Yu Ying Yang

Hot Stamping Processing Experiments of Quenchable Boron Steel

The quenchable boron steel is a novel type of ultra high strength steel used for automotive parts so as to reduce the weight of the whole automobile. The hot stamping processing experiments for bending parts were studied. The influence of the hot stamping processing parameters, such as the heating temperature, the heat holding time and the cooling water flow velocity, on the mechanics properties and microstructure of the hot stamping parts is obtained. And then the optimal ranges of these parameters are determined, which provides a basis for the control of the hot stamping process applied in complicated shape parts’ production.

Experiment Study on Shape Defect of Cylinder Shallow Shell

In this paper, the shape defect is studied by the experiment of drawing parts before and after trimming for the rectangle cylinder shallow shell. The mechanism of shape defect and the effect of forming condition and trimming on shape defect are discussed. And the influence laws of forming conditions on shape defect are achieved. Such as binder force, curvature radius, sheet thickness, yield strength and residual stress after trimming.

Study on Process Decision Methodology for Sheet Metal Stamping by Case Based Technology

More powerful process design methods and tools of sheet metal stamping are needed to help engineers design better products, to reduce lead times and costs, and to increase product performance and accuracy. A novel model for representation of object-oriented case information constitution relationship is presented, ‘Class-Property’ structure is proposed in order to refine the case representation, multi-types, properties are adopt to describe more detailed information, three hierarchies of index strategy are used to realize case extraction. Furthermore, experts’ knowledge and experience on previous design cases and forming problems are collected, which can provide designers useful practical experience and data to aid design procedure and to solve the potential problems of sheet metal stamping. In order to illustrate these applications, database technology is used to realize a prototype system of auto body panels, which can be used to integrate process design information and manufacture resources.

Reproducing Kernel Particle Method Numerical Modeling of Thin Sheet Superplastic Tension Forming

Superplastic forming has emerged as an important manufacturing process, large deformation always occurs during superplastic forming, time-consuming remeshing is necessary while the finite element method (FEM) is used to analyze metal forming process. Meshless methods with no meshes can avoid this problem and overcome those problems in FEM. In this paper a meshless method based on the reproducing kernel particle method (RKPM) is applied to analyze Magnesium Alloy (MB15) thin sheet superplastic tension forming. A superplastic meshless method modeling program is set up, and background cells are used to compute the integrations in weak form equations and the mixed transformation method (MTM) is used to impose the essential boundary condition exactly. Numerical example demonstrates the effectiveness of the method in superplastic forming.

Silicon Carbide Evaporator Tubes with Porosity Gradient Designed by Finite Element Calculations

Gas turbine combustors with premix burners can reduce NO, emissions. In a new premix burner concept the evaporation of the liquid fuel and the burning zone are decoupled. The liquid fuel is sprayed onto the porous outer surface of the evaporator tube. The flowing air and the fuel vapor enter the tube where the combustion takes place The tube must be gastight on the inner surface Inside the tube the temperature is about 1500 °C, at the outer surface about 550 °C Previous work shows that application of porous silicon carbide (SiC) ceramics is rather promising. Due to the temperature gradient both during steady state and transient operation high thermal stresses develop in the tube. Four different design variations of porosity gradients are investigated, a two-layer concept without FGM and three continuous porosity gradients (linear, convex, concave) By comparing the local stress distribution with the local strength of the four different design variations, a favorable porosity gradient is found Only with this tailored porosity gradient the failure probability of the component can be kept on a tolerable level.

Prediction of Fracture in Square-Cup Forming of Aluminium Alloy

Aluminum alloy sheet is becoming one of the main materials to take the place of steel components to reduce the vehicle mass due to the advantage of low special density, high strength and corrosion resistance. To predict the formability during the aluminium alloy sheet forming accurately, , a ductile fracture criterion developed by the authors, was for numerical simulation, in this paper. Fracture behavior in square-cup forming of the aluminium alloy LF21M was predicted by means of the criterion. Comparison of the predicted results with experimental values shows that the critical punch stroke and the fracture initiation position in square-cup forming of the aluminium alloy have been predicted successfully by the criterion.

Automatic Process Optimization Of Sheet Metal Forming With Multi‐objective

Its crucial for process engineers to determine optimal value and combination of process parameters in the design of sheet metal forming. The multi-objective genetic algorithm (MOGA) based on Pareto approach and numerical simulation codes were integrated in this paper to fulfill the optimal formability in the sheet metal forming. Three objective functions of local formability on fracture, wrinkling and insufficient stretching were presented based on the strains state at the end of the forming process on the Forming Limit Diagram. By using Pareto-based MOGA, the optimal global formability which represents the trade-off between different local formability was decided. For the efficiency and accuracy of optimization procedure, both inverse and incremental finite element analysis were used to evaluate the value of objective functions. This method was applied to a complex engineering optimization problem: an engine hood outer panel, the optimal blank holder force and draw bead restraining forces were determined to satisfy the given objective functions for the forming of the auto body panels. The approach proposed in this paper has been shown to be a powerful tool than manual numerical simulation procedure.

Flow Behavior of Ultra-High Strength Boron Steel at Elevated Temperature

Ultra-high strength boron steel is widely used in a new hot stamping technology which is hot formed and die quenched simultaneously in order to obtain stamping parts with 1500MPa tensile strength or higher. Tensile experiments were carried out with ultra-high strength boron steel in a range of temperature 500°C~860°Cand strain rate 0.01/s~1/s with the thermal simulation testing machine Gleeble 3800, and the stress-strain curves were obtained. The influences of the deformation temperature and strain rate on the stress-strain curves were analyzed. The results show that hot behavior at elevated temperature of ultra-high strength boron steel consists of strain hardening and dynamic recovery mechanism, which can be accurately described by the mathematic model. Keywords: Ultra-high strength boron steel, hot stamping, hot flow behavior

Experiments and Numerical Simulation of Hot Bending and Die Quenching for Ultra-high Strength Boron Steel

Hot bending and die quenching for U-shaped parts with ultra-high strength boron steel were experimented and simulated to study its quenching effect and accuracy. The results indicate that through the hot contact bending and die quenching, bending parts with higher strength and forming precision than that of cold stamping can be achieved. And the hot contact bending improves the quenching effect at the bottom of the bending part. The springback of hot contact bending decreases gradually when the blank holder force (BHF) increases, which is mainly negative for the impact of the thermal shrinkage moments. The numerical simulation results are consistent with the experiments’. Therefore, it verifies the reliability of finite element model and lays the foundation for the numerical simulation of the hot stamping process applied in complicated shape parts’ production.

Micromechanism of Plastic Deformation on Elastic Modulus

The key to enhance the precision of sheet metal stamping parts is accurate prediction and control of the springback. And one of the dominant factors of springback is the elastic modulus. The change of elastic modulus with plastic deformation was experimentally studied for the annealed LY12 and the annealed LF21 aluminum alloy respectively, and the changing role of elastic modulus with plastic deformation was obtained. By inverse pole figure from the X-ray diffraction analysis, the effects of the material original textures and their changing with plastic deformation on the elastic modulus were studied. And by positron annihilation lifetime spectrum , the influence of lattice distortion caused by crystal defect during plastic deformation on the elastic modulus was investigated. The micromechanism of the elastic modulus changing with plastic deformation for aluminum alloy is revealed, which lays a foundation for improving the stamping parts’ precision.