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Simulation of Sheet Metal Forming using Elastic Stamping Dies
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Volvo Cars, SWE.ORCID iD: 0000-0002-6526-976x
Dynamore Nordic.
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Volvo Cars, SWE.ORCID iD: 0000-0002-7730-506x
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. (Student).
Show others and affiliations
2019 (English)In: Proc. of the 12th European LS-DYNA Conference 2019, 2019, 2019Conference paper, Published paper (Other academic)
Abstract [en]

Simulation of sheet metal forming is one of the major applications of LS-DYNA. Today, a majority of the forming industry is using Finite Element models to design the stamping dies in order to prevent excessive thinning, wrinkling and producing parts within tolerance by compensating for springback deformation. All these simulations are made using the assumption of rigid forming surfaces. Depending on the type of press, tool design and sheet metal part, this assumption could prove to be incorrect which yields a forming result that depends on the elastic deformation of the stamping die and in some cases the entire stamping press. Such deformations are usually compensated during die try-out by manual rework which is costly and time consuming.

This paper presents the result of a study performed at Volvo Cars press shop in Olofström, Sweden, aiming at determining computational methods to introduce elastic stamping dies in the sheet metal forming simulations in order to minimize manual rework by performing a virtual tryout of the stamping die. The methodology to model the stamping die and the forming surfaces in LS-DYNA are presented and a simulation model is gradually improved from using nominal rigid CAD surfaces through scanned tool surfaces and finishing with an elastic model of the stamping die assembly. The part used in the study is the side door inner for Volvo XC90 and comparisons are continuously made between simulations results and measurements on parts from running production.

Place, publisher, year, edition, pages
2019.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:bth-20040OAI: oai:DiVA.org:bth-20040DiVA, id: diva2:1449445
Conference
The 12th European LS-DYNA Conference 2019, 14-16 May, 2019, Koblenz, Germany
Funder
Vinnova, 2016-03324Available from: 2020-06-30 Created: 2020-06-30 Last updated: 2020-08-24Bibliographically approved
In thesis
1. Towards Virtual Tryout and Digital Twins: Enhanced Modeling of Elastic Dies, Sheet Materials, and Friction in Sheet Metal Forming
Open this publication in new window or tab >>Towards Virtual Tryout and Digital Twins: Enhanced Modeling of Elastic Dies, Sheet Materials, and Friction in Sheet Metal Forming
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Competition and complexity in the global car market are continuously increasing. To gain an edge in the market while making a profit, each competitor in the market needs a strong focus on technology development. Such a focus will increase the value of the product for the customers. On top of the challenges of developing the technical content of the cars, it is equally important to develop the manufacturing processes. This will enable the production of technically advanced and attractive products at a competitive cost.

An important manufacturing process within the automotive industry, and the focus of this PhD thesis, is sheet metal forming (SMF). The SMF process has been simulated for the past few decades with finite element (FE) simulations, whereby factors such as shape, strains, thickness, springback, risk of failure, and wrinkles can be predicted. A factor that most SMF simulations do not currently include is die and press elasticity, limiting the reliability of SMF simulations for virtual die tryout and digital twins. This factor is instead handled manually during the die tryout, which is time-consuming and expensive.

The importance of accurately representing press and die elasticity in SMF simulations is the focus of this research project. The objective is to achieve virtual tryout and production support through SMF simulations that consider elastic die and press deformations. Accurate simulations of die tryout, or dies in running production, are found to be impossible without the inclusion of reliable representations of elastic dies and presses.

Accurate CAD models of stamping dies are common. Strategies are presented for how to include them in SMF simulations models that are easy to set up and fast to solve. Full representations of presses are rarer. Methods for measuring and inverse modeling the elasticity of presses are therefore presented together with an overview from the literature of other methods. A unified method that is reliable and cost-efficient for the stamping industry is of high interest.

SMF simulations with elastic dies will only yield accurate predictions if reliable models of sheet materials and lubrication systems are included. Friction in particular is highly dependent on die deformations since contact pressure is an important parameter in determining the friction level. Reliable models for both friction and sheet materials are dependent on accurate experimental data and characterization methods.

Including elastic die and press deformations in SMF simulations, together with reliable representations of friction and sheet materials, has immense potential to reduce the lead time of stamping dies. The simulation methods that include elasticity will also be vital for more accurate digital twins of press lines.

Abstract [sv]

Konkurrens och komplexitet ökar ständigt inom den globala bilmarknaden. För att skapa konkurrensfördelar behöver företag som verkar på marknaden fokusera på teknikutveckling, vilket i sin tur ökar produkternas värde för konsumenterna. Samtidigt som man utvecklar det tekniska innehållet i sina produkter så är det lika viktigt att utveckla sina tillverkningsprocesser. Välutvecklade tillverkningsprocesser möjliggör produktion av tekniskt avancerade, och attraktiva produkter, till en konkurrenskraftig kostnad.

En viktig process, som denna avhandling fokuserar på, är pressning av plåt. Plåtformningsprocessen simuleras sedan ett par decennium tillbaka med Finita Element (FE) simuleringar. Man kan på så sätt prediktera form, töjningar, tjocklek, återfjädring, rynkor, risk för försträckning och sprickor m.m. En faktor som för tillfället inte inkluderas i näst intill alla plåtformningssimuleringar är elastiska press- och verktygsdeformationer. Detta begränsar möjligheterna att använda plåtformningssimulering för virtuell inprovning och att skapa pålitliga digitala tvillingar. Elastiska deformationer hanteras istället manuellt under, den oftast långa och dyra, inprovningsfasen.

Detta projekt visar på vikten av att inkludera press- och verktygsdeformationer genom simuleringar av verkliga pressverktyg. I de simulerade fallen är det inte möjligt att uppnå bra resultat för inprovning och produktionssupport utan att inkludera verktygsdeformationer i modellen.

CAD-modeller finns för nästan alla pressverktyg idag. Strategier för att inkludera elastiska verktygsgeometrier i simuleringar presenteras. Modellerna är enkla att skapa och snabba att lösa. Kompletta CAD-modeller av pressar är inte lika vanligt. Metoder för att mäta upp pressar och inkludera i simuleringar är därför också presenterade, tillsammans med exempel på andra metoder från vetenskaplig litteratur. En standardiserad metod för plåtformningsindustrin är av intresse.

Simuleringar med elastiska verktyg ger endast pålitliga resultat om plåt och friktion representeras på ett bra sätt. Speciellt friktion är starkt beroende av verktygsdeformationer då kontakttryck är en viktig faktor i friktionsmodeller. Material- och friktionsmodeller vilar på väl fungerande metoder för karaktärisering utifrån god experimentell data.

Plåtformningssimuleringar med elastiska verktyg, tillsammans med pålitliga modeller av plåtmaterial och friktionssystem, har en stor potential att reducera ledtiden för pressverktyg. Dessa metoder kommer också att vara viktiga i skapandet av digitala tvillingar av verktyg och pressar.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2020
Series
Blekinge Institute of Technology Doctoral Dissertation Series, ISSN 1653-2090 ; 7
Keywords
Sheet Metal Forming, Stamping Die, Virtual Tryout, Digital Twin, Stamping Press, Structural Analysis, Finite Element Simulation, Optimization, Digital Image Correlation, Inverse Modeling
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:bth-20047 (URN)978-91-7295-406-9 (ISBN)
Public defence
2020-09-22, J1630, 13:00 (English)
Opponent
Supervisors
Funder
Vinnova, 2016-03324Vinnova, 2018-03331
Available from: 2020-08-25 Created: 2020-08-24 Last updated: 2020-12-14Bibliographically approved

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https://www.dynalook.com/conferences/12th-european-ls-dyna-conference-2019/forming/schill_dynamore_nordic.pdf

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Pilthammar, JohanSigvant, Mats

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