• Transactions of Materials Processing
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• v.21 no.7
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• pp.432-440
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• 2012

In this article, the design of the flexible forming process considering die shape compensation using an iterative over-bending method based on numerical simulation was conducted. In this method, the springback shape obtained from the final step of the first forming simulation is compared with the desired objective shape, and a shape error is calculated as a vector norm with three-dimensional coordinates. The error vector is inversely added to the objective surface to compensate both the upper and lower flexible die configurations. The flexible die shapes are recalculated and the punch arrays are adjusted according to the over-bent forming surface. These iterative procedures are repeated until the shape error variation converges to a small value. In addition, experimental verification was conducted using a 2000-kN flexible forming apparatus for thick plates. Finally, the configuration of the prototype obtained from the experiment was compared with the numerical simulation results, which had springback compensation. It is confirmed that the proposed method for compensating for the forming error could be used in the design of flexible forming of thick-curved plates.

• Transactions of Materials Processing
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• v.14 no.2 s.74
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• pp.139-144
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• 2005

It was investigated that curved aluminum products with 'ㄷ' section or with 'h' section could be bended during extrusion by the extru-bending process. In order to make bending at the exit section of die, the flow of billet inside die cavity was controlled by the shape of billet. As results of the analysis of $DEFORM^{™}-3D$, it was known that the bending phenomenon at the die exit can be happened by the asymmetric section of billet. And it was known by the experiment with plasticine or aluminum material that an symmetric product with 'c' channel section and the product with flanged 'h' section could be bended because of asymmetric shape of billet.

• Transactions of Materials Processing
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• v.17 no.8
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• pp.570-578
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• 2008

A flexible forming apparatus is composed a number of punches which have spherical pin tip shape instead of conventional solid die. The flexible forming tool consisted of punch array in a matrix form was proposed as an alternative forming method to substitute the conventional line heating method which use heat source to induce residual stress along specified heating lines. In this study, application of the flexible forming process to the small scale curved plate forming was conducted. Numerical simulations for both solid and flexible die forming process were carried out to compare the shape of the products between flexible and conventional die forming process. In addition, spring-back analysis was conducted to figure out the feasibility of the flexible forming process comparing with the die forming process in view of final configuration of the specimens. Moreover, experiment was also carried out to confirm the formability of the process. Consequently, it was confirmed that the flexible die forming method has capability and feasibility to manufacture the curved plates for shipbuilding.

• Transactions of Materials Processing
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• v.27 no.4
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• pp.236-243
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• 2018

A multi-point forming die (MPFD), which has been used for producing curved plates, is capable of forming various curved plates with just one MPFD. However, in real industries, an MPFD is difficult to be adopted since the structural properties, punch strength, elastic recovery correction and dimensional accuracy become problems. In order to overcome these problems, the hot multi-point forming die (HMPFD) was proposed in this study. This HMPFD commonly provide more less spring-back and forming load than conventional MPFD. Nevertheless, this process is very difficult to form the curved plate, because the final curved shape of the plate depends on many process variables such as the punch/nozzle arrangement (height and distance), the radius of punch, contact conditions between plate and punch. In this study, the forming characteristics of HMPFD and conventional MPFD are compared with each other through the finite element analysis.

• Transactions of Materials Processing
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• v.13 no.8
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• pp.663-670
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• 2004

The bending phenomenon has been known to be occurred by the difference of velocity at the die exit. The difference of velocity at the die exit section can be obtained by the different velocity of billets through the multi-hole container. The difference of velocity at the die exit can be controlled by the two variables, the one of them is the different velocity of extrusion punch through the multi-hole container, the other is the difference of hole diameter of muliti-hole container. In this paper the difference of hole diameter is applied. So it can bend during extruding products because of the different amount of two billets when billets would be bonded in the porthole dies cavity. And the bending curvature can be controlled by the size of holes. The experiments with aluminum material for the curved tube product had been done for circular or rectangular curved tube section. The results of the experiments show that the curved tube product can be formed by the extru-bending process without the defects such as distortion of section and thickness change of wall of tube and folding and wrinkling. The curvature of product can be controlled by shape of cross section and the difference of billet diameters. And it is known that the bonding and extruding and bending process can be done simultaneously in the die cavity by the experiments that rectangular hollow curved tubes could be extruded by porthole dies with four different size billets made of aluminum material. And it shows that bending phenomenon can happen during extruding with for different billets from the analysis by DEFORM-3D.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.346-356
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• 1997

The fiber orientation distribution and interface bonding in hot extrusion process have an effect on the maechanical properties of metal matrix composites(MMC's). Aluminium alloy matrix composites reinforced with alumina short fibers are fabricated by compocasting method. MMC's billets are extruded at high temperature through conical and curved shaped dies with various extrusion ratios and temperature. This present study was directed to describe the systematic correlation between extrusion die shape and subsequent results such as fiber breakage, fiber orientation and tensile strength to hot extruded MMC's billet. Extrusion load, tensile strength and hardness for variation of extrusion ratios and temperature are investigated to examine mechanical properties of extruded MMC's SEM fractographs of tensile specimens are observed to analyze the fracture mechanism.

• Design & Manufacturing
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• v.12 no.3
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• pp.13-18
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• 2018

Flexible display tends to grow every year, It tends to be larger, slimmer, and higher in image quality. Therefore, accuracy is required in the manufacturing process of each part. In the curved monitor, the bottom chassis has a structure to which other parts can be attached. The accuracy of the curvature which the bottom chassis of the curve monitor monitors has is important. If the curvature error is large, serious defects such as cracks, warpage, twisting and the like occur. Curvature was analyzed using 3D scanner. In the Forming process and Restriking process steps, spring go occurred, and spring back occurred in the Notching process and Bending process steps. Even in the same process, it was confirmed that the curvature value varied depending on the formed shape.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.285-288
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• 2003

The bending phenomenon during extruding one product using four billets can be obtain by the difference of hole diameters in the multi-hole container. The difference of hole diameter caused the difference of billet amount inserted in the die cavity. As results, it can bend during extruding products by the different amount of two billets and by the cohesion of billets in the porthole dies cavity. And the bending curvature can be controlled by the size of holes and billets. The experiments using aluminium material had been done for the rectangular and square curved tube product. The results of the experiment show that the curved aluminum tube product can be bended by the extru-bending process without the defects such as the distortion of section and the thickness change of the wall of tube and the folding and wrinkling. The curvature of product is affected by shape of cross section and the difference of billet diameters. It is known that the welding and extruding and bending can be done simultaneously in the die cavity when a rectangular hollow curved tube would be extruded by porthole dies using four different size billets made of aluminum material.

• Korean Journal of Computational Design and Engineering
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• v.14 no.2
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• pp.129-136
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• 2009

Generally, curved surfaces of ship hull are deformed by flame bending (line heating), multi-press forming, and die-less forming method. The forming methods generate the required in-plane/bending strain or displacement on the flat plate to make the curved surface. Multi-press forming imposes the forced displacements on the flat plate by controlling the position of each pressing points based upon the shape difference between the unfolded flat plate and the curved object shape. The flat plate has been obtained from the unfolding system that is independent of the ship CAD. Apparently, the curved surface and the unfolded-flat surface are expressed by different coordinate systems. Therefore, one of the issues is to find a registration of the unfolded surface and the curved shape for the purpose of minimum amount of forming works by comparing the two surfaces. This paper presents an efficient algorithm to get an optimized registration of two different surfaces in the multi-press forming of ship hull plate forming. The algorithm is based upon the ICP (Iterative Closest Point) algorithm. The algorithm consists of two iterative procedures including a transformation matrix and the closest points to minimize the distance between the unfolded surface and curved surfaces. Thereby the algorithm allows the minimized forming works in ship-hull forming.

• Transactions of Materials Processing
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• v.25 no.1
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• pp.12-20
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• 2016

Press machines and dies are commonly used for 3D curved sheet forming. Using conventional die forming can cause economic problems since various modifications of the die shape are required depending on the product shape. Various types of flexible forming such as multi-point dieless forming (MDF), flexible incremental roll forming have been developed to improve the needed process flexibility. Although MDF can reduce the production cost using reconfigurable dies, it still has significant material loss. Drawbacks such as wrinkling, dimpling, and forming errors can also occur despite continuous investigations to mitigate these defects. A novel sheet forming process for 3D curved surfaces, a flexibly-reconfigurable roll forming (FRRF), has been recently proposed to overcome the economic and technical limitations of current practice. FRRF has no limitation on blank size in the longitudinal direction, and also minimizes or eliminates forming defects such as wrinkling and dimpling. Feasibility studies of FRRF have been conducted using FE simulations for multi-curved shapes and various sheet thicknesses. Therefore, the fabrication of a FRRF apparatus is required for any follow-up studies. In the current study, experiments with reconfigurable rollers were conducted using a simple design pre-FRRF apparatus prior to fabricating the full size FRRF apparatus. There are three candidates for the reconfigurable roller: a bar-type shaft, a flexible shaft, a ground flexible shaft. Among these candidates, the suitable reconfigurable roller for FRRF is determined through various forming tests.