Search Results (40)

In the leveling process of ultra-high-strength steel plates, sample scarcity—driven by high prototyping costs and small-batch production—coupled with a narrow and unevenly distributed feasible region due to high yield-to-tensile ratios and limited ductility, impedes the balanced optimization of plate shape quality and energy consumption. To address this issue, this paper develops an optimization framework for the balanced trade-off between these two objectives. First, a high-precision response surface model based on Box–Behnken experimental design and finite element simulation was constructed using initial wave height, entry roll reduction, exit roll reduction, and leveling speed as key process parameters; peak residual stress difference (characterizing potential sheet quality) and leveling energy consumption as co-optimization objectives; and post-leveling flatness as a constraint. Next, by introducing the NSGA-II multi-objective genetic algorithm, the Pareto optimal solution set for the quality and energy efficiency objectives was obtained, clearly revealing the trade-off relationship between the two; furthermore, the TOPSIS decision-making method was employed to select the comprehensive optimal process scheme that achieves a balance between quality and energy efficiency from the Pareto solution set. An adaptive recommendation curve for the leveling process parameters of MS1500 ultra-high-strength steel plates was established, covering an initial wave height range of 10.5–14.6 mm, thereby enabling intelligent parameter matching based on different incoming material conditions. Finally, industrial validation demonstrated that this optimized scheme significantly reduced leveling energy consumption while ensuring that post-leveling flatness meets the high-quality requirement of less than 3.5 mm·m⁻¹. This achieves a balanced optimization of quality and energy efficiency. This study provides a reliable theoretical basis and practical engineering solution for the efficient and environmentally friendly leveling production of ultra-high-strength steel. Full article

The quenching deformation of ultra-high-strength steel sheets is a technical challenge in the steel industry. Although air-jet quenching can effectively improve shape quality, it requires substantial energy consumption. How to improve the heat transfer intensity of air jets by improving key components has become the keypoint of using this technology in industry. In this study, a CFD model was established to investigate the impacts of nozzle shapes and jet arrangements on the flow structure, wall heat transfer intensity and wall heat transfer uniformity under the same total flow rate. The results show that the impingement heat transfer could only be realized by adopting a symmetrical nozzle design (including the symmetric nozzle shape and jet arrangement). And the intensity and uniformity of wall heat transfer were hardly affected by the specific symmetrical nozzle shape. Moreover, under the S/B (ratio of slot spacing to slot width) condition adopted in this study, multiple jets did not significantly enhance heat transfer uniformity but instead tended to reduce the overall heat transfer intensity. In this paper, the configuration of the horizontal nozzle with the central single jet was optimal due to its high heat transfer intensity, good heat transfer uniformity and lower energy consumption. Full article

Ultra-high-strength steel sheets were joined by forge joining during hot stamping. This study investigated the influence of punch cross-sectional shape and punch tip inclination shape on joint strength through experiments and finite element simulation, with applications in hat bending. The experiments systematically evaluated various punch geometries by varying the punch’s cross-sectional shape and the aspect ratio of rectangular punches. A second set of experiments focused on the influence of punch tip inclination shape. These experiments examined a rectangular punch with a slope. Joint strength is primarily assessed by measuring the tensile shear load. Finite element simulation was used to analyze joining mechanisms, investigating contact pressure and surface expansion rate distribution. The results from the experiments consistently indicated that, for a constant cross-sectional area, punch shapes with a larger punch perimeter on the upper sheet yielded a higher tensile shear load, though the changing inclination shape of the rectangular punch tip did not lead to an observed improvement in joint strength. Finite element simulation analysis revealed that punch shapes promoting a uniform distribution of contact pressure and surface expansion rate across the joint area tended to exhibit higher joint strength compared with the same punch cross-sectional area but less uniform distribution, a tendency that was more pronounced for the distribution of contact pressure than for the surface expansion rate. Full article

In the automotive industry, the most critical factor affecting dimensional stability during the forming of Advanced High-Strength Steels (AHSSs) is the springback phenomenon. This study systematically investigates the springback behavior of four distinct dual-phase steel grades (DP450, DP600, DP800, and DP1000) in U-shaped body-in-white (BIW) structures across 180 distinct scenarios. The experimental design varied sheet thicknesses (1.2, 1.6, 2 mm), die clearance angles (5°, 10°, 15°), and bending radii (R6, R8, R10, R12, R14). Numerical simulations using Autoform R8 were validated against Atos 3D optical scanning data, achieving values exceeding 0.90 for all grades. Quantitative validation metrics showed exceptional fidelity for lower-strength grades with error margins below 1.1%, while the maximum deviation was limited to 3.1% for the ultra-high-strength DP1000 grade. The findings demonstrate that while increasing material strength substantially intensifies springback, the strategic augmentation of sheet thickness and optimization of die radius effectively mitigate these deviations, thereby enhancing process stability. Full article

In the present study, the effects of electrode geometry and welding current on the tensile-shear strength, failure energy, fracture type, and joint microstructure were investigated during the RSW of ultra-high-strength MS1500 steel to high-strength low-alloy SPFC590 steel, both 1.2 mm in thickness. Three electrode geometries—designated as G0-6 mm, G0-8 mm, and A0—recommended for 1.2 mm sheets according to ISO 5821 were examined. It was found that in the G0-6 mm electrode geometry, which has the smallest contact area, excessive expulsion occurred at lower current levels compared to the other geometries. Consequently, this configuration resulted in lower maximum tensile-shear strength and failure energy values. The highest mechanical performance was achieved with the G0-8 mm electrode geometry, where the tensile-shear strength and failure energy were measured as 19.42 kN and 43.81 J, respectively. For the A0 electrode, although the maximum tensile-shear strength (19.68 kN) was comparable to that of the G0-8 mm geometry, the failure energy was approximately 7% lower (40.94 J). For all electrode geometries corresponding to maximum mechanical strength, a pull-out failure mode was observed, where the nugget region of the SPFC590 steel detached from the base metal and remained adhered to the ultra-high-strength MS1500 sheet. Full article

Initially, the effects of sheet combinations for joining two sheets, including 780 MPa steel and A5052 aluminum alloy sheets, on the joined cross-sectional shapes of the sheets in a clinch-bonding process and the tension-shear load of joined sheets were investigated. The effect of an adhesive on the amounts of the interlock and the minimum thickness in the upper sheet was not large, whereas the effect of the sheet combination was observed. Subsequently, for joining the upper 980 MPa ultra-high-strength steel and lower aluminum alloy sheets in the clinch-bonding process, the effects of the die shape, punch velocity, and sheet holding force on the joinability were investigated. As a result, defect-free conditions were narrowly constrained. Finally, a method that involved controlling material flow using an adhesive with fine particles to increase friction between the sheets was introduced. The upper 980 MPa steel and lower aluminum alloy sheets were successfully joined using this approach. Full article

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, the microhardness profile, the tensile behavior, and the experimentally obtained residual stresses (by x-ray diffraction) of the steels in dissimilar (PHS-DP) and similar (PHS-PHS, DP-DP) pair combinations have been analyzed. Results indicated that the ultimate tensile strength (UTS) of the dissimilar pair PHS-DP achieves a similar strength to the DP-DP joint, whereas the elongation was similar to that of the PHS-PHS weldment. The failure location of the tensile specimens was expected and systematically observed at the tempered and softer sub-critical heat-affected zone (SC-HAZ) in all welded conditions. Compressive residual stresses were consistently observed along the weldments in all specimens; the more accentuated negative RS were measured in the PHS joint attributed to the higher volume fraction of martensite; furthermore, the negative RS measured in the fusion zone (FZ) could be well correlated to weld restraint due to the sheet anchoring during the welding procedure, despite the presence of predominant ferrite and pearlite microstructures. Full article

This study presents the development of a deep drawing process under an indirect hot stamping method for manufacturing an automotive internal combustion engine oil pan from ultra-high-strength steel (UHSS) sheets, specifically 22MnB5. The forming process involves two stages—cold stamping followed by hot stamping—and is finalized with rapid quenching to achieve a martensitic microstructure. Finite element simulation using AutoForm R8 was conducted to determine optimal forming conditions. The simulation results guided the design of the forming tools and were validated through experimental trials. The final oil pan component exhibited no cracks or wrinkles, with maximum thinning below 18%, a hardness of 550.63 HV, and a fully martensitic phase. This research demonstrates a novel and effective solution for producing deep-drawn, high-strength components using indirect hot stamping, contributing to the advancement of automotive forming processes in Thailand. Full article

Due to the need for weight reduction in the automobile structure, effective and accurate forming is demanded to take advantage of ultrahigh-strength steels. Research on the deep-drawing formability of Usibor^®2000 has an important impact on the application of lightweight automotive bodies. The microstructure and formability of Usibor^®2000 sheets at different temperatures were investigated by the Swift test. The positive effects of increasing the temperature on improving the forming limit and forming quality of Usibor^®2000 were demonstrated by LDR results, thickness, and hardness measurement. The microstructure evolution of Usibor^®2000 steel plates under warm forming and hot forming conditions was discussed in terms of microstructure characterization and precipitate morphology. The phase composition of the sample deformed at 860 °C is analyzed by two-step etching metallographic analysis and numerical simulation, which provides a reference for the application of Usibor^®2000 ultrahigh-strength steel in automotive lightweight. Full article

In the V-bending of sheet metals using a pair of plastic punch and die manufactured by a 3D printer, the effects of two different dimensions designed with the same tool geometry on the deformation behaviors of the punch, die, and sheet were evaluated. The deformation behavior and strain distribution of the punch, die, and sheet were analyzed using a digital image correlation method. Sheets from pure aluminum to ultra-high-strength steel were bent using the two tools with different spans; one was designed on the assumption of tool steel material, and the other was designed on the assumption of plastic material. In both tools, the large compressive strain appeared around the center of the punch tip and on the corners of the die. The tools with a long span for the plastic material gave a lower bending force and small deformation of the plastic tools. The angle difference between a bent sheet at the bottom dead center and a tool was smaller for the tools with the long span, although the springback in the bent sheet appeared. It was found that the design method on the assumption of the plastic material is effective for the V-bending plastic tools. Full article

Deep drawing is a cost-efficient way of producing sheet metal parts in high production volumes. Prototypes and very small series are expensive due to the cost of steel-forming tools. Ultra-high-performance concrete (UHPC) tools offer a cheap and fast alternative to conventional steel-forming tools. However, the flexural and tensile strength of UHPC limits its use in complex loading situations occurring in the forming die during deep drawing. To overcome this challenge, we propose pre-stressing UHPC by using expansive UHPC in a mechanically restrained condition. An aluminum powder-based expansive agent can be used to induce a free volume increase in UHPC specimens. With push-out test specimens, the increase in strength was tested when restraining the free volume increase with a steel reinforcement. After 3 and 12 months, no notable pre-straining effect could be measured when restraining the expansion of UHPC. Nonetheless, in deep-drawing experiments, the die made of expansive UHPC in a restrained condition withstood a maximal load during deep drawing of 110 kN. Compared to the die made from UHPC only, the failure mode changed from complete fracture to surface degradation of the drawing radius after 15 strokes. Full article

In recent years, with the rapid advancement of automotive lightweight technology, the mechanical clinching process between aluminum alloy and ultra-high-strength steel sheets has received extensive attention. However, the low ductility of ultra-high-strength steel sheets often results in conventional mechanical clinching processes producing joints that either fail to establish effective interlocks or cause the steel sheets to fracture. To address this issue, a novel mechanical clinching process is presented, called center-punching mechanical clinching (CPMC). This innovative process employs a method of punching, flanging, and bulging gradation to achieve the mechanical clinching of aluminum alloy and ultra-high-strength steel sheets in a single step. In order to determine the effects of different parameters on the quality and strength of the joint, an experimental study was carried out for various die depths and diameters based on the condition of constant punch size. Based on tensile and shear tests, the static strength and failure modes of CPMC joints were analyzed. The results indicated that the CPMC process significantly enhances the connectivity of joints for AA5052 aluminum alloy and DP980 ultra-high-strength steel. Optimal tensile and shear strengths of 1264 and 2249 N, respectively, were achieved at a die depth of 2.2 mm and a diameter of 10.4 mm. The CPMC process provides new ideas for the mechanical clinching of aluminum alloy and ultra-high-strength steels. Full article

With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets. Full article

In the hot stamping process, the friction and wear interaction between the high-temperature sheet metal and the water-cooled die has a significant impact on the final quality of the product and the durability of the die. Currently, most research on the wear of the stamped parts during the hot stamping process mainly involves analyzing the wear morphology and wear mechanism of the sheet surface, and there is little research on its wear assessment. In this study, to better assess the forming quality of hot stamping parts, the research takes the direct hot stamping of galvanized ultra-high-strength steel sheets as the object and proposes a wear amount calculation method of galvanized ultra-high-strength steel sheets based on the real contact area of the high-temperature sheet metal and the water-cooled tools. At different temperature conditions, the galvanized layer and steel substrate have different mechanical properties. The model is validated using the sheet characteristics at 650 °C, 700 °C, and 750 °C. The results indicate that the model can predict the wear of the galvanized steel sheet under different conditions within a certain range. Full article

Explosions, once limited to military and accidental contexts, now occur frequently due to advances in warfare, local disputes, and global conflicts. Recent incidents, like urban bombings, emphasize the urgent need for infrastructure to withstand explosions. Slabs, critical in architectural frameworks, are vulnerable to explosive forces due to their slimness, making them prime targets for sabotage. Scholars have explored various strategies to fortify slabs, including the use of advanced materials like CFRP laminates/strips, steel sheets and ultra-high-strength concrete, along with reinforcement techniques such as two-mesh and diagonal reinforcements. A novel approach introduced in current research involves integrating vertical short bars, or studs, to enhance slab resilience against touch-off explosions. The aim of this research endeavor is to assess the impact of studs and their utilization in bolstering the anti-contact-blast capabilities of a concrete slab. To achieve this goal, a specialized framework within the ABAQUS/Explicit 2020 software is employed for comprehensive analysis. Initially, a conventionally reinforced slab devoid of studs serves as the benchmark model for numerical validation, facilitating a comparative assessment of its anti-contact-blast effectiveness against the findings outlined by Zhao and colleagues in 2019. Following successful validation, six additional distinct slab models are formulated utilizing sophisticated software, incorporating studs of varying heights, namely, 15 mm and 10 mm. Each configuration encompasses three distinct welding scenarios: (i) integration with upper-layer bars, (ii) attachment to bottom-layer bars, and (iii) connection to both upper- and bottom-layer bars. The comparative merits of the slabs are evaluated and deliberated upon through the examination of diverse response parameters. The research revealed that the incorporation of studs within slabs yielded notable enhancements in blast resistance. Specifically, taller studs demonstrated exceptional resilience against deformation, cracking, and perforation, while also diminishing plastic damage energy. Particularly noteworthy was the superior performance observed in slabs with studs welded to both upper and lower layers of re-bars. This highlights the critical significance of both the integration of studs and their precise positioning in fortifying structural integrity against blast-induced loadings. Full article