• Transactions of Materials Processing
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• v.17 no.5
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• pp.328-336
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• 2008

A criterion which predicts wrinkle initiation on workpiece in groove rolling process based on finite element analysis is proposed. Fundamental idea considered in the criterion is using the difference between flat rolling which don't cause wrinkling at all and groove rolling which usually accompanies it. The proposed criterion assumes that irregular distribution of shear strain on workpiece during groove rolling is attributable to the initiation of wrinkling. The proposed criterion has been applied to roughing train in the rod mill of SEAH BESTEEL Inc. A new design of 2nd pass (square roll groove) was suggested, machined and applied. Results reveal that the proposed criterion could point out the location of wrinkle initiation and could reduce onset of wrinkle.

• Transactions of Materials Processing
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• v.19 no.6
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• pp.344-351
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• 2010

This paper presents a precision on-line model for the prediction of the roll force and tension distributions across the strip in hot strip rolling. The approach is based on an approximate 3-D theory of rolling, and in particular, considers the effect of pre-deformation of the strip, which occurs near the roll entrance before the strip enters the bite zone. The prediction accuracy of the proposed model is examined through comparison with the predictions from the 3-D finite element models.

• International Journal of Highway Engineering
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• v.13 no.4
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• pp.221-229
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• 2011

Road design needs to ensure the economic justification and the preservation of nature by adapting road alignment to the natural terrain. Though current road design guideline only defines a flat and a mountainous terrain, classification including rolling terrain should be needed while considering the fact that about 25.8% of our land can be classified as rolling and the road design guideline of developed countries such as United States and Australia has a terrain classification including rolling in order to take a deep consideration on the natural environment. The study attempts to draw a criterion to classify the assumed three individual terrains in a quantitative way by using a index like the undulation of the original ground profile. The study carried out a case study based on a conceptual frame developed in the study as an approach to differentiate each terrain. As a result, the study suggests a criterion in that a flat terrain has less than 40 meters in the difference between the highest and the lowest point of original ground from 40 to 60 meters for rolling terrain, and greater than 60 meters for mountainous respectively.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.581-587
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• 2011

The production of high-precision micro-sized screws, used to fasten parts of micro devices, generally utilizes a cold thread-rolling process and two flat dies to create the teeth. The process is fairly complex, involving parameters such as die shape, die alignment, and other process variables. Thus, up-front finite-element(FE) simulation is often used in the system design procedure. The final goal of this paper is to produce high-precision screw with a diameter of $800{\mu}m$ and a thread pitch of $200{\mu}m$ (M0.8${\times}$P0.2) by a cold thread rolling process. Part I is a first-stage effort, in which FE simulation is used to establish process parameters for thread rolling to produce micro-sized screws with M1.4${\times}$P0.3, which is larger than the ultimate target screw. The material hardening model was first determined through mechanical testing. Numerical simulations were then performed to find the effects of such process parameters as friction between work piece and dies, alignment between dies and material. The final shape and dimensions predicted by simulation were compared with experimental observation.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.13-22
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• 2012

Forged and flat-bar rolled STD11 tool steel shows anisotropic dimensional change during heat treatment. The dimensional change in the rolling direction is larger than that in the transverse direction. The cause of the anisotropic dimensional change is that the steel is anisotropic in composition, microstructure and other properties. The decrease of anisotropic distortion in tool steel is important for making better precision cold working dies. In this study, the effect of ingot weight and hot rolling reduction ratio on the anisotropic dimensional change of STD11 during heat treatment has been studied. Dimensional change was evaluated by simulating a real heat treatment process, including gas quenching and tempering. Experimental results showed that all the rolled flat-bar products had anisotropic distortion to some degree, but the anisotropic distortion was reduced as hot rolling ratio increased. Ingot weight had a little effect on anisotropic distortion. Microstructural observation showed that the anisotropic dimensional change of STD11 tool steel was closely related to the amount, shape and distribution of coarse carbides.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.11
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• pp.66-72
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• 2008

During the plate and foil cold rolling process, considerable values of the force of material pressure on the tool occur. These pressures cause the elastic deformation of the roll, thus changing the shape of the deformation legion. Rolled copper foils should be characterized by a good quality and light dimensional tolerances. Because of automation that is commonly implemented in flat product rolling mills, these products should meet the requirements of tightened tolerances, particularly strip thickness, and feature the greatest possible flatness. The shape of the roll gap is influenced by the elastic deformation of rolls parts of the rolling process affecter of the pressure force. However, to control roll deformation should be difficult. Because the foil thickness is very thin and the permissible deviations in the thickness of foil are small. In this paper, FE-simulation of roll deformation in thin foil cold roiling process is presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.964-971
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• 2008

This paper compares the performances of cyclic delay diversity and phase rolling techniques for SC-FDE(Single Carrier with Frequency Domain Equalization) systems with multiple transmit antennas assuming time-flat and frequency-flat channels. In OFDM(Orthogonal Frequency Division Multiplexing) systems generation of time varying channels using phase rolling can result in performance gains comparable to those of frequency-selective channels made by cyclic delay diversity However, in SC-FDE systems making time-selective channels may produce better results than creation of frequency-selective channels.

• Transactions of Materials Processing
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• v.23 no.3
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• pp.145-150
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• 2014

Precision control of the slab is crucial for product quality and production economy in hot strip mills. The current study presents a new model for predicting width spread of a slab with a rectangular cross section during roughing. The model is developed on the basis of the extremum principle for a rigid plastic material and a three dimensional admissible velocity field. This model incorporates the effect of process variables such as the shape factor and the ratio of width to thickness. We compare the results of this model to 3-D finite element (FE) process simulations and also to results from a previous study.

• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.379-387
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• 2004

A novel flatness sensing system which is called the Flatness Sensing Inter-stand Looper(FlatSIL) system is suggested and a self-tuning PI control system using the FlatSIL is designed for improving the flatness of hot strip in finishing mill processes. The FlatSIL system measures the tension along the direction of the strip width by using segmented rolls, and the tension profile is approximated through the tension of each segmented roll. The flatness control system is operated by using the tension profile. The proposed flatness control system as far as the tension profile-measuring device works for the full strip length during the strip rolling in finishing mills. The generalized minimum variance self-tuning (GMV S-T) PI control method is applied to control the flatness of hot strip which has a design parameter as weighting factor for updating the PI gains. Optimizing the design parameter in the GMV S-T PI controller, the Robbins-Monro algorithm is used. It is shown by the computer simulation and experiment that the proposed GMV S-T PI flatness control system has better performance than the fixed PI flatness control system.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1068-1071
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• 1996

Good shape on flat rolled product is necessary to meet today's customer quality requirement. To meet the increasing demand in quality of strip shape from downstream customers, POSCO has replaced the Automatic Shape Control(ASC) system with the existing one that had used noncontact type measuring system at No.2 Cold Rolling Mill, Pohang works in October, 1995. The strip shape is influenced by the profile, roll crown, bending control, skew control system, as well as work roll cooling system. We have used ASC to adjust those factors in Cold Rolling Mill that could get a satisfactory result, almost less than .+-.5 1-unit deviation from the target shape. However, the downstream customer(i.e. Continuos Annealing Line) wants a good shape not only at the moment of exit of roll bite, but after rolling without tension. In this investigation, the difference will be discussed and how deal with this problem.