An Analysis on the Parameters influencing failure in Tube Hydro forming A review

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1 An Analysis on the Parameters inluencing ailure in Tube Hydro orming A review S. John Alexis 1 Dr. G. Chandramohan 2 1. Assistant Proessor, Department o Mechanical Engineering, Sri Krishna College o Engineering and Technology, Coimbatore , Tamil Nadu, India. johnalexis@redimail.com 2. Proessor, Department o Production Engineering, PSG College o Technology, Peelamedu, Coimbatore , Tamil Nadu, India. Abstract: The use o computers in design and analysis, have reached steps ahead in reducing the production time and cost. The process, which is being widely accepted presently by the sheet metal orming industries, is the hydro orming process. This orming process alls under the category o internal high pressure orming using liquid media. Researchers have proved that even tubes can also be ormed using liquid media. This process tube hydro orming is gaining popularity among the automotive and aerospace industries or their inherent beneits like improved part quality and lie. Automobile and aerospace industries use number o tubular components like exhaust maniolds, muler casings, chassis rames to reduce the weight o the vehicle. Special methods, processes and equipments are required to abricate these parts. The tube hydro orming is one o the promising processes that can be employed or orming tubes. This paper reviews the parameters that inluence the ailure o the tubes while orming. The results o the review consolidated can be used as a quick reerence by the automotive and aerospace industries. The main criteria or the tube ailure can be best understood and remedies can be taken to avoid ailures in orming the tubes. Key words: Tube, Formability, Axial Compression, Tube expansion, Anisotropy 1. Introduction: The promising beneits exhibited by the Tube Hydro orming should be exploited to the maximum extent possible. It is the process o manuacturing tubular shaped complex parts by using axial compression o the Tubes and orming with pressurized luid rom inside. The advantages o this process compared to the Conventional processes o Tube orming are 1. Reduction in part counts and Weight 2. Improved Strength and Stiness 3. Lower Tooling cost and higher dimensional accuracy. Some o the parts made by Tube Hydro orming are ound in exhaust parts, cam shats, Frames o radiator, Front and Rear axles, Seat rames, Body parts, Space rames, Pillars, Sills and roo rails. Researches or the past one-decade have tried their best to know in and out about the process. Doege.E et. al have determined the optimized control parameters or internal High Pressure orming Processes with FEM [1]. An adaptive simulation o Tube Hydro orming has been done by Tibari et. al [9].Strano has developed a simulation concept or Tube Hydro orming [7]. Hydro orming High strength Steel Tube or Automotive structure applications had been studied by Murphy G. [3]. Also he has explained in detail about the process, in Tube Hydro orming Analysis [4]. Srinivasan et. al have correlated experimental and

2 simulation results in Tube Hydro orming process [8]. Liu et. al ocused on Tube Hydro orming Analytical and experimental limits [2]. The Mechanics o Tube Hydro orming has been explained by Qian et. al [5]. Siehert.K. has ocused on the Hydro orming o Tubes, Sheets and Extrusions [6]. This paper reviews the parameters inluencing the Tube ailure in Tube Hydro orming process. 2. Tube Hydro orming: The Tube Hydro orming Principle involves the orming o Tube blanks or preormed blanks being axially compressed by mechanical means and the walls being made to deorm by hydrostatic luid pressure to the shape o the die. [Re ig 1]. The typical orming deects that occur during Tube hydro orming are bursting, Wrinkling, Global buckling and olding. The typical orming deects that occur during Tube Hydro orming are bursting, Wrinkling, Global buckling and olding. Fig2 ( ) Fig 1.High Pressure Tubular hydro orming 3. Tube ailures and Reason or Tube ailures: The bursting o the tube is an instability phenomenon, where the Tube could not withstand the increased tensile loading by the luid pressure. Splitting ollows due to extreme deormation in the working area. Wrinkling due to excessive compressive loading by axial eeding. Folding due to localized wall thinning and Buckling due to disproportional length to diameter ratio. 4. Tube Failure Analysis: For the successul Hydro orming o Tube to the required proile the ollowing actors must be eectively taken into consideration. 1. Tube material and its ormability 2. Friction and Lubrication 3. Internal Pressure o Fluid 4. Axial eeding orce 5. Deormation path Tube material and its ormability: The quality o the Tube material is critical or successul Tube Hydro orming Process. The material properties like material composition, yield strength, ultimate tensile strength, Percentage elongation, low properties play a signiicant role in Tube Hydro orming. The Tube properties are estimated rom the bulge test. The values obtained can be plotted to get the ormability o the Tube. The possible loading conditions is shown in igure (Re Fig 2). In this case o Tube Hydro orming a combination o biaxial load, which will maximize the orming limit Postponing the

3 Fig 2 Loading conditions in Bulge orming local thinning is taken or considerations because o the stress induced by axial compression and that by the internal luid pressure. These two have to be synchronized to a desired ratio, which will avoid thinning. In the vicinity o deormation theory, the associated strain ratio ollows a constants path Friction and Lubrication: The axial compression leads to increase o sliding riction value. A proper lubrication will avoid these riction parameters, which imposes an increased value o axial compression. The lubrication between die wall and the Tube outer surace also prevents sticking and galling o the Tube to reduce tool wear, axial orces and excessive thinning. The lubricant used should posses the required properties so as to get a quality ormed component. The lubricant used should have to withstand high pressures, be cheap and easily available, unabrasive to reduce erosion, with no pollutants Internal Pressure o luid: The internal luid Pressure (P) is determined by the orce equilibrium as σθt Ρ r Where 2 R) σθ 2R σ ( e R θ + x e R r t L t Tube thickness rl r radius o the tube, r, t, L Final radius, thickness and length o the tubes respectively. e x 0 R 2R n l l 2 x + 2R R 2 θ + x θ l n r r l R normal anisotropy The above equations are related to deormation theory o plasticity, which can be applied or proportional loading. In such cases it is mandatory that stresses are monotonically increasing along a ixed direction. The loading path as explained above is being carried out by the hydrostatic pressure o the luid. The above equation indicates that the pressure

4 required or tube expansion is proportional to the thickness and hoop stresses and inversely proportional to the present tube thickness. The pressure will initially increase, reaches a peak value and then it decreases urther. The peak value is the value o pressure, which can be applied to deorm the tube, and ater which the tube will burst ing Force: This is another important criteria, which is to be taken care o in Tube Hydro orming. The extent o bulging o the tube or deormation o the tube generally depends on this axial eed value. The tube is being compressed axially so that the length decreases. The poor axial compression results in low deormation o the tube wall but an excessive axial compression results in wrinkling. A tube o radius r has been uniormly expanded under an Internal pressure o p, the axial compression L l a L The bulging or orming o the tube mainly depends on the axial eed value. The volume constancy principle is used to manipulate the strain values Deormation Path: One o the important actor to obtain a quality tube product, which is to be controlled, is this deormation path. Special yielding positions are recorded in the Tube Hydro orming limit graph. Thinning o the Tube walls doesn t occur when the incremental thickness strain ( d t ) is greater than or equal to zero. When a point on the yield locus approaches the point 6, thickening occurs. Wrinkling due to axial compression occurs when the path is between 3 and 6 (Re Fig 3). It will be better i the deormation path is designed rom the higher axial compression zone to the lower or the biaxial tensile one. 1-biaxial tension; 2,6 plane strain; 3 uniaxial tension; 4 pure shear; 5 uniaxial compression; Fig 3 Stress Strain states o Tube Hydro orming

5 5. Parameters inluencing Tube ailure: The important parameter enhancing or promoting Tube ailure which are to be controlled or obtaining a deect ree component are related to material property, orming Geometry, Deormation modes, Axial compressive stress and inside pressure. Researches have conducted a no. o laboratory trials on dierent materials to consolidate the process. The main actors inluencing are material property, Material anisotropy, Tube geometry, Axial eed and Internal Pressure Material Property: From the theoretical analysis, it is understand that the material properties play a major role in aecting the tube orming or three dierent Tube materials Hydro ormed( Re ig 4). The orming zone is wider or materials having higher yield strength and narrow or materials having lower yield strength. Also Tube materials with lower yield strength are easier to Hydro orm than the one with higher yield strength (Re Fig 5). The loading conditions or the dierent material do not signiicantly aect the wrinkling wavelength. Materials having lower yield strength have slight short wrinkling wavelength than those materials having higher yield strength. Fig 4 Inluence o Material Property Fig 5 Working zone or three dierent materials 5.2. Tube Geometry: The hoop stress acting depends on the tube length ratio, radius ratio and material properties i.e. the higher the thickness to radius ratio the pressure required is also more and vice versa.(re ig 6) r/r Fig 6 Tube radii or three dierent materials

6 5.3. Material Anisotropy: As the Anisotropy value o the Tube material changes it adversely aect the bursting and wrinkling behaviour. Material with smaller value o R exhibit lower bursting pressure or a given axial eed and also these materials are easily prone to wrinkling. Higher the value o R, higher the bursting the pressure and less wrinkling is achieved. The concept is that larger value o R makes the material more diicult to deorm and so less wrinkling occurs(re Fig 7 & 8). Fig 7 Eect o Anisotropy on Bursting Pressure Fig 8 Eect o Anisotropy on Wrinkling 5.4. Internal Pressure: Normally in Tube Hydro orming the internal Pressure to be applied is a dependent variable on axial eed and Tube geometry. So combined eect o axial eed and Pressure are taken into account while orming. For a particular value o R as the axial eed is increased the bursting pressure decrease and at the same time as the axial eed increased the wrinkling tendency also increases and hence one has to select a proper loading path. The loading path can be linear, proportional, increased initial pressure keeping axial eed zero and increasing initial axial eed and keeping pressure zero and then increasing the value. It is ound that the bursting Pressure is highest or the loading path where the axial eed is increased irst with nil initial pressure and then increased (Re Fig 9). Fig 9 Eect o Dierent Loading paths on Bursting Pressure

7 6. Conclusion: The Tube Hydro orming Process is a very potential process, which has been concentrated by many researches. Failure analysis shows that the material properties are the ones primarily responsible or Tube ailure than that o the processing conditions. The Processing parameters such as internal pressure, Axial eed and loading path also have signiicant eect on the bursting and wrinkling behaviour o the Tubes. Reerences: 1.Doege E, Kosters,R. Ropers.C Proc. o the International Conerence on Sheet metal 98, Ed K. Gaiger et.all Liu S.D. Mechleman.D, Thomson K. SAE Technical Paper , Murphy G. Automotive Engineering 106 PP 91 94, Murphy G. SAE Technical Paper NO , Qian.Y. Cattran.D and Karima M, SAE Technical Paper NO , Siehert.K. (Eds), Proc. O the International Conerence on Hydro orming, ellback, Stuttgart Germany, Oct 12 13, Strano M. Jirathearanat, S. Proc. International Conerence on Sheet metal Srinivasan T.M, Shan.J.R and Thomson K SAE Technical Paper NO , Tibari K, Jiratharanat S Strano.M Altan.T, ERC / NCM report NO THF / ERC / NSM 00 - R