Key Engineering Materials Vols. 535-536

Abstract: The high cost of manufacturing and manufacturing time is required for preliminary experiment by manufacturing various type of coil every time for the forming of the required shape, it is essentially required to develop the coil design technology using a FEM. Thus, in order to form the required shape, it is important to design the coil using a FEM and predict the final forming product. Therefore, in this study developed electro-mechanical coupled FE-model for thin aluminum plate forming using electromagnetic force. In order to carry out this, magnetic pulse forming was carried by electromagnetic forming system total energy of 24kJ. Peck current and discharge speed acquired through magnetic pulse forming experiment using Rogowski current waveform transducer was used as input data in electromagnetic FE-model. Then, calculated electromagnetic force between forming coil and workpiece through the developed electromagnetic model was inputted as a load of mechanical FE-model for the prediction of thin aluminum plate forming shape. As results, developed electromagnetic-mechanical coupled model shall be able to be usefully used when designing the forming coil to secure the required forming shape later.

Abstract: The dimensional change of tooth profile by heat treatment of helical gear was investigated by experimental and numerical approaches. Especially, the three-dimensional elasto-plastic finite element (FE) simulation was adopted to analyze the elastic deformation during load, unloading, ejecting of workpiece. Quenching simulation was also carried out to investigate the change of tooth profile on the forged gear. In experiments, the amount of elastic deformation of the forged gear was quantitatively determined by comparing the tooth profiles on the forged gear and die. The dimensional change of the forged gear tooth after quenching was also evaluated from the comparision of the cold forged and quenched gear teeth. From experimental works, it was found that the amounts of dimensional changes after forging and quenching of helical gear are 10 and 10 μm, respectively.

Abstract: Tube hydroforming is a metal forming technology that utilizes internal pressure and axial compressive loads to generate designed product shapes with complex sections from tubular materials. The tube hydroforming process has been used in the automotive, aircraft, and bicycle industries for many years. With the pursuit of lighter bicycles, aluminum alloys have been utilized as an alternative to steel. To obtain adequate strength, the aluminum alloys should undergo heat treatment processes before being used. However, the mechanical properties of the alloys vary with the tempering conditions. This paper aims to evaluate the effects of tube hydroforming characteristics on different kinds of tempered aluminum alloys. Based on numerical simulations, suitable tube hydroforming processing conditions for each tempered aluminum alloy are suggested.

Abstract: During the last three decades, numerical simulation has gradually extended its applicability in the field of sheet metal forming. Constitutive modeling is one of the domains closely related to the development of numerical simulation tools. The paper is devoted to a comprehensive testing of the advanced materials models as implemented in the finite-element code. The test proves the capability of the advanced materials models response of DC04 steel sheet to describe the effects of the plastic anisotropy of the sheet metals subjected to industrial forming processes.

Abstract: In order to obtain a refined and uniform microstructure in the final billet, the radial forging process needs to be optimized and controlled with various process parameters such as temperature of ingot and die, die size, ram speed, upset ratio, etc. Grain size control is one of the most effective ways for the control of mechanical properties. The change in grain size is significantly related with strain, strain rate and temperature of forged part. To understand material properties and to analyze stability and instability area of forged workpiece, hot compression test of Ti-6Al-4V was carried out within the strain-rate range 10-2 to 10 s-1, and the temperature range 800 to 1100oC. And dynamic material map of Ti-6Al-4V was tabulated. In this study, a three-dimensional rigid-plastic finite element method(FEM) was used to analyze the radial forging process, focusing on the effects of feed rate and rotation angle for appropriate forging pass schedule. And the simulation result was confirmed with dynamic material model of Ti-6Al-4V. The optimal combination of feed rate and rotation angle has been determined by quantifying the radius profile in the longitudinal direction, roundness of the product and uniform strain distribution.

Abstract: The thermo-stress sizing is a technology that enables sheet metal part using high elastic material such as titanium alloy to eliminate spring-back and distortion. The paper expounds and proves the principle of fixing shape of thermal stress sizing, that is, they are synthetic effects of materia1 softening and stress relaxation in short time．Then the theoretical rule of hot sizing for bending spring-back is established by this principle．On the basis of principle of the thermo-stress sizing, relevant replication experiment is implemented. The results show quantitatively effects of main factors, such as material property, part geometry, temperature and time for the rule of hot sizing． The theoretical values of spring-back in the process of hot sizing are in good agreement with that of experiments. They may be used to estimate technological parameters of thermal stress sizing．In addition thermo-mechanical characteristics under standard temperatures of forming or sizing and the experimental curves of thermo-stress sizing for Ti-6Al-4V and Ti-2A1-1.5M n are given．

Abstract: In the present work, FLDs of AZ31 magnesium alloy sheet for non-proportional strain paths were investigated by performing two-step stretch forming experiments at various forming speeds (3, 30 and 300 mm.min^-1) at elevated temperatures of 150, 200 and 250°C. The forming limit strains, both for proportional and non-proportional deformations, increased with temperature rise and with decreasing forming speed. A FLC after a uniaxial pre-strain lies outside of the proportional FLC for a given condition of temperature and forming speed, whereas a biaxially pre-strained FLC lies inside of the proportional FLC. It was found that the accumulated effective plastic strain and the direction of plastic strain increment at the final stage of forming are two major factors that influence the forming limits for non-proportional deformations.

Abstract: Hot working behavior of an aluminum alloy matrix composite reinforced with TiC particulates was investigated by a high temperature compression test. Power dissipation maps were constructed using a dynamic material model and the deformation mechanism was investigated by means of an EBSD analysis. The interrelationship between the microstructure evolution and the efficiency of power dissipation was derived and the roles of TiC particles and other constituent phases in determining processing maps were further discussed.

Abstract: Using the finite difference code FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) and UST (Unified Strength Theory), the influence of the intermediate principal stress effect on the problems of flat punch are analyzed in this paper. The values of the ultimate bearing capacity resulting from numerical analyses and the analytical solution of Prandtl’s strip punch problem are compared. The three-dimensional problems of strip, rectangular, square and circular punches on a semi infinite metallic medium have been analyzed.

Abstract: This paper reports on a novel microforming technique, Flexible-Pad Laser Shock Forming (FPLSF) which uses laser-induced shock waves and a flexible pad to induce plastic deformation on metallic foils. Thickness distribution at the cross-section of the craters formed by FPLSF is analyzed experimentally with respect to laser fluence, which is a significant process variable that controls the deformation pressure. Furthermore, hardness of the deformed samples at the cross-section is measured by nanoindentation testing. It is found that the thinning of copper foil by FPLSF ranges from 7% to 25% for laser fluence ranging between 7.3 J/cm² and 20.9 J/cm². Thinning is maximum at the crater center, which can be attributed to the maximum compressive stresses in the thickness direction, and minimum at the edge portions. With increase in laser fluence, thinning of the foil increases whereas minimum change in hardness is observed. The variation in thinning across different crater locations ranges between 6% and 8% only, which indicates that FDLSF can be developed as a competitive technique to produce components with uniform thickness distribution.