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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Friction and material modelling in Sheet Metal Forming Simulations / Friktion och materialmodellering i simuleringar av plåtformning

Bentsrud, Herman January 2020 (has links)
In today’s car manufacturing industry, sheet metal forming is a important process that takes preparation, which is time consuming and complex when new processes are made. When new metal grades and alloys are provided to the industry, tests are conducted to determine it’s behaviour and strengths. This gives the data for complex material models that can approximate the metal behaviour in an accurate way in a simulation environment. One of the unknown factors from tests is the friction coefficient on the sheet metal. The software Triboform is able to provide an adaptable friction coefficient model that depends on multiple simulation and user input conditions. The problems that occur when acquiring data for the material model is that testing is time consuming and the friction model has to be adjusted to give accurate results. At Volvo Cars there are two material models used with their different advantages, BBC 2005 and Vegter 2017.The purpose with this work is to compare the two material models using the Triboform friction models implemented to see if any combination provides accurate simulation results and then create recommendations for which model is best suited for different cases. Some side studies is also done with an older Vegter model, a strain rate sensitive BBC 2005 model and a Triboform model on all simulation parts.The purpose is achieved by implementing the Triboform model in Autoform and run a simulation of a Limiting Dome Height (LDH) test with both material models and compare the results with experimental data for several different materials. The data that is directly compared from the LDH test is the major and minor strain from two perpendicular sections at four different stages and also the force from the punch tool. The material models will be evaluated by how it manages to mimic the strain behaviour of the metals and how it estimates the punch force.The results point towards an improvement of the accuracy for most of the metals tested and BBC 2005 is the better model if there’s available biaxial data from tests, Vegter 2017 is decent if there’s not. However Vegter 2017 is not a good option for aluminum alloys simulations when the punch force is compared. Side study also shows that Vegter 2017 is bit of a downgrade when it comes to strain values, compared to the old Vegter.The work, in summary shows a dynamic friction model can improve the accuracy for strain predictions in the simulation process. If there’s biaxial yield data available for the metal or if it’s an aluminum alloy, BBC 2005 is the superior choice, but if only tensile tests are available for metals, Vegter 2017 is a decent choice for some cases. / I dagens bilindustri är plåtmetalformning en viktig process som kräver förberedelser som är tidskonsumerande och komplex när nya processer tillkommer. När nya metallslag kommer in till industrin, så utförs tester för att avgöra dess egenskaper och styrka. Denna testdata används till materialmodeller som kan approximera metallens beteende på ett noggrant sätt i en simuleringsmiljö. Den okända faktorn från dessa test är friktionskoefficienten på plåten. Programvaran Triboform är kapabel att göra en dynamisk friktionsmodel som beror på användar- och simuleringsdata. Problemen som uppstår vid framtagning av data är att det är tidskonsumerande och flera simuleringar måste göras för att bestämma friktionen. Volvo Cars använder sig av två modeller med olika fördelar, BBC 2005 och Vegter 2017.Syftet med detta arbete är att jämföra de två materialmodellerna med Triboform modeller implementerat för att se om de påverkar noggrannheten i simuleringar och sedan förse rekommendationer för vilken modell passar bäst för olika fall. Några sidojobb i studien som görs är en jämförelse med gamla Vegter modellen, ett test med en modell som är känslig för töjningshastighet och test med att implementera Triboform modellen på alla pressverktyg.Detta utförs med att implementera Triboform modellerna i Autoform och köra en simulering på ett LDH-test med båda materialmodeller och jämföra resultaten med experimentell data för flera olika metaller. Data som skall jämföras från LDH-testet är första och andra huvudtöjningen i två vinkelräta sektioner i fyra processsteg och stämpelkraften genom hela processen. Modellerna kommer evalueras genom hur de lyckas imitera töjningens beteende och hur den estimerar stämpelkraften.Resultaten pekar mot en förbättring när Triboform är implementerat i simuleringar för de flesta metaller som ingår i testen och BBC 2005 är den model som föredras om det finns tillgänglig biaxiel spänning data från tester, Vegter 2017 är en duglig modell om dessa data inte finns. Vegter 2017 är dock inte ett bra alternativ när det kommer till jämförelse av töjning och stämpelkraften för aluminium. Sidojobb med gamla Vegter visar att den nya Vegter 2017 inte är en direkt förbättring med hänsyn till noggrannheter av krafter och töjningar.Arbetet visar att en dynamisk friktionsmodel kan förbättra prediktering av töjningar i simuleringar. Om det finns biaxiel data för metallen eller om det gäller att simulera aluminium är BBC 2005 det bättre altermativet, om det endast finns dragprovsdata för metallen så är Vegter 2017 duglig för vissa fall.
2

Comparison of Accuracy in Sheet Metal Forming Simulation Software

Torstensson, Alexander January 2022 (has links)
As competition in the car market increases, the techniques for car manufacturing are developed and becomes more advanced to be able to keep up with the pace. The development process of car body components has shifted over the years to involve more simulation driven testing than ever before to save time and money in the early stages of development. As the importance of reliable sheet metal forming simulations grows, inconsistencies between simulations and physical stamping can be detrimental to the development time if stamping dies need to be reworked because of poor correlation between physics and simulations.                        The aim of this study is to improve the coherence between physical stamping and the simulation software used by Volvo Cars. The coherence is determined by studying different properties of the result in simulations and comparing them to measurements taken on the corresponding physical stamped parts. A comparison was done between the current standard simulation software, Autoform Forming R8 and a beta version of Autoform Forming R10. The objectives of this study were to compare the sheet thickness, strain, draw-in and ability to predict material failure between the two simulation software to see which of them correlate best to the physical measured parts.                       The workflow consisted of initially setting up the simulations in Autoform Forming R8. Some of the simulations could begin testing right away, while others required needed some geometry rework as the physical tested parts had been stamped with modified stamping dies. When the simulation setups were completed copies of the simulations were taken and run on Autoform Forming R10 to compare with. The simulations were run with a varied Triboform friction models and some of the simulations were run using symmetry to reduce the simulation time. When data was compared Autoform Forming was used when possible and when additional tools were needed the simulated geometries were exported and compared in software such as SVIEW and GOM Correlate.                       The result showed relatively low differences in the comparisons of sheet thickness and major and minor strain as neither of the simulations seemed to give more accurate values compared to the measurements. A slight improvement in the draw-in comparison was found for the Autoform Forming R10 compared to the R8 simulation. In the material failure prediction a major difference was found where the Autoform Forming R10 simulations were better at determining splits than R8. However the splits were only discovered with 2 of the 4 tested friction models in the R10 simulations while the 1 of the 4 simulations indicated risks for a split in the R8 simulation.                       In conclusion the simulations run on Autoform Forming R10 seem to be better at predicting splits and draw-in dimensions while no major differences were found in the comparisons of strain and sheet thickness.

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