• Transactions of Materials Processing
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• v.8 no.4
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• pp.393-398
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• 1999

The plastic instable flow phenomenon happens in practical forming process, I. e. upsetting, backward extrusion, piercing, indentation. And also, it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfections in the lubrication, billet eccentricity, inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and for better control of forming operation, we should necessarily find out their phenomena. In this study, we introduced the friction disturbance due to inclined punch angle. Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity. Also, we considered the buckling parameters of billet with the large aspect ratio in upset forging.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.244-248
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• 1997

In the rolling process, keeping the accuracy of the slab width is a very important problem. So the edge rolling is used with the plate rolling. But in the edge rolling, a local contraction of width, called "width necking", occurs in the top and tail portion of a slab and becomes the cause of crop loss. In this investigation, the three dimensional deformation behavior in the edge-plate rolling is simulated by rigid plastic FEM(PROLL). And the influence of the rolling condition on "width necking" and the accuracy of width is examined.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.145-151
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• 1998

Unlike the drawing of round section from round bar, the shaped drawing like polygonal section is known to have influence not only drawing stress but also corner filling. Therefore. this study analyze the drawing process of suqare rod from round bar using nonsteady state rigid-plastic FEM. To investigate effects of process variables of the drawing process of square rod from round bar, FE-simulations with variety of reduction in area and semi-die angle for a given frictional condition have been conducted. By this results, it has to suggest optimal process condition on the drawing stress and the corner filling. In addition, it has determined forming limit considering necking and bulging.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1290-1300
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• 1996

The finite element method, based on rigid-plastic formulation, is widely used to simulate metal forming processes. In order to improve the computational efficiency of the rigid-plastic FEM, one-point integration is used to evaluate the stiffness matrix with four-node rectangular elements and eight-node brick elements. In order to control the hourglass modes, hourglass strain rate components were introduced and included in the effective strain rate definition, Numerical tests have shown that the proposed one-point integration scheme reduces the stiffness matrix evaluation time without deteriorating the convergence behavior of Newton-Raphson method. Simulations of a ring compression, a plane-strain closed-die forging and the three-dimensional spike forging processes were carried out by using the proposed integration method. The simulation results are compared to those obtained by applying the conventional integraiton method in terms of the solution accuracy and computational efficiency.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.98-101
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• 1999

The plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. And also it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfection in the lubrication billet eccentricity inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and it is for better control of forming operation we should necessarily find out their phenomena. In this study we used the friction disturbance due to inclined punch angle and introduced the method considering kinematic hardening effect Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity.

• Transactions of Materials Processing
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• v.5 no.2
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• pp.130-137
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• 1996

The sheet formability can be improved by the optimum drawbeads installation because draw-beads can control the flow of the metal into the die cavity when the punch enters into the die opening, In this study the drawing characteristics for step drawbead are analyzed by 2-D rigid -plastic FEM and also are measured experimentally. In addition for the validity of FEM theoretical results are compared with the experimental results. Especially the draw bead restrain-ing forces and the strain distributions of drawn specimens are obtained in both FEM and experiment. Also the effects of the drawbead dimensions drawing angles and blank holding forces on the drawing characteristics are investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.40-44
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• 1997

The governing functional in plastic deformation has to satisfy the incompressible condition. This incompressible condition imposed on the velocity fields can be removed by introducing either the Langrange multiplier or the penalty function into the functional. In the study two-dimensional rigid plastic FEM programs using by Lagrange multiplier and penalty function are developed. A compression of cylinder and a spike forging are simulated to compare the data of loads, local mean stresses and reductions of volume.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.57-61
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• 1997

The governing functional in plastic deformation has to satisfy the incompressible condition. This incompressible condition imposed on the velocity fields can be removed by introducing either the Langrange multiplier or the penalty function into the functional. In this study two-dimensional rigid plastic FEM programs using by Langrange multiplier and penalty function are developed. A compression of cylinder and a spike forging are simulated to compare the data of loads, local mean stresses and reductions of volume.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.265-270
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• 1995

In orthogonal cutting a new approach for modeling of burr formation process when tool exits workpiece is proposed. The approach is based on the rigid-plastic FEM combined with the ductile fracture criterion and the element kill method. The approach is applied to simulate a plane strain cutting process. The results of the FEM are compared with those of the experiment. It is shown that the fracture location and fracture angle as well as cutting force can be predicted using the proposed approach with a good correlation to experimental results.

• Transactions of Materials Processing
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• v.3 no.2
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• pp.178-188
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• 1994

A design methodology is applied for manufacturing a disk-brake piston component. The design criteria are the limit drawing ratio and the forging load within the available press limit. Also, the final product should not have any geometrical defect. The rigid-plastic FEM has been applied to simulate the conventional four stage manufacturing processes, which include deep drawing and forging process. Simulation of one stage process from a selected stock to the final product shape is performed for generating information on additional requirements for metal flow. Two stage forming processes with different punch corner and nose geometries are also simulated to identify the possible best solutions. Finally, the best manufacturing process is selected, which is using a hemispherical punch int he deep drawing process.