Advanced Materials Research Vols. 189-193

Abstract: Uniaxile tensile tests of auto-body steel sheet were performed at strain rate of 10-4 to 101s-1 and temperature of room temperature to 180°C. Strain rate and temperature sensitivity of flow stress were analyzed. It is found that the stress-strain curve is obviously heavily weighted on the temperature and strain rate. A new constitutive model was constructed and implemented into Abaqus/Explicit commercial software using user subroutine VUMAT. Verification of constitutive model shows that it has good agreement with experimental result.

Abstract: In the design of die casting mould，the design of the interior sprue gate is very important. The high-velocity filling operation of metal liquid and flow order are the main factors of determining product quality in the die-casting process. Based on the working experience for many years, after carrying on investigation, counting, analyzing a lot of moulds that have been proved through production, think:In all factors of design of the interior sprue gate, the position, direction, dimensions, sectional shape are four important factors.

Abstract: Inert gas atomized (IGA) superalloy Inconel 625 powder was consolidated by hot isostatic pressing (HIPing) directly under the HIPing parameters of 1100°C/110MPa/3h. The structure and properties of the as–HIPed samples were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and tensile tests at room temperature, and its relative density was measured by drainage. The fracture surface morphology of the tensile specimens have been investigated using SEM. The results showed that full density alloy can be obtained under the HIPing parameters of 1100°C/110MPa/3h. Due to the effect of prior particle boundaries (PPBs), the strength of the as-HIPed alloy is comparatively high, but its ductibility is comparatively low.

Abstract: In the present study, the effect of injection temperature, velocity and delay time on the interface morphology of the co-injection molded plates was studied. The results showed that the core penetration parallel to the flow direction becomes less as the skin injection velocity and temperature increases and delay time decreases. Among the parameters, temperature was the most significant in affecting the interface morphology, followed by delay time, while injection velocity seemed to play no significant role. The results were analyzed by taking account of rheological properties of the two feedstocks. Calculations and comparisons of viscosity ratios encountered in experiments were made. It was demonstrated the differences in the rheological properties of the metal feedstocks involved are key factors in determining the interface morphology of the molded parts.

Abstract: The paper presents the result of an experimental investigation on the fabrication of Al/SiC composites with high volume fraction of SiC particles by pressure infiltration of liquid aluminum into preforms prepared by powder injection molding (PIM). To obtain the required high particle volume fraction, SiC powders with a bimodal particle size distribution were used. The influence of powder loading and particle size on the bending strength of the prepared composites has been investigated. It is demonstrated that pressure infiltration permits to achieve high relative densities for the composites (i.e. 98.8%). The microstructure studies revealed a uniform distribution of SiC particles in the composites without interface reactions between the particles and the aluminum matrix. The bending strength increases with increasing powder loading and decreasing particle size of the coarse powders in the bimodal powder system.

Abstract: To make full use of the promotion potential of hydrostatic stress on the formability of sheet metal, several foundational questions met in practical application of double-sided pressure forming technique are studied in this paper. The theoretical analysis of sheet metal deformation during the double-sided pressure bulging process is carried out, and an analytical approximation for normal pressure loading path that secures out-of-plane stress ratio, γ, continuously increasing (dγ ≥ 0 holds) is presented. Utilization of the relationship between the theoretical approximation for normal pressure load and material hardening properties, a novel double-sided pressure forming method is proposed—the viscous pressure bulging (VPB) of the overlapping sheet metals, in which a highly viscous but flowable semi-solid medium is used as the soft die and the target sheet metal is deformed under the constraints from viscous medium on one side and overlapping sheet on another side. To confirm the efficiency of the proposed method, the VPB test of overlapping sheet metals is simulated by DEFORM-2D, and the experimental tests are also carried out. The results show that σ3 provided by overlapping sheet can overcome the diminishing of γ value caused by evolving strain-hardening and geometric softening effect in the post-diffuse necking stage. The experimental obtained increase of the limit dome height (LDH) of double-sided pressure bulging specimen is 12.6% compared with that of single-sided pressure bulging specimens.

Abstract: Springback compensation of Multi-point forming (MPF) was analyzed in the paper based on the ideal elastic-plasticity and linear hardening material models. The calculation formulas for adjusting radius of MPF die, both single-curvature and double-curvature, were obtained. Cylinder and spherical surfaces were formed by MPF equipment. Experimental results show that the errors between formed surface and target shape are within 5%. Moreover, when using formulas derived from linear hardening model, it is found that the formed surface is more close to target contour, and the presented formula can be used to determine the adjusting radius of MPF die in practice.

Abstract: A prototype for multi-mode linear ultrasonic motor has been proposed and designed. It is designed using a combination of the first longitudinal and the first bending mode. The piezoelectric ceramics convert energy using the longitudinal d33 effect which allows an improved reliability, large vibration amplitudes and excellent piezoelectric coupling. The normal direction motion of the driving element is excited by the first longitudinal mode. The tangential direction motion of the driving element is excited by the first bending mode. The resulting displacement of the driving element is transmitted by the frictional force between the vibrator and the rail in a linear motion. The analysis on the modals of the composite vibrator by using the ANSYS finite element software has been presented in this paper. Finally, the vibrator structure of the motor and the motor's own structures are designed. The basic design is discussed and simulations are compared with the experimental results, the results show that the motor characteristics can be optimized for a particular task by choosing the appropriate operating parameters such as exciting voltage, exciting frequency and normal force.

Abstract: Tailor welded blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. To take full advantage of these benefits, however, one needs to overcome the reduced formability of TWBs and be able to accurately predict the failure modes depending on the thickness ratio between the thicker and thinner sheets of a tailor welded blank with similar base materials early in the design process. In this paper, we studied the effect of the thickness ratio on the limit dome height of TWBs by using finite element method and experiments, analyzed the effect of TR on the failure mode of TWBs. A concept of the critical thickness ratio was presented to predict the failure modes of TWBs. The results show that the rapture originates on the weld of TWBs when the thickness ratio is less than the critical thickness ratio and on the thinner side when the thickness ratio exceeds the critical thickness ratio.

Abstract: In this paper, by using a practical 3D FE model, one power spinning process of parts with transverse inner rib has been simulated. The stress and strain fields have been obtained and the features of metal flow in plastic deformation zone have been discussed thoroughly. Then, the main forming defects and their origins have been explored based on the study of the metal flow, shown as follows; (1) during the non-rib process, the main forming defect is the wall fracture in finished deformation zone. The origin of this forming defect is the excessive metal flow in thickness direction ahead of the forming roller. (2) in the rib-forming process, the main forming defect is the undesired inner rib. The origin of this forming defect is the excessive metal flow in hoop direction during the former non-rib process. (3) the features of the metal flow during flange part process are almost the same as those in the non-rib process. The achievements of this study can thoroughly reveal the deformation mechanism and provide an important basis for the optimization of the process parameters and the precise control of the power spinning process of parts with transverse inner rib.