Materials Science Forum Vols. 575-578

Abstract: In lost foam casting (LFC), the foam pattern is the key qualification, and the filling process is one of the crucial processes to ensure the high quality of the foam pattern. Filling without uniformity and denseness will cause various defects and affect the quality of the surface. The influential factors of filling process are analyzed .And optimizing filling process, enhancing efficiency, decreasing waster are obtained by the numerical simulation of filling process using computer. The governing equations of the dense compressible gas-solid two-phase flow are established, and the physical signification of each one in the equations is discussed. The filling process is solved by Euler- Euler model. In the simulation, the volume of foam bead in every governing unit at different time is calculated, and the trend of foam bead flow is obtained. The filling process of various different conditions is simulated, considering different shooting methods and the position of baffles, and recorded by digital vidicon. The characteristics and the rules of the process are summarized. By contrasting the result of the numerical simulation with the one of examination, it is found that the fluid trend of foam bead in the numerical simulation is accordant to the actual process. So the numerical simulation of filling process by applying this model is an effective method.

Abstract: In injection mold, design of gate location is among the most critical factors in achieving dimensionally accurate parts and high productivity of the molding process, since it influences the manner in which the plastic flows into the mold cavity. To automatically predict the optimal gate location of injection molds based on injection-molding simulation, a new and practical method: empirical search method according to the analysis of common optimization methods has been presented in this article. In this method, the gate location scope is initiated by the practical experience of mold designer so that the core for the gate location optimization is construction of empirical library. In order to build the empirical library, in terms of shape and function characteristic of injection-molding part, all the parts are classified six kinds: shell, container, plate, structural part, ornamental part and transparent part, and the corresponding design rules are kept in the empirical library. In addition, this article combines the empirical search method and numerical simulation technique, builds the mathematics model for the gate location optimization of plate part in empirical library and obtains the gate location optimization scheme for this kind of part through one concrete numerical example. The analysis and verification by adopting the software Moldflow testify the optimization mathematics model is effective.

Abstract: Web gate system of aluminum castings in permanent molds is investigated in order to improve the quality of aluminum castings produced in permanent molds. The metal flow in the mold were observed and conducted using graphite molds and real time X-ray radiography recorded at a rate of 30 images per second through those molds. The affects of web thickness on flow patterns, gas entrapment, jetting possibility are studied and discussed. Flow and solidification simulation programs were employed to predict the flow behavior under the different conditions that can prevail in permanent mold gating. The study highlights the characteristic features of web gate system used in permanent mold aluminum foundries and recommends gating procedures designed to avoid common defects, and provides direct evidence on the filling pattern and heat flow behavior in permanent mold castings.

Abstract: The modeling of solidification in Continuous Casting demands the mechanical properties of steels at high temperature. These mechanical properties parameters provide the design data for the target surface temperature curve and dynamic control modeling of secondary cooling system, and are used to research hot delivery and crack mechanisms of cast slab. The properties parameters of steels can be obtained by physics simulation experiment. Following processing parameters in Continuous Casting, the stress-strain curves and mechanical properties of steel Q345 were tested and analyzed. Then the curves of relationships between the yield strength, tensile strength, reduction of area, Young’s modulus, plastic modulus of steel Q345 and temperature were obtained. We found the strength of steel Q345 cast slab felled down basically; the ductility was decreased below 700°C, in the range of 725°C-900°C and 1275°C-melting point. The plastic modulus was analyzed with the different temperatures and the different strains in detail. The parameters of mechanical properties for steel Q345 were obtained for using in elastic-plasticity stress model.

Abstract: During the continuous casting process, physical properties of slab for continuous casting at high temperature have an important effect on the slab quality in different part and the curve establishment of external target temperature for slab. It has significance to simulate and investigate the physical behaviors of slab at high temperature during the continuous casting process. Investigation existent in this field is scarce around the world. Continuous casting process is a complicated cooling process in unsteady state that sometimes the external temperature of slab will rise. In allusion to temperature rise and temperature drop, the paper simulated and investigated the physical properties of slab AH36 at high temperature under conditions of different temperatures and different temperature variation velocities, such as thermal expansion property, differential thermal analysis curve (DSC), isobaric thermal capacity (CP) and so on. Results of the investigation have provided a scientific data base for a further study on continuous casting technology and quality control for steel AH36.

Abstract: A two dimensions (2D) multiphase solidification model is used to study the liquid core solidification in the influence of deformation during soft reduction of continuous casting (CC). The transient transport equations (mass, momentum and enthalpy) for each phase of a thin steel slab CC are solved. Four different cases including of density-temperature function and deformation reduction factor on this CC are simulated. The solidification ending point position of liquid core, temperature, velocity and fracture of liquid and solid phases are compared. Understandings to the deformation and liquid core formation mechanism on soft reduction solidification process of CC are improved.

Abstract: Techniques of numerical simulation on mold filling process of casting are investigated in this paper. The mathematical model is formed on the ground of some selected theories in computational fluid dynamics (CFD), Numerical Heat Transfer (NHT) and computational methods to interfacial tracking. The discrete solution to the governing equations appeals to Finite Volume Method (FVM) on structured mesh. As for viscous turbulence flow and multiphase fluid flow in mold filling, engineering turbulence model and Volume of Fluid (VOF) method are adopted in the algorithms, respectively. As a debut, the general-purpose CFD software is used to establish the practicable mechanical model for the simulation. By means of numerical simulation, variation and distribution of velocity, temperature, stress and configuration of casting, etc. with respect to time and space in the filling process can be quantitatively analysed in detail, which is helpful for engineers to optimize their design of technics with less time and less cost and is meaningful to provide the subsequent simulation, solidification process of casting, with initial conditions.

Abstract: Thread whirling process is a cutting process in which a series of cutting edges on the whirling ring remove material by turning over the rotating workpiece. Whirling unit attached to a thread whirling machine influences much on the machining accuracy because the main sources of heat generation are assumed as bearings, servo motor and chip formation during machining. Analysis of temperature distribution, thermal deformation and thermal stress of the whirling unit has been carried out. It is revealed that the highest temperature of 91°C reaches in the bearing and relative displacement from point A to tool reaches 0.02~0.03mm along X, Y and Z axis. The maximum thermal stress of 31.9MPa is developed in the unit.

Abstract: The solidification process, the formation mechanism and distribution law of microporosity of the ball milling machine head cover made by SVEDALA corporation of USA were simulated by computer. The Solidworks software was used to generate three-dimensional model of cast parts and the Hua-casting software was employed to simulate the casting process. The simulated results show that significant microporosity was found in the middle of two casting heads and at the place of gudgeon journal because of insufficient chilling degree. The processing rationality was judged through the computer-aided technology, by which some drawbacks of the traditional process were overcome and the process design quality was improved.

Abstract: In the numerical simulation of mold filling process, the calculation efficiency has been a key point for practical applications due to the complexity and thin-section of die castings. In current research work, a fractional step method was applied in the solution of the unsteady Navier-Stokes equations, which can be implemented with a single solution to the momentum/pressure equations at each time step. This method may avoid the decrease in efficiency induced by iteration. A water analog system was designed and developed to simulate the die casting process. The flow patterns were recorded by a high speed camera with a capturing rate of 500 frames per second. The simulation results were consistent with the experimental ones. Besides, the fluid flow patterns of several components were simulated by the fractional step and VOF algorithm, and the SOLA-VOF algorithm respectively. The simulation results showed that the combination of the fractional step method and VOF method can improve the computational efficiency to some extent in numerical simulation of mold filling process.