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•Guanidine-catalyzed asymmetric catalysis is introduced.•Guanidine-catalyzed construction of C-heteroatom bonds-forming reaction is described.•CN, CO, CP, CS bond-forming reaction is ...featured.
Guanidine-containing molecules have been employed as organocatalysts, and chiral guanidines have been widely explored as catalysts for mediating asymmetric reactions by constructing an asymmetric reaction environment. Currently, many guanidine-catalyzed asymmetric reactions are available, and some excellent reviews have appeared. In this Digest, we focused on recent progress in the guanidine-catalyzed asymmetric construction of CN, CO, CP, and CS bonds, especially developments since 2010.
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.
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Industrial emissions must be dramatically reduced to avoid the potentially dangerous effects of climate change. In order to contribute to the necessary cuts, this article focuses on ...the energy and material efficiency of sheet metal forming. The processes considered include traditional methods, such as drawing and stretch forming, and newer technologies developed in recent decades such as hydroforming (fluid cell forming), superplastic forming, and incremental sheet forming.
In this analysis, we conduct case studies on forming processes at leading US car and aerospace manufacturers. The case studies include electrical power measurements on the forming machines and also consider the impacts of making the dies, sheet metal, and lubricant. Cradle-to-gate energy demands and environmental impacts are modeled in SimaPro using data based on ecoinvent 3.1 database values. The results show that idling consumes significant electricity; however, other than for incremental forming, the impacts of press electricity are small compared to the impacts of making the sheet metal. The case studies inform generalized models for each process that allow per part impacts to be estimated based only on final part material, size (surface area, thickness, and depth), and the number of parts produced over the die-set lifespan. The models are used to investigate the potential to reduce cradle-to-gate energy requirements by using incremental forming instead of drawing to form parts. It is found that there are significant potential savings for small production runs, consistent with part development/prototyping. However, these savings vary depending on the part size and the relative buy-to-fly ratio (material yield) of the two processes.
The results of this study highlight that for small production numbers over the die lifespan the impacts of die-making are important. However, as production numbers increase above one hundred parts per die-set, the impacts of making the sheet metal become dominant. It is therefore concluded that researchers interested in reducing the environmental impacts of sheet metal forming concentrate on innovations that would reduce sheet metal blanking and post-forming trimming losses.
This reprint focuses on the forming technologies and mechanical properties of advanced materials. Plastic working is the most efficient and an important manufacturing technology in today's industry. ...Plastic working technologies enable giving the material the appropriate functional properties, which depend on the rheological conditions of the plastic forming process and on the thermoplastic treatments carried out during the forming process. Metal processing is one of the most important sectors of the economy. In addition to the continuous improvement in the existing methods of plastic working, new technologies are also implemented, the purpose of which is to reduce the energy consumption of processing and the modernization of technological machines and tools. The subjects of research articles published in this reprint are multidisciplinary, including friction and lubrication in sheet metal forming, the single-point incremental forming of polymeric and lightweight metallic sheets, the optimization of shear spinning parameters and the cutting performance of cutting tools, the numerical and experimental analysis of titanium sheet forming, the mechanical and structural properties of titanium alloy subjected to impact-oscillatory loading, macro- and microdeformation characteristics of Ti-2.5Al-1.5Mn foil, and the optimisation of the thermomechanical process of nickel-based oxide-dispersion-strengthened superalloys.
Electromagnetic forming is an impulse or high-speed forming technology using pulsed magnetic field to apply Lorentz’ forces to workpieces preferably made of a highly electrically conductive material ...without mechanical contact and without a working medium. Thus hollow profiles can be compressed or expanded and flat or three-dimensionally preformed sheet metal can be shaped and joined as well as cutting operations can be performed. Due to extremely high velocities and strain rates in comparison to conventional quasistatic processes, forming limits can be extended for several materials. In this article, the state of the art of electromagnetic forming is reviewed considering:
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basic research work regarding the process principle, significant parameters on the acting loads, the resulting workpiece deformation, and their interactions, and the energy transfer during the process;
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application-oriented research work and applications in the field of forming, joining, cutting, and process combinations including electromagnetic forming incorporated into conventional forming technologies.
Moreover, research on the material behavior at the process specific high strain rates and on the equipment applied for electromagnetic forming is regarded. On the basis of this survey it is described why electromagnetic forming has not been widely initiated in industrial manufacturing processes up to now. Fields and topics where further research is required are identified and prospects for future industrial implementation of the process are given.
This Special Issue and Book, ‘Latest Hydroforming Technology of Metallic Tubes and Sheets’, includes 16 papers, which cover the state of the art of forming technologies in the relevant topics in the ...field. The technologies and methodologies presented in these papers will be very helpful for scientists, engineers, and technicians in product development or forming technology innovation related to tube hydroforming processes.
This paper presents a detailed literature review on the current research of incremental sheet forming relating to deformation mechanism, modelling techniques, forming force prediction and process ...investigations. First, a review of the fundamental deformation mechanism and formability in incremental sheet forming (ISF) is provided. Subsequently, the modelling techniques for ISF are reviewed and categorised into two approaches: analytical modelling and finite element modelling. Special interest is given to a critical review regarding the forming forces analysis and prediction during the process. Then, previous publications related to geometric accuracy, surface finish and forming efficiency in ISF are reviewed. Finally, several potential hybrid incremental sheet-forming strategies are discussed. This leads to a statement of conclusion which may act as an inspiration and reference for the researcher.
•A model is proposed to describe shear ductile fracture from shear to the balanced biaxial tension.•The stress invariant-based Drucker yield function is specified for BCC and FCC metals to the ...balanced biaxial tension.•The model is successfully employed to predict ductile fracture of AA6082 in wide loading conditions.•The model could also be used to describe ductile fracture under low and negative stress triaxiality with improved flexibility.
A ductile fracture model is proposed to describe shear fracture of sheet metals from shear to balanced biaxial tension via uniaxial and plane strain tension. The fracture criterion models plastic damage as strain-induced void nucleation, triaxiality-governed void enlargement, Lode-controlled void torsion, and shear-restrained coalescence of voids. Its flexibility is investigated by a parameter study of the ductile fracture model proposed. The fracture model is employed to describe ductile fracture behavior of an aluminum alloy AA6082 T6 (thickness: 1.0mm). Dogbone specimens are strained to characterize the strain hardening properties, while another four different specimens are tested to characterize fracture behavior in shear, uniaxial tension, plane strain tension and balanced biaxial tension. The loading processes are analyzed numerically with the stress invariant-based Drucker yield function which is for the first time specified for body-centered cubic and face-centered cubic metals. Fracture strains in various loading conditions are measured with a hybrid experimental-numerical approach. The measured fracture strains are then used to calibrate the ductile fracture model proposed. The ductile fracture model calibrated above is employed to predict the onset of ductile fracture for these four specimens. For the purpose of comparison, the predicted fracture strokes of these four loading conditions are compared with those predicted by the modified Mohr–Coulomb model (Bai and Wierzbicki, 2008), and two micromechanism-inspired criteria proposed recently (Lou et al., 2012, 2014). The comparison reveals that the proposed model predicts the fracture behavior in much better agreement compared with experimental results from shear to the balanced biaxial tension. Accordingly, the proposed ductile fracture criterion is recommended for the prediction of ductile fracture in sheet metal forming processes, optimization of forming parameters and design of tools for both solid elements and shell elements. Besides, the ductile fracture model proposed can also be applied in various bulk metal forming processes in case that the model is calibrated by proper sets of experiments.
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.
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.
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