• Transactions of Materials Processing
• /
• v.7 no.4
• /
• pp.340-346
• /
• 1998

A kinematically admissible velocity field is developed for the analysis of twisting of the extruded products with elliptical shapes from round billet. The twisting of extruded product is caused by the lin-early increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product in creases with the die twisting angle, the aspect ratio of product the friction condition, the reduction of area, and decreases with the die length.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.4
• /
• pp.524-530
• /
• 2003

This paper presents a new model on deformation characteristics of cylindrical tubes under pure bending. The model is based on the upper bound method that minimizes total strain energy of a system. It does not assume inextensibility condition. Geometric relations and displacement fields are derived by analysis of deformation behaviors of elastic tubes. Simulations are calculated using numerical optimization and integration techniques. The results give information about cross-sectional deformation of cylindrical tubes. Simulation results are compared with available data in literatures, which show that this method predicts deformation characteristics of tube bending process.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.3
• /
• pp.330-336
• /
• 1989

In analyzing the axisymmetric backward extrusion process a new method of analysis using upper-bound theorem is proposed in which the plastic zone and dead metal zone cam be predicted. Experiments are carried out with commercial aluminum. The metal flow on the meridional plane has been visualized experimentally by using the gridded specimens. It is shown that the theoretical results both in extrusion load and deformation pattern are in good agreement with the experimental results and they can be used for effective punch and die design to consider various process parameters in axisymmetric backward extrusion.

• Transactions of Materials Processing
• /
• v.10 no.4
• /
• pp.302-310
• /
• 2001

The twisting and extrusion process of the product with involute helical fin from the round billet is developed by the upper bound analysis. The twisting of extruded product is caused by the twisted inclined die surface connecting the die enterance section and the die exit section linearly. In the analysis, the internal shear surface is defined as the curved twisted plane from the twisting of die surface and the shear work is calculated by the consumption of shear energy. The increase rate of angular velocity is determined by the minimization of plastic work. The angular velocity of die exit can be controlled by the land length and the length of inclined die. The alular velocity assums to be increased linearly by the axial distance from the die enterance to the die exit. The results of the analysis show that the angular velocity of the extruded product increases with the die twisting angle, the reduction of area, and decreases with the die length, the friction constant.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.7
• /
• pp.1314-1321
• /
• 1992

In analyzing the plastic flow of axisymmetric tube extrusion a new method of formulation using the stream function approach and upper-bound theorem is proposed which permits the prediction of plastically deformed zone in analytic expression as well as metal flow. It is shown that the formulation proposed in this work covers the solid extrusion and tube extrusion in axisymmetric case. The effect of some process parameters such as area reduction, the ratio of radii(inner radius to outer radius) and friction factor on extrusion pressure, deformation zone and plastic flow through stream-lined dies has been studied. The presented theoretical analysis can be effectively used for the prediction of deformation zone and plastic flow.

• Journal of the Korean Society for Precision Engineering
• /
• v.5 no.4
• /
• pp.24-31
• /
• 1988

The Upper Bound Solution has been used to investigate the effect of the various parameters on the floating-plug tube-drawing precess. A kinematically admissible velocity field considering the change of the tube thickness is proposed for the deformation process. Taking into account the position of the plug in the deforming region, shear energy at entrance and exit, friction energy on contact area, homogeneous energy are calculated. The theoretical values in proposed velocity field are good agreement with experimental values, It is investigated that the tube thickness in the deforming region is changed slightly toward minimization of deforming energy and then the drawing stress in lower than the crawing stress in the velocity field that the tube thickness is uniform.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.03a
• /
• pp.210-213
• /
• 1998

A kinematically admissible velocity field is developed for the analysis of twisting of extruded products. The twisting of extruded product is caused by the linearly increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance and is increased linearly by axial distance from die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increase with the die twisting angle and the aspect ratio of product and friction condition and reduction area and show that angular velocity increases with the decreases in die length.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.03a
• /
• pp.214-219
• /
• 1998

Analytic and experimental methods have been used for the characterization of flow behavior of semi-solid Al2024 alloy. Backward extrusion experimnet was chosen to avoid the crack on the unconstrained surface. The material constants for the flow stress by the upper bound technique that agreed with experimental results were determined. The various material constants obtained for al temperature range above the solidus temperature have been fitted and represented in the function of temperature and solid fraction. The obtained result has good agreement only in the high solid fraction.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1996.03b
• /
• pp.145-155
• /
• 1996

The extrusion velocity of billet through a die and the shapes of the die are the important factors in the metal forming process of the extrusion of billet. in recent years, the life cycle of products is goingfaster. Although the former finite element method was capable of yielding a detailed analysis, it requires lots of time and extensive coding effort. Then, some simple devices were developed and based on upper bound method. For this purpose , a kinematically admiasible velocity field is formulated for extrusion of cylinders with arbitrary cross section and die profile on their outer surfaces by using a modified upper bound approach, which configures simulataneous extruding speeds in three directions . Also, In order to display mesh of the cold forward extrusion process using the approach , the automatic three-dimentional mesh generation produced by the approach coupled finite element method with upper bound method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1996.03b
• /
• pp.23-30
• /
• 1996

The purpose of this study was to investigate changes in thewall thickness of tube sinking and working forces by the upper bound method and ABAQUS code. The independent variables were : Workpiece material, original wall thickness of tube, die angle, friction, and diameter reduction. The results indicated that of these five variables were a factor in wall-thickness increase and working forces. Three variables, a inner tube wall angle and two angles of the velocity discontinuous surfaces, are optimized in this proposed velocity field by the upper bound method. In this method, we can estimate the working forces and final tube thicknesses whcih are similar to acturla forming process. Optimized process variables which are obtained by upper bound method are used in ABAQUS pre-model . In ABAQUS analysis, the stress and the strain contours which are considered to be heat generation occured by the friction during forming process are observed.