Materials Science Forum Vols. 575-578

Abstract: The forming process of spline cold rolling was analyzed. The unit average pressure, contact area and rolling force in the cold rolling precision forming process were analyzed and solved. The mechanical and mathematical model has been set up on the basis of the analysis. The numerical simulation of spline cold rolling process was carried out. The results obtained by comparison of theoretical analysis, numerical simulation and experiment provide a theoretical basis for the study and application of spline cold rolling process.

Abstract: Based on generalized Hele-Shaw(GHS) model, numerical simulation of compression-molding flow of sheet molding compound (SMC) in complicated dies is realized by control volume/finite element method (CV/FEM). Finite element computing and post analysis programs have been written. The flow fronts of SMC charge during compression molding are tracked, and the time needed of mold filling in complicated dies is predicted. The results of simulation are helpful for the placement of SMC charge, the design of mold and the optimization of technological parameters.

Abstract: In this paper, penalty finite element method is applied to the simulation of three-dimensional incompressible viscous steady flow, and the program is coded for analysis of three-dimensional flow process of plastic melt in extrusion die. Slit die is typical in polymer extrusion process, and the relevant part is used widely. Because the flow law is different for various polymers with different rheological character even in the same die, the polymer flow in slit die is simulated for Newtonian fluid and power-law fluid by the program and ANSYS, respectively. Flow laws of two kinds of fluid are compared, and the result shows that the non-uniform velocity distribution in outlet is caused by the non-Newtonian effect of material. The penalty factor is important for the penalty finite element model, which decides the precision and efficiency to a great extent. The proper penalty value is decided by some factors, for example, the character of the whole equations and geometric model. Numerical solution with change of penalty value and viscosity is analyzed, and the result shows that the penalty value should be suited with viscosity in special range for penalty finite element model. The experiment has been developed, and the velocity distribution in outlet of slit die is measured. The result of finite element analysis is consistent with experimental result basically, and the reason of result divergence of the two ways is analyzed. The results show that the given model is suited for the polymer extrusion process, and the advice of the selection of penalty value is instructional for penalty element model.

Abstract: Temperature evolution is one of the important parameters of mechanical properties of thin strip products. So the ability of prediction of temperature history before processing is critical to the processing scheme of controlling rolling and controlling cooling. In this paper an integrate model of finite element method is presented for the prediction of the temperature evolution in the finishing rolling during hot strips. The model takes into account the interaction between thermal behavior and mechanical behaviors. By using the second-development method based on the commercial code thermal behavior and temperature distribution of strips through seven-pass finishing rolling are described in detail. A method for computing the mean temperature at the exit of each pass is approached. Using this method the mean temperature can be attained after each pass. In one seven-pass thin strip rolling mills the temperature at the exit after each pass is measured by the pyrometer. The measured results and the simulation results are compared. The validity of the proposed analysis model is examined. The computing results are in agreement with the measured results.

Abstract: In order to solve the problems such as cracking, uneven property and poor forming controllability in the traditional hot forging of Mn18Cr18N retaining ring, a new intramode canning hot forging process was developed. In this paper, the hot deformation behavior of the material was invstigated by thermo-mechanical molding tests. Based on the results of the tests, the new process was studied in detail and the main parameters were optimized by means of numerical simulation method. The experiment shows that the process was reasonable for forging Mn18Cr18N retaining ring.

Abstract: The warm powder compaction process is simulated by the finite element analysis software which is MSC/MARC. The thermal mechanically coupled analysis method is applied based on the updated Lagrangian Method to study the influence of different velocities ratio of die and punch υdie/υup-punch on the properties of green under different frictional condition. The results indicate that for cylindrical powder metallurgic products, different velocity ratios have great influence on the distribution of relative density and equivalent stress. The frictional force can be converted to the favorable force through adjusting the velocity ratio, and this method can obtain higher uniform distribution of relative density and stress of green.

Abstract: The stress fields of rectangular and T shape compression dies were simulated by three dimensional photo-elasticity of stress freezing method. The rules of stress distribution of σx, σy, σz on the surface of rectangular and T-shaped dies were discovered, and the rules were also found inside the dies. The results indicate that the stress distribution of rectangular die is similar to that of T shape die. Obvious stress concentration in corner of die hole was observed. σz rises from die hole to periphery until it achieves maximum value then it diminishes gradually, and σz between die hole and fix diameter zone is higher than it is in other position. At the same time, the equations of stress field of extrusion dies were obtained by curved surface fitting experimental values in every observed point with multiple-unit regression analysis method and orthogonal transforms. These works can provide stress distribution model for die computer aided design and make.

Abstract: This paper studies FGH96 P/M Superalloy dynamic recrystallization phenomenon under isothermal forging conditions. Curves of work hardening rate θ versus flow stress σ and RTT curve of dynamic recrystallization are gained through the analysis. At the same time, some parameters are confirmed including peak strain, critical strain and the maximal softening strain. On the basis of the analysis, the type of FGH96 P/M Superalloy dynamic recrystallization is exactly estimated. The quantitative metallography method is adopted to determine the recrystallized grain size. With combining the obtained data and parameters, FGH96 P/M Superalloy dynamic recrystallization mathematic model is established by regression method. At the same time, the forging process of FGH96 P/M superalloy is simulated by using software MSC/Superform under different deformation conditions such as deformation temperature and deformation velocity. The contour images of the grain size distribution under different conditions and different deformation degree are gained and analyzed. With the analysis, it is known that the effect of the different deformation conditions on the microstructure of the forging is obvious and there is different distribution of the grain size on various locations, which indicates that the deformation degree of the billet also has influence on the grain size.

Abstract: The rapid market need of MEMS (Micro Electromechanical System) and metal microparts are increasing gradually. The plastic microforming has received more interests and applications in MEMS because it ensures high precision and manufacturing efficiency. However, it raises the higher demand on the microforming and plastic processing technology. Here we present one new process to micro-extrude microparts with laser-aided heating method. The new process is to selectively heat the workpiece with the laser radiation method to the suitable temperature that is between room temperature and recrystallization temperature, and to extrude the workpiece. This process is characterized by decreasing the influence of strain strengthening and lowering the resistance to deformation, and increasing the uniformity of material flow. The key elements of the approach concerning the warm micro-extrusion and temperature control, such as process parameters, laser heating system, micro-extrusion die structure, have been advanced. Furthermore, an important aspect of the research is that the developed system and theory of micro warm extrusion based on laser heating can be explored for further investigation and understanding of plastic microforming.

Abstract: This paper presents a simulation analysis of stress and strain of an underground rail elastic bar using the commercial finite-element simulator ANSYS-10. Under constant compression displacement of 10.4 mm or the fixed-plug-in displacement of 84 mm, the stress distributions are examined by varying the boundary condition of the corresponding fixed-plug-in displacement or the compression displacement. Results show that the maximum stress which is 1,490 Mpa occurs as the compression displacement is 10.4 mm while the fixed-plug-in displacement is 84 mm. In addition, in both group of scenarios the maximum stress is at the end of the arc of the elastic bar and exceeds the strength limit of 60Si2Mn. While both the compression displacement and the fixed-plug-in displacement affect the stress distribution and the maximum stress, it appears that the effect due to compression displacement is much more significant.