Chung Ho Lee

Three dimensional multi-step inverse analysis for the optimum blank design in sheet metal forming processes

Abstract An inverse finite element approach is employed for more capability to design the optimum blank shape from the desired final shape. Since one-step analysis is not accurate enough to calculate the initial blank shape for complicated parts, multi-step analysis is introduced to obtain more accurate blank shapes and strain distribution. Multi-step analysis deals with the sliding surface for intermediate shapes and the coordinate transformation for appropriate Newton–Raphson iterations. The present algorithm has been applied to square cup drawing and oil-pan drawing. The numerical results confirm the validity and versatility of the algorithm with the initial blank shapes calculated and comparison to experimental results.

Investigation into the improvement of welding strength in three-dimensional extrusion of tubes using porthole dies

Abstract In this work, a modified porthole die for tube extrusion has been developed in order to obtain larger welding pressure than that of conventional porthole dies, and the effect of the improved porthole die on welding pressure has been investigated by performing the finite element analysis on aluminum tube extrusion. The comparison of welding strength of tubes extruded by the modified porthole die with that of tubes made by a conventional porthole die on an expanding test has shown that the tubes from the modified die have been improved in welding strength.

Blank design and strain prediction of automobile stamping parts by an inverse finite element approach

Abstract A new finite element approach is introduced for direct prediction of blank shapes and strain distributions from desired final shapes in sheet metal forming. The approach deals with the geometric compatibility of finite elements, plastic deformation theory, minimization of plastic work with constraints, and a proper initial guess. The algorithm developed is applied to automobile stamping parts such as an oil pan and a front fender in order to confirm its versatility of application by demonstrating the reasonable numerical results in stamping processes. Rapid calculation with this algorithm enables easy determination of various process variables for design of sheet metal forming process.

Process modification of bevel gear forging using three-dimensional finite element analysis

Abstract Bevel gear forging has several advantages as compared with conventional gear forming by a cutting process. For example, it reduces the material loss, and the production lead-time and also has the advantage in product quality improvement of using plastic material flow in the gear teeth. In general, gear forging has a process sequence including preforming and final forming because of the geometrical complexity of its tooth profile. Despite the importance of designing the process sequence, conventionally it has been done by the design expert with exhaustive trial-and-error. Recently, there have been many trial approaches to find the optimal process and die design, and to acquire the quality-related information after forming from simulation using the FEM. In this study the bevel gear forging process is simulated by three-dimensional FEM based on rigid–plastic material modeling, and it is applied to the die design consideration to improve the product quality and to secure the effective material flow. Finite element simulations are performed for two types of bevel gear forging processes to find a defect-free forging process, and comparisons are made between the two processes. It has been thus shown how an improvement can be made through an improved design using finite element simulation.

Three Dimensional Forming Simulation of the Shielded Slot Plate for the MCFC Using a Ductile Fracture Criterion

The shielded slot plate, which has a sheared corrugated trapezoidal pattern, is a component of the metallic bipolar plate for the molten carbonate fuel cell (MCFC). In order to increase the efficiency of the fuel cell, the unit cell of the shielded slot plate should have a relatively large upper area. Additionally, defects from the forming process should be minimized. In order to simulate the slitting process, whereby sheared corrugated patterns are formed, ductile fracture criteria based on the histories of stress and strain are employed. The user material subroutine VUMAT is employed for implementation of the material and ductile fracture criteria in the commercial FEM software ABAQUS. The variables of the ductile fracture criteria were determined by comparing the simulation results and the experimental results of the tension test and the shearing test. Parametric studies were conducted to determine the critical value of the ductile fracture criterion. Employing these ductile fracture criteria, the thre...

Verification of the prediction of deformation-induced anisotropy for simple deformation modes: uniaxial state and pure shear state of stress

Abstract Deformation texture with preferred orientation is developed by external disturbance applied to the grain during the deformation process such as rolling. The formation of deformation texture is strongly influencing the mechanical property of the product, and material anisotropy is observed from the deformation texture, macroscopically. Therefore, the proper consideration and analysis of deformation texture is required. In the present work, the method for prediction of deformation-induced anisotropy employing the phenomenological yield potential is proposed. The proposed algorithm is applied to the anisotropic evolution for simple deformation modes, such as uniaxial stress state and pure shear stress state in X – Y direction. In order to verify the effectiveness of the method, the result from the proposed algorithm is then compared with that from the crystallographic texture analysis.