Hot Stamped Parts Research Articles

Cooling system of hot stamping of quenchable steel BR1500HS: optimization and manufacturing methods

The innovative hot stamping press of quenchable steel mainly includes two stages: hot forming of blank at elevated temperature and quenching of hot stamped part in closed water-cooled tools. Crucial stage in hot stamping process is quenching of hot formed part in water-cooled tool to achieve final high ultimate tensile strength. In quenching stage, cooling rate of hot stamped part has a significant effect on final mechanical properties of hot stamped part. Hence, in this paper, a new method is proposed to optimize cooling system to improve effectiveness of quenching and thus final mechanical properties of hot stamped part. In this method, cooling channel is introduced in tools, and hot stamping experiments are combined with corresponding finite element numerical simulations to optimize cooling system. According to cooling system optimization, two different sets of tools used to manufacture square-box-shaped part and B pillar of automobile are manufactured using drilling method and pre-embedding method, respectively. Hot stamping experiments and corresponding simulations are performed to verify the effectiveness of optimized cooling system.

Hot Stamping and Blank Designing for a Vehicle Bumper Using Ultra High Strength Steel (UHSS)

Full-scaled hot stamping dies were designed for a vehicle bumper, based on evaluation of cooling system by FE simulation and the temperature variation assessment by analytical model. The blank shape was gained using inverse algorithm and well-designed according to production practice. Experiments were conducted to verify the reliability of both the die and blank design, as well as tests for microstructure and mechanical properties of the hot-stamped part. Results show that, CAE analysis provides a robust support for hot stamping die and blank design; Position stability of hot blank is greatly improved during robotic transport process after shape designing; Metallographic analysis demonstrates the hot-stamped bumper obtained a fully martensitic microstructure, its tensile strength is about 1550 MPa, microhardness is 47.5 HRC, and the elongation is up to 6%.

Experimental and Numerical Analyses of Hot Stamped Parts with Tailored Properties

Experimental and Numerical Analyses of Hot Stamped Parts with Tailored Properties

Hot formation quality of high strength steel BR1500HS for hot stamping without cooling system

Experiments were designed to manufacture square-box-shaped part, and the effects of hot stamping process parameters including blank holder force (BHF), forming temperature and tool temperature on the hot formation quality were investigated. Since the hot formation quality is highly sensitive to BHF, a BHF controlling system was developed using six hydraulic cylinders to improve the accuracy of applied BHF to ±10 N. The experimental results showed that a mixture microstructure of martensite and bainite with large fraction of martensite at forming temperature of 850 °C was obtained in the hot stamped part, while the microstructure was dominated by the softened phase of pearlite as the forming temperature decreased to 550 °C. The tensile strength was raised from 1550 MPa to 1750 MPa as the tool temperature decreased from 200 °C to ambient temperature. The optimum BHF of 1.62 MPa was determined which can avoid the formation of drawbacks of wrinkle and crack.

Enhanced Mechanical Properties of a Hot-Stamped Advanced High-Strength Steel via Tempering Treatment

The hot stamping process has an extensive range of applications due to its advantages over the traditionally used stamping techniques developed in the past. To enhance the mechanical properties of the indirectly hot-stamped parts, the quenching and partitioning (Q&P) process has been recently applied on boron-alloyed steel. In the current research, it was observed that the tempering treatment on the directly hot-stamped boron steel resulted in better mechanical properties and higher formability index compared with the reported results using the Q&P process. The nano-carbide formation and the dislocation annihilation during the tempering treatment were suggested as the evident reasons for the occurrence of the mentioned robust properties. The ease of the practical implementation of the tempering route together with the markedly enhanced mechanical properties of the tempered parts make the suggested method privileged. Additionally, the variations in the yield strength before and after tempering were quantitatively evaluated.

State‐of‐the‐Knowledge on Coating Systems for Hot Stamped Parts

AbstractIn the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe–Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zn‐induced embrittlement are analyzed. The use of Zn–Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol–gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al–Zn alloy coatings, dual layer Zn–Al and Zn–Al–Mg coatings is also introduced. The application of Zn–Al–Mg post‐process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.

Investigation of Cooling Effect of Hot-stamping Dies by Numerical Simulation

Abstract As the development of hot-stamping technology, the designing of hot-stamping dies has more and more request. The cooling effect of hot-stamping dies can affect the mechanical properties of hot-stamping parts and the production efficiency of hot-stamping process directly, so it is an important index to evaluate the performance of dies. The cooling effect of hot-stamping dies was simulated by CFX software, and the define method of contact thermo resistance was presented in the process of simulation. Besides, the effect of processing parameters, such as pressure–holding time and cooling water velocity, on the cooling effect of hot-stamping dies was investigated and verified by experiments. Comparisons show that numerical simulation results have a good agreement with experimental results, so the FE model is effective in simulation of hot-stamping process.

Al-Si 코팅층 Laser Ablation 변수에 의한 LWB 보론강판의 기계적 특성 평가

Recent years have seen advent of hot stamped parts made from laser-welded blanks of boron steels for structures requiring high crash energy absorption. However, the presence of Al-Si coating interfered with satisfactory mechanical characterizations after laser butt welding. In this study, laser ablation technology was considered in order to facilitate adequate mechanical characterization of the final hot-stamped panels.

Comparative study of the prediction of microstructure and mechanical properties for a hot-stamped B-pillar reinforcing part

Automobile manufacturers have been increasingly adopting hot-stamped parts for use in newly designed vehicles to improve crash worthiness and fuel efficiency. However, the hot-stamped parts require extreme mechanical properties with ultimate tensile strengths as high as 1500 MPa (∼450 Vickers hardness) while still maintaining adequate formability during the stamping operation. The ultra high strength of hot-stamped components is attributed to the martensitic phase transformation that occurs after the part has been formed at temperatures corresponding to the austenite phase field where formability is enhanced. In the present study, a computer-aided design method incorporating Kirkaldy and Venugopalan type phase transformation models has been implemented following a thermo-mechanical coupled finite element analysis to predict the mechanical properties of hot-stamped parts made with a boron-modified steel. Three empirical models which are typically used for hot stamping analysis are employed and the prediction capability of the models is compared using continuous cooling dilatometry and forming experiments of a modified B-pillar part.

Effect of Dies Temperature on Mechanical Properties of Hot Stamping Square-Cup Part for Ultra High Strength Steel

The numerical simulation of hot-stamping process was carried out for UHSS square-cup parts, and the influence of dies temperature on the hot-stamping process was anlysised. Besides, through the microstructure analysis and mechanical properties testing of the formed parts, effects of dies temperature on microstructures and mechanical properties of hot-stamping square-cup parts were obtained. The experiment and simulation results showed that the mechanical properties of the UHSS are strongly dependent on the temperature, so the dies temperature is one of the most important parameters that have to be taken into account in designing the hot-forming dies and the hot-forming process.

Thermo-mechanical finite element analysis incorporating the temperature dependent stress-strain response of low alloy steel for practical application to the hot stamped part

The isothermal stress-strain responses of a low alloy steel sheet (0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel, 1.2t) at elevated temperature, which simulates the material response in the hot stamping process, were measured by the Gleeble3500 thermo-mechanical simulator. The measured stress-strain responses fitted to the Swift equations discretized within the deformation temperature were used for the practical finite element simulation of the hot stamping process, in which the complicated effects of the volumetric mismatch between phases and phase transformation inducing plasticity were effectively ignored due to the significant constraints by the press stamping. The material parameters for the thermo-mechanical FE simulations were determined by considering the effects of plastic work and phase transformation on the temperature history. A mini-sized b-pillar reinforcing part was used as the simulation model. In spite of the simplified approach adopted in this paper, the finite element procedure could provide important information on the temperature distribution, martensitic phase distribution (or final product hardness), and the effect of process parameters such as punch force on the performance of the final hot stamped product.

Tools and Technologies for Hot Forming with Local Adjustment of Part Properties

In general hot stamped car body parts show a uniform strength distribution. Especially for safety relevant parts with high requirements concerning crash performance, this uniform strength distribution can cause problems. During a crash a B-pillar e. g. can absorb more energy when the lower part is relatively flexible while the middle and upper part has to be high-tensile to prevent the intrusion into the passenger compartment. Also during the production of hot stamped parts, the high strength causes trouble. When the trimming takes place after the hardening process, the durability of the tool is limited. Thus at the moment the only economic process for trimming of ultra-high-strength steels is laser cutting. This paper presents different approaches to reach local different strength distributions in hot stamped components. In particular the results of a research project of the Institute Tools & Forming, Graz University of Technology are shown where precisely defined areas of different strengths could be obtained in one part. This was achieved by the use of simple and cheap ceramic inserts in conventional press hardening tools.

Formation of an Aluminide Coating on Hot Stamped Steel

The degradation of type 1 aluminized coating during hot stamping leads to the coating cracking due to the formation of a brittle FeAl2 intermetallic phase. The formation of an aluminide coating prior to hot stamping was investigated as a method to simultaneously improve the coating ductility and achieve a good hot corrosion resistance of the hot stamped parts. A formable aluminide coating was obtained when the coating alloying was achieved during the pre-heating of the steel and an Fe content higher than 70 at% (83 wt%) was reached. The coating was identified as Fe3Al phase at room temperature. The formation of this aluminide coating on 22MnB5 hot stamping steel was investigated in detail. The effect of this alternative hot stamping thermal cycle on the room temperature mechanical properties of the steel was also investigated.

ホットスタンピング部品の形状凍結性に<br>及ぼす成形条件の影響

For the past decade, hot stamping technology has been gradually applied to the production of super high strength automotive parts. Although auto-parts such as bumpers, door impact beams, center pillar reinforces have been produced by hot stamping and installed in many cars all over the world, this promising technology has not spread as much as was expected. One of the major reasons is the high production costs owing to the low productivity of this technology. In this study, we investigate the effect of forming conditions on the shape fixability of hot stamped hat-type parts. On the basis of the obtained results, we introduce a new hot-stamping technology characterized by a markedly high productivity.

WIELAND-S40

Abstract Wieland-S40 has very high wear resistance. The alloy is used in hot stamped parts requiring high mechanical strength and wear resistance. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fatigue. It also includes information on corrosion and wear resistance as well as forming, heat treating, and joining. Filing Code: CU-701. Producer or source: Wieland Metals Inc., Wieland-Werke AG.

WIELAND-N31

Abstract Wieland-N31 is a leaded nickel silver with excellent machining properties. It is suitable for manufacturing a wide variety of sections and precision turned and hot stamped parts requiring higher mechanical strength and higher corrosion resistance than that for brass. This datasheet provides information on composition, physical properties, hardness, tensile properties, and shear strength. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: CU-676. Producer or source: Wieland Metals Inc., Wieland-Werke AG.