International Journal of Material Forming最新文献

The benchmark 2024 project on Incremental Sheet Forming (ISF), involving 15 research institutes in 13 experimental contributions, provided a unique opportunity to compare experimental outputs from various setups and forming strategies in ISF. This collaboration led to the development of uniform data exchange formats, measurement guidelines, and standardized nomenclature, fostering efficient future collaborations. The project addressed challenges in geometric accuracy when forming a relatively large part (400 × 400 mm) using Single Point Incremental Forming (SPIF) and focused on multiple common pitfalls in ISF, in particular the tent effect and pillow effect. Additionally, some experiments have been conducted using Two Point and Double Sided Incremental Forming (TPIF and DSIF). By combining the knowledge and experience of all participating institutes, this project aimed to provide insights into effective parameter choice and toolpath strategies, and shows the importance of multi-stage processes to increase the geometric accuracy. Despite the theoretical simplicity of SPIF setups, such multi-stage toolpath strategies directed toward improved geometric accuracy also add some new challenges. The study highlighted the need for multi-stage strategies that focus on local effects, as well as geometric compensation techniques to enhance ISF's industrial applicability. Alternative process variants like TPIF and DSIF, showed promising results, but they also had limitations and presented challenges, emphasizing the importance of predictive simulation tools to further increase geometric accuracy. The scalability of ISF experiments remains a significant challenge, necessitating further research into scale laws for process optimization.

Despite its critical importance in governing the weld strength and residual stress of dissimilar aluminum/magnesium welds by friction stir welding, the in-process temperature characteristics remain a subject of ongoing debate. This paper aims to resolve this debate through computational fluid dynamics simulation with the best accuracy to date, enabled by a state-of-the-art shear boundary model that allows fully coupled analysis of interfacial friction, material flow, heat generation and heat transfer. It is revealed that the temperature on the magnesium side is higher than that on the aluminum side, despite nearly identical total heat generation rates on both sides. This asymmetry is attributed to magnesium’s lower thermal conductivity, which impedes heat conduction. It is interesting to note that the circumferential temperature variation is reduced in high-velocity zones near the tool pin due to enhanced convection. The accuracy of the simulation is rigorously validated via comprehensive comparison between the measured welding temperature and the observed joint macrograph, confirming its capability to resolve the long-standing debate in the in-process temperature characteristics. These insights shed new lights on the thermal processes regarding the dissimilar aluminum/magnesium FSW, offering a foundation for optimizing welding process and weld performance.

The supply chains of extruded aluminum are materially inefficient, with up to two-fifths of the billet being scrapped before the profile is incorporated into a final product. A significant source of process scrap arises from removing the tongue-shaped transverse weld—also known as the front-end defect or charge weld—that is formed between the consecutive billets being extruded, primarily because of concerns over weld integrity. Optimizing process settings and die geometry can reduce the transverse weld length—and thus the amount of scrapped material—but only by approximately 15%. We investigate a novel methodology for significant scrap reduction, where an initially profiled interface—rather than a flat one—between consecutively extruded billets compensates for the differential velocities of material across the billet cross-section as it moves through the die ports, resulting in shorter welds. This profiled interface is created using profiled billets that fit into a dummy block shaped with the inverse of the billet profile. We present a design process to define the shape of the profiled dummy block and billet. For a given part, we first determine the ideal shape by obtaining the velocity field from finite element simulations of the conventional extrusion process, assuming perfectly rigid tooling and no constraints on the creation of profiled tooling or billets. Next, we rationalize this shape by applying stress and deflection limits to the dummy block, ensuring it avoids plastic deformation and interference with the container wall. Additionally, we consider ductile damage limits for the billet to prevent cracking during a pre-extrusion hot forging stage, which is one method of generating profiled billets. The design process is applied to four profiles of increasing complexity: solid round and rectangular bars, a square-tube hollow, and a complex multi-hollow profile. Extrusion and forging trials using custom-built tooling are conducted to validate the design process. The experimental case studies demonstrate that profiled dummy blocks and billets can achieve weld length reductions of over 50% and that the same tooling can offer scrap savings across a range of similar extruded shapes. In the tests, a profiled dummy block with an air escape vent showed zero-to-negligible plastic deformation and neither air entrapment nor clogging of the vent during extrusion, while a conventional billet was hot-forged to produce profiled ends without cracking or deforming the forging tools. Overall, this study highlights that profiled billet extrusion is a promising technology for significantly reducing scrap from transverse weld removal in aluminum extrusions.

Tin bronze valve bodies are widely used in fluid control systems requiring high corrosion resistance. However, conventional casting introduces defects such as porosity, segregation, and “sweating tin,” while forging is limited by the alloy’s thermal brittleness and difficulty in forming complex geometries. These issues hinder the integration of structural complexity with high mechanical performance. To address this, a novel integrated casting-forging process is proposed, consisting of three stages: casting, thermal holding at forging temperature, and hot forging. Using C83600 tin bronze, hot compression tests were conducted to construct a processing map and determine the optimal hot working parameters. A coupled simulation framework based on THERCAST and FORGE was developed to model solidification, homogenization, and forging, validating the feasibility of both bidirectional and triaxial extrusion schemes. Experimental trials confirmed that forging the billet while hot enabled seamless process transition, enhanced stability, and reduced cycle time. The resulting valve bodies exhibited significantly improved density of 9.25 g/cm³ and mechanical properties, hardness of 169 HB. This integrated approach demonstrates clear technical feasibility and practical potential for high-performance tin bronze component manufacturing.

Deep rolling has advantages to modify local residual stresses in AA2024 sheets. A previous study about deep rolling for tailoring residual stresses [1] is extended in order to examine the homogeneity of the residual stress field. For the experimental residual stress analysis, the incremental hole drilling method with electronic speckle pattern interferometry is used with two different drill diameters. A numerical evaluation scheme is applied to simulation results of an existing process model with the aim of mimicking the experimental analysis technique. The volume under the deep rolled surface is classified in three sections based on the history of the process. Comparisons between experimental and simulative results yield a number of observations: Deeper evaluation with higher driller diameter does not come at a price of higher in-plane averaging of spatial gradients. Simulating a number of paths lower than those of the experiments shows similar homogeneity of the simulatively and experimentally analyzed stress field. Stretching the evaluation scheme from cylindrical volumes to cubic volumes shows very good qualitative agreement and validates the choice of classification.

The complete parameterization of complex anisotropic material models for forming simulation of tubes presents significant challenges due to the inherent limitations of tube material testing. Furthermore, the impact of anisotropic material behavior on the hydroforming process, along with the relevance of specific parameters, remains inadequately understood. This study aims to investigate how selected parameters within elastic-visco-plastic anisotropic material models influence hydroforming simulations. Sensitivity analyses are conducted across three distinct characteristic hydroforming geometries, employing a zone-based approach to enable systematic comparison of parameter sensitivities and their correlation with the underlying hydroforming geometries. The results reveal substantial variations in sensitivity driven by differences in plastic strains, diverse strain or stress states, and interactions between neighboring zones. For accurate material modeling of E235 carbon steel tubes in hydroforming applications, determining the true stress–strain curve is basically important. Additionally, experimental quantification of strain rate sensitivity (p), uniaxial yield stress ({sigma}_{90}), and biaxial yield stress ({sigma}_{b}) is essential for ensuring simulation precision.    

Single point incremental forming (SPIF), which is a method that can be controlled by CNC processes without the need for a mold, as in traditional sheet metal forming, reduces costs and is suitable for low production series. In this study, the thickness change, surface roughness, and spring-back behaviours of AA5754-H22 alloy, which is widely used in many industries, especially in aviation and automotive, after forming with the SPIF method, were experimentally investigated. The geometric shape used in the study is hexagonal. The study was carried out using the parameters of increment (0.25, 0.5 mm), feed rate (500, 1000 mm/min), spindle speed (1000, 1500 rpm), tool diameter (6, 10 mm), wall angle (50, 55°), lubricant (machine oil, sunflower oil). The results were analysed after the experiments were conducted using an L16 orthogonal experimental design with the Taguchi method, and variance analysis was performed. As a result of the experiments, it was determined that the most important parameter affecting the wall thickness was the wall angle with a rate of 95.33%, the most important parameter affecting the surface quality was the tool diameter with a rate of 70% and the most important parameter affecting the spring-back was the wall angle with a rate of 52.76%. From here, it was understood that the parameters affecting the spring-back were in a wider range. In addition, when all the results were taken into consideration, it could be said that the most effective parameter was the wall angle.

The aims of present work are to apply the Bressan-Barlat mathematical model to predict the FLC curve and the proposed new equations of r-values to accurately predict the Lankford and the equal biaxial stress coefficients of anisotropy in sheet metal forming operations, using the non-associated Barlat´s Yld 2000-2d plastic potential. The Forming Limit Curve by shear stress fracture, FLC-S, was predicted employing Bressan-Barlat critical shear stress criterion combined with the non-associated Barlat´s Yld 2000-2D plastic potential. The predicted coefficients of anisotropy were calculated and validated by the new Bressan´s anisotropy equations in conjunction with the Lankford and equal biaxial stress material anisotropy parameters, r-values, and the non-associated Barlat´s Yld 2000-2d plastic potential. New Barlat´s coefficients of anisotropy a_i were defined and calibrated from material experimental data of r-values for specimens under simple uniaxial tension and equal biaxial stress tests. The examined distinct metal alloys were the highly anisotropic AISI 439 steel sheets and AA 6016-T4 aluminium sheets presented in the ESAFORM 2021 cup drawing benchmark articles obtained from published literature. In the results analysis and discussion, the new coefficients of anisotropy of the Barlat´s non-associated plastic flow rule were calculated and validated by plotting on the same graph the predicted r-value and s-value curves and experimental data for the anisotropic steel sheets. Correlation analyses have revealed that the Barlat´s yield criterion and the plastic flow stress potential were not coincident. Prediction of FLC-S of AISI 439 steel was quite good, when using the Bressan-Barlat shear stress fracture criterion combined with the non-associated Barlat´s Yld 2000-2d plastic stress potential. For both AISI 439 and AA 6014-T4, the non-associated Barlat´s Yld 2000-2d flow rule, calibrated by 7 r-values, provided a better fit to the experimental Lankford and equal biaxial coefficients of anisotropy. Exponent m = 10 was excellent and improved prediction accuracy over m = 8 for the AA 6014-T4.

Multi-pass compression deformation experiments for a high-strength container steel have been conducted on the DIL805A/D thermal expansion instrument. The true stress- plastic strain curves of experimental steel were plotted. Three typical flow stress models are used to predict the flow stress of the first pass deformation, and Model-1 flow stress model with the highest fitting accuracy is selected as the basic model form. Also, high precision static recrystallization volume fraction model and austenite grain size model have been established. The genetic algorithm is used to optimize the parameters in Model-1 model according to the second pass flow stress data. The relationships between static recrystallization volume fraction, the initial austenite grain size, the dislocation density before deformation, the deformation temperature, the strain rate and the model parameters are established through the Support Vector Machine (SVM) algorithm. The established flow stress model not only has high accuracy but also conforms to physical metallurgical principles under multi-pass steel deformation conditions according to a maximum plastic strain of 0.25. The research results can provide an important theoretical guidance for the load distribution of the rolling mill for the production of high-strength container plate.