• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.400-403
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• 2008

For the effective manufacture of doubly curved metal plates, a line array roll set (LARS) process is proposed. The suggested process utilizes a pair of upper and lower symmetric roll assemblies. In the process, the initial plate is progressed into the final shape in a stepwise or pathwise manner according to the basic principle of the incremental forming process. The deformation proceeds simultaneously in the longitudinal and transverse directions. Moreover, there is a close correlation between the deformation in the longitudinal direction and that in the transverse direction of the plates. Therefore, the finally formed shape in the incremental forming process is strongly dependent upon process conditions, such as the forming path and the forming increment. The manufacturing of arbitrary doubly curved plates with various curvatures is not an easy task because of such complicated behaviors of the plate; thus, the forming schedules for the desired shape should be carefully and accurately designed. In this study, several experiments with the LARS system were carried out for the fundamental investigation on process design for manufacturing of doubly curved plates.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1545-1548
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• 2003

In rigid-plastic finite element method, there is a heavy computation time and convergence problem. In this study. static-explicit rigid-plastic finite element method will be introduced. This method is the way that restrict the convergence interval. In result, convergence problem and computation time due to large non-linearity in the existing numerical analysis method were no longer a critical problem. Also, we investigated the effect of punch stroke and the strain increment this method. It is expected that various results from the numerical analysis will give very useful information for the design of tools in sheet metal forming process.

• Transactions of Materials Processing
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• v.9 no.3
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• pp.293-303
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• 2000

Recent developments of Fe technology make it possible to apply CAD/CAE/CAM techniques successfully to the stamping die design among the automotive parts industries. Those successful applications are greatly attributable to the development of commercial S/W. Up to now most commercial S/W for the analysis of sheet metal forming is based on the dynamic explicit algorithm. The main characteristics of dynamic explicit algorithm is that there is no convergence problem if the time increment is taken less than the stability limit. The stability of the analysis is guaranteed in the commercial code, since the adequate time increment is computed from the so called "Courant Condition". However excess computing time is often pointed out in the dynamic explicit analysis according to the characteristics of process parameters taken. In the study, various parameters that may affect the stability and the method how to improve computational efficiency of analysis have been investigated.estigated.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.233-245
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• 1998

A new approach has been proposed for the incremental analysis of the nonsteady state large deformation of planar anisotropic elastic-plastic sheet forming. A mathematical brief review of a constitutive law for the incremental deformation theory has been presented from flow theory using the minimum plastic work path for elastic-plastic material. Since the material embedded coordinate system(Lagrangian quantity) is used in the proposed theory the stress integration procedure is completely objective. A new return mapping algorithm has been also developed from the general midpoint rule so as to achieve numerically large strain increment by successive control of yield function residuals. Some numerical tests for the return mapping algorithm were performed using Barlat's six component anisotropic stress potential. Performance of the proposed algorithm was shown to be good and stable for a large strain increment, For planar anisotropic sheet forming updating algorithm of planar anisotropic axes has been newly proposed. In order to show the effectiveness and validity of the present formulation earing simulation for a cylindrical cup drawing and front fender stamping analysis are performed. From the results it has been shown that the present formulation can provide a good basis for analysis for analysis of elastic-plastic sheet metal forming processes.

• Transactions of Materials Processing
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• v.18 no.8
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• pp.616-624
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• 2009

In this work we demonstrate the hot-embossing process under different forming conditions such as forming temperature, load, and holding time in pressing, in order to determine the suitable conditions required for linear patterning on polymer plates (PC). Results showed that the replicated pattern depth increased in proportion to an increase in the forming temperature, load, and time. The reduction of the workpiece thickness increased according to the holding time in the pressing process. In the process of time, the reduction ratio of the workpiece thickness decreased due to the surface area increment of the workpiece, while the pressure on the workpiece declined. In order to reduce the bulging ratio we introduced a temperature difference between the upper and the lower punch.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.277-280
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• 2008

Recently, a demand of nano/micro patterned polymer for display or biochip has been rising. Then many studies have been carried out. Nano/micro-embossing is a deformation process where the workpiece materials is heated to permit easier material flow and then forced over a planar patterned tool. In this work, the hot-emboss process is performed with different forming conditions; forming temperature, load, press hold time, to get the proper condition for linear pattern fabrication on plated-type polymers (PC). Replicated pattern depth increases in proportion to the forming temperature, load and time. Reduction of the workpiece thickness increases according to press hold time. In process of time, reduction ratio of workpiece thickness decreases because of surface area increment of the workpiece and pressure decline on it.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.642-647
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• 2007

Determination of loading conditions for tube hydroforming(THF) process that implies an amount of the increment in axial feeding and internal pressure for each step is one of the most important constituents at the process design level. On account of the fact that those design factors mentioned above are imposed simultaneously during the process, suitable loading conditions are required to obtain robust products without any failure such as buckling, necking, bursting and so on. In which, especially, bursting is well known as the most frequently occurred failure in general THF process. In this study, therefore, determination of the loading condition based on the adaptive method was carried out to obtain safe loading paths. In addition, forming limit curves are applied to evaluate the derived loading conditions by using the simulation results. Consequently, it is found that described method in this study for THF process design is useful and has a feasibility.

• Transactions of Materials Processing
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• v.11 no.1
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• pp.84-89
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• 2002

This study is concerned with the analysis of the forming characteristics of radial-forward extrusion. Angle between radial and forward extrusion, gap height, and friction factor are considered as important design factors to affect forming characteristics in radial-forward extrusion. The rigid-plastic finite element method is adopted to analyze the effects of design factors on forming loads. The incremental rates of loads are nearly constant except the deformation zone from radial to forward extrusion. The smaller angle induces lesser force increment, therefore forming load increases as the angle increases. Maximum load also increases as gap-height decreases and friction factor increases.

• Transactions of Materials Processing
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• v.32 no.6
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• pp.360-366
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• 2023

This study is concerned with the surface quality of products according to the material and coating condition of the forming tool in incremental sheet forming. Three forming tools, SKD11 with and without diamond-like-coating (DLC) and polymer tool tip, were used to form conical and pyramidal geometries to take into account the influence of friction between the forming tool and the sheet on the surface quality including geometric accuracy of deformed samples. Each test was performed using SUS304 with a thickness of 0.4 mm according to different incremental depths per lap of 0.5 mm, 1.0 mm, and 1.5 mm for the contour tool path, considering the increase in normal force which is associated with the frictional behavior during local deformation. The surface quality was then investigated through surface roughness measured with KEYENCE VR-6000 and relative strain distribution including deformed shape analyzed with ARGUS which is a non-contact optical strain measurement system. Differences between 3D CAD surfaces and captured geometry from experiments were evaluated to compare the effect of friction on geometric accuracy. From comparisons of experimental results, it was revealed that the polymer-based tool tip can improve surface quality and geometric accuracy by reducing the undesired material flow due to local friction in the increment sheet forming process.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.3
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• pp.249-256
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• 1983

The study is concerned with the analysis of sheet metal for the prediction of limit drawing ratio and forming load. The direct redrawing process is analyzed by using an equilibrium approach and strain increment theory both for non-workhardening material and for workhardening material. Computations are carried out numerically for the workhardening case. Limit drawing ratios are predicted for some chosen variables. The forming loads are also computed with respect to punch travel. Then the predicted loads are compared with the experimental results. For ordinary lubricated conditions, the comparison shows reasonable agreement between the theory and experimental observation. It is also shown that limit drawing ration can be increased by using a greater die angle and proper lubrication significantly reduces the punch load. Finally numerical results show that material of greater R-value and strain-hardening exponent(n)is better for direst redrawing of sheet metal.