Search

This paper explores the potential to hot stamp third-generation steels, in this case, a 980 MPa grade, while retaining or improving on the as-received microstructure, in particular the retained austenite (RA) fraction, and corresponding strength and ductility. Three classes of thermomechanical processes were investigated using a thermo-mechanical simulator system (Gleeble 3500). The first two processing routes considered a quenching and partitioning process starting from either a fully austenitic condition prior to quenching, designated the "Q&P" process, or an inter-critical partial austenitic condition, designated the "IC Q&P" process. In the two simulated Q&P processes, the samples were quenched to a predetermined temperature and then immediately transferred to a partitioning furnace. In the third processing route, designated the "Q&T" process, the samples were partially austenitized and then quenched to room temperature, followed by a tempering process to restore ductility. The conventional Q&P process resulted in excessive martensite formation, with high hardness and low ductility. The Q&T process produced a tempered martensite microstructure with hardness equivalent to the as-received sheet but with lower elongation and bendability. The IC Q&P heat treatment process increased the amount of retained austenite compared to the as-received sheet which translated into a higher yield strength, total elongation, and v-bend fracture angle. The IC Q&P ultimate tensile strength was approximately 8% lower than that of the as-received material. A sensitivity study was conducted to evaluate the influence of variations (± 25 °C) in the intercritical austenitization temperature, quench temperature, and partitioning temperature on the resulting microstructure and microhardness. The final mechanical properties were observed to be relatively independent of these process variations, indicating that the IC Q&P hot stamping process appears to be robust. [ABSTRACT FROM AUTHOR]

Hot stamping is a well‐established process in the automotive industry for structural parts to decrease the weight of a vehicle without reducing the safety and stiffness of components. In this work, a bainitic approach during the hot stamping process is studied by anisothermal annealing. The effect of different strategies on the microstructure and mechanical properties of the hot‐stamped parts is investigated. The microstructure is analyzed using light microscopy (LM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques. Tensile and hardness tests are applied to analyze mechanical properties. A microstructure consisting of a carbide‐free bainite matrix containing martensite, fine‐grained ferrite, and retained austenite is obtained. SEM analysis of fracture surfaces from tensile samples reveals that the bainitic microstructure showed mainly a ductile fracture by dimples and voids along with some quasi‐cleavage fracture. [ABSTRACT FROM AUTHOR]

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and high-ductility sections, by controlling the cooling rate. The process is versatile in terms of the microstructures and mechanical properties that can be obtained. This versatility, however, puts high demands on the materials pertaining their stability, wear resistance, costs, etc. This study has focused on understanding the effect of temperature on the tribological response of different tool materials when these are exposed to high temperatures. The results show that friction significantly stabilises with increased temperature for most tool steels. One tool steel behaves more unstably at high temperature, and this is attributed to the presence of Cr7C3, MoO3, and VO and severe wear on the workpiece material. The most severe wear on the workpiece is caused by a partially melted interdiffusion layer, which facilitates the detachment of the Al-Si coating and subsequent transfer onto the tool; this effect is maximised at the highest temperatures of the workpiece. An important finding is that friction and material transfer severity decrease as the workpiece temperature decreases, and friction is stabilised as tool temperature increases without minimising wear or the average friction coefficient. [ABSTRACT FROM AUTHOR]

AA7075-T6 sheets with 1, 1.5, and 2 mm thicknesses were tailor-welded using the gas tungsten arc welding process. The welded blanks were solution heat treated, hot stamped, and simultaneously quenched to produce U-shaped components, and finally artificially aged. A finite element model using the ABAQUS software was developed to simulate the forming process. The experimental and numerical results showed no rupture in the components. Tensile and hardness tests revealed that the maximum tensile strength, yield strength, and microhardness of the aged specimen were approximately 96%, 93%, and 107% of the initial material, respectively. Maximum and minimum microhardness of 196 and 145 HV were observed in the heat-affected and fusion zones of the specimens, respectively. Increasing the tailoring ratio increased the strengthening behavior of the components. With a tailoring ratio of 1, the maximum and minimum elongations at break were 70% and 40% of the original aluminum sheet for 2 mm and 1 mm thick sheets, respectively. [ABSTRACT FROM AUTHOR]

Hot stamping is a widely adopted technique for manufacturing high-strength vehicle body parts using boron-alloyed steels, such as 22MnB5. This process involves heating the material to 900 ℃ or higher in a furnace, followed by in-die quenching to achieve a strength of over 1.5 GPa. The process includes heating, forming, in-die quenching, and trimming. Laser trimming is the conventional method used for this purpose. However, laser trimming has limitations in terms of productivity and energy cost, and alternative methods have been explored, such as mechanical piercing during the hot stamping process at high temperatures. This study aims to optimize the process parameters, including the piercing temperature, time and clearance between the die-punch, to achieve optimal performance and their mechanical stability. The results show that hot piercing is the feasible method for cutting the boron-alloyed steel parts during the hot stamping process. In this study, the optimal performance is achieved under specific process conditions used for hot mechanical piercing, which is corresponding to differential clearance and mechanical piercing time, respectively. The size and distribution of the burr generated by the shearing process were not significantly affected by the hot mechanical piercing time with lower clearance. However, with the larger clearance, the hot mechanical piercing time significantly affected the size and distribution of the burr. In addition, hydrogen embrittlement becomes more severe as the martensitic phase transformation completes, and the hot mechanical piercing time has the greater influence on the process than the clearance conditions. Therefore, when designing the process for optimal performance of hot mechanical piercing, it is crucial to consider the effects of clearance and time as significant variables and verify their effects. [ABSTRACT FROM AUTHOR]

In this study, the viscoelastic constitutive equation of continuous glass fiber reinforced polypropylene composites based on the generalized Maxwell model and SCFM model was constructed by combining genetic algorithm. Based on this, a multi-scale numerical model for describing material relaxation and creep is proposed, and the accuracy of different scale models was compared through experiments. The forming state of the workpiece under various stamping speeds and preheating temperatures was also examined using a hot stamping numerical model. The independent design of the hot stamping hemispherical mold was used to confirm the hot stamping model's accuracy. The study's findings demonstrate that the macroscopic model can accurately simulate the relaxation and creep of composite materials. The hot stamping simulation results are match up well with experimental results. Composite molding defects appeared at the waist of the part, and defects were accompanied by resin loss. [ABSTRACT FROM AUTHOR]

Hot stamping of high-strength steel plays an increasingly important role as the demand for automotive lightweighting increases. However, the existing hot stamping process faces challenges such as a lack of digital monitoring, limited monitoring scope, unintuitive production data, and untimely analysis of production events. This paper proposes a framework for a hot stamping production monitoring system based on digital twin technology. By exploring key technologies, including finite state machine (FSM) modeling of the production process, collection, and storage of multi-source data, a digital twin monitoring system for the hot stamping line was developed by combining the data with virtual 3D equipment for multi-dimensional information integration. The system can visualize production information from multiple dimensions and reproduce the production process to analyze production events. Finally, the feasibility and effectiveness of the digital twin system were verified through real-world scenarios, providing valuable insights for hot stamping production process monitoring. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Through the study of the thermal rheological behavior of Ti6Al4V alloy at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C) and different strain rates (0.1 s−1, 0.05 s−1, 0.01 s−1, and 0.005 s−1), a constitutive model was developed for Ti6Al4V alloy across a wide temperature range in the hot stamping process. The model's correlation coefficient reached 0.9847, indicating its high predictive accuracy. Hot processing maps suitable for the hot stamping process of Ti6Al4V alloy were developed, demonstrating the significant impact of the strain rate on the hot formability of Ti6Al4V alloy. At higher strain rates (>0.05 s−1), the hot processing of Ti6Al4V alloy is less prone to instability. Combining hot processing maps with hot stamping experiments, it was found that the forming quality and thickness uniformity of parts improved significantly with the increase in stamping speed. The phase composition and microstructures of the forming parts under different heating temperature conditions have been investigated using SEM, EBSD, XRD, and TEM, and the maximum heating temperature of hot stamping forming was determined to be 875 °C. The recrystallization mechanism in hot stamping of Ti6Al4V alloys was proposed based on EBSD tests on different sections of a hot stamping formed box-shaped component. With increasing deformation, the effect of dynamic recrystallization (DRX) was enhanced. When the thinning rate reached 15%, DRX surpassed dynamic recovery (DRV) as the dominant softening mechanism. DRX grains at different thinning rates were formed through both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), with CDRX always being the dominant mechanism. [ABSTRACT FROM AUTHOR]

The increasing demand for lightweight vehicles, while ensuring collision safety, has led to the growing utilization of high-strength steel sheets. Accordingly, the hot stamping process, which involves heating the material and shaping it in a die while simultaneously cooling it, has gained significant attention. However, the inclusion of heating and cooling processes in the hot stamping engineering presents competitive disadvantages in terms of cost. As a result, numerous studies are being carried out to overcome these challenges and improve productivity. In particular, the sidewall areas of the vehicle body parts, which thin out during the stamping process, can experience a reduced cooling rate compared to other areas. To counteract the potential risk of a relative decrease in strength in these areas, extending the pressurization time of the press becomes necessary. In this study, by introducing groove patterns on the surface of the die used in the hot stamping forming and cooling processes, it was investigated how to enhance the cooling rate of the sidewall of the vehicle part without necessitating additional press dwell time. Using this approach, it was possible to achieve a strength of over 1.6 GPa and a dimensional accuracy of -0.06 mm within a short in-die quenching time of 6 s. [ABSTRACT FROM AUTHOR]

Medium-Mn steel with M3 microstructural characteristics (multiphase, multiscale, and metastable) is a promising third-generation automotive steel owing to its remarkable combination of ultrahigh strength and ductility. Hot stamping of medium-Mn steel is a new approach that integrates steel stamping and quenching, during which the formability and mechanical properties of the steel are enhanced. However, there exists an increasing danger of hydrogen-induced degradation of mechanical properties with increasing steel strength grade, and minimal research is available on the hydrogen embrittlement (HE) susceptibility of hot stamped medium-Mn steel. With this aim, the susceptibility to HE of a widely used medium-Mn steel 0.1C–5Mn subjected to hot stamping at 850, 950, and 1000 ℃ was examined using electrochemical hydrogen charging, hydrogen permeation test, and slow strain rate tensile test. The results of microstructural evaluation reveal that all hot stamped samples have a full martensite microstructure with a certain amount of needle-like ε-carbide precipitates owing to self-tempering during the hot stamping process. With increasing heating temperature, the prior austenite grain size increased, whereas the strength and ductility of the tested steel gradually decreased. At 850 ℃, a good combination of strength and ductility was obtained, and the product of the ultimate tensile strength and total elongation was 22 GPa·%. With increasing heating temperature, the content of diffusible hydrogen remarkably decreased, and that of nondiffusible hydrogen increased, whereas the HE index (HEI) expressed by the relative notch tensile strength loss and effective hydrogen diffusion coefficient initially increased and then decreased. The HE susceptibility of the sample heating to 1000 ℃ with an HEI value of ～65% was the lowest among the three samples examined. Further fracture analysis demonstrated that the prehydrogen-charged samples were fractured by intergranular cracking along the boundaries of prior austenite grains in the crack initiation region. It is concluded that the variations in the susceptibility to HE of the tested medium-Mn steel with heating temperature are primarily owing to the changes in strength and self-tempered ε-carbide precipitates during the hot stamping process. Compared with the currently widely used hot stamping steel 22MnB5 with an HEI value of ～62%, the susceptibility to HE of the hot stamped medium-Mn steel of interest remains a little higher than the steel 22MnB5, which is primarily owing to its relatively low martensite transformation start temperature (Ms) and thus low self-tempering degree.

Digital image correlation (DIC) outperforms other strain measurement technologies due to its versatility, accuracy, non-contact nature, and capability to capture full-field strains. However, for aluminium alloys like AA6082 under high-temperature and large-deformation conditions, the shiny effects observed in the gauge area degrade the quality of the captured deformation images, leading to failures in the DIC analyses. In this study, the source of the shiny effects was investigated by analysing the evolution of AA6082 specimen surfaces painted with speckle patterns during hot stamping deformation. It was found that the shiny effects were attributed to the exposure of the reflective base material due to paint peeling and cracking. To overcome these problems, the DIC method was improved by developing a novel procedure for generating more effective speckle patterns and utilising a cross-polarisation optical system (XPOL) to mitigate the shiny effects. The improved DIC method was applied to AA6082 in both uniaxial and biaxial tensile tests under diverse hot stamping conditions, along with applications to boron steel for comparison. These improvements significantly reduced the shiny effects and increased the time over which full-field strains can be measured for AA6082, reaching over 96% (up from 75%) of the fracture time in the uniaxial tests and even 100% in the biaxial tests. The improved DIC method enables the full-field strain measurement for aluminium alloys under hot stamping conditions, allowing for the accurate determination of their thermomechanical properties.

As a promising solution to the growing demand for lightweighting, hot stamping has gained considerable applications in the automotive industry. Over the past few decades, the market for hot stamping has experienced explosive growth, with ongoing advancements offering potential for further expansion of its applications. This paper provides a historical overview of hot stamping alongside an in-depth analysis of future trends. Scientific publications, patents and industrial applications of hot stamping are systematically reviewed, with major developments in materials, processes, tools, and other relevant aspects being highlighted. Through data analysis, the current state of hot stamping is comprehensively depicted, and the trends in the development of hot stamping are revealed. Additionally, the future of extending hot stamping technologies to a broader range of materials is discussed, with suggestions furnished from both academic and industrial perspectives.

A method for assessing the thermal fatigue material resistance is proposed, which ensures testing under conditions close to real hot-stamping. To implement the proposed technique, an installation is designed and manufactured that provides heating of the sample end surfaces with regulation of the thermal cycle frequency and ratio of heating-cooling periods. The results of theoretical and experimental studies of the temperature conditions of operation of the working tool of an automatic hot-stamping press are presented. The application of the proposed evaluation method of thermal fatigue material resistance makes it possible to study the patterns of thermal fatigue destruction of the hot-stamping tool material and, on this basis, to develop and optimize laser heat treatment technology and other technological processes. [ABSTRACT FROM AUTHOR]

Titanium alloy hot stamping technology has a wide range of application prospects in the field of titanium alloy part processing due to its high production efficiency and low manufacturing cost. However, the challenges of forming titanium alloy parts with large depths and deformations have restricted its development. In this study, the hot stamping process of a Ti6Al4V alloy box-shaped part was investigated using ABAQUS 2020 software. The thermodynamic properties of a Ti6Al4V alloy sheet were explored at different temperatures (400 °C, 500 °C, 600 °C, 700 °C, 800 °C) and different strain rates (0.1 s−1, 0.05 s−1, 0.01 s−1). In addition, the influence law of hot stamping process parameters on the minimum thickness of the formed part was revealed through the analysis of response surface methodology (RSM), ultimately obtaining the optimal combination of process parameters for Ti6Al4V alloy hot stamping. The experimental results of the hot stamping process exhibited a favorable correlation with the simulated outcomes, confirming the accuracy of the numerical simulation. The study on the microstructure evolution of the formed parts showed that grain refinement strengthening occurred in the part with large deformation, and the formed box-shaped parts exhibited a uniform and fine microstructure overall, demonstrating high forming quality. The achievements of the work provide important guidance for the fabrication of titanium alloy parts with large depths and deformations used in heavy industrial production. [ABSTRACT FROM AUTHOR]

Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high‐boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies. [ABSTRACT FROM AUTHOR]

Tailoring the properties of hot-stamped components offers the potential to enhance crash performance while simultaneously improving downstream joining processes. In recent years, an innovative technology suited for achieving tailored properties involving the utilization of a specialized furnace chamber, known as the TemperBox®, has been introduced. Within this chamber, a cooled aluminum mask shields specific areas of the blank from incoming heat radiation and concurrently absorbs the blank's own radiation. The duration of the heat radiation exchange can influence the diffusion-dependent phase transformation and, consequently, the resulting mechanical properties. Hence, the intermediate cooling duration assumes a pivotal role as a parameter, as is investigated in this study. To examine the effects, specimens of the steel 22MnB5 AS150 are subjected to intermediate cooling of varying durations, followed by forming and partial quenching. The temperature profile of the blank during intermediate cooling prior to forming and quenching is analyzed. Subsequently, the tailored hot-stamped components are assessed for hardness, strength, ductility, and thickness strain. The study reveals that with increasing duration of partial intermediate cooling and targeted radiation exchange, a homogeneous ferritic–pearlitic structure is formed from an austenitic structure. This uniform structure of ferrite and pearlite is reflected in lower hardness and strength values, along with improved ductility. Additionally, this paper introduces a simulation methodology designed to calculate the dynamics of thermal radiation and the kinetics of phase transformation. [ABSTRACT FROM AUTHOR]

A hot-stamping method was established for manufacturing high-strength automotive parts with good shape fixability. The hot-stamping method has recently been applied to high-performance parts with tailored properties. CAE is indispensable for the design of such parts. To design hot-stamped parts, the forming simulation must be coupled with thermal analysis to consider the effect of temperature on formability. The final shape does not need to be predicted because of its good fixability. However, for high-performance parts with tailored properties, predicting the effect of phase transformations on the final shape is important. A CAE method that considers the phase transformation effects was developed to predict the final shape of the hot-stamped parts. The accuracy of the final shape calculation utilizing the CAE method is also investigated. Hotstamping experiments were conducted to obtain parts of different shapes via cooling control, and a CAE analysis of the final shape for each experimental condition was conducted. It was clarified that the final shape varied by changing the cooling process and that the results of CAE, including phase transformation, agreed with the tendency for shape change in the cross-section. [ABSTRACT FROM AUTHOR]

Hot stamping is an innovative technology that enables the production of high-strength automotive body parts by heating the material to a high temperature and simultaneously forming and quenching it in-die. The process results in parts with excellent strength-to-weight ratios, which are essential for the automotive industry. The widely used 22MnB5 material is heated to temperatures above 900 °C, and an Al-Si coating is applied to prevent the formation of oxide scale on the sheet surface. The distinctive color on the sheet surface after hot stamping is produced by the Al-Si coating. This phenomenon is attributed to the formation of Al2O3 on the surface of the Al-Si coating layer and the diffusion of Fe from the substrate into the Al-Si coating layer, both of which are significantly influenced by the heating time and temperature. The hot stamping materials coated with Al-Si show an increase in the thickness of the inter-diffusion layer as the heating temperature and time increase. This leads to an increase in welding resistance and the potential for weld performance. Moreover, as hydrogen uptake increases, the likelihood of hydrogen embrittlement becomes significantly higher. Thus, the optimal heating temperature and duration time are critical parameters in the hot stamping process. To confirm that hot stamping components were subjected to the proper heating conditions, it was essential to extract a sample for analysis. However, in this study, a neural network approach was utilized, enabling the heating temperature and duration time conditions of the hot stamping section to be determined based solely on image information. Furthermore, an image-based model was applied to quantitatively predict the thickness of the inter-diffusion layer that affects weldability and the hydrogen uptake that influences hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Non-isothermal hot forming processes are of great scientific and industrial interest to produce e.g. high-strength aluminum components for lightweight applications. The interfacial heat transfer coefficient (IHTC) is a key factor in the design of these forming processes. However, the IHTC values reported in the literature vary significantly, even for the same material combinations and load conditions. The present work reveals the causes of these variations by a combined experimental and model-based approach. It is shown that the measurement of dynamically changing blank temperatures and the determination of the die surface temperature are two core aspects of non-isothermal experimental IHTC analysis. [ABSTRACT FROM AUTHOR]

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and high-ductility sections, by controlling the cooling rate. The process is versatile in terms of the microstructures and mechanical properties that can be obtained. This versatility, however, puts high demands on the materials pertaining their stability, wear resistance, costs, etc. This study has focused on understanding the effect of temperature on the tribological response of different tool materials when these are exposed to high temperatures. The results show that friction significantly stabilises with increased temperature for most tool steels. One tool steel behaves more unstably at high temperature, and this is attributed to the presence of Cr7C3, MoO3, and VO and severe wear on the workpiece material. The most severe wear on the workpiece is caused by a partially melted interdiffusion layer, which facilitates the detachment of the Al-Si coating and subsequent transfer onto the tool; this effect is maximised at the highest temperatures of the workpiece. An important finding is that friction and material transfer severity decrease as the workpiece temperature decreases, and friction is stabilised as tool temperature increases without minimising wear or the average friction coefficient.

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.