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Elastic Press and Die Deformations in Sheet Metal Forming Simulations
Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.ORCID iD: 0000-0002-6526-976X
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Never before has the car industry been as challenging, interesting, and demanding as it is today. New and advanced techniques are being continuously introduced, which has led to increasing competition in an almost ever-expanding car market. As the pace and complexity heightens in the car market, manufacturing processes must advance at an equal speed.

An important manufacturing process within the automotive industry, and the focus of this thesis, is sheet metal forming (SMF). Sheet metal forming is used to create door panels, structural beams, and trunk lids, among other parts, by forming sheets of metal in press lines with stamping dies. The SMF process has been simulated for the past couple of decades with finite element (FE) simulations, whereby one can predict factors such as shape, strains, thickness, springback, risk of failure, and wrinkles. A factor that most SMF simulations do not currently include is the die and press elasticity. This factor is handled manually during the die tryout phase, which is often long and expensive.

The importance of accurately representing press and die elasticity in SMF simulations is the focus of this research project. The research objective is to achieve virtual tryout and improved production support through SMF simulations that consider elastic die and press deformations. Loading a die with production forces and including the deformations in SMF simulations achieves a reliable result. It is impossible to achieve accurate simulation results without including the die deformations.

This thesis also describes numerical methods for optimizing and compensating tool surfaces against press and die deformations. In order for these compensations to be valid, it is imperative to accurately represent dies and presses. A method of measuring and inverse modeling the elasticity of a press table has been developed and is based on digital image correlation (DIC) measurements and structural optimization with FE software.

Optimization, structural analysis, and SMF simulations together with experimental measurements have immense potential to improve simulation results and significantly reduce the lead time of stamping dies. Last but not least, improved production support and die design are other areas that can benefit from these tools.

Abstract [sv]

Aldrig tidigare har bilindustrin varit så utmanande, intressant och spännande som idag. Ny och avancerad teknik introduceras i en allt snabbare takt vilket leder till ständigt ökande konkurrens på en, nästan ständigt, ökande bilmarknad. Den ständigt ökande komplexiteten ställer även krav på tillverkningsprocesserna.

En viktig process, som denna licentiatuppsats fokuserar på, är pressning av plåt. Tillverkningstekniken används för att forma plåtar till dörrpaneler, strukturbalkar, motorhuvar, etc. Plåtar formas med hjälp av pressverktyg monterade i plåtformningspressar. 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 hanteras istället manuellt under, den oftast långa och dyra, inprovningsfasen.

Detta projekt har visat på vikten av att representera press och verktygsdeformationer i plåtformningssimuleringar. Detta demonstreras genom en analys av ett verkligt pressverktyg som belastas med produktionskrafter. Det är inte möjligt att uppnå bra simuleringsresultat utan att inkludera verktygsdeformationer i simuleringsmodellen.

Uppsatsen beskriver även numeriska metoder för att optimera och kompensera verktygsytor mot press och verktygsdeformationer. För att dessa kompenseringar ska stämma är det viktigt att man representerar både verktyg och press på ett korrekt sätt. Förslag på en metod för att mäta och inversmodellera pressdeformationer har utvecklats, metoden är baserad på mätningar med DIC-systemet ARAMIS och optimering i FE-mjukvaror.

Optimering, strukturanalys, och plåtformningsanalys tillsammans med experimentella mätningar har en stor potential att förbättra plåtformningssimuleringar samt reducera ledtiden för pressverktyg. Sist men inte minst, andra positiva effekter är en enklare och smidigare konstruktionsprocess och förbättrad produktionssupport.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2017.
Series
Blekinge Institute of Technology Licentiate Dissertation Series, ISSN 1650-2140 ; 2
Keyword [en]
Sheet Metal Forming, Stamping Die, Stamping Press, Structural Analysis, Finite Element Simulation, Optimization, Digital Image Correlation, Inverse Modeling
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:bth-15481ISBN: 978-91-7295-345-1 (print)OAI: oai:DiVA.org:bth-15481DiVA: diva2:1156163
Presentation
2017-12-14, 10:00 (Swedish)
Opponent
Supervisors
Funder
VINNOVA, 2016-03324
Available from: 2017-11-10 Created: 2017-11-10 Last updated: 2017-12-08Bibliographically approved
List of papers
1. Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door
Open this publication in new window or tab >>Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door
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2016 (English)In: IOP Conference Series: Materials Science and Engineering, 2016, Vol. 159, no 1, 012021Conference paper, Published paper (Refereed)
Abstract [en]

The quality of sheet metal formed parts is strongly dependent on the tribology, friction and lubrication conditions that are acting in the actual production process. Although friction is of key importance, it is currently not considered in detail in stamping simulations. This paper presents a selection of results considering friction and lubrication modeling in sheet metal forming simulations of the Volvo XC90 right rear door inner. For this purpose, the TriboForm software is used in combination with the AutoForm software. Validation of the simulation results is performed using door inner parts taken from the press line in a full-scale production run. The results demonstrate the improved prediction accuracy of stamping simulations by accounting for accurate friction and lubrication conditions, and the strong influence of friction conditions on both the part quality and the overall production stability. © Published under licence by IOP Publishing Ltd.

Keyword
Drawing (forming), Friction, Metal forming, Sheet metal, Stamping, Tribology, Friction conditions, Full-scale production, Lubrication condition, Lubrication models, Part quality, Prediction accuracy, Production process, Stamping simulations, Lubrication
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:bth-14041 (URN)10.1088/1757-899X/159/1/012021 (DOI)2-s2.0-85014714526 (Scopus ID)
Conference
International Deep Drawing Research Group Conference on Challenges in Forming High-Strength Sheets, IDDRG , Linz
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-11-10Bibliographically approved
2. Introduction of elastic die deformations in sheet metal forming simulations
Open this publication in new window or tab >>Introduction of elastic die deformations in sheet metal forming simulations
2016 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146Article in journal (Refereed) Epub ahead of print
Abstract [en]

Simulations of sheet metal forming (SMF) with finite element models (FE-models) for stamped parts in the car industry are useful for detecting and solving forming problems. However, there are several issues that are challenging to analyze. Virtual tryout and analyzes of stamping dies in running production are two important cases where many of these challenging issues are present. Elastic deformations of dies and press lines and a physically based friction model is often missing when these types of cases are analyzed. To address this, this research aims to develop a method wherein the results of two separate FE-models are combined to enable SMF simulations with the inclusion of elastic tool and press deformations. The two FE-models are one SMF model with two-dimensional (2D) rigid tool surfaces and one structural model of the die and press. The structural model can predict surface shapes and pressure distributions for a loaded stamping die. It can also visualize relatively large and unexpected deformations of the die structure. The recommended method of transferring the deformations from the structural model to the 2D surfaces is through an FE technique called submodeling. The subsequent SMF simulations show that the method for calculating and using the deformed surfaces together with the TriboForm friction model yields a result that matches measured draw-in and strains. It is verified that the ability to virtually deform a die and include the resulting geometry in forming simulations is of high importance. It can be used for the virtual tryout and optimization of new dies or analyses of existing dies in running production. It is suggested that future research focus on a more efficient and automated workflow. More experimental data and simulations are also needed to verify the assumptions made for the simulation models. This will enable the method to be adopted in a reliable way for standard SMF simulations. © 2017.

Place, publisher, year, edition, pages
Elsevier Ltd, 2016
Keyword
Elastic tooling, Friction, Sheet metal forming, Structural analysis, Surface compensation, Automotive industry, Computer supported cooperative work, Deformation, Dies, Metal forming, Presses (machine tools), Sheet metal, Stamping, Tribology, Automated workflow, Forming simulations, Friction modeling, Physically based, Research focus, Structural modeling, Two Dimensional (2 D), Finite element method
National Category
Materials Engineering
Identifiers
urn:nbn:se:bth-14475 (URN)10.1016/j.ijsolstr.2017.05.009 (DOI)2-s2.0-85019444887 (Scopus ID)
Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-11-10Bibliographically approved
3. Framework for Simulation-Driven Design of Stamping Dies Considering Elastic Die and Press Deformations
Open this publication in new window or tab >>Framework for Simulation-Driven Design of Stamping Dies Considering Elastic Die and Press Deformations
2017 (English)In: AIP Conference Proceedings, American Institute of Physics (AIP), 2017, Vol. 1896, 010001Conference paper, Published paper (Refereed)
Abstract [en]

Sheet metal forming (SMF) simulations are used extensively throughout the development phase of industrialstamping dies. In these SMF simulations, the die and press are normally considered as rigid. Previous research has howevershown that elastic deformation in these parts has a significant negative impact on process performance. This paperdemonstrates methods for counteracting these negative effects, with a high potential for improved production support anda reduced lead time through a shorter try-out process. A structural finite element model (FE-model) of a simplified die isstudied. To account for elastic deformation, the blankholder surfaces are first virtually reworked by adjusting the nodalpositions on the die surfaces attaining a pressure distribution in accordance to the design phase SMF simulations with rigidsurfaces. The elastic FE-model with reworked surfaces then represents a stamping die in running production. The die isnow assumed to be exposed to changed process conditions giving an undesired blankholder pressure distribution. Thechanged process conditions could for example be due to a change of press line. An optimization routine is applied tocompensate the negative effects of the new process conditions. The optimization routine uses the contact forces acting onthe shims of the spacer blocks and cushion pins as optimization variables. A flexible simulation environment usingMATLAB and ABAQUS is used. ABAQUS is executed from MATLAB and the results are automatically read back intoMATLAB. The suggested optimization procedure reaches a pressure distribution very similar to the initial distributionassumed to be the optimum, and thereby verifying the method. Further research is needed for a method to transform thecalculated forces in the optimization routine back to shims thicknesses. Furthermore, the optimization time is relativelylong and needs to be reduced in the future for the method to reach its full potential.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-15392 (URN)10.1063/1.5008124 (DOI)
Conference
20th International ESAFORM Conference on Material Forming, Dublin
Funder
VINNOVA, 2016-03324
Available from: 2017-10-30 Created: 2017-10-30 Last updated: 2017-11-10Bibliographically approved
4. Characterizing the Elastic Behaviour of a Press Table throughTopology Optimization
Open this publication in new window or tab >>Characterizing the Elastic Behaviour of a Press Table throughTopology Optimization
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2017 (English)In: Journal of Physics: Conference Series / [ed] Volk W., Institute of Physics Publishing (IOPP), 2017, Vol. 896, 012101Conference paper, Published paper (Refereed)
Abstract [en]

Sheet metal forming in the car industry is a highly competitive area. The use ofdigital techniques and numerical methods are therefore of high interest for reduced costs andlead times. One method for reducing the try-out phase is virtual rework of die surfaces. Thevirtual rework is based on Finite Element (FE) simulations and can reduce and support manualrework. The elastic behaviour of dies and presses must be represented in a reliable way in FEmodelsto be able to perform virtual rework. CAD-models exists for nearly all dies today, butnot for press lines. A full geometrical representation of presses will also yield very large FEmodels.This paper will discuss and demonstrate a strategy for measuring and characterizing apress table for inclusion in FE-models. The measurements of the elastic press deformations iscarried out with force transducers and an ARAMIS 3D optical measurement system. The presstable is then inverse modelled by topology optimization using the recorded results as boundaryconditions. Finally, the press table is coupled with a FE-model of a die to demonstrate itsinfluence on the deformations. This indicates the importance of having a reliable representationof the press deformations during virtual rework.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keyword
Automotive industry, Finite element method, Flanges, Fracture, Fracture testing, High strength steel, Materials testing, Metal forming, Metal testing, Metals, Strain
National Category
Applied Mechanics
Identifiers
urn:nbn:se:bth-15394 (URN)10.1088/1742-6596/896/1/012068 (DOI)
Conference
36th IDDRG-2017 - MATERIALS MODELLING AND TESTING FOR SHEET METAL FORMING, MUNICH
Funder
VINNOVA, 2016-03324
Note

open access

Available from: 2017-10-30 Created: 2017-10-30 Last updated: 2017-11-10Bibliographically approved

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