• 소성∙가공
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• 제29권5호
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• pp.282-289
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• 2020

Flexible roll forming is an advanced sheet-metal-forming process that allows the production of parts with various cross-sections. During the flexible process, material is subjected to three-dimensional deformation such as transverse bending, inhomogeneous elongations, or contraction. Because of the effects of process variables on the quality of the roll-formed products, the approaches used to investigate the roll-forming process have been largely dependent on experience and trial- and-error methods. Web-warping is one of the major shape defects encountered in flexible roll forming. In this study, an SVR model was developed to predict the web-warping during the flexible roll forming process. In the development of the SVR model, three process parameters, namely the forming-roll speed condition, leveling-roll height, and bend angle were considered as the model inputs, and the web-warping height was used as the response variable for three blank shapes; rectangular, concave, and convex shape. MATLAB software was used to train the SVR model and optimize three hyperparameters (λ, ε, and γ). To evaluate the SVR model performance, the statistical analysis was carried out based on the three indicators: the root-mean-square error, mean absolute error, and relative root-mean-square error.

• 소성∙가공
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• 제22권7호
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• pp.401-406
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• 2013

The use of roll-formed products increases every year due to its advantages, such as high production rates, reduced tooling cost and improved quality. However, till now, it is limited to part profiles with constant cross section. In recent years, the flexible roll forming process, which allows variable cross sections of profiles by adaptive roll stands, was developed. In this study, an attempt to optimize profile design for the flexible roll forming process was performed. An equation that predicts the longitudinal strain for part geometries with variable cross-sections was proposed. The relationship between geometrical parameters and the longitudinal strain was analyzed and investigations on the optimal profile design were performed. Experiments were conducted with a lab-scale roll forming machine to validate the proposed equation. The results show that the profile design method proposed in this study is feasible and parts with variable cross sections can be successfully fabricated with the flexible roll forming process.

• 소성∙가공
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• 제22권5호
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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.

• 소성∙가공
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• 제23권6호
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• pp.369-375
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• 2014

Flexible roll forming allows profiles to have variable cross-sections. However, the profile may have some shape errors, such as, warping which is a major defect. The shape error is induced by geometrical deviations in both the concave zone and the convex zone. In the current study, flexible roll forming was modeled with FE simulations to analyze the shape error and the longitudinal strain distribution along the flange section over the profile. A distribution of analytically calculated longitudinal strains was used to develop relationships between the shape error and the longitudinal strain distribution as a function of the defined shape parameters for the profile. The FE simulations showed that the shape error is primarily affected by the deviations between the distribution of analytically calculated longitudinal strain and the longitudinal strain distribution of the profile. The results show that the shape error can be controlled by designing the shape parameters to control the geometrical deviations at the flange section in the transition zones.

• 한국정밀공학회지
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• 제21권9호
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• pp.95-102
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• 2004

A flexible incremental roll forming process has been developed by adopting the advantages of the incremental forming process and the roll forming process: i.e., inherent flexibility of the incremental forming process and continuous bending deformation of the roll forming process. It has an adjustable roll set as a forming tool composed of one upper center roll and two pairs of lower support rolls, which plays a key role during forming process. Through the experiments based on the various combinations of process parameters, it is shown that the incremental roll forming process is so effective as to manufacture various doubly curved sheet metals including concave-convex combination shapes in which there exists a line of inflection. The proposed relationship of the experimental parameters and the radius of curvature of the formed sheet boundary is found to be useful in prediction and control of the final shape.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.978-981
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• 2005

In order to manufacture a doubly curved sheet metal effectively, a flexible incremental roll forming process has been developed by adopting the advantages of the incremental forming process and the roll forming process by combining inherent flexibility of the incremental forming process and continuous deformation of the roll forming process. The forming method has been further enhanced to form general quadrilateral blanks (including a square, a rectangle, a symmetrical trapezoid and an asymmetrical trapezoid, etc.) into doubly curved shapes by controlling the forming paths developed by various experiments.

• 소성∙가공
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• 제25권1호
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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.

• 소성∙가공
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• 제25권3호
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• pp.161-168
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• 2016

Sheet metals are often required to be formed into three dimensional curved shapes for use as skin structures. As a result various sheet metal forming methods, such as press die forming, stretch forming, and line heating have been used over the years in industrial production lines. Although they are extensively used in industry, these methods are not suitable for small quantity batch productions. Studies have been conducted to improve or replace these methods with plausible flexible forming technologies. As a part of these studies, we developed a new and more efficient forming device named flexibly-reconfigurable roll forming (FRRF). The current study presents the process development and experimental verification for the applicability of this device. To improve the efficiency of the FRRF apparatus, several hardware components were invented and a suitable operating program was developed using MFC of visual C++. The ways to make the FRRF apparatus fully functional are also described. Sheet metal was formed into three dimensional shapes using the FRRF apparatus and the final products are presented as evidence for the applicability of the developed device.

• 소성∙가공
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• 제26권3호
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• pp.168-173
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• 2017

A new sheet metal forming process, called flexibly reconfigurable roll forming (FRRF), is expected to resolve the economical limitation of the existing 3D curved sheet metal forming processes. The height-controllable guides and a couple of flexible rollers are utilized as the forming tool. Recently, as the 3D curved sheet metal is increasingly demanded in various fields, the application of FRRF to diverse materials is necessary. In addition, the formability comparison of several materials is needed. Therefore, in this study, we investigated the applicability of FRRF for different materials such as aluminum, magnesium, and copper alloys, and also the formability of these materials was compared using FRRF. The numerical simulation was conducted using ABAQUS, the commercial software, and the experiments were carried out using an FRRF apparatus to validate the simulation results. Finally, the applicability of FRRF for the chosen materials and the formability of these materials on FRRF process were confirmed by comparing the simulation and experimental results.

• 한국인쇄학회지
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• 제30권3호
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• pp.45-56
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• 2012

Printing technology is accepted by appropriate technology that smart phones, tablet PC, display(LCD, OLED, etc.) precision recently in the electronics industry, the market grows, this process in the ongoing efforts to improve competitiveness through the development of innovative technologies. So printed electronics appeared by new concept. This technology development is applied on electronic components and circuits for the simplification of the production process and reduce processing costs. Low-temperature process making possible for widening, slimmer, lighter, and more flexible, plastic substrates, such as(flexible) easily by forming a thin film on a substrate has been studied. In the past, the formation of the electrode used a screen printing method. But the screen printing method is formation of fine patterns, high-speed printing, mass production is difficult. The roll-to-roll printing method as an alternative to screen printing to produce electronic devices by printing techniques that were used traditionally in the latest technology and processing techniques applied to precision control are very economical to implement fine-line printing equipment has been evaluated as. In order to function as electronic devices, especially the dozens of existing micro-level of non-dot print fine line printing is required, the line should not break at all, because according to the specifications required to fit the ink transfer conditions should be established. In this study of roll-to-roll printing conductive paste suitable for gravure offset printing by developing Ag paste for forming fine patterns to study the basic physical properties with the aim of this study were to.