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Sökning: WFRF:(Pilthammar Johan)

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1.
  • Pilthammar, Johan, 1987-, et al. (författare)
  • Framework for Simulation-Driven Design of Stamping Dies Considering Elastic Die and Press Deformations
  • 2017
  • Ingår i: PROCEEDINGS OF THE 20TH INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING (ESAFORM 2017). - : American Institute of Physics (AIP). - 9780735415805
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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2.
  • Sigvant, Mats, et al. (författare)
  • Friction in sheet metal forming : Influence of surface roughness and strain rate on sheet metal forming simulation results
  • 2019
  • Ingår i: Procedia Manufacturing. - : Elsevier B.V.. ; , s. 512-519
  • Konferensbidrag (refereegranskat)abstract
    • 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 body parts at Volvo Cars, both parts in early tryout for new car models as well as parts in production have been presented. However, the introduction of a new friction model in the sheet metal forming simulations forces the user to gain knowledge about accurate values for new input parameters and question current modeling assumptions. This paper presents results from studies on the influence on the sheet metal forming simulation results from stamping die surface roughness and introduction of strain rate sensitivity in the sheet material model. The study will use a FE-model of a part presented in previous papers. © 2019 The Authors. Published by Elsevier B.V.
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3.
  • Tatipala, Sravan, 1993-, et al. (författare)
  • Introductory study of sheet metal forming simulations to evaluate process robustness
  • 2018
  • Ingår i: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics Publishing (IOPP).
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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4.
  • Barlo, Alexander, et al. (författare)
  • A Study of the Boundary Conditions in the ISO-16630 Hole Expansion Test
  • 2022
  • Ingår i: IOP Conference Series. - : IOP Publishing. - 1757-8981 .- 1757-899X. ; 1238
  • Tidskriftsartikel (refereegranskat)abstract
    • As new and more advanced sheet metal materials are introduced to the market, more accurate techniques for determination of failure limits are needed. One area that needs attention is edge formability, where the ISO-16630 standardized Hole Expansion Test currently is used to express this through the Hole Expansion Ratio. Over the years, this standard has been criticized for producing a large scatter in repeated tests. This paper investigates a new setup for the Hole Expansion Test which introduces draw beads into the setup to ensure sufficient restraining of the specimen during the test in an effort to reduced the scatter. In total 62 tests of a DP800 steel alloy were executed, but a large scatter in the results were still seen. It was therefore concluded that a lack of restraining force in the Hole Expansion Test was not the primary cause of the reported scatter seen in other tests.
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5.
  • Barlo, Alexander, M.Sc. Eng. 1994-, et al. (författare)
  • Creating a Virtual Shadow of the Manufacturing of Automotive Components
  • 2024
  • Konferensbidrag (refereegranskat)abstract
    • Within the automotive industry, there is an increasing demand for a paradigmshift in terms of which materials are used for the manufacturing of the automotive body. Globalclimate goals are forcing a rapid adaption of new, advanced, sustainable material grades suchas the fossil free steels and materials containing higher scrap content. With the introduction ofthese new and untested materials, methods for accounting for variation in material propertiesare needed directly in the press lines.The following study will focus on creating an initial virtual shadow of the manufacturing of aVolvo XC90 inner door panel through the application of Artificial Neural Networks (ANN). Thevirtual shadow differs from the concept of the digital twin by only being a virtual representationof the production line, with training data generated exclusively by numerical simulations, andhaving no automated communication with the physical press line control system. The virtualshadow can be used as an assistance to the press line operators to see how different press linesettings and material parameter variations will impact the quality of the stamped component.The study aims to validate the virtual shadow through accurate predictions of the materialdraw-in measured in the physical press line.
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6.
  • Barlo, Alexander, M.Sc. Eng. 1994-, et al. (författare)
  • Determination of Edge Fracture Limit Strain for AHSS in the ISO-16630 Hole Expansion Test
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • With the increased demand for application of sustainable materials and lightweight structures, the sheet metal forming industry is forced to push existing materials to the limits. One area where this is particular difficult is when it comes to assessing the formability limit for sheet edges. For decades, the ISO-16630 Hole Expansion Test (HET) has been the industry standard for expressing the edge formability of sheet metals through the Hole Expansion Ratio (HER). However, in recent years, this test has been criticized for its high scatter in results for repeated experiments. This scatter has been suspected to be caused by the operator-reliant post-processing of the test, or variations in the cutting conditions for the different test specimens. This study investigates the impact of shifting the evaluation point of the test from the through-thickness crack to the onset of surface failure on the reported scatter, as well as performs inverse modeling of the Hole Expansion Test to obtain an edge limit strain value.
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7.
  • Barlo, Alexander, et al. (författare)
  • Failure Prediction of Automotive Components Utilizing a Path Independent Forming Limit Criterion
  • 2022
  • Ingår i: Key Engineering Materials<em></em>. - : Trans Tech Publications Inc.. - 9783035717594 ; , s. 906-916
  • Konferensbidrag (refereegranskat)abstract
    • An area in the automotive industry that receives a lot of attention today is the introduction of lighter and more advanced material grades in order to reduce carbon emissions, both during production and through reduced fuel consumption. As the complexity of the introduced materials and component geometries increases, so does the need for more complex failure prediction approaches. A proposed path-independent failure criterion, based on a transformation of the limit curve into an alternative evaluation space, is investigated. Initially, the yield criterion used for this transformation of the limit curve was investigated. Here it was determined that the criterion for the transformation could not be decoupled from the material model used for the simulation. Subsequently, the approach using the transformed limit curve was tested on an industrial case from Volvo Cars, but a successful failure prediction was not obtained. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.
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8.
  • Barlo, Alexander, M.Sc. Eng. 1994- (författare)
  • Failure Prediction of Complex Load Cases in Sheet Metal Forming : Emphasis on Non-Linear Strain Paths, Stretch-Bending and Edge Effects
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • With the increased focus on reducing carbon emissions in today’s society, several industries have to overcome new challenges, where especially the automotive industry is under a lot of scrutiny to deliver improved and more environmentally friendly products. To meet the demands from customers and optimize vehicles aerodynamically, new cars often contain complex body geometries, together with advanced materials that are introduced to reduce the total vehicle weight. With the introduction of the complex body components and advanced materials,one area in the automotive industry that has to overcome these challenges is manufacturing engineering, and in particular the departments working with the sheet metal forming process. In this process complex body component geometries can lead to non-linear strain paths and stretch bending load cases, and newly introduced advanced materials can be prone to exhibit behaviour of edge cracks not observed in conventional sheet metals. This thesis takes it onset in the challenges seen in industry today with predicting failure of the three complex load cases: Non-Linear Strain Paths, Stretch-Bending,and Edge Cracks. Through Finite Element simulation attempts are made to accurately predict failure caused by aforementioned load cases in industrial components or experimental setups in an effort to develop post-processing methods that are applicable to all cases.
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9.
  • Barlo, Alexander, M.Sc. Eng. 1994-, et al. (författare)
  • Investigation of Temperature Impact on Friction Conditions in Running Production of Automotive Body Components
  • 2024
  • Konferensbidrag (refereegranskat)abstract
    • During the running production of automotive body components drifts in theprocess window is seen causing problems with non-conforming parts. Up until now, these driftshave been counter-acted based on the knowledge and experience of the press line operators.This experience-based process control will however become more troublesome in the future asrecycled material grades will undoubtedly present larger in-coil variations in material parametersand effect also the friction conditions from component to component.The following study will present two cases from production of the Volvo XC60. For thetwo cases, the initial simulations made for the components showed a safe part, but duringrunning production failure occurred suspected to be due to temperature effects in the tribologysystem. The study will furthermore present updated simulations considering developing thermaleffects to replicate the failures, as well as present both standard and thermal simulations of theadjustments made in production.
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10.
  • Barlo, Alexander, M.Sc. Eng. 1994-, et al. (författare)
  • Proposal of a New Tool for Pre-Straining Operations of Sheet Metals and an Initial Investigation of CR4 Mild Steel Formability
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • With the increased focus on reducing carbon emissions in the automotive industry, more advanced materials are introduced to reduce the vehicle weight, and more complex component geometries are designed to both satisfy customer demands and to optimize the vehicle aerodynamically. With the increase in component complexity, the strain paths produced during the forming operation of car body components often display a highly non-linear behavior which makes the task of failure prediction during the manufacturing feasibility studies more difficult. Therefore, CAE engineers need better capabilities to predict failure induced by strain path nonlinearity. This study proposes a new tool designed for creating bi-linear strain paths, by performing a pre-strain of a sheet large enough to cut out Nakajima specimens to perform the post-straining in any direction. From five pre-straining tests the tool present a stable pre-straining operation with a uniform strain field in a radius of 100 [mm] from the centre, corresponding to the region of interest of a Nakajima specimen. From the five pre-strained samples, different Nakajima specimens are cut transverse and longitudinal to the rolling direction and a failure prediction approach in an alternative, path independent evaluation space was used to predict the onset of necking with promising results.
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11.
  • Chezan, A. R., et al. (författare)
  • Material variability effects on automotive part production process
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • The current efforts to reduce the carbon footprint throughout the chain in the automotive industry by increased use of recycled materials poses new challenges for materials production and their use. The increase of steel scrap fraction in the current primary steel making processes, used for producing steel sheet metal for automotive components, possibly affects the material properties variability beyond the limits observed in the materials produced today despite mitigating actions in steel production. In this paper material variability increase was modelled by selecting deterministic values outside the range of the material grade used to design and manufacture an automotive part. The values were selected from an experimental data set representing the cold rolled mild steels material class range. The effects were studied numerically on a reverse engineered model of an existing automotive part production process. It was found that the manufacturing feasibility in this particular case is mainly affected by the weighted average plastic strain ratio and less by the degree of planar anisotropy.
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12.
  • Manopulo, N., et al. (författare)
  • On the mechanics of edge cracking and the reliable determination of edge formability limits
  • 2021
  • Ingår i: INTERNATIONAL DEEP-DRAWING RESEARCH GROUP CONFERENCE (IDDRG 2021). - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • Blanked edge surfaces are rough and hardened. They therefore lead to inhomogeneous deformation on the edge, which can trigger localization within the shear affected zone (up to few mm from the edge). The size and extent of these phenomena are primarily a function of the shearing process and are only marginally coupled to the global/homogeneous deformation behavior of the blank A direct numerical simulation of such local deformation effects would require a prohibitively high resolution to capture the microgeometry of the edge and thus remains unfeasible in the current industrial practice. A predictive model can therefore only be achieved by determining limit strains on the edge, which are compatible with the homogeneous numerical framework used. The present contribution aims discussing the basic mechanics of edge cracking based on tensile tests with edges blanked with different die clearances. The local and global strain evolutions in the vicinity of the edge are analysed and a new evaluation procedure is proposed for the reliable determination of limit strains. The application of this method in industrial context is also discussed.
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13.
  • Ottosson, P., et al. (författare)
  • Substitutive models of press deflections for efficient numerical die cambering
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • Cost and time for stamping die tryouts are significant within the car industry. A major contributing factor is that elastic deflections of stamping dies and presses are usually not considered during the virtual die design and forming simulation phase. Active surfaces of stamping dies are only cambered based on previous experiences of tool types and stamping presses. However, almost all stamping dies and presses are unique, and available experiences are not valid for new sheet materials. This leads to component deviations and often several loops of tool adjustments are needed. Previously partners within the SMART Advanced Manufacturing research project CAMBER have developed advanced deflection measuring devices to quantify the elastic deformations of stamping presses. Using these measurements, cambering methodologies can be utilized in sheet metal forming simulations. In this paper numerical substitutive stamping press models are described which are capable of compensating for measured stamping press dynamics. The result show that a numerical compensated tool can improve the contact by over 80% compared to the corresponding contact without compensation.
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14.
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15.
  • Pilthammar, Johan, et al. (författare)
  • An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.
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16.
  • Pilthammar, Johan, et al. (författare)
  • BBC05 with non-integer exponent and ambiguities in Nakajima yield surface calibration
  • 2021
  • Ingår i: International Journal of Material Forming. - : SPRINGER FRANCE. - 1960-6206 .- 1960-6214. ; 14:4, s. 577-592
  • Tidskriftsartikel (refereegranskat)abstract
    • Reliable sheet metal forming simulations depend on accurate descriptions of real process conditions. These conditions include material behavior, lubrication systems, tool deformations, press dynamics, and more. Research on material models is the most mature area for describing these conditions in a reliable way. Several advanced and flexible models exists. This study focuses on two versions of yield criteria for sheet materials that are assumed to follow the plane stress assumption: the BBC05 model with integer exponent and the BBC05 model with non-integer exponent. The literature has previously described the BBC05 model with integer exponent. This paper elaborates on a modified version with non-integer exponent that offers more flexibility in the mathematical description. Furthermore, it outlines the implementation of this material model and similar yield criteria as user subroutines in finite element software. As mathematical flexibility increases, it enables more physically correct material approximations. However, it also becomes more challenging to calibrate because of ambiguities due to a larger number of mathematical variables. These ambiguities is demonstrated by using a Nakajima test without lubrication during inverse modeling of parameters for the BBC05 model. It shows that it is impossible to accurately identify the physically correct combination of friction coefficient and the yield surface exponent, k, using strain distributions and punch force. It is suggested to use two Nakajima tests in the inverse modeling process where friction can be neglected due to testing conforming to ISO12004-2. One test that corresponds to equi-biaxial strain of the sheet, and one that corresponds to plane strain in the transverse direction of the sheet. By utilizing these samples in the inverse modeling it is possible to separate friction from the exponent k. A non-integer value of k is found to yield the most reliable prediction of strains and forces in the simulations, thereby also demonstrating the need of flexible yield surface models such as BBC05 with non-integer exponent, YLD2000, Vegter and more advanced yield criteria.
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17.
  • Pilthammar, Johan, 1987-, et al. (författare)
  • Characterizing the Elastic Behaviour of a Press Table throughTopology Optimization
  • 2017
  • Ingår i: Journal of Physics: Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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18.
  • Pilthammar, Johan, 1987- (författare)
  • Elastic Press and Die Deformations in Sheet Metal Forming Simulations
  • 2017
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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19.
  • Pilthammar, Johan, et al. (författare)
  • Including die and press deformations in sheet metal forming simulations
  • 2016
  • Ingår i: NUMISHEET 2016. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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20.
  • Pilthammar, Johan, et al. (författare)
  • Introduction of elastic die deformations in sheet metal forming simulations
  • 2018
  • Ingår i: International Journal of Solids and Structures. - : Elsevier Ltd. - 0020-7683 .- 1879-2146. ; 151:S1, s. 76-90
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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21.
  • Pilthammar, Johan, et al. (författare)
  • New press deflection measuring methods for the creation of substitutive models for efficient die cambering
  • 2021
  • Ingår i: INTERNATIONAL DEEP-DRAWING RESEARCH GROUP CONFERENCE (IDDRG 2021). - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • Cost and time for die tryout are significant within the car industry, and elastic deflections of dies and presses are most commonly not considered during the virtual die design and forming simulation phase. Because of this, active surfaces of stamping dies are only cambered based on previous experiences of tool types and presses. However, almost all stamping dies and presses are unique, and available experiences are not valid for new materials. Partners within the Eureka SMART Advanced Manufacturing research project CAMBER have developed advanced deflection measuring devices to quantify the elastic deformations of presses. Using these measurements, cambering methodologies can be utilized in sheet metal forming simulations. Important breakthroughs in recent years enabling the cambering methodology consists of efficient simulation strategies for full scale simulations with elastic dies and optimization techniques for creating substitutive press structures based on measurements. Furthermore, modem press deflection measurement methods are beneficial in applications such as Industry 4.0, predictive maintenance, product quality control, etc. through a more advanced understanding and live monitoring of the press system.
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22.
  • Pilthammar, Johan, et al. (författare)
  • Simulation of Sheet Metal Forming using Elastic Stamping Dies
  • 2019
  • Ingår i: Proc. of the 12th European LS-DYNA Conference 2019, 2019.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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23.
  • Pilthammar, Johan, et al. (författare)
  • Surpassing Threshold Concepts within Engineering Mechanics Interactive Computer Aided Learning (CAL) to support the learning process
  • 2022
  • Ingår i: Högskolepedagogisk debatt. - : Högskolan i Kristianstad. - 2000-9216. ; :2, s. 77-98
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • This paper is based on a scientific literature review and interviews with teachers and researchers active in the area of Engineering Mechanics in Swedish higher education. The paper aims to identify and highlight troublesome knowledge and threshold concepts within the field of Engineering Mechanics. Moreover, the ambition is to present ideas of how to overcome these identified threshold concepts. Recent scientific research acknowledges many benefits of introducingdigital and interactive tools, denominated Computer Aided Learning (CAL), at an early stage. Digital and interactive tools can help engineering students overcome threshold concepts. A selection of these digital tools is discussed in this paper. The study concludes that elearning is an efficient way to enhance and complement the learning process. It also makes teaching material available from anywhere, at any time. Hence, students can individually adjust their learning pace. The interviews with teachers contributed to a clearer view of how dig-ital tools can be utilized and transform learning in mechanical engineering.Master students in mechanical engineering are expected to create, operate, and understand advanced digital tools. However, on the B.Sc. level, the implementation of digital tools seems to be scarce. Instead, textbooks, exercises with pen and paper, and traditional teaching are the preferred tools for learning. Implementing digital and interactive computer tools already on a basic teaching level (B.Sc.) can assist students to understand complex theories and overcome threshold concepts.
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24.
  • Pilthammar, Johan, et al. (författare)
  • Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies
  • 2023
  • Ingår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.
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25.
  • Pilthammar, Johan, 1987- (författare)
  • Towards Virtual Tryout and Digital Twins : Enhanced Modeling of Elastic Dies, Sheet Materials, and Friction in Sheet Metal Forming
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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26.
  • Sigvant, Mats, et al. (författare)
  • Experiments and FE-simulations of stretch flanging of DP-steels with different shear cut edge quality
  • 2017
  • Ingår i: Journal of Physics. - : Institute of Physics Publishing.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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27.
  • Sigvant, Mats, et al. (författare)
  • Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door
  • 2016
  • Ingår i: IOP Conference Series.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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28.
  • Sigvant, M., et al. (författare)
  • Friction and lubrication modelling in sheet metal forming simulations of the Volvo XC90 inner door
  • 2016
  • Ingår i: NUMISHEET 2016. - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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29.
  • Sigvant, Mats, et al. (författare)
  • Friction in Sheet Metal Forming : Forming Simulations of Dies in Try-Out
  • 2018
  • Ingår i: Journal of Physics. - : Institute of Physics Publishing.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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30.
  • Sigvant, Mats, et al. (författare)
  • Friction in Sheet Metal Forming Simulations : Modelling of New Sheet Metal Coatings and Lubricants
  • 2018
  • Ingår i: IOP Conference Series. - : Institute of Physics Publishing.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
31.
  • Sigvant, Mats, et al. (författare)
  • SMART STAMPING : IMPROVED QUALITY IN STAMPING BY MODEL DRIVEN CONTROL
  • 2018
  • Konferensbidrag (refereegranskat)abstract
    • Sheet Metal Forming is a very complex manufacturing process with a number of non-linearities, e.g. large deformations, localisation, elastic-plastic materials, pressure and velocity dependant friction conditions and structural deficiencies in the die and press, present and interacting simultaneously. This leads to disturbances in running production that results in production waste, e.g. down time for the press line and cost for rework and scrapping of parts. These production problems are also hard to understandand solve based on experience and analytical models due to the presence of several non-linearities. An alternative is to try to solve these problems proactively before they occur. This could be done with model based control by creating a digital twin of the die-set and the press line. Therefore, a virtual production process is developed to be able to use as knowledge building and as engineering tool during development, manufacturing, issue resolution and optimization. In this paper presents the authors ideas and plans for research and other activities within the area of model based control of sheet metal forming.
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32.
  • Tatipala, Sravan, et al. (författare)
  • Simulation-Driven Design Approach for Design and Optimization of Blankholder
  • 2017
  • Ingår i: <em>Journal of Physics: Conference Series</em> (JPCS). - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596.
  • Konferensbidrag (refereegranskat)abstract
    • 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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