• Journal of Advanced Marine Engineering and Technology
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• v.40 no.7
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• pp.587-592
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• 2016

Bellows for LNG carriers must be corrosion resistant in order to operate in seawater environments. They must also have long fatigue lives in order to withstand the expansion and contraction caused by large temperature changes and continuous vibration in extreme environments. In order to incorporate these properties into bellow design, it is important to use materials that are resistant to cold brittleness and corrosion, and maintain their optimized forming condition. The design conditions and forming methods used for bellows must be optimized in order to incorporate these characteristics. In this study, finite element analysis was used to develop cryogenic bellows, which have good mechanical strength and reliability. In addition, two different forming methods (mechanical and hydroforming) were used to design and produce bellows, in order to derive their forming condition. The height, thickness, and hardness of the convolutions of bellows produced by each method were measured and compared with each other. The results confirmed that the two forming methods produced bellows with different mechanical properties.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.6
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• pp.66-72
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• 2014

Incremental forming is a relatively novel sheet forming process, in which parts can be formed without the use of dedicated dies. In this paper, the influence of the process parameters (tool diameter, step size, feed rate, existence of a die, forming methods, and kinds of tool path) on surface roughness in the case in which parts are processed by incremental forming was discussed. Al 1050 material is used in the experiments. A table of orthogonal arrays is used to design the experiments and the ANOVA method is employed to statistically analyze the results. The obtained results show that the process parameters of tool diameter, step size, and the existence of a die have a significant effect on the surface roughness, whereas the feed rate, forming methods and kinds of tool path are insignificant.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1136-1141
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• 2003

Among various methods to manufacture the PDP barrier ribs, the pressing and the roll forming methods are simple and economical because they form the ribs by utilizing the plastic flow of the green tape in a relatively short time without generating air-polluting dusts. In the present study, the roll forming method was investigated by experiments as well as numerical analyses and in result the groove roll and the preform were designed. The effect of draft angle, comer radius, and initial thickness of the green tape on the plastic flow was examined by a series of parametric studies. The preform was recommended to ease the plastic flow into the grooves and to avoid the occurrence of crack during rolling and sintering processes.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.5
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• pp.800-805
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• 2013

Incremental forming of sheet metal is a modern method of forming sheet metal, where parts can be formed without the use of dedicated dies. Existing experimental configurations for incremental forming can be broadly classified into two categories, i.e., negative and positive forming. In this paper, forming qualities such as shape accuracy and surface roughness of Al 1050 material were discussed for different forming methods. The formed and the corresponding opposing surfaces were measured with a three-dimensional scanner and a surface roughness tester. It was found that in terms of shape accuracy, the best opposing surface was obtained with positive forming, whereas the worst formed surface was obtained with negative forming; furthermore, the opposing surface is always better than the formed surface, regardless of the forming method used.

• Transactions of Materials Processing
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• v.18 no.7
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• pp.556-564
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• 2009

Flexible forming process for sheet material using reconfigurable die is introduced based on numerical simulation. In general, this flexible forming process using the reconfigurable die has been utilized for manufacturing of curved thick plates used for hull structures, architectural structures and so on. In this study, numerical simulation of sheet metal forming process is carried out by using flexible dies model instead of conventional matched die set. The numerical simulation and experimental verification for sheet metal forming process using a flexible forming machine that is more suitable for thick plate forming process are carried out to confirm the appropriateness of the simulation process. As an elastic cushion, urethane pads are utilized using hyperelastic material model in the simulation for smoothing the forming surface which is discrete due to characteristics of the flexile die. In the flexible forming process for sheet metal, effect of a blank holder is also investigated according to blank holding methods. Formability in view of occurrence of dimples is compared with regard to the various punch sizes. Consequently, it is confirmed that the flexible forming for sheet material using urethane pad has enough capability and feasibility for manufacturing of smoothly curved surface instead of conventional die forming method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.5
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• pp.512-518
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• 2014

In this paper, the influence of part shape complexity and die type on forming accuracy in incremental sheet metal forming is presented. The part shape complexities are classified into two types, namely, of one and two-step shapes. Correspondingly, die types are classified into three types, namely, of no-, partial, and full die types. The experimental tests are performed separately on negative and positive forming methods. It is shown that for the one-step shape, there are no significant differences in forming errors between the cases of no- and full die types when the negative forming method is used. Furthermore, the full die type is better than the partial die when positive forming is used. For the two-step shape case, the full die type always exhibits better forming accuracy than the no- and partial die types, irrespective of the forming method used.

• Transactions of Materials Processing
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• v.22 no.5
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• pp.243-249
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• 2013

The multi-point forming (MPF) process for three-dimensional curved sheet metal has been developed as an alternative to the conventional die forming process since MPF allows the manufacturing of various shapes using one die set and reduce the cost of production. However, the MPF process cannot provide high quality products yet due to defects occurring in the sheet such as dimples and wrinkles. It can also lead to economic loss because of long tool setup time and additional machining required outside of the sheet formed area. In this study, a new sheet metal forming method, called flexible roll forming (FRF), is proposed to solve the problems of existing processes for three-dimensional curved sheet metal. This progressive process utilizes adjusting rods, as well as upper and lower flexible rollers as forming tools. In contrast with the existing processes, FRF can reduce the additional production costs because of the possible blank size for the part longitudinal direction, which is unrestricted. In this research, methods and procedures of the flexible roll forming technology are described. Numerical forming simulations of representative three-dimensional curved sheet products are also carried out to demonstrate the feasibility of this technology.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06b
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• pp.54-59
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• 1998

In this study, two kinds of life prediction method for hot forming die are developed . One is empirical method requiring some experiment that evaluate thermal softening of die material accoring to operating conditions. The other is analyticl method that calcuate wear quantity of die occuring during the forming process. Wear is a predominant factor as well as plastic deformation and heat checking . And, these methods are applied to prodict tool life real die producting part for automobile. Thus , the applicability and the accuracy of the presented methods are investigated. Using the verified life prediction method above , optimal blocker die design minimizing the finisher die is done.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.462-467
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• 2002

New methods for screw and spline production has been developed recently by Japan and other developed countries in the basis of Rolling Dies work to cut down the production cost. These methods give us high precision of the products. But we in Korea mostly import Dies for manufacturing forming products. It is thought that if we don't develop our own technology for Rolling Dies, we will have to spend much money for importing Forming concerned equipments. In this paper, we designed the rolling dies based on the diameter of material and calculated the proper number of teeth of gear to establish desirable method for Rolling dies. And the result is shown after manufacturing Involute spline with the rolling dies.