Naksoo Kim

A parametric study on forming length in roll forming

Abstract A simulation program has been developed in order to examine the roll forming process. The program is based on the three-dimensional finite element analysis of shape and roll forming under kinematically steady-state condition. In this study, the forming length of the strip in the roll forming process was estimated in consideration of some factors such as material properties, strip thickness, roll diameter, roll velocity, and the deformation of the material that influence the forming length decisively. The sensitivity of the forming length to these factors was considered, and the interaction between factors that affect the forming length was considered also. To verify the reliability of the simulation program, the simulated results for longitudinal strain were compared with experimental results available in the literature. It was concluded that the work-hardening exponent plays a major role in the forming length of the pre-deformed strip.

Prediction of spread, pressure distribution and roll force in ring rolling process using rigid-plastic finite element method

Abstract The ring rolling process involves 3D non-steady flow and continuous change of radius and thickness of the ring workpiece. In this study, a commercial FEM-code that is especially tailored to ring rolling process, SHAPE-RR™, is used to predict spread, pressure distribution and roll force in plain and T-shaped ring rolling processes. Two cases of plain and T-shaped rings are, respectively, simulated for the prediction of side spread by changing feed-rate and groove factor. Plain ring rolling is simulated for the prediction of pressure distribution and roll force. Compared with earlier experimental works, the results of simulations show good quantitative agreements. It is concluded that the solution tool can be utilized in design and analysis of ring products, process, and tooling and equipment.

Optimum blank design of an automobile sub-frame

A new blank design method is proposed to predict the optimum initial blank shape in the sheet metal forming process. The rollback method for blank shape design takes the difference between final deformed shaped and target contour shape into account. Based on the method a computer program composed of blank design module FE-analysis program and mesh generation module is developed. The rollback method is applied to square cup drawing process with the flange of unifiorm size around its periphery to confirm its validity. The optimum initial blank shape is obtained from an arbitrary square blank after three modification. Good agreements are recognized between the numerical results and the published results for initial blank shape and thickness strain distribution. The optimum blank shape for two parts of automobile sub-frame is designed, The thickness distribution and the level of punch load is improved. Also the method is applied to design the weld line in the tailor-welded blank. It is concluded that the rollback method is an effective and convenient method for an optimum blank shape design.

Optimum conditions for parallel translation of maxillary anterior teeth under retraction force determined with the finite element method.

INTRODUCTION In this study, we used the finite element method to examine the optimum conditions for parallel translation of the anterior teeth under a retraction force. METHODS Finite element models of the 6 maxillary anterior teeth and the supporting structures (periodontal ligament and alveolar bone) were generated as a standard model based on a dental model (Nissin Dental Products, Kyoto, Japan). After designating the position and length of the power arm as variables, the initial displacement of each tooth was measured with finite element simulation, and the rotation angle of each tooth was calculated. RESULTS The relationship between the position and length of the power arm was analyzed, and model equations for this relationship were proposed. As a result, the length of the power arm was either 4.987 or 8.218 mm when it was located either between the lateral incisor and the canine or between the canine and the first premolar, respectively. CONCLUSIONS The length of the power arm increased as its position was moved from the lateral incisor to the premolar. This was because the length of the power arm must be increased to be in equilibrium mechanically. Overall, it is expected that the efficient positions and lengths of the new dental models can be calculated if these total procedures are established as a methodology and applied to new dental models. Moreover, the parallel translation of the maxillary anterior teeth can be generated more effectively.

A study on process improvements of multi-stage deep-drawing by the finite-element method

Abstract Multi-stage deep-drawing processes, including normal drawing, reverse drawing, and redrawing, to shape the front shell of a master VAC for an automobile have been analyzed sequentially by the use of the rigid-plastic finite-element method, computational results on the punch/die loads and thickness distributions being obtained. The thickness strains were compared with the results of experiments on current drawing processes, good agreement being found. Deep-drawing processes of the redesigned shell to improve the specific strength and stiffness were simulated with the numerical method developed. By varying several process parameters, such as the blank size, the corner radii of the tools, and the clearances, the simulation results showed improvements in reducing the forming loads. Also, forming defects were found during simulation and the appropriate blank size could be verified.

Finite element modeling of the deformation behavior of semi-solid materials

Abstract In the current study, the deformation behavior of semi-solid materials was modeled using the von Mises yield criterion in which the semi-solid material was treated as a single phase material with the incompressibility condition in a global sense. The flow stress of the material was modeled as a function of strain in consideration of the solid fraction and the breakage ratio of dendritic structure. An algorithm based on mixture theory and D’Arcy’s law was developed to update the solid fraction, the distribution of which varies within the material due to relative velocity between the solid and liquid phases during deformation. The parameters involved with the proposed model were determined through a parametric study in which numerous finite element analysis results were compared with the data from existing isothermal upsetting experiments for semi-solid Sn–15%Pb alloy. Comparison with experimental results showed that the current approach is improved compared to previous compressible approaches. The generality of the current approach was examined through rigid–thermoviscoplastic finite element analyses of the semi-solid forging of a ball-joint case under various preheating temperatures in consideration of the release of latent heat. The simulation results agreed well with the trend of the experimental findings but showed some quantitative errors.

Prediction and design of edge shape of initial strip for thick tube roll forming using finite element method

Abstract Increasing demands for electric resistance welded pipes of high quality with thick wall require close investigations in edge deformation by slitting, strip deformation during break down forming, and difference of circumferential length. In order to obtain good quality of a welding zone, it is necessary to predict the edge shape of the initial strip. The modeling of the multi-pass thick tube roll forming process with rigid–plastic finite element method and the edge shape prediction of an initial strip with second-degree polynomial regression method are presented in this paper. Edge shapes of initial strip have been analyzed by the finite element method and designed by the regression method to satisfy the requirements at target fin pass. It is concluded that the proposed edge design method results in optimal edge shapes satisfying the design requirements.

Rigid–thermoviscoplastic finite-element analysis of the semi-solid forging of Al2024

Abstract In the present investigation, material characterization of globular Al2024 alloy in terms of breakage ratio, solid-fraction, strain and strain rate was obtained at the semi-solid state through backward extrusion experiments. Axisymmetric rigid–thermoviscoplastic finite-element analysis of semi-solid forging of a ball-joint case was performed using the currently determined flow stress. In the analysis, the solid-fraction considering phase change was updated at each time increment by calculating the volume of the liquid component under the assumption that the relative flow of liquid to solid components obeys D’Arcy’s law. The simulation results were compared to those of the experiments to test the validity of the currently determined flow stress. In addition, the effects of process variables such as die preheating and initial workpiece temperatures and forming speed on formability were investigated. It was construed that the forming speed was the most dominant process variable in effecting variation in the distribution of solid-fraction.

Finite-element analysis and experimental verification for drawbead drawing processes

Abstract Theoretical and experimental drawing characteristics for single-circular and single-square drawbeads are discussed. The strain distributions on the upper and the lower skins of the specimens and the die reactional forces during the blank-holding process are calculated by the finite element method (FEM), the simulational results being compared with experimental results. The effects of the drawing length and the drawing angle on the drawbead restraining forces and the strain distributions in the drawn specimens are investigated and the calculations are compared with the results of experiment. It is concluded that the theoretical simulations and results are useful for the prediction of real cases.

Experimental investigation and numerical simulation of SMC in compression molding

Abstract Experimental investigation and numerical simulation were performed to study the compression molding of SMC. Laboratory-scaled molds were designed and built for experimental study of the SMC charges with different colored layers to enable visualization of the flow patterns. Temperature and flow patterns inside the SMC charge were measured for various process parameters such as mold temperature, mold geometry and closing speed. A thermo-viscoplastic finite-element program was developed to simulate compression molding. In the analytical study, the deformation of the material was modeled using a flow rule taking the fiber distribution into account. A kinetic model was adopted to describe the cure behaviour. The results of analysis and experiment were compared, showing good agreements with each other. The experimental findings combined with analytical results provided a sound understanding of SMC in compression molding.