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  • 1.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Elastic Press and Die Deformations in Sheet Metal Forming Simulations 2017Licentiate 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.

  • 2. Pilthammar, Johan
    et al.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hansson, Mårten
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pálsson, Einar
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Rutgersson, Wilhelm
    Cascade Control AB, SWE.
    Characterizing the Elastic Behaviour of a Press Table throughTopology Optimization2017In: Journal of Physics: Conference Series / [ed] Volk W., Institute of Physics Publishing (IOPP), 2017, Vol. 896, article id 012101Conference 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.

  • 3.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Volvo Cars, SWE.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Including die and press deformations in sheet metal forming simulations2016In: NUMISHEET 2016: 10TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES, PTS A AND B / [ed] Cardoso, RPR Yoon, JW Dick, RE Neto, ES DeSa, JMAC Adetoro, OB, IOP PUBLISHING LTD , 2016, article id UNSP 032036Conference paper (Refereed)
    Abstract [en]

    Structural analysis, in Abaqus, of a stamping die and subsequent morphing of the tool surfaces in AutoForm were performed to improve a sheet metal forming simulation. First, the tool surfaces of the XC90 rear door inner were scanned. They were not matching when the die was unloaded and could therefore not give any satisfying results in sheet metal forming simulations. Scanned surface geometries were then added to a structural FE-model of the complete stamping die and some influential parts of the production press. The structural FE-model was analysed with Abaqus to obtain the structural deformations of the die. The calculated surface shapes were then transferred to AutoForm where a forming simulation was performed. Results from the different sheet metal forming simulations were compared to measured draw in curves and showed a substantial increase in accuracy and ability to analyse dies in running production when the morphed surfaces were used.

  • 4.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Introduction of elastic die deformations in sheet metal forming simulations2018In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 151, no S1, p. 76-90Article in journal (Refereed)
    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.

  • 5.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Wall, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Framework for Simulation-Driven Design of Stamping Dies Considering Elastic Die and Press Deformations2017In: PROCEEDINGS OF THE 20TH INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING (ESAFORM 2017) / [ed] Brabazon D.,Ul Ahad I.,Naher S., American Institute of Physics (AIP), 2017, Vol. 1896, article id 010001Conference 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.

  • 6.
    Sigvant, M.
    et al.
    Volvo Cars, SWE.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, J.
    TriboForm Engn, NLD.
    Wiebenga, J. H.
    TriboForm Engn, NLD.
    Chezan, T.
    Tata Steel, NLD.
    Carleer, B.
    AutoForm Engn, DEU.
    van den Boogaard, A. H.
    Univ Twente, NLD.
    Friction and lubrication modelling in sheet metal forming simulations of the Volvo XC90 inner door2016In: NUMISHEET 2016: 10TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES, PTS A AND B / [ed] Cardoso, RPR Yoon, JW Dick, RE Neto, ES DeSa, JMAC Adetoro, OB, IOP PUBLISHING LTD , 2016, article id UNSP 032090Conference paper (Refereed)
    Abstract [en]

    The quality of sheet metal formed parts is strongly dependent on the 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 project results considering friction and lubrication modelling in stamping simulations of the Volvo XC90 inner door. For this purpose, the TriboForm software is used in combination with the AutoForm software. Validation of the simulation results is performed based on door-inner parts taken from the press line in a full-scale production run. The project results demonstrate the improved prediction accuracy of stamping simulations.

  • 7.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Falk, Johannes
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Experiments and FE-simulations of stretch flanging of DP-steels with different shear cut edge quality2017In: Journal of Physics: Conference Series / [ed] Volk W., Institute of Physics Publishing , 2017, Vol. 896, no 1, article id 012101Conference paper (Refereed)
    Abstract [en]

    Dual-Phase (DP) steels are today used in the automotive industry due to its large strength to weight ratio. However, the high strength of DP-steel does have a negative impact on the general formability in sheet metal forming. Unfavourable process conditions in the press shop will, on top of this, reduce the formability of DP-steels even more. This paper addresses the problem of edge fracture in stretch flanges in sheet metal parts made of DP-steel. The experimental part involves tests of ten different DP590 and DP780 steel grades with three different shear cut qualities. The influence on the fracture strain of the sample orientation of the shear cut are also studied by facing the burr away or towards the punch and testing samples with the cut edge parallel with the rolling direction and the transverse direction. The strains are measured with an ARAMIS system in each test, together with punch displacement and punch force. All tests are then simulated with AutoFormplus R7 and the results from these simulations are compared with the experimental results in order to find the appropriate failure strain for each combination of supplier, coating, thickness and shear cut quality. © Published under licence by IOP Publishing Ltd.

  • 8.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, J.
    TriboForm Engineering, NLD.
    Wiebenga, J. H.
    TriboForm Engineering, NLD.
    Chezan, T.
    Tata Steel, NLD.
    Carleer, B.
    AutoForm Engineering, DEU.
    Van Den Boogaard, A. H.
    University of Twente, NLD.
    Friction in Sheet Metal Forming Simulations: Modelling of New Sheet Metal Coatings and Lubricants2018In: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing , 2018, Vol. 418, no 1, article id 012093Conference paper (Refereed)
    Abstract [en]

    The quality of sheet metal formed parts is strongly dependent on the tribology and friction conditions that are acting in the actual forming process. These friction conditions are then dependent on the tribology system, i.e. the applied sheet material, coating and tooling material, the lubrication and process conditions. Although friction is of key importance, it is currently not considered in detail in sheet metal forming simulations. The current industrial standard is to use a constant (Coulomb) coefficient of friction, which limits the overall simulation accuracy. Since a few years back there is an ongoing collaboration on friction modelling between Volvo Cars, Tata Steel, TriboForm Engineering, AutoForm Engineering and the University of Twente. In previous papers by the authors, results from lab scale studies and studies of a door-inner part in Volvo Cars production have been presented. This paper focuses on the tribology conditions during early tryout of dies for new car models with an emphasis on the effect of the usage of new steel material coatings and lubricants on forming results. The motivation for the study is that the majority of the forming simulations at Volvo Cars are performed to secure the die tryout, i.e. solve as many problems as possible in forming simulations before the final design of the die and milling of the casting. In the current study, three closure parts for the new Volvo V60 model have been analysed with both Coulomb and TriboForm friction models. The simulation results from the different friction models are compared using thickness measurements of real parts, and 3D geometry scanning data of the parts. Results show the improved prediction accuracy of forming simulations when using the TriboForm friction model, demonstrating the ability to account for the effect of new sheet metal coatings and lubricants in sheet metal forming simulations. © Published under licence by IOP Publishing Ltd.

  • 9.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, J.
    TriboForm Engineering, NLD.
    Wiebenga, J. H.
    TriboForm Engineering, NLD.
    Chezan, Toni
    Tata Steel, NLD.
    Carleer, Bart
    AutoForm Engineering Deutschland GmbH, DEU.
    Van Den Boogaard, A. H.
    University of Twente, NLD.
    Friction in Sheet Metal Forming: Forming Simulations of Dies in Try-Out2018In: Journal of Physics: Conference Series, Institute of Physics Publishing , 2018, no 1Conference paper (Refereed)
    Abstract [en]

    The quality of sheet metal formed parts is strongly dependent on the tribology and friction conditions that are acting in the actual forming process. This paper focuses on the tribology conditions during early try-out of dies for new car models. The motivation for the study is that the majority of the forming simulations at Volvo Cars are performed to secure the die try-out, i.e. solve as many problems as possible in forming simulations before the final design of the die and milling of the casting. In the current study, three closure parts for the new Volvo V60 model have been analysed with both Coulomb and TriboForm friction models. The simulation results from the different friction models are compared using thickness measurements of real parts, and 3D geometry scanning data of the parts. Results show the improved prediction capability of forming simulations when using the TriboForm friction model, demonstrating the ability to accurately describe try-out conditions in sheet metal forming simulations. © 2018 Institute of Physics Publishing. All rights reserved.

  • 10.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, Jeroen
    TriboForm Engineering, NLD.
    Wiebenga, J. H.
    TriboForm Engineering, NLD.
    Chezan, T.
    Tata Steel, NLD.
    Carleer, Bart
    AutoForm Engineering, DEU.
    Van Den Boogaard, A. H.
    University of Twente, NLD.
    Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door2016In: IOP Conference Series: Materials Science and Engineering, 2016, Vol. 159, no 1, article id 012021Conference 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.

  • 11.
    Tatipala, Sravan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Volvo Cars.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering. Volvo Cars.
    Wall, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Johansson, Christian
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Introductory study of sheet metal forming simulations to evaluate process robustness2018In: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing (IOPP), 2018, Vol. 418, article id 012111Conference paper (Refereed)
    Abstract [en]

    The ability to control quality of a part is gaining increased importance with desires to achieve zero-defect manufacturing. Two significant factors affecting process robustness in production of deep drawn automotive parts are variations in material properties of the blanks and the tribology conditions of the process. It is imperative to understand how these factors influence the forming process in order to control the quality of a formed part. This paper presents a preliminary investigation on the front door inner of a Volvo XC90 using a simulation-based approach. The simulations investigate how variation of material and lubrication properties affect the numerical predictions of part quality. To create a realistic lubrication profile in simulations, data of pre-lube lubrication amount, which is measured from the blanking line, is used. Friction models with localized friction conditions are created using TriboForm and is incorporated into the simulations. Finally, the Autoform-Sigmaplus software module is used to create and vary parameters related to material and lubrication properties within a user defined range. On comparing and analysing the numerical investigation results, it is observed that a correlation between the lubrication profile and the predicted part quality exists. However, variation in material properties seems to have a low influence on the predicted part quality. The paper concludes by discussing the relevance of such investigations for improved part quality and proposing suggestions for future work.

  • 12.
    Tatipala, Sravan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Suddapalli, Nikshep Reddy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Sigvant, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Johansson, Christian
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Simulation-Driven Design Approach for Design and Optimization of Blankholder2017In: Journal of Physics: Conference Series (JPCS), Institute of Physics Publishing (IOPP), 2017, Vol. 896, article id 012045Conference paper (Refereed)
    Abstract [en]

    Reliable design of stamping dies is desired for efficient and safe production. The design of stamping dies are today mostly based on casting feasibility, although it can also be based on criteria for fatigue, stiffness, safety, economy. Current work presents an approach that is built on Simulation Driven Design, enabling Design Optimization to address this issue. A structural finite element model of a stamping die, used to produce doors for Volvo V70/S80 car models, is studied. This die had developed cracks during its usage. To understand the behaviour of stress distribution in the stamping die, structural analysis of the die is conducted and critical regions with high stresses are identified. The results from structural FE-models are compared with analytical calculations pertaining to fatigue properties of the material. To arrive at an optimum design with increased stiffness and lifetime, topology and free-shape optimization are performed. In the optimization routine, identified critical regions of the die are set as design variables. Other optimization variables are set to maintain manufacturability of the resultant stamping die. Thereafter a CAD model is built based on geometrical results from topology and free-shape optimizations. Then the CAD model is subjected to structural analysis to visualize the new stress distribution. This process is iterated until a satisfactory result is obtained. The final results show reduction in stress levels by 70% with a more homogeneous distribution. Even though mass of the die is increased by 17 %, overall, a stiffer die with better lifetime is obtained. Finally, by reflecting on the entire process, a coordinated approach to handle such situations efficiently is presented.

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