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Hydro-mechanical forming of aluminium tubes: on constitutive modelling and process design
Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tube hydroforming is a forming method which has several advantages. By using pressure in combination with material feeding it is possible to manufacture products with high structural integration and tight dimensional tolerances. The forming method is especially suited for aluminium alloys which have a relatively low ductility. Finite Element simulations are used extensively in the sheet metal stamping industry, where the methodology has contributed to a better understanding of the process and the new prediction capability has significantly reduced costly die tryouts. Similarly, the tube hydroforming industry can benefit from Finite Element simulations, and this simulation methodology is the topic of this dissertation.

Deep drawing and tube hydroforming have a basic difference, namely that the latter process essentially is a force controlled process. This fact, in combination with the anisotropic behaviour of aluminium tubes, enforces a need for accurate constitutive descriptions. Furthermore, the material testing needs to account for the specifics of tube hydroforming. The importance of proper material modelling is in this work shown for hydrobulging and hydroforming in a die with extensive feeding.

The process parameters in hydroforming are the inner pressure and the material feeding, where a correct combination of these parameters is crucial for the success of the process. It is here shown, that Finite Element simulations together with an optimisation routine are powerful tools for estimating the process parameters in an automated procedure.

Finally, the reliability and quality of the simulation results depend on how failure is evaluated, which in the case of hydroforming mainly oncerns wrinkling and strain localisation. Since tube hydroforming often is preceded by bending operations this fact also demands the criteria to be strain path independent. In this work, it is shown that the prediction of strain localisation depends on the ability to predict diffuse necking, which in turn is strongly related to the chosen constitutive model.

Place, publisher, year, edition, pages
Institutionen för konstruktions- och produktionsteknik , 2006.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1048
Keyword [en]
Hydroforming, Aluminium Extrusions, Anisotropic material
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:liu:diva-8161ISBN: 91-85643-78-5 (print)OAI: oai:DiVA.org:liu-8161DiVA: diva2:23012
Public defence
2006-11-17, Planck, Hus E, Campus Valla, Linköpings universitet, Linköping, 00:00 (English)
Opponent
Supervisors
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2009-02-26
List of papers
1. On constitutive modeling of aluminum alloys for tube hydroforming applications
Open this publication in new window or tab >>On constitutive modeling of aluminum alloys for tube hydroforming applications
2005 (English)In: International Journal of Plasticity, ISSN 0749-6419, Vol. 21, no 5, 1041-1058 p.Article in journal (Refereed) Published
Abstract [en]

The increased interest in lightweight materials for automotive structures has also lead to a search for efficient forming methods that suit these materials. One attractive concept is to use hydroforming of aluminum tubes. The advantages of this forming method includes better tolerances, decreased number of parts and an increased range of forming options. By using FE simulations, the process can be optimized to reduce the risk for failure, i.e. bursting or wrinkling. However, extruded aluminum is highly anisotropic and it is crucial that the material model used for simulations is able to accurately describe this behavior. Also, tube hydroforming occurs predominantly in a biaxial stress state which should be considered in the material testing, where uniaxial tests are used extensively in the industry today. The present study accentuates the need for improved constitutive models. It is shown that a material model, which accurately describes the anisotropic behavior of aluminum tubes, can be obtained from simple and robust experiments.

Keyword
Aluminum alloys; Hydroforming; Anisotropic material; Biaxial loading
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14246 (URN)10.1016/j.ijplas.2004.06.005 (DOI)
Available from: 2007-01-25 Created: 2007-01-25
2. The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications
Open this publication in new window or tab >>The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications
2007 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 184, no 1-3, 69-76 p.Article in journal (Refereed) Published
Abstract [en]

When considering finite element simulations of aluminium tube hydroforming, the user is facing several challenges. Firstly, extruded aluminium is anisotropic in yield stress and plastic flow. Secondly, the hydroforming process introduces new issues concerning friction and process control. This imposes a demand for accurate constitutive models as well as for hydroforming process related testing methods. The present study focuses on how biaxial tests can be used to calibrate and validate a constitutive model. It is also shown that by using inverse modelling, additional information can be obtained through these types of tests, such as, e.g. the frictional behaviour for different lubrication conditions.

Keyword
Aluminum alloys, Hydroforming, Anisotropic material, Friction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14247 (URN)10.1016/j.jmatprotec.2006.09.039 (DOI)
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2017-12-13
3. Tube hydroforming of aluminium extrusions using a conical die and extensive feeding
Open this publication in new window or tab >>Tube hydroforming of aluminium extrusions using a conical die and extensive feeding
2008 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 198, no 1-3, 14-21 p.Article in journal (Refereed) Published
Abstract [en]

Tube hydroforming is gaining increasing interest from the metal forming industry. Complicated parts with a high level of structural component integration, e.g. engine cradles, subframes and exhaust systems, can be manufactured at a low cost with excellent repeatability. By using finite element (FE) simulations, there is a possibility to reduce the cost of expensive prototypes and reduce the trial and error design process to a minimum. However, when simulating a hydroforming process, the knowledge and computational methods used in conventional metal forming simulations are not always applicable. This concerns, e.g. the material modelling and validation. In this work, the influence of constitutive modelling on the results from a hydroforming process with extensive feeding is studied. In addition, interrupted tests have been used in order to validate the prediction of radial deformation and wall thickness throughout the complete process.

Keyword
Aluminium alloys; Hydroforming; Anisotropic material
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14248 (URN)10.1016/j.jmatprotec.2007.09.043 (DOI)
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2017-12-13
4. On process parameter estimation for the tube hydroforming process
Open this publication in new window or tab >>On process parameter estimation for the tube hydroforming process
2007 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 190, no 1-3, 1-11 p.Article in journal (Refereed) Published
Abstract [en]

Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.

Keyword
Aluminium alloys, Hydroforming, Adaptive process, Optimization
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14249 (URN)10.1016/j.jmatprotec.2007.02.050 (DOI)
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2017-12-13
5. On strain localisation in tube hydroforming of aluminium extrusions
Open this publication in new window or tab >>On strain localisation in tube hydroforming of aluminium extrusions
2008 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 195, no 1-3, 3-14 p.Article in journal (Refereed) Published
Abstract [en]

One important issue when simulating tube hydroforming is to predict bursting, i.e. when the increase in cavity pressure cannot be compensated by hardening of the tube material. Traditionally, this is made by a forming limit diagram (FLD), where the limit strains determine whether a material point is experiencing necking or failure. However, the experimental FLD depends on the strain path, and the methods which are used to determine the FLD are adapted to conventional deep drawing which, depending on the process characteristics, could make it unsuitable for tube hydroforming applications. In this work, analytical and numerical forming limit predictions are studied from a hydroforming point of view. These predictions are then applied to free bulge cases, and a case with extensive feeding in a die where the results from the latter case is compared to experiments. Further, the influence from extrusion welds and a circumferential thickness distribution on the forming limit is also evaluated.

Keyword
Aluminium alloys, Hydroforming, Forming limit, Extrusion weld
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14250 (URN)10.1016/j.jmatprotec.2007.05.040 (DOI)
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2017-12-13

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