3D FE Modeling Simulation of Cold Rotary Forging with Double Symmetry Rolls X. H. Han 1, a, L. Hua 1, b, Y. M. Zhao 1, c

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1 Materials Science Frum Online: ISSN: , Vls , pp di: / Trans Tech Publicatins, Switzerland 3D FE Mdeling Simulatin f Cld Rtary Frging with Duble Symmetry Rlls X. H. Han 1, a, L. Hua 1, b, Y. M. Zha 1, c 1 Schl f Materials Science and Engineering, Wuhan University f Technlgy, Wuhan, Hubei, , P. R. China a hanxinghuihlp@126.cm, b lhuasvs@yah.cm.cn, c zhayumin@whut.edu.cn Keywrds: Cld rtary frging with duble symmetry rlls, FE mdeling, Field-variables Abstract. A nvel metal plastic frming technlgy, cld rtary frging with duble symmetry rlls, is presented n the basis f cld rtary frging with single rll. A reasnable 3D elastic-plastic dynamic explicit FE mdel f cld rtary frging with duble symmetry rlls is develped under the ABAQUS sftware envirnment. Thrugh simulatin, the distributins and histries f different field-variables such as stress, strain and frce and pwer parameters are investigated in detail. The research results nt nly prvide an advanced and innvative technlgy fr metal plastic frming, but als help t better understand cld rtary frging with duble symmetry rlls. Intrductin Cld rtary frging with single rll is an advanced and innvative incremental metal frming technlgy and it ffers the fllwing advantages: lwer level f nise and vibratin, unifrm quality, smth surface, clse tlerance and cnsiderable savings in energy and materials cst. Due t the ptential advantages and wide applicatin prspects, many studies have been dne n cld rtary frging with single rll by using the analytics [1], experiment [2-3] and simulatin [4-6]. Hwever, because f the eccentric lad impsed by the rll in cld rtary frging with single rll, the stress state f the mill is much cmplex and it is easy fr the mill t vibrate. Therefre, it is urgent and valuable t imprve the stress state f the mill s as t btain the desired prducts. Cnsequently in this paper, cld rtary frging with duble symmetry rlls, which vercmes the abve mentined defects f cld rtary frging with single rll, is presented. A reasnable 3D elastic-plastic dynamic explicit FE mdel f the prcess is develped under the ABAQUS sftware envirnment. Thrugh simulatin, the distributins and histries f different field-variables such as stress, strain and frce and pwer parameters are investigated. The research results help t better understand the new plastic frming technlgy f cld rtary frging with duble symmetry rlls. Wrking Principles f Cld Rtary Frging with Duble Symmetry Rlls The wrking principles f cld rtary frging with single rll and duble symmetry rlls are illustrated in Fig.1 (a) and Fig.1 (b), respectively. In cld rtary frging with single rll, the cnical upper die (Rll) with an inclinatin angle γ cntinuusly scillates arund the vertical machine axis and the lwer die pushes the wrkpiece vertically s as t cause it t defrm. In cld rtary frging with duble symmetry rlls, tw cnical upper dies (Rlls) with apex angle f 90 are installed at the tw sides f the vertical machine axis symmetrically. Obviusly, because f the symmetry installatin f tw upper dies, the actin line f the lad is cincident with the vertical machine axis, resulting in the mre stable prcess in cld rtary frging with duble symmetry rlls. All rights reserved. N part f cntents f this paper may be reprduced r transmitted in any frm r by any means withut the written permissin f Trans Tech Publicatins, (ID: , Pennsylvania State University, University Park, USA-04/03/16,17:18:53)

2 624 Advances in Materials Manufacturing Science & Technlgy XIII Vlume II Machine axis n z Upper die axis Machine axis z n S y y Upper die Upper die axis Upper die (Rll) Pivt pint x Ring wrkpiece Lwer die v y Upper die axis Upper die (Rll) v x Ring wrkpiece Lwer die R Cntact area R Cntact area r x Cntact area r (a) Cld rtary frging with single rll (b) Cld rtary frging with duble symmetry rlls Fig.1 Schematic diagram f cld rtary frging f the ring wrkpiece Establishment f 3D FE Mdel f Cld Rtary Frging with Duble Symmetry Rlls Based n the frming characteristics, a 3D elastic-plastic FE mdel f cld rtary frging with duble symmetry rlls is develped under the ABAQUS sftware envirnment, as shwn in Fig.2. The 3D FE mdel has the fllwing features: (1) The elastic-plastic FE methd is adpted t imprve the cmputatin accuracy. (2) The dynamic explicit FE prcedure is used t avid the huge cmputatin time and cnvergence prblem f the static implicit prcedure. (3) The cntact between the dies and wrkpiece is defined as surface-t-surface cntact type. The Culmb frictin mdel is adpted t describe the frictin cnditin f the cntact pairs. (4) The upper die is cnstrained t rtate nly arund the glbal 2-axis while the lwer die is cnstrained t translate nly alng the glbal 2-axis. Because f the scillatin f the upper die, the ring wrkpiece may rtate tgether with it. Based n the frming characteristics, the cnstraint type Distributing cupling is adpted t cnstrain the rtatin f the ring wrkpiece. (5) The 3D linear reductin integratin cntinuum element with eight ndes (C3D8R) is used t discretize the ring wrkpiece. And the adaptive mesh technlgy is emplyed t reduce the distrtin f elements. Results and Discussin Upper die (Rlls) Ring wrkpiece Fig.2 3D FE mdel f cld rtary frging with duble symmetry rlls Lwer die The prcessing parameters adpted in the simulatin are listed in Table 1. The ring wrkpiece material is AISI1020 and its mechanical prperties are shwn in Table 2. Cntact Area between the Dies and Ring Wrkpiece. Fig.3 shws the variatin curves f the cntact area between the dies and ring wrkpiece with time. At the beginning f the frming prcess, the tw upper dies begin t cntact with the ring wrkpiece, s the cntact area between

3 Materials Science Frum Vls them increases rapidly frm zer t a certain value. After that, the ring wrkpiece reaches a steady defrmatin state and the cntact area between the upper die and ring wrkpiece increases slwly until t the maximum values. The cntact area between the lwer die and wrkpiece firstly Table 1 Prcessing parameters adpted in the simulatin decreases significantly. And then it decreases slwly. By cmparing the tw curves, it can be fund that the cntact area between the upper die and ring wrkpiece is smaller than that between the lwer die and ring wrkpiece at any time f Parameters Initial uter radius f ring wrkpiece R 0 [mm] Initial inner radius f ring wrkpiece r 0 [mm] Initial height f ring wrkpiece H 0 [mm] Height reductin H/H 0 [%] Feed rate f the lwer die v [mm s -1 ] Rtatinal speed f the upper die n [r min -1 ] Frictin cefficient between the dies and wrkpiece Values the prcess. Thus, the axial unit Table 2 Mechanical prperties f the ring wrpiece pressure n the metal near the upper die is higher than that near the lwer die. Cnsequently, the metal near the upper die is easier t satisfy the yield cnditin t enter the plastic defrmatin state. Material Densityρ[kg m -3 ] Yung s mdulus E [GPa] Pissn s ratiμ Cnstitutive equatin AISI PEEQ Distributin f the [ 10-3 ] Defrming Ring Wrkpiece. Fig.4 shws the PEEQ (Equivalent plastic strain) 3.0 Cntact area between upper die and wrkpiece distributin f the defrming ring Cntact area between lwer die and wrkpiece 2.5 wrkpiece with time. As described abve, 2.0 the metal near the upper die is easier t 1.5 satisfy the yield cnditin t cme int the 1.0 plastic defrmatin state. S the plastic 0.5 defrmatin zne is firstly frmed n the 0.0 upper surface cntacting with the tw upper dies, as shwn in Fig.4 (a). And then the plastic defrmatin zne gradually develps axially tward the lwer surface f the ring Cntact area between dies and wrkpiece (m 2 ) Fig.3 Variatin curves f the cntact area between the dies and ring wrkpiece with time wrkpiece and alng the circumferential directin, as shwn in Fig.4 (b). As the frming prcess cntinues, the whle ring wrkpiece has entered the plastic defrmatin state, as shwn in Fig.4 (c) and Fig.4 (d). It can be als seen frm Fig.4 that the PEEQ distributin is very inhmgeneus in the axial and radial directins. In the circumferential directin, the ring wrkpiece exhibits a hmgeneus defrmatin characteristic. When the height reductin H/H 0 is 20%, the maximum and minimum PEEQ values are and , respectively. Frm the abve analysis, it can be fund that the PEEQ distributin in any axial sectin f the ring wrkpiece is identical. Thus, the PEEQ distributin laws in the axial sectin are investigated in detail. Fig.5 illustrates the PEEQ distributin in the axial sectin. Frm Fig.5, it can be bserved that the PEEQ distributin in the axial sectin has the fllwing characteristics: (1)The upper regin cntacting with the tw upper dies firstly prduces the plastic defrmatin, as shwn in Fig.5 (b).

4 626 Advances in Materials Manufacturing Science & Technlgy XIII Vlume II (a) t=0.032s (b) t=0.08s (c) t=1.488s (d) t=3.2s Fig.4 PEEQ distributin f the defrming ring wrkpiece with time (2) As the frming prcess cntinues, the plastic defrmatin zne gradually expands axially tward the lwer surface f the ring wrkpiece, as shwn in Fig.5 (c). At the end f the prcess, the axial height f the ring wrkpiece has been penetrated thrughly, as shwn in Fig.5 (d). (3) Just as a kind f wave, the PEEQ distributin exhibits the transfer characteristic frm the upper surface t the lwer surface. S the defrmatin f the upper regin is larger than that f the lwer regin and the axial sectin f the defrmed ring wrkpiece exhibits an inverted trapezium, as shwn in Fig.5 (d). (4) The PEEQ value in the middle zne f the upper surface is the largest and the middle zne f the lwer surface has the smallest PEEQ value during the frming prcess. (a) t=0s (b) t=0.32s (c) t=1.744s (d) t=3.2s Fig.5 PEEQ distributin in the axial sectin f the defrming ring wrkpiece with time Additinally, sme special pints are selected t mnitr the strain variatin, as shwn in Fig.6. Fig.7 prvides the PEEQ evlutin histries f the selected pints in the axial sectin f the ring wrkpiece. It is bvius that the strain f every nde increases stepwise, which is caused by the cntinuus transfer f the plastic defrmatin zne. Obviusly, each step crrespnds t ne revlutin f the upper die. When the upper die cntacts with the ring wrkpiece, the strain f the nde lcated in the cntact area increases rapidly. That is t say, the height f the step represents the strain f the nde in a single revlutin. S the desired ttal strain f each nde is achieved by a

5 Materials Science Frum Vls large number f small steps and cld rtary frging with duble symmetry rlls can thus be described as an incremental metal frming prcess. The level part f the step crrespnds t the time when the upper die deviates frm the cntact area. Equivalent Stress Distributin f the Defrming Ring Wrkpiece. Fig.8 prvides the equivalent stress distributin f the defrming ring wrkpiece with time. It can be seen that the cntact area between the dies and wrkpiece firstly becmes the stress zne, as shwn Fig in Fig.8 (a). And then the stress zne gradually 1.4 expands circumferentially, as shwn in Fig.8 (b). As 1.2 the frming prcess cntinues, the whle ring 1.0 wrkpiece has becme the stress zne, as shwn in 0.8 Fig.8(c) and (d). It can be als fund that stress 0.6 cncentratin exists in the cntact area between the 0.4 dies and wrkpiece, while the nn-cntact area has 0.2 the relatively smaller equivalent stress. 0.0 PEEQ Outer surface 1 Upper surface Inner surface Lwer surface Selected pints in the axial sectin Nde 1 Nde 2 Nde 3 Nde 4 Nde 5 Nde 6 Nde 7 Nde 8 Nde Fig.7 PEEQ evlutin histries f the selected pints (a) t=0.032s (b) t=0.064s (c) t=1.424s (d) t=3.2s Fig.8 Equivalent stress distributin f the defrming ring wrkpiece with time Frce and Pwer Parameters. Fig.9 shws the variatin curves f frce and pwer parameters with time. It is bserved that the curve variatin is cmpsed by three stages. At the first stage, the tw upper dies begin t cntact with the ring wrkpiece, s the axial frging frce and frging mment increases rapidly frm zer t a certain value. As the frming prcess cntinues, the ring wrkpiece reaches a steady defrmatin stage and thereby the frce and pwer parameters increase slwly until t the maximum values. At the end f the prcess, the lwer die stps the axial feed, resulting in the significant decrease in the axial frging frce and frging mment. The maximum axial frging frce and frging mment are KN and N m, respectively. It can be als seen that the variatin curves f frce and pwer parameters scillate with time. This is because that

6 628 Advances in Materials Manufacturing Science & Technlgy XIII Vlume II cld rtary frging is a cmplex dynamic cntact and nn-steady-state defrmatin prcess Axial frging frce (kn) (a) Variatin curve f axial frging frce with time (b) Variatin curve f frging mment with time Fig.9 Variatin curves f frce and pwer parameters with time Cnclusins A nvel metal plastic frming technlgy, cld rtary frging with duble symmetry rlls, is presented n the basis f cld rtary frging with single rll. A reliable 3D elastic-plastic dynamic explicit FE mdel f the prcess is develped. The distributins and histries f different field-variables such as stress, strain and frce and pwer parameters have been investigated in detail. The results shw the fllwing: (1) Cld rtary frging with duble symmetry rlls is a prcess f strain accumulatin by a number f small strain steps and thus it is cnsidered t be an incremental frming technlgy. The PEEQ distributin exhibits a transfer characteristic frm the upper surface t the lwer surface and thereby the axial sectin f the defrmed ring wrkpiece is like an inverted trapezium. (2) The stress cncentratin exists in the cntact area between the dies and ring wrkpiece at any time f the prcess, while the nn-cntact area has the relatively smaller equivalent stress. (3) The frce and pwer parameters change has experienced three stages. At the first stage, the frce and pwer parameters increase rapidly frm zer t a certain value. At the secnd stage, they increase slwly until t the maximum values. At the last ne, they decrease rapidly. Acknwledgment Frging mment (N m) The authrs wuld like t thank the Natural Science Fundatin f China fr Distinguished Yung Schlars (N ) fr the supprt given t this research. References 1) M. Zhang: Prc. 3rd Int. Cnf. n Rtary Metalwrking Prcesses (Tky, Japan, September 8-10, 1984). 2) T. Canta, D. Frunza, D. Sabadus and C. Tintelecan: J. Mater. Prcess. Technl Vl (1998), p.195 3) D. C. Zhu, Y. D. Han and Z. R. Wang: J. Mater. Prcess. Technl Vl. 31(1-2) (1992), p.161 4) G. C. Wang and G. Q. Zha: J. Mater. Prcess. Technl Vl. 95(1-3) (1999), p ) G. Liu, S. J. Yuan, Z. R. Wang and D. C. Zhu: J. Mater. Prcess. Technl Vl. 151(1-3) (2004), p ) L. Hua and X. H. Han: Mater. Des Vl. 30(6) (2009), p

7 Advances in Materials Manufacturing Science & Technlgy XIII Vlume II / 3D FE Mdeling Simulatin f Cld Rtary Frging with Duble Symmetry Rlls / DOI References [10] 1016/S (98) ) D. C. Zhu, Y. D. Han and Z. R. Wang: J. Mater. Prcess. Technl Vl. 31(1-2) (1992), p /j.jmatprtec ) L. Hua and X. H. Han: Mater. Des Vl. 30(6) (2009), p.2133