Design of hydroforming process for an automobile subframe by FEM and experiment

Baosteel Technical ResearchVolume 6 ,Number 1 ,March 2012 ,Page 22Design of hydroforming process for an automobile subframe by FEM and experimentJIANG Haomin':2) , YANG Bing'.2) , CHEN Xinping'.2) and sU Haibo'.2)1) Auto Steel Division,Reseaarch Institute. Baoshan Iron & Steel Co., Ltd, Shanghai 201900. China2) State Key Laboralory of Development and Application Technology of Automotive Steels ( Baosteel) , Shanghai 201900, ChinaAbstract: Tube hydroforming technology has shown the attention of the automotive industry due to its advantages overconventional stamping and welding methods. ln this study, the tube hydroforming process including tube bending,preforming and hydroforming process for an automobile subframe is analyzed and dessigned !! the simulation :AutoForm of a fnite element methodEM )program. A parametric study is caried out to obtain the effect of theforming parameters such as initial tube size andforming results. The simulation results are alsocompared with experiment results. The research indicates that the multiple forming operation of the tube hydroformingprocess can be simulated accurately by using the implicit code AutoForm , and the formability of tube hydroforming can beimproved by designing suitable forming parameters.Key words: FEM; bending; preforming; tube; hydroforming; subframedoi: 10. 3969/j. issn. 1674 - 3458.2012. 01.005parameters on tube hydroforming. But few reportsfocused on the process parameters designing of real1 Introductionengineering partsi461 .Tube hydroforming technology has shown itself to beIn this study, the specialized hydroforming toola competitive forming technology for tubular parts bydesign and simulation software AutoForm is applied toreducing process steps and overall cost. One of thedie design, process layout and complete processmost important advantages of tube hydroforming isimulation for an automobile subframe. The simulationimproving the strength and stiffness of a structuralresults are verified by experiment. A parametric studycomponent compared with that consisting of severalis also carried out to obtain the effects of the formingstamped sheets' . This allows weight reduction withoutparameters, such as the initial tube size and loadinglosing component performance, so tube hydroformingpath ,on the forming results.has drawn the attention of the automotive industries. Itcan be used for producing a wide range of products2 Partsincluding subframe . exhaust pipe and body structuralA subframe is one of the suspensions in a car，whichcomponents of car and so on.The tube hydroforming process starts from a straightsupporting an engine. It plays an important role nottube with the right diameter and proper length. Firstly,the tube will be bent to an approximate centerline conly in supporting the engine weight, but also inthe part , enabling the tube to be placed in the part dieabsorbing energy when a crash happens. When acavity. If the initial tube diameter is larger than thesubframe is produced by hydroforming process, it cansmallest section dimension of the part . the bent tube isreplace a conventional stamping and welding one withpreformed in a preforming die. Then, the preformedthe same function, but lower weight and lowertube is placed in a hydroforming die. During theFig. 1 shows the shape and several typical crOSs-hydroforming operation， the tube is illel withsections along the axis of this part. As shown in Fig. 1，hydraulic liquid while two axial cylinders seal the tubethe section shape of most regions is a square with sideends. Simultaneously, the liquid is pressurized andlength of 52 mm and circumference of 187.3 mm, likeSection A - A. The section shape at both ends is flat withcylinders are axially fed in from both sides:2maximum circumference of 232 mm, like Section E -E.The success of the hydroforming process requiresThere are 12 bends along the part axis. The minimumcorrect control of forming parameters. Some deformingcircumference section located near the top-bendingfailures such as buckling . wrinkling . folding back andcomer with small area of concave wall has abursting will be caused when incorrect processcircumference of 173 mm. The wall thickness of thisparameters are used'. Finite element method ( FEM)part is a uniform value of 4 mm.is a good way to predict the effects of different formingThe sheet materialproposed for this study wasparameters and determine some suitable processBS6323. Pt 5 with中国煤化工. ultimateparameters. Some reports have studied the effects of tensile strength ofMHCNMH Gof 20%.Coresponding author: JIANG Haomin; E-mail: hnmjiang@ bascel. com20Basteel Technical Research, Vol.6, No.1, Mar. 2012shows comparisons of the thickness distribution predictedon the forming results. The comparison between thwith FEA and measured from experiments of thissimulation result and experiment indicates that thesubframe at Section A - A and E - E, respectively.multiple forming operations of the tube hydroformingCorresponding to the minimum wall thickness 3. 22 mmprocess , including tube bending , preforming and hydro-in FEA, the wall thickness around this point is 3. 19 mmforming ,can be simulated accurately.in the experiment part. The results indicate that for thissubframe ,the simulation predicts metal flow in the tubeReferencesbending，preforming and hydroforming process are[ 1 ] Kristoffer Trana. Finite element simulation of the tubeaccurately.hydroformingforming[J]J Mater Process Technol, 2002 (Mater Dopeeeratoal 200117).401-408.[2 ] Yang Jaebong, Jeon Byunghee and Oh Soolk. The tubebending technology of a hydroforming process for anautomotive part [J]. J Mater Process Technol, 2001(111):175-181.[3] Dohmann F and Harl Ch. Tube hydroforming rechearchand practical application[ J]. J Mater Process Technol ,1997(71) :174-186.[ 4 ] Manabe Kenichi and Amino Masaaki. Efects of processparameters and material properties on deformationprocess in tube hydroforming [ J]. J Mater ProcessTechnol, 2002( 123 ) :285-291.Fig. 12 Hydroformed part in experiment[5]Carleer B , van der Kevie G and de Winter L. Analysis ofthe effect of material properties on the hydroformingprocess of tubes[J]. J Mater Process Technol, 20004.50( 104) :158-166.[6] Hama T,Asakawa M and Makinonchi A. Investigation of; 4.40 I112 13factors which cause breakage during the hydroforming of4.35 t14131211公Experimnentan automotive part[J]. J Mater Process Technol, 20044.30( 150) :10-17.xperiment4.25 F[ 7] Jrathearanat Suwat , Hartl Christoph and Altan Taylan.4.20 FHydroforming of Y-shapes- -product and process design4.15 tusing FEA simulation and experiments [ J]. J Maters 4.10Process Technol ,2004( 146) :124-129..05 t4.002 4~68101214 16Measurment pointFig. 13 Comparisons of the thickness distribution5 ConclusionThe hydroforming of the subframe requires properselection of many process parameters,i. e. the initialJIANG HaominYANG Bing .CHEN Xinpingtube size., intemal pressure and axial feeding. In orderto reduce the trial-and-error effort in designing theprocess parameters ，FEM was used to simulate the tubebending, preforming and hydroforming operations. Itcan be concluded that it is better to choose an initialtube with outer diameter of 60 mm, but not 52 mm forthis part. The preforming process is needed for a tubewith outer diameter of 60 mm and the preformingprocess benefits the part wall thickness distribution andsU Haibocan shorten the addendum. Even for this type of multi-bending part , the loading path has some obvious effects中国煤化工MHCNMH G .