軸承上蓋零件的滑柱式鉆床夾具設計含2張CAD圖

軸承上蓋零件的滑柱式鉆床夾具設計含2張CAD圖,軸承,零件,滑柱式,鉆床,夾具,設計,CAD Applied Surface Science 257 (2010) 15891595Contents lists available at ScienceDirectApplied Surface Sciencejournal homepage: of laser energy on the deformation behavior in microscale laserbulge formingChao Zheng, Sheng Sun, Zhong Ji, Wei WangKey Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (MOE), School of Materials Science and Engineering, Shandong University,17923 Jingshi Road, Jinan 250061, PR Chinaa r t i c l ei n f oArticle history:Received 11 June 2010Received in revised form 18 August 2010Accepted 18 August 2010Available online 3 September 2010Keywords:Microscale laser bulge formingLaser shock wavesPlastic deformationResidual stress distributionAbsorbent coatingSurface morphologya b s t r a c tMicroscale laser bulge forming is a high strain rate microforming method using high-amplitude shockwavepressureinducedbypulsedlaserirradiation.Theprocesscanserveasarapidlyestablishedandhighprecision technique to impress microfeatures on thin sheet metals and holds promise of manufacturingcomplex miniaturized devices. The present paper investigated the forming process using both numericaland experimental methods. The effect of laser energy on microformability of pure copper was discussedin detail. A 3D measuring laser microscope was adopted to measure deformed regions under differentlaser energy levels. The deformation measurements showed that the experimental and numerical resultswere in good agreement. With the verified simulation model, the residual stress distribution at differentlaser energy was predicted and analyzed. The springback was found as a key factor to determine thedistribution and magnitude of the compressive residual stress. In addition, the absorbent coating and thesurface morphology of the formed samples were observed through the scanning electron microscope.The observation confirmed that the shock forming process was non-thermal attributed to the protectionof the absorbent coating. 2010 Elsevier B.V. All rights reserved.1. IntroductionSince the first experimental research in the 1960s using high-power laser pulses to generate shock wave pressures in solidtargets, the laser shock technique has been widely investigated13. The application of the laser-induced shock wave pressure insheetmetalformingderivesfromthecapabilityofmodifyingacur-vature of the metal target through the impact of a laser pulse 4. Inthemeantime,Zhouetal.reportedtheinvestigationonanultrahighstrain rate forming technique driven by laser shock, and showedthat the process had potential to become a flexible manufacturingmethod with excellent properties and short manufacturing time5.Recently, the quickly increased requirement for miniaturizeddevices shows a growing demand on developing new tech-niques varying from conventional ones to manufacture morecomplex microproducts. To date there have been many reportsof microforming using laser shock. Fan et al. 6 employed bothexperimental and numerical methods to study the laser-inducedmicrobending process of copper strips. The interaction of theshock wave pressure and the metal target during the processwas analyzed in detail. Wang et al. 7 investigated the relation-Corresponding author. Tel.: +86 531 88392817; fax: +86 531 88392315.E-mail address: zhongjiumich.edu (Z. Ji).ship between phenomena about convex and concave bending andpatterns of residual stress distribution in microscale laser peenforming. The forming mechanism was explained in terms of com-bined effects of the shock loading, bending moment and inducedcompressive stress. Oca na et al. 8,9 studied laser microbend-ing of stainless steel strips in a one-side pinned configuration bymeans of numerical simulations and experiments, and presented adiscussion on the influences of processing parameters on the netbendingangle.Laser-inducedstretchformingandmicrodeepdraw-ing were explored in which the laser shock wave acted as a punch,and a series of experiments were implemented to reveal formingmechanisms and effects of processing parameters on deformationbehaviors of metals, such as pure aluminum, copper and stain-less steel 1012. Cheng et al. 13 systematically characterizedthe microstructure and mechanical properties of metal foils aftermicroscale laser dynamic forming. They showed that the met-als were strengthened significantly after the shock forming dueto refined structure and large dislocation density. Gao et al. 14further investigated the deformation process of microscale laserdynamicforminganddiscussedtheeffectsofcriticalparametersondeformation behaviors of materials based on experimentations aswellasnumericalsimulations.Obviously,lasershockmicroformingas a new technology has attracted wide attention.At present, we are interested in a laser microforming pro-cess known as microscale laser bulge forming, which combinesthe beneficial effects of microscale laser shock peening with the0169-4332/$ see front matter 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.apsusc.2010.08.0991590C. Zheng et al. / Applied Surface Science 257 (2010) 15891595advantages of laser thermal forming and high strain rate forming.In accordance with other laser shock processes, microscale laserbulge forming is a non-thermal laser forming method using thehigh-amplitude shock wave pressure induced by laser irradiation.The process can serve as a rapidly established and high precisionmethod to impress microfeatures on thin sheet metals. Moreover,since the laser can provide non-contact, tool-less, and superb flexi-bility, it is possible to employ the process to manufacture complexminiaturized devices, especially in the case that the conventionalmicrostamping process is not available. In this paper, microscalelaser bulge forming was studied using both numerical and experi-mental methods. The effect of laser energy on microformability ofpure copper was investigated experimentally, and the experimen-tal results were compared with the corresponding data obtainedfrom a finite element analysis model. With the verified simula-tion model, the residual stress distribution at different laser energylevels was predicted and analyzed. In addition, the effect of laserirradiationontheabsorbentcoatingandthesurfacemorphologyofthe formed samples were observed through the scanning electronmicroscope (SEM).2. Forming mechanismMicroscale laser bulge forming originates from the ability todrive the shock wave into sheet metals to cause plastic deforma-tionbytheimpactofahigh-powerlaserpulse.Typically,thepowerdensityofthelaserpulseismorethan1GW/cm2andthelaserpulseduration is in the range of 10100ns. The samples surface facinglaser irradiation is pre-coated with an absorbent coating and thencoveredbyaconfiningoverlay.Theabsorbentcoatingabsorbslaserenergy and vaporizes to form a plasma for its lower breakdownthreshold than that of the metal target, so it protects the metalssurface from laser ablation and melting. Black paint is often cho-sen as the absorbent coating due to its high energy absorbabilityand easy removal after the process. The confining overlay confinesthe plasma from expanding rapidly away from the metals surface,resulting in higher pressure compared with the open-air condition.Quartz glass usually acts as the confining overlay. As illustrated inFig. 1, the microdie is placed beneath the metal foil, and a holder isused to confine the material outside the die cavity. While the metalis impacted by a laser pulse with sufficient intensity, the absorbentcoating instantaneously vaporizes and forms a high temperatureand high pressure plasma. The rapid expansion of the plasma inthe confined regime creates a high-amplitude pressure pulse andsubsequently the shock wave pressure propagates into the metaltarget. If the peak pressure of the shock wave exceeds the dynamicyield strength of the metal, plastic deformation occurs and theFig. 1. Schematic of microscale laser bulge forming.metal bulges towards the die cavity at extremely high strain rates(106107/s).3. Experimental conditionsA Q-switched Nd: yttrium aluminum garnet (YAG) laser with awavelengthof1064nmwasusedintheexperiment.Thelaserpulseduration is 11ns and the laser beam diameter is set at 1mm. Thelaser pulse is conducted to the target through a series of reflect-ing mirrors and a convergent lens with a focal length of 100mm.A thin layer of black paint (about 50?m thick) was spread evenlyby hand on the samples top surface as the absorbent coating. A1mm thick quartz glass was placed above the sample as the con-fining overlay. Each experiment was carried out by a single laserpulse.The microdie with a through hole of 1.2mm in diameter wasmanufacturedforlaserbulgeforming.Purecopperfoilswith30?min thickness have been chosen. Copper is often used for micro-electromechanical systems (MEMS) materials since it has goodplasticity, ductility and resistance of corrosion.Aftertheshockpro-cess,theremainingblackpaintwassolvedbyacetonesolution,andanhydrous alcohol was adopted to clean the samples surface. TheOlympus SZX12 optical microscope and LEXT OLS4000 3D mea-suring laser microscope were used to observe and measure thedeformation. The absorbent coating and the surface morphologyof the formed samples were observed by the scanning electronmicroscope.4. Numerical modelingThe laser-induced shock wave pressure was calculated fol-lowing Fabbros model 15. This model assumes that the laserirradiation is uniform and shock wave propagation in both the con-fining overlay and the metal target is one-dimensional. The shockwave pressure P(t) and the plasma thickness L(t) can be expressedas functions of time t by the following relationship:dL(t)dt=2ZP(t)(1)AP(t)I(t) = P(t)dL(t)dt+32ddtP(t)L(t)(2)where AP(t), I(t) and are the absorption coefficient, laser powerdensity and the fraction of the internal energy devoted to thethermal energy, respectively; Z=2/(1/Z1+1/Z2) is the shock waveimpedance, where Z1is the impedance of the metal target and Z2is the impedance of the confining overlay. In current research, is 0.1; the impedance of pure copper is 3.83107kg/m2s and theimpedance of quartz glass is 1.31107kg/m2s.The spatial profile of the laser beam is non-uniform over theentire area of the spot and the shock wave pressure obeys Gaussianspatial distribution proposed by Zhang and Yao 16. The spatiallyuniform shock wave pressure P(t) relates to the spatially non-uniform shock wave pressure P(r, t) isP(r,t) = P(t)exp?r22r20?(3)where r is the radial distance from the center of the laser beam; r0is the radius of the laser spot (r0=0.5mm in current study).Johnson and Cook firstly presented a constitutive model formaterials subjected to large strains, high strain rates and high tem-peratures 17. The model has been widely used for high strainrate deformation of metals. In a single laser shock process, onlythe absorbent coating is vaporized so that it protects the metal tar-get from laser thermal effect. Therefore, the temperature effect canC. Zheng et al. / Applied Surface Science 257 (2010) 158915951591Fig. 2. Finite element analysis model for microscale laser bulge forming.be neglected here. A modified JohnsonCook model can be writtenas:? = (A + Bn)?1 + C ln? 0?(4)where ? is the dynamic yield strength; is the strain; is thestrain rate and 0is the reference strain rate ( 0= 1/s) A, B, C andn are material constants. For pure copper, A=90MPa, B=292MPa,C=0.025 and n=0.31 17.The commercial finite element code MSC.MARC was employedto accomplish the numerical simulation of microscale laser bulgeforming. The simulation is composed of two steps. Firstly, anexplicit dynamic transient analysis is performed to obtain thedynamic response of the material. The central difference time inte-grationisusedtosolvethenonlinearmotionequationsoftheshocksystem. While the dynamic analysis has finished, the field informa-tion including strains, displacements and stresses will be importedinto MSC.MARC again to perform static analysis. Eventually, thespringbackdeformationandtheresidualstressfieldinsteadyequi-librium are obtained. MSC.MARC Mentat provides the powerfulpre- and post-processing capabilities to model the numerical anal-ysis system and review calculated results.In the simulation, an axisymmetric deformation state isassumed since the shape of the die hole is round and the metalis subjected to a circular laser spot. The mesh in the axial direc-tion is constant with a size of 5?m, which is far smaller than thelaser spot radius of 0.5mm. The section of the metal within the diehole is not restricted so that it can deform freely, while the remain-ing material out of the die hole is fixed in position because it isclamped tightly by the holder. The quadrilateral axisymmetric ringelements are employed in the analysis. The sheet metal is assumedto be isotropic and the von Mises yield criterion is adopted. Fig. 2shows the established finite element model for microscale laserbulge forming.5. Results and discussion5.1. Deformation and simulation model validationTo quantitatively characterize the deformation, a 3D measuringlaser microscope is used to profile deformed regions under differ-ent laser energy levels. Fig. 3(a) and (b) show the cross-sectionalmeasurement and the 3D plot of the formed sample. As seen, acup-shape sample with good geometry is obtained, indicating anoccurrence of strong plastic deformation during the forming pro-cess. Note the cup is round with a diameter of 1.2mm, which iscorresponding to the die diameter.Fig. 3. Measurement of the formed sample using 3D measuring laser microscope:(a) measurement of cross section; (b) 3D plot of the formed sample. Pulse energyE=400mJ.From the measurements, the profile and the maximum defor-mationdepthareobtainedandcomparedwithsimulations.Fig.4(a)shows the profiles of copper samples with laser pulse energy400mJ. Each experimental data point is the average of three fea-tures, and the error bar represents standard deviation. As seen inFig.4(a),thesimulatedprofilesgenerallyagreewiththeexperimen-tal results, yet some discrepancies are seen around the edge of thelaser spot. Experimental measurements show a smoother profilein this region. This is perhaps due to the fact that in the simulationthe laser-induced shock wave is assumed to propagate only in theaxial direction in the confining overlay and the metal target, whileit does spread out three-dimensionally in practice.Fig. 4(b) shows the variation of the maximum deformationdepth with the increase of laser pulse energy. Obviously the simu-lated cup heights are in good accordance with the measurements.Itismanifestthatthecupdepthincreaseswiththeenhancementoflaser energy. This is understandable because when the laser energyincreases, the ablation of the absorbent coating becomes more effi-1592C. Zheng et al. / Applied Surface Science 257 (2010) 15891595Fig. 4. (a) Comparison of numerical and experimental profiles at E=400mJ; (b) themaximum deformation depth at different laser energy levels.ciently and a stronger plasma can be generated. After that, a morepowerful shock wave pressure is induced and propagates into themetaltarget.Asaresult,thecupdepthacceleratessincemoreform-ing energy is available.In addition, as shown in Fig. 4(b), to induce noticeable plasticdeformation, laser pulse energy in microscale laser bulge formingcannot be too small. On the other hand, the laser energy cannot betoohigh,either.Toomuchpulseenergymayburnouttheabsorbentcoating and lead to serious thermal effect in the sample. More-over, fracture may occur when the plastic deformation exceeds theforming limit of the material. In this study, the energy range of200400mJ can induce sufficient plastic deformation without fail-ure for 30?m copper. It should be emphasized that none of theresults shown here represent the optimum or maximum benefitcondition for the particular material.It is interesting to note that a thin sheet metal can obtain solarge deformation in the shock process. The deformation depth atE=400mJ can reach 159?m in the experiments. The generation oflarge plastic deformation of thin metals may be attributed to twomechanisms. In microscale laser bulge forming, the plastic strainrate can reach 106/s. It has a significant effect on the flow behaviorof the material and helps to improve the local deformation ability.The other reason is that the inertial effect can also improve theformability of the thin metal. The response of the material duringlaser shock is dynamic and the inertial effect is not negligible. It hasbeen found that fracture in a tensile sample can be delayed wheninertial forces are relatively large. This phenomenon is related toinertialforcesstabilizingthedevelopmentoftheneckinthesample13,18. Thus, the formability of the thin copper sample can be wellimproved and continuous plastic deformation can be obtained.5.2. Residual stress distributionsMicroscale laser bulge forming is one of the tension type pro-cesses. The material beneath the laser spot bulges towards the diecavity when the generated pressure exceeds the dynamic yieldstrength of the metal. The remaining material within the die holeis also stretched into the cavity due to the continuity of the mate-rial. It is noticed that no material outside the die hole will flow intothe die cavity because of the confinement of the holder. The plasticdeformation of the sample depends on the reduction in thicknessand the elongation in radial and tangential directions. Thus, thematerial is subjected to compressive strain in the axial directionand tensile strain in both the tangential and radial directions dueto the principle of constant volume. During the deformation, theaxial stresses are rather smaller than those in radial and tangentialdirections, so the sheet metal can be considered under biaxial ten-sile stresses. Fig. 5 illustrates the stress and strain states during thedeformation process.During the dynamic analysis of the shock process, the materialexpands downwards and the deformation proceeds by inertia afterthe loading. While the dynamic analysis is completed, the staticanalysis is performed until the springback finishes and the samplereaches a stabilized mechanical state. Hence, the final shape of thesample and the distribution of residual stresses are dependent onthe springback. Fig. 6 shows the contours of the radial stress distri-bution at the end of the dynamic analysis and of the static analysis.AsshowninFig.6(a),radialstress?ristensileinawideregionofthematerial. However, the material around the die entrance takes on asignificantstressgradient;thatis,thetopsideistensilestress,whilethe bottom side alters to compressive. Due to the confinement ofthe holder, the material under the holder is fixed and there is nomaterial flowing into the die cavity. This explains why the stressFig. 5. Stress and strain states during the laser-induced bulge forming process.C. Zheng et al. / Applied Surface Science 257 (2010) 158915951593Fig. 6. Contours of the radial stress distribution: (a) dynamic analysis result; (b)static analysis result. Pulse energy E=400mJ.concentration occurs near the die entrance. While the springbacktakes place, the elastic strain energy releases and the stress fieldis redistributed. Fig. 6(b) shows the result of the stress relaxation.Within the laser spot, a compressive residual stress is generatedon the bottom side (opposite to the laser shocked surface), whilethereisatensileresidualstressonthetopsurface(thelasershockedsurface). However, it should be noted that there is an undesirablecomplicated stress distribution outside the laser spot, which mayaffect the post-processed properties. To avoid having this periph-eralstressdistribution,apracticablewayisthatthelaserirradiationarea is large enough to move this stress state outside the formingarea.To examine the effect of laser energy on the residual stressdistribution, laser energy of 200, 300, and 400mJ is used in thesimulation. Fig. 7 shows the distribution of radial residual stress ?ron the top and bottom surfaces at different laser energy levels. It iso