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On strain localisation in tube hydroforming of aluminium extrusions
Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
2008 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, 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.

Place, publisher, year, edition, pages
2008. Vol. 195, no 1-3, 3-14 p.
Keyword [en]
Aluminium alloys, Hydroforming, Forming limit, Extrusion weld
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-14250DOI: 10.1016/j.jmatprotec.2007.05.040OAI: oai:DiVA.org:liu-14250DiVA: diva2:23011
Available from: 2007-01-25 Created: 2007-01-25 Last updated: 2009-05-04
In thesis
1. Hydro-mechanical forming of aluminium tubes: on constitutive modelling and process design
Open this publication in new window or tab >>Hydro-mechanical forming of aluminium tubes: on constitutive modelling and process design
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
Hydroforming, Aluminium Extrusions, Anisotropic material
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-8161 (URN)91-85643-78-5 (ISBN)
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

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Jansson, MikaelNilsson, LarsgunnarSimonsson, Kjell

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