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Finite Element Analysis of Sheet Metal Assemblies: Prediction of Product Performance Considering the Manufacturing Process
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the development of methodologies to be used to simulate complete manufacturing chains of sheet components and the study of how different mechanical properties propagate and influence succeeding component performance.

Since sheet metal assemblies are a major constituent of a wide range of products it is vital to develop methodologies that enable detailed evaluation of assembly designs and manufacturing processes. The manufacturing process influences several key aspects of a sheet metal assembly, aspects such as shape fulfilment, variation and risk of material failure.

Developments in computer-aided engineering and computational resources have made simulation-based process and product development efficient and useful since it allows for detailed, rapid evaluation of the capabilities and qualities of both process and product. Simulations of individual manufacturing processes are useful, but greater benefits can be gained by studying the complete sequence of a product's manufacturing processes. This enables evaluation of the entire manufacturing process chain, as well as the final product. Moreover, the accuracy of each individual manufacturing process simulation is improved by establishing appropriate initial conditions, including inherited material properties.

In this thesis, a methodology of sequentially simulating each step in the manufacturing process of a sheet metal assembly is presented. The methodology is thoroughly studied using different application examples with experimental validation. The importance of information transfer between all simulation steps is also studied. Furthermore, the methodology is used as the foundation of a new approach to investigate the variation of mechanical properties in a sheet metal assembly. The multi-stage manufacturing process of the assembly is segmented, and stochastic analyses of each stage is performed and coupled to the succeeding stage in order to predict the assembly's final variation in properties.

Two additional studies are presented where the methodology of chaining manufacturing processes is utilised. The influence of the dual phase microstructure on non-linear strain recovery is investigated using a micromechanical approach that considers the annealing process chain. It is vital to understand the non-linear strain recovery in order to improve springback prediction. In addition, the prediction of fracture in a dual phase steel subjected to non-linear straining is studied by simulating the manufacturing chain and subsequent stretch test of a sheet metal component.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 47 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1605
National Category
Metallurgy and Metallic Materials Applied Mechanics
Identifiers
URN: urn:nbn:se:liu:diva-106637DOI: 10.3384/diss.diva-106637ISBN: 978-91-7519-300-7 (print)OAI: oai:DiVA.org:liu-106637DiVA: diva2:717630
Public defence
2014-06-05, C3, Hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2014-05-16 Created: 2014-05-16 Last updated: 2014-05-23Bibliographically approved
List of papers
1. Finite element simulation of the manufacturing process chain of a sheet metal assembly
Open this publication in new window or tab >>Finite element simulation of the manufacturing process chain of a sheet metal assembly
2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 7, 1453-1462 p.Article in journal (Refereed) Published
Abstract [en]

An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Finite element simulation, Assembly, Sheet metal, Forming, Springback
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77853 (URN)10.1016/j.jmatprotec.2012.02.012 (DOI)000304020800001 ()
Note

Funding Agencies|Swedish foundation for strategic research||ProViking programme||

Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2017-12-07Bibliographically approved
2. The effects of forming history on sheet metal assembly
Open this publication in new window or tab >>The effects of forming history on sheet metal assembly
2014 (English)In: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 7, no 3, 305-316 p.Article in journal (Refereed) Published
Abstract [en]

As demand for faster product development increases, physical prototypes are replaced by virtual prototypes. By using finite element simulations to evaluate the functional behaviour of the product as well as its manufacturing process, more design alternatives can be evaluated while a considerably smaller number of physical prototypes are needed. As sheet metal assemblies are common in a wide range of products, reliable methods for predicting their properties are necessary. By sequentially simulating the complete manufacturing process chain of an assembly, early predictions concerning the geometry and material properties of the assembly can be made.

In this study a simulation-based sensitivity study is performed in order to investigate the influence of the forming history on the predictions of assembly properties. In the study, several simulations of the assembly stage are performed in which different types of forming histories are retained from the forming stage. The simulations of the assembly stage will range from a case with linear elastic conditions without forming history, to a case with the full forming history state and consistent material modelling throughout all simulations. It is found that the residual stress state is the most influential history variable from the forming stage. Especially for more complex geometries in which large residual stresses can be retained.

Place, publisher, year, edition, pages
Springer, 2014
Keyword
Finite element simulation, Assembly, Sheet metal, Forming, History variables, Chaining of manufacturing processes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-78765 (URN)10.1007/s12289-013-1128-9 (DOI)000338323600004 ()
Note

On the day of the defence date of the Ph.D. thesis the status of this article was Manuscript.

Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2017-12-07Bibliographically approved
3. A study of the unloading behaviour of dual phase steel
Open this publication in new window or tab >>A study of the unloading behaviour of dual phase steel
2014 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 602, 119-126 p.Article in journal (Refereed) Published
Abstract [en]

It is important to understand the strain recovery of a steel sheet in order to predict its springback behaviour. During strain recovery, the stress–strain relation is non-linear and the resulting unloading modulus is decreased. Moreover, the unloading modulus will degrade with increasing plastic pre-straining. This study aims at adding new knowledge on these phenomena and the mechanisms causing them. The unloading behaviour of the dual-phase steel DP600 is characterised experimentally and finite element (FE) simulations of a representative volume element (RVE) of the microstructure are performed. The initial stress and strain state of the micromechanical FE model is found by a simplified simulation of the annealing processes. It is observed from the experimental characterisation that the decrease of the initial stiffness of the unloading is the main reason for the degrading unloading modulus. Furthermore, the developed micromechanical FE model exhibits non-linear strain recovery due to local plasticity caused by interaction between the two phases.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Micromechanics; Representative volume element; Dual phase steel; Unloading modulus; Non-linear recovery
National Category
Metallurgy and Metallic Materials Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-106318 (URN)10.1016/j.msea.2014.02.069 (DOI)000335098500015 ()
Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
4. Prediction of fracture in a dual-phase steel subjected to non-linear straining
Open this publication in new window or tab >>Prediction of fracture in a dual-phase steel subjected to non-linear straining
2014 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, 2748-2758 p.Article in journal (Refereed) Published
Abstract [en]

In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Sheet metal failure, high strength steels, forming limits, non-linear strain paths, forming history
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-105211 (URN)10.1016/j.jmatprotec.2014.05.028 (DOI)000340300400059 ()
Note

Funders: SSF ProViking project entitled "SuperLight Steel Structures"

Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2017-12-05
5. Stochastic analysis of a sheet metal assembly considering its manufacturing process
Open this publication in new window or tab >>Stochastic analysis of a sheet metal assembly considering its manufacturing process
2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In order to accurately predict the mechanical properties of a sheet metal assembly it has been shown important to account for how the geometry and material properties are affected by the manufacturing process. It is also of a great interest to predict the variations of important responses, and how these variations depend on the manufacturing process.

In this study, the variation of properties during the multi-stage manufacturing process of a sheet metal assembly is evaluated and the variability of a response due to loading is studied. A methodology to investigate how variations evolve during the assembling process is presented. The multi-stage assembling process is virtually segmented, such that stochastic analyses of each process stage are performed and coupled to succeeding stages in order to predict the variation in properties of the final assembly. The methodology is applied to an industrial assembly and experimental validations have been conducted. The prediction of the geometry of the final assembly is in good agreement with the experimental results, while the prediction of the variation of this geometry is in fair agreement.

Keyword
Finite element simulation, Assembly, Sheet metal, Forming, Monte Carlo analysis, Chaining of manufacturing processes
National Category
Metallurgy and Metallic Materials Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-106636 (URN)
Available from: 2014-05-16 Created: 2014-05-16 Last updated: 2014-05-16Bibliographically approved

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