Search Results (178)

The constitutive model is widely employed to characterize the rheological properties of metallic materials under high-temperature conditions. It is typically derived from a series of high-temperature tests conducted at varying deformation temperatures, strain rates, and strains, including hot stretching, hot compression, separated Hopkinson pressure bar testing, and hot torsion. The original experimental data used for establishing the constitutive model serves as the foundation for developing phenomenological models such as Arrhenius and Johnson–Cook models, as well as physical-based models like Zerilli–Armstrong or machine learning-based constitutive models. The resulting constitutive equations are integrated into finite element analysis software such as Abaqus, Ansys, and Deform to create custom programs that predict the distributions of stress, strain rate, and temperature in materials during processes such as cutting, stamping, forging, and others. By adhering to these methodologies, we can optimize parameters related to metal processing technology; this helps to prevent forming defects while minimizing the waste of consumables and reducing costs. This study provides a comprehensive overview of commonly utilized experimental equipment and methods for developing constitutive models. It discusses various types of constitutive models along with their modifications and applications. Additionally, it reviews recent research advancements in this field while anticipating future trends concerning the development of constitutive models for high-temperature deformation processes involving metallic materials. Full article

The development of technology has driven a rising need for high-accuracy and high-efficiency manufacturing of low-volume products. Incremental forming technology, characterized by die-free flexibility and low production costs, can effectively replace stamping processes for manufacturing customized small-batch products. However, high-performance aluminum alloys generally exhibit poor room-temperature plasticity but excellent high-temperature plasticity, necessitating the integration of thermal-assisted methods for manufacturing such products. However, the temperature of the forming region will excessively rise without temperature control, which will affect the forming performance of the material in hot incremental sheet forming of AA2024-T4 aluminum alloy. This study focuses on AA2024-T4 aluminum alloy and proposes a uniform temperature control method for the electric hot tube-assisted incremental sheet forming process, incorporating an adaptive fuzzy PID algorithm. The temperature difference of the forming region is lower than 6% under the various temperatures. On this basis, the forming limit angle and the microstructure state of the material are analyzed, and the grain feature of the material exhibits significantly refined grains and the uniform fine grain distribution under 180 °C with the temperature control of the adaptive fuzzy PID algorithm. Full article

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The purpose of this work was to establish an appropriate constitutive model to characterize the rheological behavior of a hot-formed steel plate (22MnB5 steel) produced through the TSCR (Thin Slab Casting and Rolling) process under practical deformation temperatures (150–250 °C) and strain rates (0.001–3000 s⁻¹). Subsequently, the material flow behavior was modeled and predicted using the Johnson–Cook flow stress constitutive model. In this study, uniaxial tensile tests were conducted on 22MnB5 steel at room temperature under varying strain rates, along with elevated-temperature tensile tests at different strain rates, to obtain the engineering stress–strain curves and analyze the mechanical properties under various conditions. The results show that during room-temperature tensile testing within the strain rate range of 10⁻³ to 300 s⁻¹, the 22MnB5 steel exhibited overall yield strength and tensile strength of approximately 1500 MPa, and uniform elongation and fracture elongation of about 7% and 12%, respectively. When the strain rate reached 1000–3000 s⁻¹, the yield strength and tensile strength were approximately 2000 MPa, while the uniform elongation and fracture elongation were about 6% and 10%, respectively. Based on the experimental results, a modified Johnson–Cook constitutive model was developed and calibrated. Compared with the original model, the modified Johnson–Cook model exhibited a higher coefficient of determination (R²), indicating improved fitting accuracy. In addition, to predict the material’s damage behavior, three distinct specimen geometries were designed for quasi-static strain rate uniaxial tensile testing at ambient temperature. The Johnson–Cook failure criterion was implemented, with its constitutive parameters calibrated through integrated finite element analysis to establish the damage model. The determined damage parameters from this investigation can be effectively implemented in metal forming simulations, providing valuable predictive capabilities regarding workpiece material performance. Full article

The heating rates and forming temperatures during the hot forming process of titanium alloys cause significant differences in phase transformation, grain size, and dislocation evolution. The formability and service performance of titanium alloy formed components are affected by these factors. This study investigated the hot flow behaviors of Ti-6Al-4V at temperatures ranging from 800 to 900 °C and heating rates ranging from 0.1 to 10 °C/s. These were tested via Gleeble hot tensile experiments, and the grain size and phase evolution were quantitatively characterized via EBSD and XRD. The results suggest that a higher heating rate decreases the β-phase transformation and dislocation density and inhibits grain coarsening, leading to better formability. The heating rate was introduced into the viscoplastic constitutive model for the first time to achieve accurate predictions of the microstructure and hot flow behavior under different heating rates. The prediction accuracy of the hot flow behavior and phase volume fraction reaches 92.93% and 94.97%. The current-assisted hot stamping experiments and finite element (FE) simulations of Ti-6Al-4V irregular cross-section components were carried out at temperatures of 800 and 900 °C and at heating rates of 1 and 3 °C/s. The results show that the rapidly heated formed components exhibit better thickness uniformity and yield strength. The FE simulation guided by the optimized constitutive model has achieved a 96.96% and 92.76% prediction accuracy for the thickness distribution and β-phase volume fraction, respectively. Full article

In order to determine the failure reason for the non-working area of a cracked A-pillar hot-stamping die insert, various instruments were used to detect the properties and microstructures of the cracks and matrix. The results show that the cracks are located in the area where the oxidative corrosion is more serious, and the cracks do not appear in the pitting area, verifying that crack initiation is related to the stress concentration on the upper half of the inner wall of the cooling channel. Meanwhile, pores and cracks exist in the grain boundary and crystal, making the impact energy of the die steel poor. Therefore, crack initiation and propagation easily occur along the brittle oxide layer. In summary, the die insert is damaged by stress-induced corrosion. In engineering applications of hot-stamping dies, we should pay more attention to the cracking of the cooling channel caused by stress and corrosion. 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

Tensile tests are a common method for characterizing plastic behavior for sheet metal forming applications. During tensile testing at the beginning of the deformation, the stress state is uniaxial; however, as the deformation proceeds, the state changes to triaxial, making the post-processing of experimental data challenging using analytical methods. In contrast, inverse approaches in which the behavior is represented by constitutive equations and the parameters are fitted using an iterative procedure are extremely dependent on the empirical equation chosen at the outset and can be computationally expensive. The inverse piecewise flow curve determination method, previously developed for compression tests, is extended in this paper to tensile testing. A stepwise approach is proposed to calculate constant strain rate flow curves accounting for the unique characteristics of tensile deformation. To capture the effects of localized strain rate variations during necking, a parallel flow curve determination strategy is introduced. Tensile test flow curves for manganese-boron steel 22MnB5, a material commonly used in hot stamping applications, are determined, and the approach is demonstrated for virtual force–displacement curves. It has been shown that these curves can replicate the virtual experimental flow curves data with a maximum deviation of 1%. Full article

In the automotive industry, structural components are often produced via press hardening, enabling rapid production and the use of ultra-high-strength steels. In this process, steels are heated to an austenitic state and are then formed and quenched in rapid succession. The initial steel that enters the press-hardening production line varies, where the microstructure is a result of previous production steps. This work was performed to investigate the possible effects of the initial microstructure on the final mechanical properties for rapidly quenched samples. Although the initial microstructure is transformed during austenitization, the steel can still be affected by its prior history. Steels with three different initial microstructures were evaluated, with only minor variations in chemical composition and thicknesses. The Lankford coefficients and the failure strains were dependent on the orientation of the samples. However, for a given orientation, there were only minor variations between the different steels with respect to anisotropy, strength, and ductility. The anisotropy could be correlated with the microstructure through the calculation of Taylor factors based on measurements using electron backscatter diffraction. The minor influence from the initial steel microstructure on the final mechanical properties indicates robustness suitable for mass production. Full article

Hot stamping is a promising method to manufacture ultra-high-strength automotive steel components with high dimension accuracy. In this work, two actual industrial production flows (with and without Al-Si hot dipping) were investigated to reveal their microstructural evolution and hydrogen content at different production steps. Meanwhile, the variations in composition and phase structures of the Al-Si coating layer were studied in terms of energy-dispersive spectrometry and electron backscattering diffraction techniques. The results showed that the microstructure at the steel substrate changed from the pancake-shaped pearlite and ferrite, degenerated pearlite and annealed ferrite, lath martensite, and then tempered martensite with the progress of the production steps, which was not affected by the Al-Si hot dipping. The final coating layer exhibited a multi-sublayer structure with the alternative distribution of FeAl and Fe₂Al₅, which contained many microcracks on the brittle phase Fe₂Al₅. The Al-Si-coated specimens always had higher hydrogen content than the bare steel specimens because of the hydrogen generation at the hot stamping stage and hydrogen absorption during the hot-dip aluminizing stage. Full article

Aluminum alloy hot stamping technology has quickly become a research hotspot for many scholars due to its ability to solve key challenges such as poor formability, large rebound, and low dimensional accuracy of aluminum alloy sheets at room temperature. This work systematically reviews the progress of Hot-Forming-Quenching (HFQ^®) technology and its optimization processes. The effects of key forming parameters are summarized, including temperature, forming rate, friction, and crimping force on the forming properties of aluminum alloys. Additionally, an ontological model of thermal deformation behavior and damage evolution during hot forming is analyzed. A multifactorial strength prediction model, integrating grain size and reinforcement mechanisms, is highlighted for its ability to accurately predict post-forming yield strength. To address the limitations of HFQ^®, optimization methods for solid solution and aging heat-treatment stages are categorized and evaluated, along with their advantages and disadvantages. Furthermore, the latest advancements in two innovative hot stamping processes (Low-Temperature Hot Form and Quench (LT-HFQ^®) and pre-hardened hot forming (PHF)) are reviewed. LT-HFQ^® improves formability by pre-cooling the sheet while maintaining solution treatment, while PHF utilizes pre-hardened aluminum alloys, enabling brief heating, forming, and quenching to significantly reduce cycle time while ensuring component strength. Finally, by summarizing current technological progress and challenges, future directions for aluminum alloy hot stamping are outlined, including advancements in forming processes, material modeling, and optimization through multidisciplinary collaboration and artificial intelligence to drive further innovation. Full article

A unified viscoplastic constitutive model based on internal physical variables was proposed to predict the viscoplastic mechanical behavior and microstructure evolution of metals during hot forging. Based on the phase transformation theory of materials under the effect of temperature, the evolution mechanism of residual stress during the cooling process after hot forging and stamping was explored. The determined unified viscoplastic constitutive equation was written in the VUMAT subroutine and employed for the explicit FE analysis of the hot forging and stamping process of thin-walled spherical shells. In the data transfer process, the stress field, temperature field, and deformation characteristics calculated during the high-temperature transient of the hot forging and stamping process were inherited. Meanwhile, the thermoplastic constitutive equation considering the influence of phase transformation was written in the UMAT subroutine and utilized for the implicit FE analysis of the cooling process of thin-walled spherical shells. Through comparison with the measured stress results of the spherical shells after actual forging, it was shown that the proposed constitutive model can effectively predict the microstructural evolution and the final residual stress distribution pattern of medium-carbon steel during the hot forging process. Full article

This investigation aimed at evaluating the weldability of a 2.1 GPa-grade hot stamping steel (HSS) containing 0.40 wt.% carbon using laser butt welding. It is shown that the subject HSS can be properly joined by laser welding without welding defects, such as voids and micro-cracks. The mechanical properties of joints before and after hot stamping were examined using cross-weld uniaxial tension and Vickers hardness, while microstructure was systematically characterized using optical microscopy and electron backscatter diffraction. The experimental results demonstrate that fresh martensite was formed in the weld nugget after welding, leading to a hardness much higher than that of the base metal. Nevertheless, such cross-weld microstructural heterogeneity was erased after hot stamping and low-temperature baking heat treatments, resulting in a uniform microstructure of lath martensite across the weld. As a result, the joint after hot stamping and baking exhibited an ultimate tensile strength of 2140 MPa and a total elongation of 12.03%, with the fracture occurring in the base metal. Such excellent mechanical properties of the joint demonstrate the great weldability of the present 2.1 GPa-grade HSS during laser welding. Full article

The hot forming-quenching integrated process (HFQ^®) organically combines the deformation and heat treatment, which can improve the forming performance of aluminum alloy while ensuring the final strength of formed parts. Thermal deformation in HFQ^® has a non-negligible influence on precipitation behavior in subsequent artificial aging treatment and affects the mechanical properties of the formed parts. In this study, the relationship between the precipitation behavior and thermal deformation ratios was investigated. Results indicated that the formation temperatures of η′ and η decreased with an increasing deformation ratio; however, the former decreased more than the latter. The activation energy of η′ precipitation decreased linearly with increasing deformation ratio. Additionally, the phase transition fraction of η′ increased with the deformation ratio, leading to shorter times required to reach equivalent phase transition fractions. Deformation accelerated the phase transition of η′, and greater deformation resulted in a shorter transition time. The aging time required for peak Vickers hardness decreased with increasing deformation ratio, reflecting the promotion of precipitated phase formation and transformation by introduced dislocations. Consequently, peak hardness and yield strength were achieved in shorter aging times. In terms of industrial applications, this discovery offers significant advantages for shortening the production cycle of the hot stamping process and reducing production costs. Full article

This study involved the investigation of the mechanical and tribological behaviors of DIN 1.2344 and WP7V tool steels, quenched in a salt bath after austenitization at 1050 °C, followed by triple tempering for 2 h. The selection of tempering temperatures produced two hardness levels under four metallurgical conditions, with the hardest level found only for WP7V steel (54 and 57 HRC). The mechanical properties were evaluated using Rockwell C, Vickers, and nanoindentation methods, along with unnotched impact tests, according to the SEP 1314 guidelines. Wear tests were conducted in a tribometer configured for a reciprocating setup, with a frequency of 5 Hz, a load of 25 N, and a time of 60 min, at room temperature and at 200 °C. As counterbodies, alumina balls of 5 mm in diameter were used. Wear tracks were evaluated through scanning electron microscopy, EDS, interferometry, and Raman spectroscopy. Friction and wear behaviors were affected by the variation in temperature for softer steels (DIN 1.2344 and WP7V of 48.5 HRC): the higher the temperature, the better the tribological performance. The harder steels were not sensitive to temperature testing. These effects depend on maintaining iron oxide (hematite) at the point of contact. The wear rates determined for the hardest material (57 HRC), considering its impact resistance, make it unsuitable for severe conditions such as hot stamping. Full article

Conventional lubricant testing methods focus on lab-scale constant contact conditions, which cannot represent the scenarios in actual hot-stamping processes. In recent studies, the concept of the ‘digital characteristics (DC)’ of metal forming has been proposed by unveiling the intrinsic nature of the specific forming, which presents a timely solution to address this challenge. In this work, the transient behaviours of three dedicated lubricants during the hot stamping of AA6111 material were investigated considering the effects of various contact conditions using an advanced friction testing system, and the interactive friction modelling was established accordingly. The lubricant limit diagram (LLD) of each lubricant was then generated to quantitatively evaluate the lubricant performance following the complex tool–workpiece interactions based on the tribological DCs, and a detailed investigation on the lubricant failure regions was conducted based on the interactive friction modelling. Finally, the industrial application index (IAI) was proposed and defined as a comprehensive evaluation of lubricant applications in the industry, and the most suitable lubricant was identified among the three candidates for mass production. Full article