Hot Stamping Research Articles

Damage failure prediction study of carbon fiber metal laminates in hot stamping process

In addressing the difficulty of forming Fiber Metal Laminates (FMLs), a laminate composed of a 0.1 mm-thick 304 Stainless Steel Foil (SSF) and Carbon Fiber Reinforced Plastics (CFRP) as the base material is prepared using a specific process. Subsequently, forming limit diagrams are obtained through hemispherical bulge forming experiments to investigate the forming performance of FMLs laminates. The damage phenomena of various forming specimens during the thermal stamping process are analyzed. Based on different damage forms, corresponding theoretical models are established to simulate and predict the forming damage modes of FMLs through simulation. The research results indicate that the stamping formability of FMLs is influenced by the damage tolerance of the thin stainless steel foil. During the thermal stamping process, FMLs may experience delamination, fracture/crack of the thin stainless steel foil, and rupture/tearing/wrinkling of the prepreg. To address these issues, cohesive elements, GTN-M-K damage, and Hashin damage models are established, providing a reasonable simulation prediction of the stamping damage phenomena of FMLs.

Enhanced Yield Strength and Total Elongation of an Ultrahigh Strength Hot‐Stamped Steel via Tempering Treatment

A 2460 MPa ultimate tensile strength (UTS) has been achieved in this experimental steel, which was processed by a conventional hot stamping process with water quenching to room temperature. Additionally, comparing the microstructure evolution and strengthening mechanism before and after tempering, the microstructure has changed from fresh martensite transformed into tempered martensite with acicular carbides, and the fracture mode has also changed from brittle fracture transformed into ductile fracture mainly. Meanwhile, the main strengthening mechanism has changed from dislocation strengthening to precipitation and dislocation strengthening. Overall, the tempering process reduces dislocation density and produces acicular carbides, which decrease UTS. However, the tempering process reduces the quenching residual stress and changes the morphology of twin martensite, resulting in an increase in ductility. Meanwhile, it enhances the effect of carbide pinning dislocations, significantly enhances precipitation strengthening, and improves yield strength.

An improved DIC method for full-field strain measurement in tensile tests on aluminium alloys under hot stamping conditions

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.

FEM model optimization study of mechanical properties and material selection in stamping process

Abstract This paper establishes a finite element model of stamping and forming and proposes solution algorithms for static and dynamic forces. The finite element simulation of the hot stamping process is carried out to analyze the thermophysical parameters of BR1500HS ultra-high-strength steel sheet material and H13 steel mold material. Set the temperatures of austenitic material in the transfer process and molding process, obtain the rheological stress data of BR1500HS ultra-high-strength steel plate during plastic deformation at high temperature, and determine the basic mechanical properties of the material at high temperature. A geometric finite element model of thermal-force-phase coupling of the hot stamping and forming process is established to simulate the temperature field change of the steel plate during the hot stamping and forming process by combining the process conditions and process parameters. At the same time, the ultra-high-strength boron steel 22MnB5 is selected to simulate the hot forming and tempering process of U-shaped parts made of high-strength steel sheet material, and the feasibility of the finite element model is verified. Different hot stamping process parameters are set to analyze the forming quality of both BR1500HS ultra-high strength steel and ultra-high-strength boron steel 22MnB5. When the stamping speed is increased from 50mm/s to 100mm/s, the maximum equivalent force of BR1500HS ultra-high strength steel decreases, and thus, when the stamping speed is 100mm/s and the holding time is 5s, the part forming performance is better, which meets the requirements of the gradient performance hot stamping process.

Development and study using digital simulation in QFORM program of hot stamping process of double-layer parts

A scheme is proposed and the hot stamping process of two-layer parts (such as mandrels for piercing mills) is studied. Digital modeling in the QForm program determined the effect of technological parameters on the power parameters of the process, the stress-strain state and temperature fields of the forging and the tool along the transitions. A die equipment scheme is proposed.

Experimental investigation and kinetic analysis of Al–Zn–Mg alloy coating

The hot-dip 55 wt%Al–Zn-1.6 wt%Si-(0–3)wt.%Mg alloy coatings were experimentally investigated, and the solidification behaviors and hot cracking susceptibility were simulated by means of CALPHAD (CALculation of PHAse Diagrams) method. The scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA) and glow discharge spectrometer method (GDS) were utilized to determine the microstructures and the distribution of elements of the Al–Zn–Mg alloy coatings with different Mg contents. It is discovered that with the increase of Mg content, the percentage of the eutectic microstructure scales up, and the surface quality of the alloy coating is improved. Meanwhile, the bending properties of Al–Zn–Mg coatings with different Mg contents still requires further improvement according to the present bending test. Subsequently, the equilibrium solidification processes of the coatings were calculated using thermodynamic approach. In general, the calculated results reflect the solidified phases and the precipitated temperatures according to theory of equilibrium solidification. However, there still exist discrepancies between the thermodynamic calculation results and the observed experimental results during the practical galvanizing process, because the cooling rates were not taken fully into consideration. Consequently, the kinetic analysis was carried out to obtain the secondary dendrite arm spacing under different cooling rates. The cracking susceptibility index (CSI) was also calculated to predict the hot workability of the Al–Zn–Mg alloy coating. In summary, the appropriate increase of the cooling rate turns out be the effective approach to benefit the microstructure and the corrosion resistance of the Al–Zn–Mg coatings in the practical galvanizing process, and the coating is not suitable for the hot stamping process.

Flexible N-Doped Graphene Electrodes Fabricated via Rapid Direct Hot Stamping for Microsupercapacitors

Flexible N-Doped Graphene Electrodes Fabricated via Rapid Direct Hot Stamping for Microsupercapacitors

Microstructure and mechanical properties of adjustable-ring-mode laser welded and hot-stamped Al–Si coated boron steel joints

The microstructure and mechanical properties of adjustable-ring-mode (ARM) laser-welded, hot-stamped 22MnB5 steel joints were analyzed and compared with those of Al–Si coated 22MnB5. Al segregation into the fusion zone (FZ) was suppressed by a ring beam introduced via ring-beam-mode (RBM) and dual-beam-mode (DBM) laser welding. Dilution of the Al–Si coating in the FZ induced α-ferrite formation during hot stamping. After hot stamping, the α-ferrite fraction in the FZ decreased (from 23 vol% to 4.27 vol%) more than that in the center-beam-mode (CBM) welded joints owing to the ring beam. Electron backscattered diffraction analysis indicated the distribution of high-density and uniform geometrically necessary dislocations, which caused coordinated deformation in the martensite grains, in the RBM and DBM FZs. The average microhardness in the FZ in the tailor-welded blank (TWB) joints was ∼30–40 HV lower than that in the RBM and DBM welded base metal (480 HV) and that in the FZ of the CBM reduced to 295 HV because of the formation of a large amount of ductile α-ferrite. The tensile strength and elongation of the TWB joint in the CBM were ∼989 MPa and 1.1 %, respectively, which were significantly lower than those of the RBM (1245 MPa and 1.96 %, respectively) and DBM (1321 MPa and 2.12 %, respectively). Finally, the 22MnB5 steel sheets were subjected to ARM laser welding without removing the coating layer to evaluate the effect of the ring beam on Al segregation suppression in the FZ and mechanical properties of the TWB joints.

Fabrication of TA2–304 SS laminated metal composite using directed energy deposition-arc: Microstructure, mechanical property, and corrosion resistance

Conventional fabricating methods of TA2–304 SS laminated metal composite (LMC) (e.g., hot rolling, hot stamping, and explosive welding) have difficulty in removing brittle TiFe intermetallic compounds (IMCs) and are not suitable for the preparation of the small size structure components or transition joints. Additive manufacturing of LMCs has the potential to achieve the desired microstructure, properties, and structure. In this study, TA2–304 SS LMC, which has been extensively employed in pipe flanges of nuclear plants and bows of sonar dome, was well fabricated by utilizing directed energy deposition-arc (DED-arc) and copper‑nickel alloy transition interlayers, and the formation of brittle TiFe IMCs was suppressed. The results of this study indicated that the standard deviation of the height of the surface morphology reconstructed by adopting Python VTK technique was evaluated as 0.67. Furthermore, copper‑nickel transition interlayers possessed the capability of isolating Ti from Fe atoms through the formation of laminar-distributed microstructure. Specifically, the Interlayer1 was comprised of (Fe, Cr) grains with different shapes and small-size (Cu) equiaxial grains, Interlayer2 covered large-size (Cu, Ni) dendritic grains and intergranular (Cu), and the TA2 layer comprised α-Ti and Ti2Cu. The result also showed that thermal cycle-induced recovery and recrystallization and diffusion-induced elemental interaction accounted for the different microstructures. Moreover, the interface between the TA2 and Interlayer2 layers contained TiCu4 + (Cu), Ti3Cu4 + TiCu4, Ti2Cu + TiCu, and TiCu + Ti2Cu eutectoid microstructures, which resulted in the highest hardness of 450Hv as well as crack initiation and extension. Furthermore, due to the uniform-distribution of microstructure in the absence of brittle IMCs, the average shear strength was 234.0 MPa, which reached the strength of the conventional method and conformed to the standard requirements. Multiple groups of galvanic reactions between different transition materials can result in reduced corrosion resistance, and the oxidation-reduction reactions can lead to the formation of massive oxides.

Design and optimization of cooling channels in hot stamping dies applying additive manufacturing design concept

The stamping process is a process that represents a key manufacturing process in the automotive industry. With the implementation of the stamping process, mechanical elements obtain mechanical resistance, in addition to a very low ratio in quantity/cost. Within the design premises that govern the automotive industry, it is worth highlighting the requirement for mechanical resistance, passenger safety, and the lightness of materials. All of this contributes to the current use of alloyed materials with high mechanical resistance. These materials in addition to keeping the mechanical requirements of the different components subjected to load, must satisfy the geometric requirements established by the designers. In the last few years, the use of the Ultra High Strength steels has grown in the automotive industry. This type of alloyed steel contributes to car safety and clean mobility. Given the mechanical nature of these ultra-high-strength alloys, they require the use of hot stamping. This makes the deformability of the different steels easier and allows that, using a conventional stamping method, would not be able to deform according to the geometric requirements of the different mechanical components.

Hot Stamping of Heavy-Gaged - Full Development and the Effect of Press Hardening Process on the Microstructure and Mechanical Properties of 22MnB5 + NbMo Alloyed

For saving mass, to improve the payloads and the durability of commercial vehicles, it is necessary to increase the thickness range of PHS - Press Hardening Steel, replacing low strength steel grades on structural and saving parts. This work presents the industrial development of Heavy-Gaged PHS-Press hardening Steel (4-8mm) starting from the alloy design concept, especially adding niobium to promote a fine and homogeneous microstructure. The development included hot forming simulations, in order to achieve martensitic microstructure through the thickness, correlating with cooling rates and mechanical characteristics, after quenching, as well as welding qualification and fatigue evaluation. Furthermore, were presented the characterization of 22MnB5(Nb+Mo) steel after industrial hot stamping that were evaluated mechanical properties, using the Vickers 10Kgf and the relationship between the microstructure and the thermodynamic aspects.

Numerical simulation analysis of forming of continuous fiber reinforced polypropylene composites: Relaxation, creep, and hot stamping

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.

Analysis of characteristic prediction of aluminized boron steel after the hot stamping process using an image color-based neural network

Analysis of characteristic prediction of aluminized boron steel after the hot stamping process using an image color-based neural network

Experimental investigation on boiling heat transfer performance of fractal microchannels for high heat dissipation applications

This study proposes novel fractal microchannels (FMCs) manufactured by additive manufacturing for direct cooling systems with high heat dissipation. The boiling heat transfer performance of water in the FMC was experimentally investigated under various operating conditions. Furthermore, a comparative heat transfer performance evaluation between the FMC and conventional microchannels (CMCs) was conducted. The critical heat flux of water in the FMC was 11 % higher than that in the CMC due to enhanced boiling heat transfer. In the low heat flux region, the boiling heat transfer coefficient (BHTC) of water in the FMC increased as the mass flow rate increased owing to the liquid replenishing and rewetting effects. However, in the moderate and high heat flux regions, the effect of the mass flow rate was not significant owing to the dominance of nucleate boiling. The BHTC of water in the FMC increased as the water temperature decreased due to the increased rewetting frequency. This study provides useful information for improving the design of direct cooling channels and for understanding the fundamental boiling heat transfer characteristics in FMCs. Furthermore, the proposed FMC can be applied in fields requiring high heat dissipation, such as electronic devices, power plants, and hot stamping.

The Influence of Precooling on Liquid Metal Embrittlement and Microstructure Properties of Galvanized 22MnB5 Tubes

To address the issue of liquid metal embrittlement (LME) susceptibility in galvanized 22MnB5 steel during the hot stamping process, the material's performance is affected. This study proposes a method combining precooling and tube hydroforging to produce galvanized tubular hot stamping parts. The primary workflow comprises four distinct stages: the heating phase, thermal retention phase, precooling phase, and the tube hydroforging phase. Notably, the precooling stage employs two distinct approaches: air precooling and boiling water precooling. The composition and morphology of the zinc coating and the microstructure and mechanical properties of the 22MnB5 steel are investigated using two precooling methods at different hydroforging temperatures. The results show that when the initial hydroforging temperature is below 800 °C, the precooling combined with the tube hydroforging process eliminates LME. With increasing precooling time, the oxidation reaction forms ZnO and Fe2O3 on the coating. By comparing the composition, morphology, and mechanical properties of the coatings at hydroforging temperatures of 800 °C and 500 °C, it is concluded that the boiling water precooling aligns more effectively with the requirements of industrial production, with the optimal forming temperature being within the range of 750–800 °C.

A Rate-Temperature-Dependent Visco-Hyperelastic Constitutive Model for UD CF/PEEK Prepregs During a One-Step Hot Stamping Forming Process

An anisotropic visco-hyperelastic constitutive model for rate-temperature-dependent deformation during one-step hot stamping forming simulation of unidirectional (UD) CF/PEEK prepregs is presented. This constitutive model is based on strain energy decomposition and a multiplicative decomposition of the deformation gradient. Two simple Maxwell models are used to characterize the viscoelastic behavior of the melted PEEK matrix and longitudinal shear deformation, respectively, and a shear invariant of [Formula: see text] is proposed to calculate the shear deformation. Moreover, the fiber stretching deformation is modeled by an anisotropic hyperelastic model. To obtain the model parameters, tensile tests at different strain rates and temperatures above the melt temperature of PEEK are performed on [Formula: see text], [Formula: see text], and [Formula: see text] CF/PEEK prepreg specimens, respectively. In parallel, the [0]8 and [45]8 curved beam specimens are experimentally fabricated to validate the constitutive model. The VUMAT subroutine is developed according to the proposed constitutive model and applied for a [Formula: see text] off-axis tensile simulation and hot-stamping forming simulation of CF/PEEK prepregs. The experimental and simulation results show that the materials flow, distribution of strain and stress, forming defects (wrinkles and overlap) of CF/PEEK curved beam can be captured by the proposed model.

Analysis of Mechanical Properties and Structural Analysis According to the Multi-Layered Structure of Polyethylene-Based Self-Reinforced Composites.

In this research, a self-reinforced composite material was manufactured using a single polyethylene material, and this self-reinforced composite material has excellent recyclability and is environmentally friendly compared to composite materials composed of other types of material, such as glass fiber reinforced composites (GFRP) and carbon fiber reinforced composites (CFRP). In this research, the manufactured self-reinforced composite material consists of an outer layer and an inner layer. To manufacture the outer layer, low density polyethylene (LDPE) films were laminated on high density polyethylene (HDPE) fabrics and knitted fabrics, and composite materials were prepared at various temperatures using hot stamping. A 3D printing process was utilized to manufacture the inner layer. After designing a structure with a cross-sectional shape of a triangle, circle, or hexagon, the inner layer structure was manufactured by 3D printing high-density polyethylene material. As an adhesive film for bonding the outer layer and the inner layer, a polyethylene-based self-reinforced composite material was prepared using a low-density polyethylene material. Input data for simulation of self-reinforced composite materials were obtained through tensile property analysis using a universal testing machine (UTM, Shimadzu, Kyoto, Japan), and the physical property values derived as output data and actual experimental values were obtained. As a result of the comparison, the error rate between simulation data and experimental data was 5.4% when the shape of the inner layer of self-reinforced composite material was a hexagon, 3.6% when it was a circle, and 7.8% when a triangular shape showed the highest value. Simulation in a virtual space can reduce the time and cost required for actual research and can be important data for producing high-quality products.

ОСНОВНЫЕ ПРЕДПОСЫЛКИ ВОССТАНОВЛЕНИЯ СТУПЕНЧАТЫХ ВАЛОВ ДАВЛЕНИЕМ

The reliability and performance indicators of the known methods currently used in the country's repair industry for the restoration of stepped shafts cannot compete with the indicators of new parts. The most progressive method of restoring step shafts is the method of hot volume stamping. The technical characteristics of pressure-remanufactured parts indicate that their quality is not inferior to serial parts.

Studying the Effect of Cr and Si on the High-Temperature Oxidation-Resistance Mechanism of Hot Stamping Steel

The surface of hot stamping steel is severely oxidized during heating, holding, and transfer from the heating furnace to the stamping die in the production of traditional automotive parts. Coating-free hot stamping steel with Cr and Si elements exhibits excellent oxidation resistance during hot stamping without the protection of a surface coating. This paper investigates the oxidation behavior of three types of hot stamping steel at 800–1200 °C. The results show that although Cr-Si hot stamping steel performs excellently short-term (≤7.5 min) for oxidation resistance, its long-term (≥15 min) or high-temperature (≥1100 °C) oxidation resistance is much lower than that of the conventional hot stamping steel 22MnB5, affecting the production and surface quality control of the new coating-free Cr-Si hot stamping steel. By analyzing the oxidation kinetics and characterizing the structure of oxide layers in hot stamping steel, it was found that the structural change in the Cr and Si element enrichment layer between the oxide scale and the substrate varied in oxidation performance at different temperatures. When the oxidation temperature was below 1000 °C, the solid Cr and Si enrichment layer acted as a barrier to prevent the diffusion of Fe ions. When the oxidation temperature exceeded 1100 °C, the molten Cr and Si enrichment layer effectively adapted to the substrate and avoided blistering. Meanwhile, Fe2SiO4 penetrated the Fe oxide layer along the grain boundary and became a rapidly diffusing channel of Fe ions, contributing to a significant increase in the oxidation rate.

The Study of Hardness Evolution during the Tempering Process of 38MnB5Nb Ultra-High-Strength Hot Stamping Steel: Experimental Analysis and Constitutive Models

To elucidate the hardness evolution behaviors for 38MnB5Nb ultra-high-strength hot stamping steel, a series of tempering processes with varying tempering temperatures and times were carried out with a dilatometer. Meanwhile, the hardness of each sample was measured after dilatometer experiments. The results indicated that the tempering process parameters (including the tempering temperature and time) play an important role in the hardness of the studied steel. The hardness of 38MnB5Nb ultra-high-strength hot stamping steel at the quenched state is about 580 Hv, while it is 240 Hv for the quasi-annealed state. As the tempering time extends, the hardness is decreased sharply at the initial stage; then, the hardness is decreased in a quasi-linear trend with a slight slope; finally, the hardness almost keeps a constant value, which depends on the tempering temperature. In addition, the tempering process has a big effect on the mechanical properties of 38MnB5Nb ultra-high-strength hot stamping steel by increasing the product of the strength and elongation by about 40%.