Advanced Materials Research Vols. 139-141

Abstract: This paper will cover some processing routes along with grading and physical/chemical attributes of silica sand. The silica sand in this experiment was divided into four lots, and each of them was processed by the methods of calcining, scrubbing, mulling or rubbing respectively. The test results show that the sand grains which processed by different processing methods are irregular, the acid demand value of sand is lower than that of the base sand, and the grain size distribution of sand is similar to that of the base sand. However, the SiO2 content of processed sand is increased, the impurities content has a downward trend. Compared with the base sand, it can be found that the tensile strength value of molding sand prepared using the processed sands is higher and the bench life is almost no change.

Abstract: It is general preferable to consider stamping effects of sheet metal forming for vehicle crash simulation nowadays. However, the present approaches for stamping simulation and coupling forming results to crash finite element model require massive pre-works. To overcome these difficulties, an inverse method for rapid and simple stamping simulation using HYCRASH is introduced, where crashworthiness analysis of front side rail under frontal crash was used as an example in this study. A detailed stamping simulation by AUTOFORM is used for comparison, also accompanied with the one without stamping effects. Through comparison of stamping results and frontal crashworthiness performance, it is concluded that effective plastic strain makes more contribution on simulation accuracy than thickness reduction, and HYCRASH shows an attractive approach for stamping analysis than AUTOFORM coupled in crash simulation in the context of computational cost.

Abstract: Drive line is the surface defect on the automotive panel. In order to investigate the causes and control methods of the drive line, the box-shaped part with curved bottom was designed based on the shape characteristics of automobile panel. Then this part was taken as an experimental model to analyze the causes and forming process of the drive line on its surface. Finally, influencing laws on the drive line from the draw bead, the important forming process parameter, were obtained by the experiments. The results showed that the draw bead has great impact on the drive line. Different setting ways of the draw beads can make good control for the formation, displacement and its direction of the drive line. Besides, it is an important way for setting the draw beads properly to prevent the stamping parts from the formation of the drive line.

Abstract: In this paper, parameter optimization of the electrical discharge machining process to Ti–6Al–4V alloy considering the multiple responses using the Taguchi method and grey relational analysis is reported. The multi-response optimization of the process parameters are material removal rate (MRR) and electrode wear rate (EWR). The machining parameters including discharge current, voltage, pulse on time and duty factor. Experiment based on the orthogonal array, The optimized process parameters simultaneously leading to a lower electrode wear ratio and higher material removal rate are then verified through a confirmation experiment. The experimental result for the optimal setting shows that there is considerable improvement in the process. The validation experiments show an improved electrode wear ratio of 2.8%, material removal rate of 45.8% when the Taguchi method and grey relational analysis are used.

Abstract: The hot deformation behavior of as-cast AZ31 magnesium alloys have been investigated at 200~400°C and strain rates 0.001~1s-1 by means of hot compression tests on a Gleeble-1500D thermal-mechanical simulator. We have analyzed the flow stress-strain curve and presented the constitutive equation by calculating stress exponent, activation energy and Zemer-Hollomon parameter. Then, the processing map of AZ31 alloys has been developed based on the dynamic material model theories and Prasad instability criterion. The flow instability domain is observed at lower temperature and the larger power dissipation rate is emerging at 300~400°C. We have analyzed the corresponding deformation microstructures and it is characteristic of dynamic recrystallization. These results have shown that AZ31 alloy has good workability at 300~400°C and lower strain rate.

Abstract: Due to the flow behavior of molten metal is affected by the back pressure of mold residual air in high pressure die casting (HPDC) process, the back pressure conditions should be considered in order to simulate the HPDC process precisely. In this study, an aluminum colander of automobile’s filling process in HPDC was calculated by combining the back pressure conditions. The optimized schemes were given by considering the simulation results. Both initial and optimized schemes simulation results were compared with actual parts. The contribution of gas porosity between simulation and actual part were in agreement when back pressure conditions were applied. The local back pressure can be controlled by coordinating the position of the vents. Therefore the flow behavior of molten metal can be changed and the porosity defects can be fixed.

Abstract: Raising processes of titanium alloy sheets TC2M were simulated by using ADINA FEM software. The shape distortions induced by plastic anisotropy during forming and springback processes were described. A series of forming tests were conducted for the comparison of simulation predictions and test measurements. Reasonable agreement was obtained between the predicted and measured profiles of formed parts. Two sorts of shape distortion phenomena exhibited in the raised workpieces fabricated in room temperature after springback or elastic recovery process: Firstly, the bottom of the flange in the specimen was distorted to be a wavy surface and not a plane. There are two highest points and two lowest points, and the highest points located in the flange periphery along the transverse direction (TD), and the lowest points located in the periphery along the rolling direction (RD); Secondly, the top surface of the raising specimen was distorted to be a wavy surface too, and the distortion shape is similar to that in the flange.

Abstract: TiAl-based alloy valves were manufactured by combining charges compressed /vacuum arc melting (VA)/ induction skull melting (ISM) procedure with permanent mold centrifugal casting method. Microstructures, compositions and mechanical properties of as-cast and hot isostatical pressed (HIPed) valves are detected. Results show that the permanent mold centrifugal casting process obviously refines the size of grain in TiAl alloy and the tensile strength of as-cast and HIPed valves are 550MPa and 580MPa at 20°C, 370MPa and 470MPa at 815°C, respectively. As-cast specimens show ~0% elongation at 20°C and 1~2% at 815°C, while HIPed ones show an elongation of 1~2% at room temperature and about 10% at 815°C. Furthermore, a 200-hour test was carried out with CA4GE-engine, which demonstrated the possibility of as-cast TiAl alloy valves for the substitution of present steel ones.

Abstract: Three-dimension rigid-plastic finite element software, DEFORM-3D, was used to simulate the integral forming processing of a lager thick-wall semi-sphere head with supporting tables. Influencing factors of integral forming, such as initial blank shape, radius of corner at the bottom of the protrusions and the preforming mode etc, were researched quantitatively. A double layer frustum cone blank was determined, which can reduce the variable amplitude of the wall thickness and cause a uniform wall thickness distribution. When radius of corner at the bottom of the protrusions of the machined blank was in 100~130mm, no crack occurred at the bottom of the any supporting tables and a rational size can be obtained after forming. Using mode C (two banding protrusions) to forging the blank for machining can prevent the center metal from thinning and reduce additional tensile stress. Based on the simulation research, the 1:3 scale experiment was done in 31.5MN hydraulic press and the test piece was measured. The result shows that the error between simulation data and test data is less than 5%, which verified the feasibility of integral forming and provided an important reference for virtual production.

Abstract: Impact line is one of important factors to affect the shape accuracy and surface quality of auto body panel design and manufacture. It is difficult to study because of the complexity shape of auto body panels. The system of test analysis on impact line is established by analyzing the shapes and forming processes of auto-body panels, of which based on hyperboloid shallow shells. The criterion and research technique of impact line are introduced. Extensive experiment results, which show the effects of forming process conditions, such as blank holding force, draw bead arrangement, and lubrication on impact line, are achieved. It can be concluded that the draw bead arrangement significantly influence the impact line, the displacement of impact line is different with difference of blank holding force and the friction coefficient.