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链条联接件的冷冲压模具设计-级进模含NX三维及8张CAD图

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链条联接件的冷冲压模具设计-级进模含NX三维及8张CAD图,链条,联接,冲压,模具设计,级进模含,NX,三维,CAD
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Journal of Materials Processing Technology 211 (2011) 644649Contents lists available at ScienceDirectJournal of Materials Processing Technologyjournal homepage: /locate/jmatprotecCold stamping formability of AZ31B magnesium alloy sheet undergoing repeatedunidirectional bending processLei Zhanga,b, Guangsheng Huanga,b, Hua Zhanga,b, Bo Songa,baNational Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400030, ChinabCollege of Material Science and Engineering, Chongqing University, Chongqing 400030, Chinaa r t i c l ei n f oArticle history:Received 11 April 2010Received in revised form 7 November 2010Accepted 28 November 2010Available online 7 December 2010Keywords:Magnesium alloy sheetRUBTextureStamping formabilityCell phone housinga b s t r a c tThe repeated unidirectional bending (RUB) process was carried out on an AZ31B magnesium alloy inorder to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of theRUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach1.5 at room temperature. It was also confirmed that cell phone housings can be stamped successfully incrank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stampingformabilityatroomtemperaturecanbeattributedtothetexturemodifications,whichledtoaloweryieldstrength, a larger fracture elongation, a smaller Lankford value (r-value) and a larger strain hardeningexponent (n-value). 2010 Elsevier B.V. All rights reserved.1. IntroductionNowadays,theproductsofmagnesiumalloys,mainlyformedbycastinganddie-casting,areusedintheaerospace,automobile,civil-ian household appliances. Compared with casting and die-casting,plastic forming technology seems to be more attractive becauseof its competitive productivity and performance. Among the fabri-cation processes of plastic forming, stamping of magnesium alloysheets is especially important for the production of thin-walledstructural components (Chen and Huang, 2003). However, magne-sium alloy sheets have low ductility at room temperature due to itsstrong (0002) basal texture, as shown in the literature (Doege andDroder, 2001). Mori and Tsuji (2007) investigated cold deep draw-ingofcommercialmagnesiumalloysheets,theydemonstratedthatthe limiting drawing ratio of rolled AZ31 magnesium alloy sheetsannealed at 773K can reach 1.7. Mori et al. (2009) have shown thata two-stage cold stamping process are also helpful for formingmagnesiumalloycups.Watanabeetal.(2004)suggestedtheductil-ityofmagnesiumalloysheetscanbeimprovedbyreducing(0002)basal texture at room temperature. The limiting drawing ratio forthe cold deep drawing of commercial magnesium alloy sheets canbeimprovedfrom1.2to1.4byreducing(0002)basalplanetextureCorresponding author at: National Engineering Research Center for Magne-sium Alloys, College of Material Science and Engineering, Chongqing University,174 Shazheng Street, Chongqing 400030, China. Tel.: +86 23 65112239;fax: +86 23 65102821.E-mail address: gshuang (G. Huang).(Iwanaga et al., 2004). It is well-known that equal channel angularpressing (ECAP) is an effective method to obtain a tilted basaltexture, which improved significantly the tensile elongation (Kimet al., 2003). But it is hard for ECAP to fabricate thin sheet. Recently,it is reported that a rolled magnesium alloy sheet, with a tiled tex-ture obtained by cross-roll rolling (Chino et al., 2006) and differentspeed rolling (DSR) process (X.S. Huang et al., 2009), exhibit higherstamping formability compared with a rolled magnesium alloysheet by normal-roll rolling. It is therefore important to improvethe formability at room temperature for a wide use of magnesiumalloy sheets by changing or weakening the basal texture.Older versions of the ASM Metals Handbook (1969) on form-ing refer to a “special bending sheet,” which was produced byDow Magnesium. The special bending sheet with a modifiedcrystallographic texture, had better forming characteristics thanconventional AZ31 sheet.Previous study (G.S. Huang et al., 2009) revealed that the RUBprocess also improved the stretch forming of magnesium alloysheets by weakening basal texture of sheets. The Erichsen valuesof the RUB processed sheet significantly increased from 3.53 to5.90 in comparison with the cold-rolled magnesium alloy sheet.However, up to now, few researchers made efforts to study thecold stamping formability of the magnesium alloy sheets. Coldstamping products, such as housings of laptop computers and cellphones, have not been reported in other investigations. Hence, itis important to investigate the cold deformation behaviors so as toestablish fundamental knowledge of the cold forming technologyof magnesium alloy.0924-0136/$ see front matter 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2010.11.019L. Zhang et al. / Journal of Materials Processing Technology 211 (2011) 644649645Fig. 1. Schematic diagram of the RUB process.In this paper, an investigation of the drawability of RUB pro-cessed AZ31 magnesium alloy sheet was performed at roomtemperature using uniaxial tensile tests, deep drawing and coldstamping of a cell phone housing. The performance of RUB sheetwas compared with that of the as-received sheet.2. Experimental material and procedure2.1. The preparation of experimental materialCommercial AZ31B magnesium alloy sheets with a thickness of0.8mm, cut into 1000mm100mm (lengthwidth) pieces, wereused in the experiments. Fig. 1 shows the schematic diagram of theRUB process. The radius of the cylindrical support was 1mm andthebendinganglewas90.ThemagnesiumalloysheetwasbentonacylindricalsupportunderaconstantforceTwithaconstantspeedv. There was six-pass bending, which indicated that there were sixbending operations in all at two orientations in the experiment.This meant that after each bending pass, the sheet was turned overand the bending orientation was also changed in the next pass. TheRUB processed sheets were annealed at 533K for 60min, and thenwere subjected to tensile tests, deep drawing, and cold stamping ofcell phone housing investigation.Previous studies (Song et al., 2010; Huang et al., 2010) haveinvestigated microstructure and texture evolution of AZ31 mag-nesium alloy sheets underwent RUB. For the as-received sheet,the grains were fine. After the magnesium alloy sheet underwentRUB was annealed at 260C, the grains near the surface of sheetgrew obviously, while those in the central region had little growth.The average grain size of two state sheets was almost the same.Fig. 2 shows 0002 pole figures of two state sheets. The as-received sheets exhibit a strong basal texture, where the majorityof grains are oriented with their 0002 basal planes parallel tothe rolling plane of the sheet. In contrast, the RUB processed sheetsFig. 3. Schematic diagram of mold.Table 1Parameters of punch and die used in the experiment.Punch diameter, dp(mm)Punch shoulderradius, rp(mm)Die clearance, z(mm)Die shoulderradius, rd(mm)5051.289.1exhibit a large inclination of c-axis around the normal direction(ND) towards the RD, which weakens basal texture of the sheet.2.2. Uniaxial tensile testsThe specimens for tensile tests had a parallel length of 57mm, awidth of 12.5mm and a thickness of 0.8mm. The specimens werecut along planes coinciding with at the angles of 0(RD) and 45and 90(TD) to the rolling direction. Prior to testing, all specimenswere polished by the abrasive paper to remove major scratches toavoid fracture occurring at an undesired location of the specimen.The uniaxial tensile tests were carried out on a CMT6305-300 KNtesting machine with an initial strain rate of 3102s1to exam-inethemechanicpropertiessuchastheyieldstrength,theultimatetensile strength and the fracture elongation. The strain hardeningexponent values (n-value) were obtained by power law regression(? =?n) of the tensile test data within a uniform strain of =15%.The Lankford values (r-value), r = w/t, where the variables wand tdenote the strains in the tensile specimens transverse andthickness directions, respectively, were measured on the speci-mens at a uniform plastic deformation of =15%.2.3. Limiting drawing ratio (LDR) testsTo evaluate the deep drawability of the RUB processed AZ31magnesium alloy sheet, limiting drawing ratio (LDR) tests werecarried out on a 600kN hydraulic press to examine the stamp-ing formability at room temperature. The schematic diagram andgeometry dimension of mold are shown in Fig. 3 and Table 1,respectively. Magnesium alloy sheets were processed into circularFig. 2. 0002 Pole figures of as-received sheet and RUB sheet. (a) as-RUB sample, max density=8.66; (b) RUB sample, max density=7.31.646L. Zhang et al. / Journal of Materials Processing Technology 211 (2011) 644649specimens with various diameter dimensions using wire-cutting.Before deep drawing, all circular specimens should be polished bytheabrasivepaperinordertoavoidcrackinthem.Specialposition-ing ring was adopted to fix the specimens. A rigid blank holder wasused on the molds, which can offer sufficient blank holder force topress the blank tightly by adjusting the spring. Consequently, theblank holder and die were uniformly lubricated with oil. The punchwas not lubricated.2.4. Cold stamping of cell phone housingThe as-received sheets and the RUB processed AZ31 magne-sium alloy sheets with a thickness of 0.6mm were used in theseexperiments; three sets of stamping dies for cell phone housingmanufacture were used, the blanking die, deep drawing die andpiercing die. Compared with the blanking and piercing die, thestructureofdeepdrawingdiewasmorecomplex.Themainparam-eters of deep drawing die were as follows: punch radius rp=1mm;die radius rd=2mm; die clearance in the straight wall C=0.6mm;dieclearanceinthecornerC=0.66mm.Thethreesetsofdiesdrivenby the crank press completed the blanking, the deep drawing andthe piercing process in turn.3. Results3.1. Mechanical propertiesFig. 4 shows that the true stressstrain curves of the as-receivedspecimens and the RUB processed specimens in the tensile direc-tions of RD, 45and TD. Compared with the as-received specimens,the RUB processed specimens exhibit larger in-plane anisotropy,and the significant differences can be observed from the truestressstrain curves at the beginning stage of the tensile defor-mation. The work-hardening effects are stronger for the tensilespecimens in the tensile directions of RD, 45and TD after the yielddeformation. The yield strength, tensile strength and the fractureelongation are shown in Fig. 5. The tensile strengths of the RUBprocessed specimens are nearly the same as that of the as-receivedspecimensregardlessofthetensiledirections.Whileyieldstrengthof the RUB processed specimens is significantly lower than that ofthe as-received specimens especially in the RD. These results indi-cate that the RUB process has a strong effect on the yield strengthbut not the tensile strength. Additionally, the fracture elongationsof the RUB processed specimens are improved in the tensile direc-tions of RD, 45and TD in comparison with those of the as-receivedspecimens, especially in the RD with the largest increase from19.2% to 26.7%. These are mainly due to the RUB processed spec-Fig. 4. The true stressstrain curves of the as-received specimens and the RUB pro-cessed specimens in the tensile directions of RD, 45and TD (RD, rolling direction;TD, transverse directions).imens with stronger work-hardening effects which contribute tothe increase in the fracture elongation. Above all, the inclinationof the c-axis toward the RD lowers the yield strength but elevateswork-hardening effects which contribute to improve the uniformelongation.Ther-valueandthen-valueoftheas-receivedspecimensandtheRUB processed specimens are shown in Fig. 6. Compared with theas received specimens, the RUB processed specimens show a muchsmaller r-value and a larger n-value especially in the RD, whichdecreasesfrom2.15to0.92andincreasesfrom0.20to0.29,respec-tively. The difference between r-values as well as that betweenn-values of the as received specimens and the RUB processedspecimens decreases with increasing the tensile angle. The aver-age r-value ( r = (rRD+ 2r45+ rTD)/4) falls from 2.45 to 1.36, andthe average n-value ( n = (nRD+ 2n45+ nTD)/4) rises from 0.175 to0.225 in comparison with those of the as-received specimens. Thedecrease in r indicates that it is easier to reduce or increase thethicknessofsheetduringtheplasticdeformation.Furthermore,theimprovementinthefractureelongationwasmainlyduetothehigh n which resulted in a low sensitivity to strain localization in theform of necking.3.2. LDRDrawingratio(DR)iscommonlyexpressedbyRD=d0/dp,whered0and dpare the blank diameter and punch diameter, respectively.The LDR is the one when the specimen is on the verge of fracture.Fig. 5. (a) Tensile strength and yield strength, (b) fracture elongation of the as-received specimens and the RUB processed specimens in the tensile directions of RD, 45andTD.L. Zhang et al. / Journal of Materials Processing Technology 211 (2011) 644649647Fig. 6. r-Value and n-value of the as-received specimens and the RUB processedspecimens in the tensile directions of RD, 45and TD.Fig. 7 shows cold deep drawn cups of the as-received specimensand the RUB processed specimens for DR=1.5. The as-receivedspecimens fractured at the punch shoulder, and the drawing depthwas only 7.2mm. However, the drawn cup of the RUB processedspecimens showed a good appearance at a drawing depth of11.8mm. Compared with the as-received specimens, the RUB pro-cessed specimens show better stamping formability. These aremainly due to the RUB processed specimens with a tiled tex-ture, which contribute to the increase in the drawing depth. Ifthe drawing depth went up to 14.8mm, the fracture occurredat the edge of the flange for the RUB processed specimens dur-ing deep drawing. Yang et al. (2008) investigated die as shownin Fig. 8(a), the force was not applied onto the edge using theflat blank holder. To apply the force onto the edge even in pass-ing though the die corner, the blank holder was exchanged forthat having a ring-shaped projection in an intermediate stage ofthe deep drawing as shown in Fig. 8(b) (Mori and Tsuji, 2007).Additionally, for magnesium alloy sheets, the fracture happenedin the top of the cup during bendingunbending as the materialpasses over the die radius. Those previous observations point outthat compared with aluminum-alloy sheets (including AA2024,6061,7075), magnesium alloys exhibit poor bending ductility dueto their strong in-plane anisotropy and mechanical twinning-induced tensioncompression strength asymmetry in two sides ofthe bending blank (Agnew et al., 2006). The blank holder with aring-shaped projection is employed instead of the flat bank holderafter the edge of the flange breaking out of the flat bank holder,which is helpful to improve unbending ductility of the sheet inthe die corner. Fig. 9 shows cold deep drawn cup using the blankholderwitharing-shapedprojectioninanintermediatestageofthedeep drawing as shown in Fig. 8(b). The LDR of the RUB processedspecimens is 1.5 under present experimental conditions. However,compared to a circular cup deep drawing, the depth of cell phonehousing is only 6mm, thus the subsequent cold stamping processof cell phone housing is carried out using one-step and flat blankholder.Fig. 10 shows the thickness strain at the angles of 0(RD), 45and 90(TD) to the rolling direction of cold deep drawn cup for theRUB processed specimens. The valleys of the curves represent thesections of the cup corners. Despite of the different r-values in thethree directions, the values at the cup corners are approximatelythe same. It is well known that the stresses in the hoop directionsaround the flange of the cup resulted in the increase in thicknessFig. 7. Cold deep drawn cups with different drawing depth of as-received specimen and the specimen undergoing RUB process for DR=1.5.648L. Zhang et al. / Journal of Materials Processing Technology 211 (2011) 644649Fig. 8. The edge of the blank passes though the corner of the die at different pressure situations: (a) No blank holder force; (b) action of blank holder force.Fig. 9. Cold deep drawn cup using the blank holder with a ring-shaped projection.Fig. 10. Distributions of wall thickness strain of drawn cups for =1.5.during deep drawing. For the RUB processed sheets with a tiltedbasal texture, the thickness strain can be generated by basal slip.Fig.11. Theresultsofcoldstampingofcellphonehousings:(a)as-receivedsample;(b) the RUB processed specimen.3.3. Cold stamping of cell phone housingsPreliminaryexperimentalresultsdemonstratethattheRUBpro-cess has an important influence on the stamping formability ofAZ31 magnesium alloy sheets. Fig. 11 shows the results of coldstamping of cell phone housings. The as-received specimen wasdrawnunsuccessfully,asshowninFig.11(a).Itcanbefoundthatthecritical section at the punch shoulder was broken before the flangeof the specimen was fully dragged into the die cavity. While theRUB processed specimen was drawn successfully, the critical sec-tion at the punch shoulder and the flange was excellent, as shownin Fig. 11(b). The experimental results show that the RUB pro-cessimprovedtheshallowdrawingformabilityofmagnesiumalloysheets. Besides, certainly, cell phone housings can be obtained suc-cessfully in crank press using the RUB processed AZ31 specimensby the cold stamping process.4. DiscussionG.S.Huangetal.(2009)revealedthatmechanicalpropertiesandstretch formability of magnesium alloy sheets with a tilted basaltexture obtained by the RUB process were improved at room tem-perature. Agnew and Duygulu (2005) and Koike et al. (2003) havenoted that for magnesium alloy sheets with a very strong basaltexture, the width strain wcan be generated by prismatic slip,whilethethicknessstrainisgeneratedbypyramidalslipandL. Zhang et al. / Journal of Materials Processing Technology 211 (2011) 644649649twinning.Therefore,thisledtothehighr-valueandthepoordefor-mationcapabilityofsheetthinningfortheas-receivedsheetsinthework of X.S. Huang et al. (2009). In contrast, the thickness strain ofmagnesium alloy sheets, with a tilted basal texture obtained by theRUB process, can be generated by basal slip, which resulted in alower r-value. It is generally expected that high r values favor sheetformability and will lead to higher limiting drawing ratios (Lee,1984). However, the RUB processed sheet exhibits a lower r valueand better drawability at room temperature. The results indicatethat the relationship between the r values and sheet formability ofmagnesium alloys should be interpreted in a different way than isusuallydoneforcubicmetals.Thelowerrvaluemeansthetendencyof increase in the thickness strain, which favors the formability ofthedrawncupcorners.Previousstudies(Chengetal.,2007;Yietal.,2010) have reached the same conclusion, but the relation betweendrawability and a lower r value is unclear and further research isneeded. It is reported that the sheets with a favored texture for thebasal slip exhibited a superior formability in both stretch form-ing (G.S. Huang et al., 2009) and deep drawing (Cheng et al., 2007).Therefore, formability of magnesium alloy sheets can be improvedby the RUB process weakening basal texture of the sheet. Com-pared with the as-received sheets, the Erichsen values of the RUBprocessed sheets increased to 5.90 from 3.53, which increased by67% at most. The LDR of the RUB processed sheets can reach 1.5from 1.2 which was proved in other study of Chino et al. (2006)at room temperature. The larger Erichsen values for the RUB pro-cessed sheets were attributed to the larger n-value and the smallerr-value, which enhanced the capability of sheet thinning duringthe stretch forming. For the as-received sheets, that formability islower may be due to its smaller uniform elongation and larger r-value, which restricted the plastic deformation accompanied withthe increase in thickness at the flange during deep drawing (X.S.Huang et al., 2009). However, the RUB processed sheets exhibitedexcellent drawability because of the larger uniform elongation andthe lower r-value. The superior formability of the RUB processedsheets at room temperature was also demonstrated in the presentstudy by punching out cell phone housings successfully in crankpress.5. ConclusionsThe formability of AZ31B magnesium alloy sheets was investi-gated in the present study by the tensile test, the deep drawingtest and the cold stamping test of cell phone housing. The researchresultsindicatethat,comparedwiththeasreceivedsheets,theRUBprocessed sheets exhibit a lower yield strength, a lower yield ratio,a larger fracture elongation, a smaller Lankford value (r-value), alarger strain hardening exponent (n-value) and a superior stretchformability. The LDR of the RUB processed sheets can reach 1.5 atroom temperature. It is verified that the magnesium alloy sheetwith a tilted texture obtained by RUB process has favorable forma-bility at room temperature. It was also confirmed that cell phonehousing could be produced successfully in crank press using theRUB processed AZ31B sheet by the stamping process.AcknowledgementsSincere thanks are given to the National Natural ScienceFoundation of China under Grant no. 50504019, Natural ScienceFoundation of CQ CSCT under Grant no. 2008BB4040 and Scientificand Technological Project of CQ CSCT under Grant no. 2008AA4028for their supports.ReferencesAgnew, S.R., Duygulu, O., 2005. Plastic anisotropy and the role of non-basal slip inmagnesium alloy AZ31B. Int. J. Plasticity 21, 11611193.Agnew, S.R., Senn, J.W., Horton, J.A., 2006. Mg Sheet metal forming: lessons learnedfrom deep drawing Li and Y solid-solution alloys. JOM 58 (5), 6269.ASM Committee on Fabrication of Magnesium, 1969. Metals Handbook, vol. 4(8),pp. 424431.Chen,F.K.,Huang,T.B.,2003.Formabilityofstampingmagnesium-alloyAZ31sheets.J. Mater. Proc. Technol. 142, 643647.Cheng, Y.Q., Chen, Z.H., Xia, W.J., 2007. Drawability of AZ31 magnesium alloy sheetproducedbyequalchannelangularrollingatroomtemperature.Mater.Charact.58, 617622.Chino, Y., Lee, J.S., Sassa, K., Kamiya, A., Mabuchi, M., 2006. Press formability of arolled AZ31 Mg alloy sheet with controlled texture. Mater. Lett. 60, 173176.Doege, E., Droder, K.
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