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Lightweight materials, such as titanium alloys, magnesium alloys, and aluminium alloys, are characterised by unusual combinations of high strength, corrosion resistance, and low weight. However, some of the grades of these alloys exhibit poor formability at room temperature, which limits their application in sheet metal-forming processes. Lightweight materials are used extensively in the automobile and aerospace industries, leading to increasing demands for advanced forming technologies. This article presents a brief overview of state-of-the-art methods of incremental sheet forming (ISF) for lightweight materials with a special emphasis on the research published in 2015–2021. First, a review of the incremental forming method is provided. Next, the effect of the process conditions (i.e., forming tool, forming path, forming parameters) on the surface finish of drawpieces, geometric accuracy, and process formability of the sheet metals in conventional ISF and thermally-assisted ISF variants are considered. Special attention is given to a review of the effects of contact conditions between the tool and sheet metal on material deformation. The previous publications related to emerging incremental forming technologies, i.e., laser-assisted ISF, water jet ISF, electrically-assisted ISF and ultrasonic-assisted ISF, are also reviewed. The paper seeks to guide and inspire researchers by identifying the current development trends of the valuable contributions made in the field of SPIF of lightweight metallic materials.

Understanding the formability limits of thin-walled tubes with square cross-sections and L-section profiles is crucial for improving manufacturing efficiency and ensuring structural reliability in industries such as automotive and aerospace. Unlike the usually studied circular tubes, square tubes and L-section profiles geometries present unique deformation and fracture behaviours that require specific analysis. To address this gap, this research establishes a novel methodology combining digital image correlation (DIC) with a time-dependent approach and precise thickness measurements, enabling accurate strain measurements essential to the onset of necking and fracture strain identification. Two experimental tests under different forming conditions allowed capturing a distinct range of strain paths leading to failure. This approach allowed the determination of the forming limit points associated with necking and the fracture forming lines associated with crack opening by tension (mode I) and by in-plane shear (mode II). The findings highlight the strong influence of geometry on the fracture mechanisms and provide valuable data for optimizing tube-forming processes for square tubes and L-section profiles, ultimately enhancing the design and performance of lightweight structural components.

Recently, soft hot strip and hard hot strip produced through ferritic rolling are projected as a direct replacement to austenitic cold-rolled sheets for many forming applications. However, industrial hot-rolling mills, with final rolling thickness limitations cannot produce these thinner products and have to be subsequently cold-rolled to the desired application thickness and further annealed. Under ferritic rolling conditions, the hot-rolling temperature of these coils governs the final properties. The temperature difference in hot-rolled sheets generates the difference in the microstructure and texture of these coils after cold-rolling and annealing and variation in their formability behaviour. In the present work, an Nb–Ti stabilized IF grade steel was hot-rolled at two different temperatures in the ferritic regime and subsequently cold-rolled and annealed for structure-property comparison. As formability is an application-specific requirement, the annealed sheets were tested for different formability characteristics. Industrially rolled samples were tested for fracture criterion, stretch-flangeability, deep drawability and stretch formability through the formability limit diagram, hole expansion ratio, earing test and Erichsen cupping test respectively. These parameters were compared with those of the austenitic regime rolled sheets. High temperature ferritic rolled sheets show improved formability in all tests due to better r˙, higher n-value, low Δr and stronger gamma fibre maxima at 111 . Low temperature ferritic rolled sheets show the lowest Δr and improved n-value, but has reduced r˙ and higher alpha fibre texture. High temperature ferritic rolled sheets show higher formability limits in uniaxial tension and low temperature ferritic rolled sheets in biaxial tension of the FLD curve. Various tests established that high temperature ferritic rolled sheets are best suited for deep drawing and stretching applications whereas low temperature ferritic rolled sheets should be preferred for stretch forming applications.

This paper presents an innovative methodology to determine the formability limits of thin-walled tubes with square cross-sections and L-section profiles. These geometries are studied for the first time in this context, providing a pioneering insight into their fracture behaviour. The methodology considered utilizes digital image correlation (DIC) and thickness measurements at the crack location and enables the extraction of strain loading paths and the determination of fracture limit strains. Several experimental formability tests were conducted under various forming conditions, capturing a wide range of strain paths leading to fracture. This allowed the experimental determination of the fracture forming line (FFL) and inplane shear fracture forming line (SFFL) for these geometries, and its representation in principal strain space. The results highlight the critical importance of geometry-specific fracture characterization for the optimization of industrial tube-forming processes. By providing a comprehensive understanding of formability limits in these novel geometries, this study offers a valuable tool for researchers and engineers aiming to enhance the reliability and efficiency of forming processes in automotive, aerospace, and other applications.

This paper is focused on the utilisation of double edge notched tension, staggered and shear tests to determine fracture toughness and the formability limits by fracture in principal strain space. The experiments were performed in test specimens with different geometries and ligament angles, and the influence of strain hardening was taken into consideration by selecting two materials (aluminium AA1050-H111 and pure copper), with very different strain hardening exponents. Results are plotted in principal strain space, and the discussion is focused on the link between formability limits, fracture toughness and macroscopic fractography characteristics of the specimens that fail by mode I, mode II or mixed-mode.

By proposing an adaptation of the methodology usually used in metal forming, this paper aims to provide a general procedure for determining the forming limits, by necking and fracture, of polymeric sheet. The experimental work was performed by means of Nakajima specimens with different geometries to allow to obtain strains in the tensile, plane, biaxial and equibiaxial states for Polycarbonate sheet with 1 mm of thickness. The application of the time-dependent and flat-valley approaches used in metals has been revealed appropriate to characterize the onset of necking and obtain the forming limits of polycarbonate, despite the stable necking propagation typical of polymeric sheets. An analysis of the evolution of the strain paths along a section perpendicular to the crack allowed for a deeper understanding of the steady necking propagation behaviour and the adoption of the methodology of metals to polymers. The determination of the fracture strains was enhanced with the consideration of the principal strains of the DIC system in the last stage, just before fracture, due to the significant elastic recovery typical of polymeric sheets. As a result of this analysis, accurate formability limits by necking and fracture are obtained for polycarbonate sheet, together with the principal strain space, providing a general framework for analysing incremental sheet forming processes where the knowledge of the fracture limits is relevant.

Using a finite element calculation code, this work analyses the influence of friction during a stamping test conducted on the AA6060 aluminium-based alloy. The study focuses on phenomena happening when the sheet necking appears. This condition, based on the Hill s localized necking theory and the Swift s diffuse necking theory, is dependent on the material hardening index. This work shows that the punch stroke at the necking condition point is maximum when the main strain measured on the sheet surface is unbalanced and close to a balanced biaxial tension condition.

This paper presents an innovative methodology to determine the formability limits of low-alloy steel tubes, with particular attention to the effects of the weld line on their performance. Digital Image Correlation (DIC) system, coupled with time-dependent methodologies is used to identify the onset of failure by necking and to measure the corresponding limit strains. Thickness measurements and gauge length strain analysis across cracked regions are employed to characterise the onset of fracture and to evaluate fracture limit strains. The methodology incorporates tensile tests in longitudinal and transversal directions and tube expansion tests using elastomers to generate strain loading paths and fracture strain pairs across a broad spectrum of forming conditions. These conditions range from biaxial stretching in the first quadrant to pure tension in the second quadrant of principal strain space. The unique influence of the weld line is highlighted, including its impact on both the Forming Limit Curve (FLC) and the Fracture Forming Line (FFL) plotted in the principal strain space. This study demonstrates, for the first time, the FFL of low-alloy steel thin-walled tubes, providing critical insights for optimising tube forming processes involving welded materials.

The strain-based forming limit curve is the traditional tool to assess the formability of metal sheets. However, its application should be restricted to proportional loading processes under uniform strain conditions. Several works have focused on overcoming this limitation to characterize the safe process windows in industrial stretch-bend forming processes. In this paper, the use of critical distance rule and two path-independent stress-based metrics are explored to numerically predict failure of AA7075-O stretch-bend sheets with 1.6 mm thickness. Formability limits of the material were experimentally obtained by means of a series of Nakazima and stretch-bending tests at different thickness-over-radius ratios for inducing controlled non-uniform strain distributions across the sheet thickness. By using a 3D calibrated finite element model, the strain-based forming limit curve was numerically transformed into the path-independent stress and equivalent plastic strain polar spaces. The numerical predictions of necking strains in the stretch-bending simulations using the above approaches were successfully compared and critically discussed with the experimental results for different values of the critical distance. It was found that failure was triggered by a critical material volume of around the half thickness, measured from the inner surface, for the both path-independent metrics analyzed.

Stamping companies are constantly evaluating improvements in their manufacturing processes aiming increased competitiveness in the market, whether by increasing productivity or by reducing costs. In this scenario, the manufacture of thin complex geometry products attending high quality standards becomes a challenge, and studies are needed to predict failures and defects during the process. This study was based on the failure limit knowledge necessity of SAE1010 steel with and without pure zinc coating (GI-85) submitted to dry wheelbarrow buckets forming process. Those limits was analyzed by using the HyperForm software. The experimental analysis was carried out, both in laboratory and industrially on a real scale, with the objectives of comparing failure limits by constriction (FLC-E) and fracture (FLC-F) and confirming results obtained virtually. It was concluded that, under the same stamping favorable friction conditions, SAE 1010 GI-85 steel fails first when compared to uncoated steel due to zinc layer cracking. The FLC-F curve obtained in the laboratory proved to be more conservative and could only be used qualitatively to predict failures in real process. It can be said that there was a good agreement between experimental and simulated results, which represented an error of only 6.5%.