Study on Numerical Simulation for Control of Winding Process of Thin Wall Spiral Tube

2012年10月贵金属Oct. 2012第33卷增刊1Precious MetalsVol. 33, No. SIStudy on Numerical Simulation for Control ofWinding Process of Thin Wall Spiral TubeZHENG Jing, MA Guang, WANG Yi, LI Yin'e, JIA Zhihua, LI Jin(Northwest Institute for Nonferrous Metal Research, Xi'an China. E-mail:13892899884@163 .com)Abstract: Being aimed at the inside wall wrinkling and sinking phenomenon of plladium ytrium aly thin wallspiral tube used for preparation of high purity hydrogen, extraction of hydrogen isotope, and purification andseparation of hydrogen in the winding process, this article analyzed the reasons for above phenomena, establisheda numerical simulation model of winding process of above tube, using elastic-plastic Finite Element methodanalyzed the max. tensile stress and max. compression stress and their locations, thereby provides a theory basefor the control of working forming course of thin wall spiral tube.Key words: Pd-Y aloy;, thin wall spiral tube; winding; Finite Element method; numerical simulationCLC number: TG146.3*6 Document Code: AArticle ID: 1004-0676(2012)S1-0227-06Because the palladium alloy membrane difusion method has unique purifcation performance, it isincomparable with other physical method or chemical method, and it is a main method to prepare high purityhydrogen and extract, purify and separate bydrogen isotopes at presentl". But the hydrogen filtration effect of thefiltrating equipment made of palladium-silver membrane and tube is not sufficient, and the volume of theequipment is big, so using palladium ytriurm thin wall spiral tube which possesses high hydrogen permeabilityand may reduce the volume of filtrating equipment, to replace palladium-silver membrane and short tube has goodreal engineering value. The palladium- ytrium alloy has big sifiness and poor toughness, and because of therequirements by hydrogen permeating, the tube wall should be thin, and tube should be long. When windingpalladium-yttrium thin wall narrow tube, the inside wall wrinkling and sinking phenomena often appear leading tothe reduction of service life. This article used the Finite Element method to study the mechanic behavior in thewinding process of thin wall spiral tube, analyzed the reason of inside wall wrinkling and sinking, provided acontrol method for winding process.1 Wrinkling mechanism of inner wallThere are many methods to wind tubes, such as commonly used push bending, compression bending, rollbending, rotating bending, NC bending, and so on at present"!. The thin wall tube has quite big plasticdeformation inevitably when it circles on a mould; there is a difference in stress condition in inside and outside ofthe tube inevitably. Regarding the push bending, compression bending and roll bending, the tube inside undergoescompression stress, the flank undergoes tensile stress. Regarding the rotating bending, a micro section was taken中国煤化工Received date: 2012-04-15MHCNMHG228Precious Metalsas the object for study. This micro section of the tube simulaneously undergoes a pulling force that is along themould tangential direction, and a compression force that is given by the mould. The outside wall of the tube is inthe tensile stress state, and the stress state of inside wall is decided by the two combined actions. When the tensilestress surpasses the tensile strength of the material, cracks appear on the outer wall( as shown in Fig.1). If thecompression stress in inside wall is too big, surpasses the flexure stability of the material, wrinkling phenomenonwill occur(as shown in Fig. 2).Fig.1 SinkingFig.2 Wrinkling2 Simulated mechanical model of thin wall spiral tube in winding processingThe winding process of a thin wall narrow tube is an extremely complex physical phenomenon. On the onehand, the winding process causes the tube to produce a certain way permanent deformation, so that a spiral tube ofneeded shape and size could be obtained. Therefore, in the processing the material has a big displacement androtation inevitably, existing geometry non-linearity. On the other hand, if the force exerted on the metal materialsurpasses the yield strength, the material enters the plastic state, the stress-strain course is no longer a linearrelation. It is related with loading process, existing material non-linearity. At the same time, when the narrow tubecircles on the mould, the contacting condition of the tube wall and convex-concave mould is unceasingly changedcausing the contact non-linearity. These non-linear phenomena cause the numerical simulation of winding processof thin wall narrow tube to become extremely complex. In recent years, domestic and foreign scholars did lots ofwork on the numerical simulation of tube bending forming processb-s, obtained many valuable conclusions, butthe forming process of these objects studied all were that process of the outer wall is pulled and the inner wall iscompressed, the study on the numerical simulation of winding process of thin wall tube is insufficient.In order to simulate this non-linear processing well, the author selects the elastic- plastic Finite Elementmethod as the study method.2.1 Finite Element equation of large deformation elastic-plastic analysis(lAccording to Total Lagrange Formulation, it supposes t time beforehand solution to extract. According toprinciple of virtual work, Describes the t +△t time sham accomplishments equation is:I +&'S$8+^EejdV-=^*W(1)Among them,' oSg， toOEy was Cauchy stress and Green strain at 1+ Ot time. West time tan oak stressand Grimm strain.SEg=6°εy +oEy(2)"4S, =oS; +oSo中国煤化工(3)MHCNMHG..No. S1.ZHENG Jing et al: Study on Numerical Simulation for Control of Winding Process of Thin Wall Spiral Tube229Among them, Sj，0Eg was stress and strainat t time, oSy， o8，was stress and strain increase at Ottime.oE=o&;+o7j(4oEj = (ou,+ou.i+oUnj oUnj+ounsounj)o7gy一ounsoUn,JWhen Ot is small, it can be approximate with linear strain increase oey replaces strain increase oEy,Then obtains the process linearity processing T.L. description increase form sham accomplishments equation:Lr CuoeqOje,dV +fvSsOondV=**W-f{v iSjSgqdV(7)The reorganization may obtain the TL. description the big strain elastic finite element equation:([6Kz]+['Km ]){ou}={*^R}-{F}(8Among them:[6Kl]= So[B{J'[D][;B,]dV(9)[^Km]=. fj['Bvw]'[6SJ[BRz]dV(10){6F}= [,[B,][D]['S]dV(11)In the frmula, [Kl] and ['KM] is the lnearty and the non-linear steel matrix; [B[] and [Bm]is the linearity and the non-inear geometry matrix; [D] is the material constant matrix; {'F} is the stressequivalent node force vector; {+ R} is the function in node external force vectorat 1+ Ot time.Entered plastic state regarding the t time the unit, Matrix [D] replaces with Elastic Plastic matrix[D],Regarding t time in elastic range, at 1+ Ot time enters plastic area the transition unit to take weighted averageElastic-Plastic matrix[D],:[D], =m[D], +(1- m)[D],(12)m is the weighting factor in the formula.2.2 The rule of wrinkling failureIn the structural strength analysis theory, there are too many destru中国煤化主e multitudinousdestruction criterions this article selects the biggest principal stressevaluation of:DYHCNMHG,wrinkling and position of palladium-yttrium alloy thin wall tube. Becauoc ul“Lu. piuvos, the tube flanks230Precious MetalsVol. 33undergo tensile stress, the inside sometimes undergoes compression stress. The basic reason for inner wall sinkingand wrinkling lies in the inside compression stress oversize, it surpasses the compression stress that the tube wallcan undergo at the stable conditions. The permanent deformation occurs. When the flank tensile stress surpassesthe yield strength of the palldium-ttriurm alloy material, it may cause the tube to produce plastic deformation,realizing the goal of winding forming, moreover, within the material strength limit scope, the bigger the tensilestress is, the bigger the plastic deformation, the better the formation effect. Therefore, in the winding process ofathin wall tube, the biggest compression stress should be controlled to less than the material yield strength, and thetensile stress is larger than yield strength of the material, but is smaller than the material tensile strength.3 Finite element analysisThe simulation object of this article is a 6 mm long palladiumyttrium capillary vessel of中2 mm in diameter,the wall thickness is 0.08 mm, using the self; manufactured tube winding equipment shown in Fig.3 to wind thetube.①The snapping back controls the pattern making②Circles the tubular axle③The Palladium yttrium alloy coil circles the tubemachine automatically④Precision guide screw❺Low speed electrical machinery⑥Electrical machinery linear control guide railFig.3 Equipment of winding tubeThe tube was made of plladium-ttrium aloyy material of annealing condition, the yield strength 0o.2=-320MPa, tensile strength o=750 MPa.Although the ratio of length to diameter of the tubeis quite big, but in order to analyze the local stresscondition during tube winding, the spatial insertiondiscs shell Yuan simulation was used. The massiveresearches indicated that during winding process, underFig.4 Model of FEAthe effect of axial tensile force a trace amount ofexpansion and contraction could be produced along the direction of mould tangent. In the just winded first circlethe stress condition is quite complex, but started from the second circle the stress condition in every place isbasically the same. In order to calculate conveniently, here we only a中国煤化工ior oof thefirstcircle of the tube. The Finite Element model is shown in Fig.4. A pulited on the tubeJTYHCNMHGhorizontal section nose, on another end a restraint is exerted, at the same ... Jo.avt iuouau 1 exerted on theNo. S1ZHENG Jing et al: Study on Numerical Simulation for Control of Winding Process of Thin Wall Spiral Tube231circles of the mould.The stress condition of the tube wall is influenced by the structural parameters of the tube, structural size ofthe mould, rotation speed of the mould and pulling force on the tube nose. The structural parameters of the tube isrestrained by the hydrogen permeation performance, and the structural size of the mould is difficult to change, thepulling force on the tube nose is directly related to mould rotation speed, therefore, the control of thin wall narrowtube winding process is esentially the control of the electrical machinery rotation speed to control rotation speedof the mould. Considered from mechanic angle, it is the control of the pulling force on the tube nose.In order to understand the stress condition of the tube under pulling force function on the nose, this articleconducted the Finite Element analysis at the pulling force 70 N, the results are shown in Fig.5 and Fig.6.1724022Fig.5 Plot of maximum main stressFig.6 Plot of least main stressIt can be seen from above two cloud patterns that there is a big difference in stress distribution of a circletube on the mould. Generally speaking, the outside walls of the tube all are at the tensile stress condition. And thestress condition of inner walls, started from just winded part on the mould, is transited from compression stress totensile stress. The max. compression stress appears on the inside wall of the tube just winded on the mould, andthe max. Dollars' stress appears on the inside wall of another end of the tube. Therefore, wrinkling of the tube walloften occurs at the time when the tube just contacts with the mould. At the same time, known from the Figuresthat the max. Dollars' stress is bigger than the max. compression stress under the identical pulling force rank. Itindicated that we may seek a tensile force to make the max. compression stress be less than the yield strength ofthe material, the wrinkling phenomenon on the inside wall of the tube could not occur. When the max. tensilestress is larger than the yield stress of the material but smaller than the ultimate strength, the tube overall producesplastic deformation realizing winding process.In order to determine appropriate working pulling force, this article analyzed 6 pulling force ranks of 60 N,65 N, 70 N, 75 N, 80 N, 85 N, respectively, the results are shown in Tab.1.中国煤化工MYHCNMHG..232Precious MetalsVol. 33Tab.1 The pulling force rank and principal stressMaximum principalMinimum principalTension/Nstress /(MPa)stress/(MPa)314-26375390-32665-2858011-34567-3078534-362From Tab.1 it can be seen that when the pulling force rank is 70 N, the Omin= 307 MPa < 0.2; and when thepulling force rank is 75 N, the Tmin=- 326 MPa > σo.2. Therefore, considered only ftom the angle of the thin wallwrinkle-free when controlling bending, the pulling force should be less than 75 N. At the same time, it may beknown that when the pulling force rank is 60 N, the σmax =314 MPa < 0.2; when the pulling force rank is 65 N, theσmx=340 MPa> 0o.2; when the pulling force rank is 85 N, the 0mx.=434 MPa > σ0.2- Therefore, the windingprocessing goal could be realized only when the pulling force is larger than 65 N. To sum up considerations, whenwinding this thin wall spiral tube of palladium-ttrium alloy, the pulling force should be controlled in the range of65 N~75 N. The pulling force for winding of the tube is controlled by the rotation number of rebound controllingmould and low speed motor in the self-manufactured tube winding equipment shown in Fig.3. According to aboveanalysis results and several times simulation experiments, the winded palladium-yttrium spiral tube is free frominside wall wrinkling and sinking phenomenon, it satisfies application requirements.4 ConclusionsThis article comprehensively considered the physical phenomenon in the winding process of palladium-yttrium alloy thin wall spiral tube, analyzed the reasons of inside wall wrinkling and sinking, analyzed the stresscondition of the tube during processing by the elastic-plastic Finite Element method, obtained the rule of stressdistribution. At the same time, the comparative study on the stress condition of palladium-ttrium alloy thin wallspiral tube under effects of different pulling force ranks was conducted, a condition for pulling force control isproposed- controlling the pulling force in the range of 65 N~75 N. The article provides a theory base for thecontrolling course of the winding processing of this thin wall and narrow long tube. Based on the aboveinvestigation and combined with simulation experiment, the authors produced palladiumyttrium alloy spiral tubefree from inside wall wrinkling and sinking phenomenon, this tube has satisfied application requirements.References:[1] Heyi W, Yibei F. Membrane science and technology[J]. 2002(6).[2] Qianming C. Northwestern Polytechnical University master's degree paper[D]. 2003.[3] Futai H. Northeast heavy duty machinery institute technology doctoral dissertation[D]. 1995.[4] Forde P., Torgeir W. Jourmal of Material Processing Technology.1996.[5] Forde P, Torgeir W, Odd P s. Jourmal of Material Processing Technology. 2001.6] Weiguo Y, Ruxun C, Xiaoming C, et al. Solid propeilant engine[J]. 1997, 3.中国煤化工MYHCNMHG..