In this study, the authors present the results of their theoretical and experimental analysis of the rolling process of Cu – Al bimetallic bars in elongation passes. The original bars were round aluminium bar, covered with copper layer. For theoretical tests, the Forge2008® computer program was used, based on FEM. The model simulated metal flow during rolling of bimetallic bars in oval – round passes. The results of the experiments were compared with the finite element calculations. The analysis demonstrated that an appropriate selection of shape and size of oval pass allows production of even distribution of the copper layer in the bimetallic roll products.O ovom su radu autori prezentirali rezultate teoretske i eksperimentalne analize procesa valjanja Cu-Al bimetalnih šipki pri istezanju. Originalne šipke su bile okrugle aluminijske šipke, sa bakrenim zaštitnim slojem. Za potrebe teorijskog istraživanja korišten je program Forge 2008, koji je baziran na MKE. Model simulira tečenje metala za vrijeme valjanja bimetalnih šipki u kružnim prolazima. Rezultati eksperimenta su uspoređeni s proračunom konačnih elemenata. Analiza pokazuje kako odgovarajući izbor oblika i veličine kružnog prolaza dopušta proizvodnju ili čak razdiobu bakarnog sloja na bimetalnim valjanim proizvodima

A. Kawałek

H. Dyja

P. Szota

S. Mróz

HRČAK - Portal of Croatian Scientific and Professional Journals

S. MRÓZ, P. SZOTA, H. DYJA, A. KAWA£EKTHEORETICAL AND EXPERIMENTAL ANALYSISOF THE Cu-Al BIMETALLIC BAR ROLLING PROCESSReceived – Prispjelo: 2010-05-26Accepted – Prihva}eno: 2010-10-19Original Scientific Paper – Izvorni znanstveni radINTRODUCTIONPredicting three-dimensional metal flow duringgroove-rolling of bimetallic bars is one of the fairlycomplex tasks facing the engineer when working out anew roll pass design 1. The knowledge of the charac-teristics of shape variation of billet being rolled (such aswidening and elongation) alone is nor sufficient for per-forming correctly a roll pass design and developing acorrect groove-rolling technology. The theoretical de-termination of local velocity fields and the uniquenessof rolled billet flow within the whole roll gap volume,while considering billet shape and temperature, rollingspeed, the rheological properties of the metal and fric-tion conditions on the metal-to-roll contact surface, hasmade it possible to speed up considerably the develop-ment of an industrial rolling technology and reduce thecost and time consuming of tests needed during practicalstarting up of the manufacture of new products in agroove-rolling mill.Computer modelling is the cheapest of the possibleways of process analysis and, at the same time, it pro-vides a huge amount of information impossible to be ac-quired by other methods. The purpose of carrying outcomputer simulations is the verification of technologiesbeing designed for bars of different shapes and of differ-ent materials in the real technical conditions of a rollingmill, prior to their implementation.By applying computer programs relying on the finiteelement method to solving plasticity-theory tasks withinthe design of bar groove-rolling process technologies,the number of laboratory and industrial tests can be lim-ited to an indispensable minimum 2-5. In the presentstudy, the Forge2008® was used for the analysis of plas-tic metal flow in stretching passes 6, 7.MATHEMATICAL MODELOF FORGE 2008® COMPUTER PROGRAMThe thermo-mechanical simulation of thegroove-rolling process was carried out with the use of avisco-plastic model in the triaxial state of strain by usingthe Forge2008® program, whereas the properties of thedeformed material were described according to theNorton–Hoff 6, 7 conservation law written in the fol-lowing form (1):S K eijn T mij    2 30 010 0 0( ) (  ) ( )    , (1)where: sij is the deviatoric stress tensor,  is the equiva-lent strain rate,  ij is the equivalent strain rate tensor,  –METALURGIJA 50 (2011) 2, 85-88 85In this study, the authors present the results of their theoretical and experimental analysis of the rolling processof Cu – Al bimetallic bars in elongation passes. The original bars were round aluminium bar, covered with cop-per layer. For theoretical tests, the Forge2008® computer program was used, based on FEM. The model simu-lated metal flow during rolling of bimetallic bars in oval – round passes. The results of the experiments werecompared with the finite element calculations. The analysis demonstrated that an appropriate selection of sha-pe and size of oval pass allows production of even distribution of the copper layer in the bimetallic roll pro-ducts.Key words: bimetallic bars, elongating grooves, FEM (Finite Elements method), numerical analysisTeoretska i eksperimentalna analiza Cu-Al bimetalnih {ipki u procesu valjanja. O ovom su radu autoriprezentirali rezultate teoretske i eksperimentalne analize procesa valjanja Cu-Al bimetalnih {ipki pri istezanju. Ori-ginalne {ipke su bile okrugle aluminijske {ipke, sa bakrenim za{titnim slojem. Za potrebe teorijskog istra`ivanjakori{ten je program Forge 2008, koji je baziran na MKE. Model simulira te~enje metala za vrijeme valjanja bime-talnih {ipki u kru`nim prolazima. Rezultati eksperimenta su uspore|eni s prora~unom kona~nih elemenata. Anali-za pokazuje kako odgovaraju}i izbor oblika i veli~ine kru`nog prolaza dopu{ta proizvodnju ili ~ak razdiobubakarnog sloja na bimetalnim valjanim proizvodima.Klju~ne rije~i: bimetalne {ipke, `ljebovi izdu`enja, MKE (Metoda kona~nih elemenata), numeri~ka analizaISSN 0543-5846METABK 50(2) 85-88 (2011)UDC – UDK 621.77:669.71:669.3=111S. Mróz, P. Szota, H. Dyja, A. Kawa³ek, Czêstochowa University ofTechnology, Czestochowa, Polandequivalent plastic strain, 0 – base strain, T is the temper-ature, K0, m0, n0, 0 represent materials constantsCONDITIONS ADOPTEDFOR COMPUTATIONSThe application of the computer program For-ge2008® using the thermo-mechanical models that itcontains requires the definition of boundary conditionswhich are decisive to the correctness of numerical com-putation. The properties of the aluminium and copperexamined, friction conditions, and the kinetic and ther-mal parameters describing the rolling process.Bimetallic bars with an outer diameter of 21,7 mmcovered with 2,8 mm copper layer, after explosive weld-ing 8-9, were rolled on a D 150 two-high shape mill.The stock material was round PA6 (according to the Pol-ish standard) aluminium bar covered with an M1-E (ac-cording to the Polish standard) copper layer. Heating ofthe bimetallic stock of an initial length of 250 mm wascarried out in a chamber furnace. Bars heated up to a tem-perature of 400 °C. Rolling speed was approx. 0,45 m/s.As a result of rolling in 2 passes (oval-round), bars of a di-ameter of about 18,0 mm were obtained. During rolling,the copper layer thickness decreased by 0,5 % comparedwith bars after explosive welding. All passes were inves-tigated using theoretical and experimental methods.The theoretical analysis was performed for the realrolling conditions: the working roll diameter D = 150mm, coefficient of friction – 0,3, coefficient of heat ex-change between the material and the tool, 	 – 3000W/Km2; coefficient of heat exchange between the ma-terial and the air, 	air – 100 W/Km2, tool temperature –60 °C; ambient temperature – 20 °C.The junction between the core and the cladding layerwas defined as closely fitting. The nodes of both gridswere shared.RESULTS AND DISSCUSIONAn experimental and a theoretical analysis of varia-tions in the shape of bars during groove-rolling werecarried out in the study. Simulations of rolling were per-formed to verify the accuracy of prediction of the shapeand dimensions of band obtained in the passes. The ob-tained computation results were compared with the tem-plates taken after rolling in a particular pass. The view ofall cross-sections is shown in Figure 1.From the data shown in Figure 1 it can be seen that asa result of rolling bimetallic strip in the oval and roundpasses an 18 mm-diameter bimetallic bar was obtained.The properly selected rolling parameters enabled a cop-per-aluminium bimetallic bar to be produced withoutany delamination at the bond boundary and with a uni-form distribution of the clad layer over the bimetallic barperimeter and length.Figures 2-3 show comparison of the shape and di-mensions of the strip and the bimetallic bar obtainedfrom numerical modelling and experimental tests.It can be seen from the data shown in Figures 2-3 thatthe shape and dimensions of the Cu-Al bimetallic stripsobtained from computer simulations are consistent withthe shape and dimensions of the passes used and theshape and dimensions of the templates taken after roll-ing. In none of the cases was any difference noticed be-tween the pass height and the strip height obtained fromsimulations and experimental tests. The differences be-tween the strip widths obtained as a result of simulationsand the strip widths obtained from the rolling processwere negligible. For the first pass (the circle-oval pass),the difference in width was 0,3 mm (Figure 2), while forthe second pass (the oval-circle pass) the differenceamounted to approx. 1,0 mm (Figure 3). In none of thepasses did any pass overfill occur.Also the geometrical parameters of the cross-sectionsof bimetallic bars obtained from numerical modelling andexperimental tests were examined in the study. A sche-86 METALURGIJA 50 (2011) 2, 85-88S. MRÓZ et al.: THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE Cu-Al BIMETALLIC BAR ROLLING PROCESSa) b) c)Figure 1 View of lateral samples taken from the billetafter rolling in particular passes: a) billet, b) 1stpass, c) 2ndpass.a) b)Figure 2 Comparison of theoretical – a) and experimen-tal – b) shapes and dimensions of bimetallicbars (copper–aluminium) after first pass.a) b)Figure 3 Comparison of theoretical – a) and experimen-tal – b) shapes and dimensions of bimetallicbars (copper–aluminium) after second pass.matic of the taking of measurements of the distribution ofthe clad layer over the Al core is shown in Figure 4.In order to determine the distribution of copper layerheight over the aluminium core, 32 measurements weretaken for strips obtained during rolling in the oval passand 36 measurements for strips obtained from the roundpass. Examinations were carried out both for strips ob-tained from numerical modelling, as well as for stripsobtained as a result of experimental tests. Measurementswere taken every 10 °.Figures 5 and 6 show the distribution of copper layerthickness over the aluminium core perimeter.When analyzing the data shown in Figures 5 and 6,an uneven copper layer thickness distribution can be ob-served over the whole aluminium core perimeter. Thegreatest “thinning” of the copper layer is noticed in thevertical axis of the strip, whereas the greatest “thicken-ing” of the copper layer – in the horizontal strip axis.This copper layer distribution over the aluminium corecan be explained by a slight flowing of the clad layerfrom the bar core towards the strip width. The presentedresults of numerical computations and experimentaltests indicate that the copper layer moves along the lat-eral strip sides during groove-rolling, so also relative tothe roll groove surface, which is consistent with the in-vestigation results provided in work 10, 11.The average copper layer thickness values ob-tained from numerical computations and from experi-mental tests were similar. The relative error did not ex-ceed 1,2 %.The difference between the maximum value of cop-per layer thickness for the first pass (Figure 5) amountedto 0,2 mm for the numerical modelling results and 0,32mm for experimental test results. For the second pass(Figure 6), on the other hand, the differences in copperlayer thickness were greater, amounting to 0,57 mm forthe numerical modelling results and 0,68 mm for the ex-perimental test results.SUMMARYThe investigation carried enables the following ob-servation to be made and conclusions to be drawn:1. Good agreement between the shape and dimen-sions of bimetallic bars obtained from numericalcomputations and experimental tests was ob-tained.2. The distribution of copper layer thickness overthe perimeter of the aluminium core was deter-mined. As a result of the groove-rolling of bime-tallic bars, a displacement of the clad layer to-wards the roll groove follows, which results in anuneven distribution of the clad layer over the bi-metallic bar perimeter.3. Computations carried out for the conditions of bi-metallic bar rolling have shown that the modelaccurately reflects the conditions of rolling inelongation grooves. A correctly performed roll-ing process assures the bimetallic bar product tobe obtained with bonding quality comparablewith a stock material after explosive welding.REFERENCES1 H. Dyja, L. Lesik, A. Milenin, S. Mróz, Journal of MaterialsProcessing Technology, 125-126 (2002), 731-735.2 A. Stefanik, Journal of Achievements in Materials and Ma-nufacturing Engineering, 1 (2008) 91-94.3 F. Capece Minutolo, M. Durante, L. Giorleo, A. Langella,Journal of Materials Engineering and Performance, 14(2005), 378-382.METALURGIJA 50 (2011) 2, 85-88 87S. MRÓZ et al.: THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE Cu-Al BIMETALLIC BAR ROLLING PROCESSa) b)Figure 4 Schematic of measurements of clad layer distri-bution after rolling: a) in the oval pass, b) inthe round pass.Figure 5 Distribution of Cu layer thickness over the alu-minium core after the first pass.Figure 6 Distribution of Cu layer thickness over the alu-minium core after the second pass.4 S.-Y. Kim, Y.-T. Im, Journal of Materials Processing Tec-hnology 127 (2002), 57-63.5 M. G³owacki, Termomechaniczno - mikrostrukturalny mo-del walcowania w wykrojach kszta³towych, UczelnianeWydawnictwa Naukowo-Dydaktyczne AGH, Kraków1998.6 FORGE3® Reference Guide Release 6.2, Sophia-Antipolis,2002.7 A. Gavrus, E. Massoni, J.L. Chenot, Journal of MaterialsProcessing Technology, 60 (1996), 447-454.8 H. Dyja, Z. Stradomski, S. Mróz, Archiwum nauki o mate-ria³ach, 23 (2002) 2, 165-188.9 H. Dyja, S. Mróz, Z. Stradomski, Metalurgija, 42 (2003) 3,185-191.10 L.Lesik, Hutnik-Wiadomoœci Hutnicze, 2 (1997), 56-60.11 L. Lesik, Proces walcowania prêtów bimetalowych wwykrojach wyd³u¿aj¹cych, Prace Naukowe Wydzia³u Me-talurgii i In¿ynierii Materia³owej, Seria: Metalurgia, Nr 1,Czêstochowa 1998.Note: The professional translator for English language is Czes³awGrochowina, Studio-Tekst, Poland.88 METALURGIJA 50 (2011) 2, 85-88S. MRÓZ et al.: THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE Cu-Al BIMETALLIC BAR ROLLING PROCESS

Teoretska i eksperimentalna analiza Cu-Al bimetalnih šipki u procesu valjanja

Abstract

Similar works

Full text

Available Versions

HRČAK - Portal of Croatian Scientific and Professional Journals

Hrčak - Portal of scientific journals of Croatia