Search Results (69)

A lubricant protective film (LP) formed on automotive Zn-coated steel sheets is a functional surface layer that controls shear resistance at the die–sheet interface while also affecting the electrical contact state during resistance spot welding and the surface reactivity during paint pretreatment. In this study, the effect of LP coating weight on surface friction, interfacial electrical resistance, and degreasing–phosphate reactivity was analyzed for 340 MPa-grade galvannealed (GA) steel sheets within a unified surface-governed framework. The LP coating weight was controlled in the range of 0–1008 mg/m² on a single-sided basis. The friction coefficient, cup-drawing limit blank holding force (BHF), resistance spot welding current range, resistance–time product obtained by integrating dynamic resistance with respect to time, residual LP after degreasing, phosphate coating formation behavior, and forming simulation results using experimentally measured friction coefficients as input were comparatively evaluated. With increasing LP coating weight, the friction coefficient decreased from approximately 0.163 to 0.130 and then increased again to approximately 0.145 in the high-coating-weight regime. This surface-state change increased the limit BHF during cup drawing, whereas it narrowed the current range and increased the resistance–time product during resistance spot welding. In addition, under conditions above approximately 550 mg/m², residual LP after degreasing increased, and local no-growth regions of the phosphate coating were identified. These results show that, within the present test conditions, LP coating weight is not merely the amount of lubricant applied but a surface-state variable that concurrently influences frictional, electrical, and chemical responses. Therefore, within the scope of the present laboratory-scale framework, an LP coating weight of approximately 300–550 mg/m² should be interpreted not as a universal optimum, but as an operational surface window derived by balancing formability, the RSW process window, and phosphate reactivity under the present experimental conditions. Full article

Additively manufactured composite architected discs offer a potential route for producing lightweight semi-finished blanks that can subsequently be shaped by conventional forming processes. However, the relationship between infill architecture, feature size, and deep-drawing formability remains poorly understood. This study investigates the deep-drawing response of material-extruded short-fibre-reinforced polymer composite discs by combining experimental tests and finite element simulations. Four infill strategies, namely perforated body, re-entrant, square and triangular, were first compared at drawing depths of 10 and 20 mm. The perforated body and re-entrant geometries were successfully formed at 10 mm, whereas only the perforated body withstood 20 mm without macroscopic failure. A second campaign focused on perforated discs with hole diameters of 2.5, 5, 7.5 and 10 mm. All configurations were drawable at 10 mm, while the 2.5 mm case failed at 20 mm. Statistical analysis confirmed that hole diameter significantly affected both retained cup height and side-hole aspect ratio. At 20 mm, larger holes reduced local ovalization but increased elastic recovery, leading to lower retained cup height. FEM simulations were used as an interpretative first-order model. They supported the experimental trends by comparing deformation modes, tensile/compressive stress redistribution, forming energy and strain localization. The results show that the formability of architected composite blanks is governed not only by material volume or porosity but by the ability of the internal architecture to accommodate deformation through a suitable balance between local stiffness and geometric compliance. These findings provide design-oriented guidelines for the development of additively manufactured architected blanks intended for hybrid additive–forming manufacturing routes. Full article

This study presents an integrated experimental methodology to determine the forming and fracture limits of welded thin-walled steel tubes, with emphasis on weld-line effects and manufacturing-induced anisotropy. The methodology combines longitudinal and transverse uniaxial tensile tests, using specimens extracted from different positions relative to the weld line, with elastomer-based tube expansion tests. Digital Image Correlation, combined with time-dependent strain analysis, was used to identify the onset of localized necking, while local strain and thickness measurements near the fracture regions supported the determination of fracture limits. This experimental work covered strain paths in the principal strain space ranging from uniaxial tension to near plane-strain expansion within the investigated conditions, enabling the experimental determination of both the Forming Limit Curve and the Fracture Forming Line for the welded tube material. Results reveal a pronounced directional dependence of mechanical response and formability. Transverse specimens exhibited higher yield and ultimate tensile strengths but lower ductility, whereas longitudinal specimens showed greater elongation and strain-hardening capacity. Strain localization and fracture were governed by the combined effects of local thickness variations, weld heterogeneity, and manufacturing-induced anisotropy. In longitudinal specimens, fracture occurred preferentially along the weld line, while in transverse specimens it developed away from the weld region, indicating distinct failure mechanisms depending on the loading direction. These findings highlight the need to account for weld-related heterogeneity and manufacturing history when assessing the formability of welded thin-walled tubes. The proposed methodology provides valuable experimental data for improving failure prediction and supporting the design, simulation, and optimization of welded tubular components. Full article

Ultra-high-strength steel (UHSS) cross-members with a high height-to-width ratio are prone to forming defects, such as splitting and wrinkling, due to localized stress concentration during the drawing process. In this study, the addendum geometry in first-stage of a two-stage drawing process was optimized to improve the formability of a cross-member made of 1 GPa-grade UHSS. The optimization was performed using the Sigma module of AutoForm, and Latin hypercube sampling was adopted for the design of experiments. The punch opening width, upper bar radius, wall angle, and lower die radius of the addendum were selected as design parameters, and multi-objective optimization was conducted to simultaneously minimize the maximum failure index and maximum wrinkle value, the two AutoForm forming-defect indicators used in this study. In the initial design, the maximum failure index was 1.044, exceeding the splitting criterion of 1.0; however, this value was reduced to 0.961 in the optimized design, thereby mitigating the risk of splitting. In addition, the maximum wrinkle value was reduced by 11.7% compared with that of the initial design. Pareto analysis was performed to quantitatively evaluate the effects of the design parameters on the forming defects, and the results confirmed that the punch opening width and lower die radius were the dominant parameters affecting both splitting and wrinkling. These results demonstrate that die addendum geometry optimization is effective for reducing splitting and wrinkling in 1 GPa-grade UHSS cross-members. Full article

High-quality, large-weight alloy wires (>200 kg per coil) for aerospace fasteners require intermediate annealing prior to final cold drawing, as well as subsequent solution and aging heat treatments, which are critical processes during their manufacturing. However, the evolution of microstructure and mechanical properties during these procedures has not been systematically investigated. In this study, different cooling methods after intermediate annealing were comparatively investigated to clarify their influence on the microstructure evolution, precipitation behavior, and mechanical properties of Al–Zn–Mg–Cu alloy wires. The results revealed that the cold heading performance of alloy wires is determined by the strength–ductility balance, crystallographic texture, and precipitation behavior. Furnace cooling promoted η′ phase coarsening, resulting in lower strength and higher ductility, which enhanced deformation homogeneity and cold heading formability. The near-zero Δr reduced strain localization and cracking susceptibility, whereas higher Δr in water- and air-cooling samples increased anisotropy and cracking tendency. After heat treatment, strength differences became negligible, whereas elongation remained texture dependent, with the weaker texture in the furnace-cooling sample yielding superior ductility. Full article

Heat-assisted metal spinning comprises incremental forming routes, conventional spinning, shear spinning and flow forming, performed at elevated temperature to increase formability. This review consolidates the main advances of the last fifteen years. It outlines spinning mechanics and the rationale for heating (higher ductility, lower forming forces and microstructure control), then compares global and local heating strategies (furnace, flame, induction, laser and hot-gas convection) in terms of temperature uniformity, industrial practicality, energy efficiency and cost. Key process parameters (spindle speed, feed rate and thickness reduction) are discussed with respect to defect formation, and representative windows for defect mitigation are reported. Progress in modeling is reviewed, including coupled thermo-mechanical finite element simulations, damage/formability prediction and emerging data-driven optimization. The review also summarizes microstructural evolution under heat-assisted conditions, phase transformation, dynamic recrystallisation and grain growth, and its impact on final properties. Across more than 100 studies, evidence shows that robust thermal management can roughly double achievable deformation before failure and enables property tailoring in difficult-to-form alloys (Ni-based alloys, high-strength steels, Al, Mg and Ti). Remaining challenges include reliable in situ temperature measurement/control and improved predictive fidelity of simulations. Future opportunities include digital twins, real-time sensing and adaptive, machine-learning-assisted control. Full article

In this study, a gradientstructured (GS) AZ31 Mg alloy sheet with high stretch formability is fabricated using turned bearing extrusion (TBE). The mechanism by which the gradient structure contributes to the improvement in formability is elucidated. The Erichsen index of the GS sheet reaches 5.51 mm, representing an increase of up to 89.3% compared to conventional extruded (CE) sheets. During the Erichsen cupping test, when the coarsegrained (CG) layer of the GS sheet is positioned on the inner side, the large grains promote the activation of deformation twins, thereby effectively enhancing the strain accommodation capacity in the thickness direction. Meanwhile, the finegrained (FG) outer layer effectively suppresses the formation of {10$\stackrel{-}{1}$1} and {10$\stackrel{-}{1}$1}-{10$\stackrel{-}{1}$2} twins, reducing local strain concentration. Full article

The VDA 238-100 tight radius bend test has gained widespread acceptance for plane strain fracture characterization of sheet metals in proportional loading without necking. The VDA test features a 60 × 60 mm² square blank with a 0.2 mm or 0.4 mm radius punch to provide plane strain bending where the fracture limit of the material is lowest. However, the through-thickness gradients that suppress necking and promote fracture on the convex surface in tension can be exploited to efficiently characterize the fracture strain from uniaxial to plane strain tension by varying the sample width. In this study, V-bend tests were conducted for various sample widths for four advanced high-strength steels: 980GEN3, DP1180, MP800-V1, and MP800-V2 with the local fracture strains measured using digital image correlation. Reducing the width-to-thickness ratio below five altered the stress state at the failure location, with an aspect ratio of one providing edge fractures under uniaxial tension. This aspect ratio was then applied to 980GEN3 and MP800 steel samples with punched edges as it provides an efficient method for sheared edge fracture characterization that is not susceptible to necking as with common sheared edge tensile tests. To mitigate strain averaging inherent in DIC near surfaces, a geometric-based arc length methodology was proposed. The sheared edge fracture limits from the V-bend tests were then compared with the results from conical hole expansion and in-plane bend tests. The sheared edge formability was observed to have a material-dependent sensitivity to the test method. MP800-V2, with centerline segregation, exhibited a pronounced sensitivity to the applied deformation mode with absolute differences in fracture strains of 0.13 while the MP800-V1 and 980GEN3 did not. Full article

The formability of reinforcement is essential for controlling shaping processes and assessing their suitability for industrial applications. The complexity of the geometries dictates the deformation modes and thus the reinforcements’ behaviours. This study is an experimental campaign to investigate the shaping of five different geometries with three reinforcements that have varying meso-structures: plain weave, interlock and Non-Crimp Fabric. The comparison concentrates on shear behaviour and defects induced. The measured parameters are chosen in relation to their potential impact on the composite’s properties at both local and macro levels. The findings reveal that geometry significantly influences the quality of the preform. Each geometry shows unique behaviours due to a different, but limited, range of mechanisms. This highlights the importance of identifying and analysing the interesting parts of these geometries and their role in triggering the different behaviours. Full article

Finite element simulations were conducted to investigate the drawing process of bimetallic rods, a key manufacturing technique used in aerospace, automotive, and advanced engineering applications. The study focused on how independent variations in the yield stress of the core and sleeve (150, 200, 250, 300 and 350 MPa) and differences in the initial core ratio (10%, 30%, 50%, 70% and 90%) affect bondability, formability, and fracture behavior. Simulations showed that the maximum achievable reduction ratio varied from approximately 50% to 55%, and hence, we focused on this range. By analyzing the maximum achievable reduction ratio and the distribution of effective strain, the simulations provided insights into the deformation mechanisms and failure modes of these composite structures. The results reveal that increasing the yield stress in either the core or the sleeve reduces the drawing limit by promoting stress concentrations at the interface, leading to premature failure and weakened bondability. Moreover, the core ratio critically influences performance: high core ratios result in thin, vulnerable sleeves prone to early fracture, while low core ratios produce thin cores that fail under high deformation loads. Strain analysis indicated that higher core yield stress increased interfacial shear stress, leading to localized failure, while a lower core yield stress resulted in more uniform material flow. A balanced core ratio (approximately 50%) yields a more uniform strain distribution, though it requires robust interfacial bonding to prevent delamination. These findings underscore the importance of optimizing both material properties and geometric configurations to enhance bondability, formability, and structural integrity during the drawing process of bimetallic rods. Full article

Through mechanical analysis, a comparison of the same type of cold rolled steel produced by two steel manufacturers, supplier 1 and supplier 2, has been carried out. The considered material is a steel that has undergone a quenching and partitioning heat treatment, i.e., a rapid cooling from the austenitizing temperature, followed by a holding treatment at a suitable temperature, so that the residual austenite is stabilized at room temperature. The following tests for mechanical properties were carried out: formability, through Nakajima test, tensile test, bending test, hole expansion test and fatigue strength analysis, through high cycle fatigue and low cycle fatigue test. In addition, to derive useful data for future simulations, tensile and Nakajima tests were analyzed by digital image correlation, which uses a monochrome camera to capture frames during the test, in order to analyze local deformations on investigated samples. Finite elements modeling has been carried out. A suitable calibration of a material card for the Abaqus Finite Element Analysis software has been performed. Through the combination of obtained results, a rational comparison of the two analyzed products has been obtained. Full article

This paper presents YOLO-FIX, an improved intelligent detection model based on YOLOv11, designed to identify glue line defects in mobile phone frames. The model addresses the challenges of complex glue line morphology, background interference, and illumination transformation. YOLO-FIX enhances the extraction of local and global features to optimize the detection accuracy by integrating advanced attention mechanisms and multi-scale feature fusion modules specifically Deformable Large-Kernel Attention (De-formable-LSKA) and Mamba-Like Linear Attention (MLLA). Experimental evaluations demonstrate that YOLO-FIX achieves a mean Average Precision (mAP50) of 95.2%, an 8.6% improvement over the baseline YOLOv11 model while maintaining a real-time detection speed of 189 FPS. It effectively identifies five common defect types: broken glue, wall climbing, glue dropping, single-tip wall climbing, and collapsed glue, showcasing exceptional robustness and generalization across varying production environments. These results affirm YOLO-FIX as a highly accurate and efficient solution for automated defects in industrial applications. Full article

Advanced high-strength steels are considered the first choice when manufacturing lighter vehicles. Quench-partitioning (QP) steels are good candidates that fulfill manufacturing and performance requirements with their outstanding strength and formability. Laser welding offers a productive solution to the challenges of liquid metal embrittlement due to a low heat input and higher welding efficiency. This study investigated the microstructural evolution and mechanical performance of dissimilar laser-welded joints between QP980 and QP1180 steels. The microstructure of the joint mainly consisted of martensite phase in the fusion zone (FZ) and super-critical heat-affected zone (HAZ). In the mid and sub-critical HAZ, the microstructure consisted of tempered martensite along with ferrite and retained austenite on both sides. Due to these microstructural evolutions, FZ and HAZ are strengthened, and thus, laser welds can be achieved without the formation of a visible soft zone. Fracture of the joints occurred in softer base metal (BM) with ductile characteristics without any considerable strength loss. However, the ductility of the joints was lower than that of BMs because of deformation localization due to microstructure, yield strength, and thickness variations in the tensile and Erichsen test specimens. These results show that laser welding can be considered an effective alternative for joining QP steels. Full article

Sheet metal forming is one of the key processes in the manufacturing of parts for several industries, such as automotive, aerospace and packaging. However, it is often constrained by the onset of plastic instability, which limits uniform deformation. To address this challenge, considerable attention has been given to methods that enhance strength, formability, and energy absorption during forming processes. One such method is the continuous-bending-under-tension (CBT) deformation mechanism, which has shown potential in mitigating localized instability during plastic deformation. This study presents a numerical investigation of the CBT process using Abaqus 2017 to evaluate the forces generated in both the CBT equipment and material when processing high-strength materials. The reference material used is the USS CR980XG3™ AHSS, a third-generation, high-strength, high-elongation steel grade with retained austenite (980T/600Y). The study systematically analyzes the effects of key parameters, such as roll diameter, distance between rolls, depth setting, specimen thickness, and the number of deformation cycles, on the evolution of forces during the CBT process. The results demonstrate that both the forces applied by the rolls and those experienced by the specimen are significantly influenced by the distance between rolls, depth setting, and specimen thickness. In contrast, the roll diameters have minimal influence. These findings contribute to the optimization of the CBT process and provide valuable insights for future studies aimed at enhancing the performance and formability of various materials. Full article

This study examines the specimen size-dependent deformation behavior of commercially pure titanium grade 4 (cp-Ti grade 4) sheets under tension, with strain paths between uniaxial tension (UT) and plane-strain tension and compares the results with cyclic bending under tension (CBT) data. Specimens of varying widths (11.7, 20, 60, 100, and 140 mm) were tested in both rolling (RD) and transverse (TD) directions. The research employed digital image correlation for full-field strain measurements, finite element simulations, and fracture surface thickness data. Contrary to traditional forming concepts, i.e., the forming limit diagram (FLD) has the lowest major strain at the plane-strain condition, and the fracture forming limit has decreased major strain with increasing (less negative) minor strain, wider specimens exhibited higher major strains at strain localization and fracture under UT. In contrast, CBT findings showed decreased formability with increasing width, i.e., closer to plane-strain deformation, as expected. Strain distribution analyses revealed a transition from nearly uniform deformation in narrow specimens to multiaxial strain states in wider specimens. Thickness measurements along the fracture surface revealed a steeper profile in UT compared to CBT, indicating more localized deformation and necking in UT. In comparison with AA6016-T4, the cp-Ti grade 4 showed greater thickness, suggesting lower susceptibility to localized thinning. Strong anisotropy was observed between the RD and TD, with TD specimens showing higher formability and steeper thickness gradients in UT. Strain fields, along with thickness reduction and adiabatic heating, are used to rationalize the observed width-sensitive deformation behavior of cp-Ti sheets. Notably, CBT improved overall formability compared to UT due to its ability to distribute strain more evenly and delay critical necking. The contrasting trends between simple UT and CBT emphasize the relationship between loading conditions, specimen geometry, and material behavior in determining formability. These findings highlight the ability of the CBT test to create known and desired deformation effects, i.e., lower major strain at failure with increasing specimen width, and more uniform deformation, i.e., consistent thinning across the specimen width, for cp-Ti. Given the observed effects of width in UT, the selection of the testing method is critical for cp-Ti to ensure that results reflect expected material behavior. Full article