Papers by Author: G.M. Lee

Abstract: Numerical analysis of radial extrusion process combined with backward extrusion has been performed to investigate the forming characteristics of an aluminum alloy in a combined extrusion process. Various variables such as gap size, die corner radius and frictional conditions are adopted as design or process parameters for analysis in this paper. The main investigation is focused on the analysis of forming characteristics of AA 2024 aluminum alloy in terms of material flow into backward can and radial flange sections. Due to various die geometries and process conditions such as frictional conditions, the material flow into a can and flange shows different patterns during the combined extrusion process and its characteristics are well summarized quantitatively in this paper in terms of forming load, volume ratio etc. Extensive simulation work leads to quantitative relationships between process conditions and the forming characteristics such as volume ratio of flange to can and the size of can and flange in terms of the can height extruded backward. It is easily seen from the simulation results that the volume ratio, which is defined as the ratio of flange volume to can volume, increases as the gap size and/or die corner radius increase. However, it is interesting to note that the frictional condition has little influence on the forming load and the deformation patterns. Usually, the frictional condition is a greatest process variable in normal forging operation. It might be believed from the simulation results that the frictional conditions are not a major process parameter in case of combined extrusion processes. It is also found that the can size, which is defined as the height of billet after forming, turns out to be even smaller than that of initial billet under a certain condition of die geometry.

Abstract: This paper is concerned with the analysis of the forming load characteristics of a forward-backward can extrusion in both combined and sequence operation. A commercially available finite element program, which is coded in the rigid-plastic finite element method, has been employed to investigate the forming load characteristics. AA 2024 aluminum alloy is selected as a model material. The analysis in the present study is extended to the selection of press frame capacity for producing efficiently final product at low cost. The possible extrusion processes to shape a forward-backward can component with different outer diameters are categorized to estimate quantitatively the force requirement for forming forward-backward can part, forming energy, and maximum pressure exerted on the die-material interfaces, respectively. The categorized processes are composed of combined and/or some basic extrusion processes such as sequence operation. Based on the simulation results about forming load characteristics, the frame capacity of a mechanical press of crank-drive type suitable for a selected process could be determined along with securing the load capacity and with considering productivity. In addition, it is suggested that different load capacities be selected for different dimensions of a part such as wall thickness in forward direction and etc. It is concluded quantitatively from the simulation results that the combined operation is superior to sequence operation in terms of relatively low forming load and thus it leads to low cost for forming equipments. However, it is also known from the simulation results that the precise control of dimensional accuracy is not so easy in combined operation. The results in this paper could be a good reference for analysis of forming process for complex parts and selection of proper frame capacity of a mechanical press to achieve low production cost and thus high productivity.

Abstract: In the present study, the finite element analysis has been conducted to investigate the deformation characteristics of forward and backward can extrusion process using AA 1100 aluminum alloy tubes in terms of maximum forming load and extruded length ratio in a combined material flow. A commercially available code is used to conduct rigid-plastic FEM simulation. Hollow tubes are selected as initial billets and the punch geometries follow the recommendation of ICFG. Selected design parametrs involved in simulation includes punch nose radius, die corner radius, frictional condition, and punch face angle. The investigation is foucused on the analysis of deformation pattern and its characteristics in a forward tube extrusion combined simultaneously with backward tube extrusion process main in terms of force requirements for this operation according to various punch nose radii and backward tube thickness. The simulation results are summarized in terms of load-stroke relationships for different process parameters such as backward tube thickness, die corner radii, and punch face angle, respectively, and pressure distributions exerted on die, and comparison of die pressure and forming load between combined extrusion and two stage extrusion process in sequencial operation. Extensive analyses are also made to investigate the relationships between process parameters and extruded lengths in both forward and backward directions. It has been concluded from simulation results that a) the combined operation is superior to multi-stage extrusion process in sequential operation in terms of maximum forming load and maximum pressure exerted on die, b) the length of forward extruded tube increases and that of backward extruded tube decreases as the thickness ratio decreases, and c) the forming load is influenced much by the thickness ratio and the other design factors such as die corner radius and punch face angle does not affect much on the force requirement for the combined extrusion process.

Abstract: The rigid-plastic finite element method has been applied to three variants of radial extrusion processes to investigate the influence of die geometry on the material flow into the flange gap. Case I involves forcing a cylindrical billet against a flat die, which is a single action pressing process. In case II, another single action pressing process, the upper punch forces a billet against a stationary punch recessed in the lower die. Both the upper and lower punches move together in Case III toward the center of billet at the same speed with a double action tool. Major process parameters are identified as the relative gap height and the die corner radius in constant relative deformation. The relative gap height is defined as the ratio of gap height to billet diameter. Extensive simulation work for various combinations of process parameter value has been performed and then the main characteristics of the deformation patterns of each case are observed to define the terms which represent the forming characteristics of the flange in radial extrusion processes in terms of separation height, asymmetric ratio of height, and asymmetric ratio of angle, respectively. The effect of major process parameters on the material flow into the flange gap has been also analyzed in terms of flange radius and flange angle. The effect of frictional condition on the separation height has been also analyzed to investigate the edge separation of flange from the flat die. AA 6063 aluminum alloy is selected as a model material throughout the analysis. Simple comparison between AA 6063 and AISI 1006 steel has been also made to investigate the effect of material selection on the deformation pattern, especially in terms of separation height in Case I and asymmetry in Case II, respectively.

Abstract: In this paper, the forming process of a central hub by radial-forward extrusion has been analyzed by the rigid-plastic finite element method. In this process, the material flows in radial direction and then deflects 90 degrees into the same direction as that of punch movement. Radial extrusion is used to produce parts that generally feature a central hub with radial protrusions. Design factors such as mandrel diameter, punch nose radius, deflection corner radius, gap width in annular direction, and frictional conditions are applied to the present study by simulation. AA 6063 aluminum alloy is selected as a model material for analysis in the present study. The influence of these design factors on the force requirement during the forming operation and the pressure exerted on the tooling such as the punch and mandrel is investigated and the simulation results are quantitatively summarized in terms of pressure distribution, force-stroke relationships, and maximum force requirement, respectively. The main goal of this study is to investigate the effect of those process parameters on the deformation pattern in radial-forward extrusion process, especially the effect of deflection corner radius. It has been concluded from the simulation results that a) the frictional condition between workpiece and tool does not affect the punch load very much, but the load supported by mandrel is more or less significantly influenced by the frictional condition compared to that of punch, b) the deflection corner radius turns out to be a major process parameter in terms of maximum force requirement, and c) a similar trend is found in the punch and mandrel forces during the radial extrusion process.