDMD contains this conserved motif, explaining the species specificity of IpaH7.8. The GSDMB pore structure shows the alternative splicing-regulated interdomain linker in GSDMB as a regulator of GSDMB pore formation. GSDMB isoforms with a canonical interdomain linker exhibit normal pyroptotic activity whereas other isoforms exhibit attenuated or no pyroptotic activity. Overall, this work sheds light on the molecular mechanisms of Shigella IpaH7.8 recognition and targeting of GSDMs and shows a structural determinant in GSDMB critical for its pyroptotic activity. The authors report the cryogenic electron microscopy structures of human GSDMB in complex with Shigella IpaH7.8 and the GSDMB pore, shedding light on the molecular mechanisms of Shigella IpaH7.8 recognition and targeting of GSDMs and GSDMB pore formation.

Fibre metal laminates, hybrid composite materials built up from interlaced layers of thin metals and fibre reinforced adhesives, are future-proof materials used in the production of passenger aircraft, yachts, sailplanes, racing cars, and sports equipment. The most commercially available fibre–metal laminates are carbon reinforced aluminium laminates, aramid reinforced aluminium laminates, and glass reinforced aluminium laminates. This review emphasises the developing technologies for forming hybrid metal–polymer composites (HMPC). New advances and future possibilities in the forming technology for this group of materials is discussed. A brief classification of the currently available types of FMLs and details of their methods of fabrication are also presented. Particular emphasis was placed on the methods of shaping FMLs using plastic working techniques, i.e., incremental sheet forming, shot peening forming, press brake bending, electro-magnetic forming, hydroforming, and stamping. Current progress and the future directions of research on HMPCs are summarised and presented.