1,721,009 research outputs found
Interactive computer-aided-design system for roll pass and profile design in bar rolling
No full textIn this study, a computer-aided-design (CAD) system to support roll pass and roll profile design of bar rolling, where simple shapes like round and square bars are produced, was developed in order to minimize trial and errors in industry. An interactive design methodology was used in the developed system to provide various design examples from which decisions for an optimal design can be made. In addition, an algorithm for generating automatic roll pass design of local passes was proposed. In order to effectively assist the interactive design process, material flow and engineering data such as roll separating force and required power, based on reliable empirical formulas, were calculated and displayed. For more accurate engineering calculations, roll speed was calculated for continuous rolling and an approximate heat transfer model was proposed. Finally, the developed system was applied in the process design for rolling a square bar. It was found that the system will improve the efficiency of designing process by reducing time and cost. (C) 2002 Elsevier Science B.V. All rights reserved.The authors wish to thank the Grant from the Korea Science Foundation (95-0200-14-04-3), under which this research work was possibl
Experimental and numerical prediction of austenite grain size distribution in round-oval shape rolling
No full textTo determine austenite grain size (AGS) distribution during round-oval shape rolling of mild carbon steel (0.2 wt% C), three-dimensional non-isothermal finite element analysis in couple with an AGS evolution model available in the literature was carried out in the present investigation. A hot rolling test was conducted at the laboratory to verify the numerical data obtained from the analysis. For more accurate prediction of the temperature history during the process, interface heat transfer coefficient between the billet and rolls was determined by comparing the numerical temperature history with the measured data at three locations in the billet. Metallographic investigation of the rolled specimen after quenching showed that recrystallization behavior could be classified into two regions: interior zone with refined grain dominated by metadynamic recrystallization, and exterior zone with less refined grain due to static recrystallization. It was found that the numerically predicted AGS distribution was in good agreement with the experimentally measured one. In addition, the conventional additivity rule generally used for the prediction of recrystallization behavior for non-isothermal rolling conditions was modified in order to bear a better comparison with the experimentally measured AGS values.The authors wish to thank the Plate and Rod Group of
pasco for their financial support as BK21 program, without
which this research may have been impossible. Also,
the efforts of Mr. S.N. Bae in the pasco technical research
laboratory and Mr. Y.B. 1m at the Research Institute
of Industrial Science and Technology in conducting pilot
mill experiments and metallographic treatments are greatly
appreciated. Valuable discussions with Professors P.D.
Hodgson and J. Yanagimoto are also greatly appreciated
Instability map based on specific plastic work criterion for hot deformation
No full textEstimating workability is very important to complete the hot or cold working process successfully without making any crack. Instability map was developed by utilizing conventional plastic work criterion in the current study. Hot compression tests were conducted using Gleeble 3800 simulator to obtain flow stress curves as a function of temperature and strain rate. Based on the compression results, new instability map based on the specific plastic work was developed for estimating the instability during the hot deformation process. The critical specific plastic work value was determined by investigating the surface irregularity and shear band formation in the compressed specimens. Then, the instability map determined was applied for predicting surface wrinkle defect during the multi-pass hot bar rolling in combination with the finite element analysis. The predicted results using new instability map suggested matched well with the observations obtained from the industry. The developed approach is easy to apply to the available simulation tools to determine necessary processing parameters.The authors wish to thank for the grants from the
POSCO and Korea Science and Engineering Foundation
(KOSEF) through the National Research Laboratory
Program funded by the Ministry of Science
and Technology (No. R0A-2006-000-10240-0). The
technical support of the POSCO to carrying out the
hot compression tests was very much appreciated
The bending of an aluminum structural frame with a rubber pad
No full textIn this study, research for process design in the bending of a structural frame of AA6061-T6 with a rubber pad was conducted. In this process, the conventional lower die made of metal is replaced with a polyurethane pad, resulting in high flexibility during bending. Vulcanized polyurethane rubber with a shore A hardness of 60 was used for the pad. Experiments on a newly developed bending machine were carried out by controlling the stroke of the roller and the horizontal movement of the roller pad lower die. From this, the relation between the roller path and the geometry of the materials bent was obtained for the process design of producing a roof-rail part of a passenger car, the experimental result being compared with the target profile. For more accurate process design, it is required to control the roller path interactively. Based on experience in developing the prototype bending machine, it is construed that a fully automated bending system with a rubber pad to produce various light-weight components for automotive body frames can be successfully developed. (C) 2001 Elsevier Science B.V. All rights reserved.The authors express their thanks for a grant from the Ministry of Commerce, Industry and Energy under which this work was possible
Determination of forming limit of a structural aluminum tube in rubber pad bending
No full textRubber pad bending is a novel technique for producing space frame to reduce the weight of automobiles because it can produce bent profiles with various curvatures in a single production set-up. As in other bending processes, cross-section of the aluminum tube deforms during the process. Such a deformed geometry diminishes bending rigidity, making it inappropriate for a structural use in some cases. Thus, it is important to determine a minimum radius of curvature with sufficient bending resistance. In this study, experimental set-up was developed to investigate deformation characteristics of an extruded rectangular aluminum tube in rubber pad bending. For better understanding of the effect of process parameters such as the material property of rubber and roller diameter, finite element (FE) analyses were also conducted. The ratio of the second moment of inertia of the initial and deformed cross-sections of the tube was introduced as a measure of cross-sectional deformation to represent the variation of bending rigidity of the bent tube. In result, a critical value of sectional deformation and minimum formable radius of curvature with maintaining suitable sectional bending rigidity were, respectively, determined under the present process conditions investigated. (C) 2003 Elsevier B.V. All rights reserved.The authors wish to thank the grant from the Ministry of
Commerce, Industry and Energy under which this work was
possible. The experimental assistance from the laboratory
of rubber mechanics in Korea Institute of Machinery and
Materials is also acknowledged
Numerical investigation of austenite grain size distribution in square-diamond pass hot bar rolling
No full textIn this study, the austenite grain size (AGS) for hot bar rolling of AISI4135 steel was predicted based on two different AGS evolution models available in the literature. In order to predict the AGS more accurately, both models were integrated with a three-dimensional non-isothermal finite element program by implementing a modified additivity rule. The predicted results based on two models for the square-diamond (S-D) and round-oval (R-O) pass bar rolling processes were compared with the experimental data available in the literature. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to compare both mode Is and investigate the effect of these parameters on the AGS distributions. Such numerical results were found to be beneficial to understand the effect of the microstructure evolution model on the rolling processes better and control the processes more accurately. (C) 2007 Elsevier B.V. All rights reserved.The authors wish to thank for the Grants of International Col-
laboration between KAIST and Deakin University and National
Research Laboratory Program funded by the Ministry of Sci-
ence and Technology, without which this research would not be
possible
Magnetic field dependence of the resistance anomaly in superconducting mesoscopic aluminum structures
No full textA mesoscopic aluminum wire of 0.28 mu m width was prepared to investigate the resistance anomaly found in the superconducting transitions. We found that the radio-frequency (rf) radiation is an important factor in the anomaly, which strongly supports the recent work of Strunk et al. [Strunk, C., Bruyndoncx, V., Van Haesendonck, C., Moshchalkov, V. V., Bruynseraede, Y., Burk, B., Chien, C. -J. and Chandrasekhar, V., Phys. Rev. B, 1996, 53, 11332]. We performed a systematic study of the magnetic field dependence of the anomaly, which revealed the "mesa" type magnetoresistance near H = 0 for 1.13 K < T < 1.16 K. The boundary of the anomalous region in H-T space coincides with the upper critical field curve of the 2 mu m wide leads connected to the wire, implying a crucial role of the wide leads for the anomaly, having different T-c and dimensionality from those of the narrow wire. As soon as the leads become superconducting, the undissipated rf field transmits to the wire and induces the phase-slip centers to manifest the anomalous behavior. (C) 1998 Elsevier Science Ltd. All rights reserved
Plastic work approach for surface defect prediction in the hot bar rolling process
No full textIn this study, a numerical technique was developed to study the effect of processing parameters on instability of the steel during five passes hot bar rolling process. For this a processing map developed based on the plastic work approach was used with finite element analyses to judge occurrence of instability during the process. The effect of roll geometry and processing temperature on hot rolled bars was examined with the help of a parametric study by employing the numerical technique developed. Based on this parametric study, the improved roll pass design and initial processing temperature were determined, respectively, for reducing flow instability during the process. The laboratory rolling mill was used to validate the numerical results. It was found that with the increase of the initial temperature in the process the less flow instability was observed compared to the change of the roll geometry introduced at each pass under the present investigation condition. It was found that the current numerical technique implemented will be useful in identifying the important parameters governing the formation of surface cracks in the multi-stage hot bar rolling process. (C) 2007 Elsevier B.V. All rights reserved.The authors wish to acknowledge the grant of National
Research Laboratory program of the Ministry of Science and
Technology through KOSEF (no. R0A-2006-000-10240-0)The
financial and technical supports from the POSCO technical
research laboratory were very much appreciated as well
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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