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Macro-Geometric Defects, A numerical and experimental study of springback and surface defects

Andersson, Alf LU (2004)
Abstract (Swedish)
Popular Abstract in Swedish

Idag har kravet på kortare ledtider i bilindustrin dramatiskt ökat behovet av effektivare utvecklingsmetoder vid varje steg i processutvecklingskedjan. För att minska de långa ledtiderna för framtagning av ett formningsverktyg har man introducerat Finita Element (FE) simulering av formningsprocessen. Även om FE-simulering används inom bilindustrin idag finns fortfarande utmaningar att anta. Två viktiga exempel är prediktering av återfjädring och ytdefekter. Om pålitliga predikteringar av dessa fenomen kan göras skulle mycket pengar sparas i minskade ledtider och justeringskostnader.



Dessa områden, tillsammans med dragvulster, var även belysta som områden av stort intresse när... (More)
Popular Abstract in Swedish

Idag har kravet på kortare ledtider i bilindustrin dramatiskt ökat behovet av effektivare utvecklingsmetoder vid varje steg i processutvecklingskedjan. För att minska de långa ledtiderna för framtagning av ett formningsverktyg har man introducerat Finita Element (FE) simulering av formningsprocessen. Även om FE-simulering används inom bilindustrin idag finns fortfarande utmaningar att anta. Två viktiga exempel är prediktering av återfjädring och ytdefekter. Om pålitliga predikteringar av dessa fenomen kan göras skulle mycket pengar sparas i minskade ledtider och justeringskostnader.



Dessa områden, tillsammans med dragvulster, var även belysta som områden av stort intresse när användningen av FE-simulering jämfördes med användning av provverktyg. Vid denna utvärdering användes Production Performance Matrix (PSM) och Process Correspondence Matrix (PCM). För att utnyttja den erhållna informationen effektivt föreslogs en metod för effektivt informationsutbyte för FE-simulering.



Det huvudsakliga syftet med detta projekt var att hitta metoder för att kunna analysera makro geometriska defekter (som återfjädring och ytdefekter). Analys av ytdefekter innefattar svårigheter i både experimentell och numerisk bedömning. Eftersom defekterna är väldigt små och beror på både position och form i klassificeringsproceduren är det svårt att hitta ett utvärderingssystem som detektera både små varianser i ytans form och klassificera defekterna. Dessutom beror de numeriska resultaten både på noggrannhet i prediktering av formningen och av återfjädringen. För att kunna jämföra resultaten med samma klassificeringsprocedur utvecklades en metod där ytorna kan analyseras i samma mjukvara oavsett om de är numeriska eller experimentella. På detta sätt blir klassificering samma och resultaten direkt jämförbara.



En parameterstudie m.a.p. återfjädring visade att de viktigaste parametrarna att ta hänsyn till var, bl.a., användning av små element, låg hastighet på verktygen samt ha bra materialmodeller. Resultaten applicerades på en fordonsdetalj, främre sidobalk. Simuleringsresultaten överdrev vridningen men felet var relativt litet för mjukt stål samt Rephos stål. Man testade även TRIP-stål och där var avvikelsen mycket större.



I formningsprocessen kontrolleras materialflödet bl.a. av dragvulster. Materialflödet är väldigt viktigt om man skall få en korrekt spänningsdistrubution i den formade detaljen, som i sin tur påverkar återfjädring och ytdefekter. I detta arbete har en metod utvecklats för optimering av “återhållande kraft” (vilken representerar dragvulster i FE-simulering) med ett litet antal iterationer. (Less)
Abstract
Today, shortened lead-times in the automotive industry have dramatically increased the need for more efficient development methods at every stage of the process development chain. In order to decrease the long lead-time for producing a forming tool, sheet-metal-forming simulation was introduced. Even though sheet-metal-forming simulation is widely used in the automotive industry today, there are still challenges to be overcome. Two important examples are the prediction of springback and surface defects. If reliable predictions of these phenomena could be achieved, much money could be saved in reduced lead-times and adjustment costs.



These areas, together with drawbeads, were also highlighted as areas of significant... (More)
Today, shortened lead-times in the automotive industry have dramatically increased the need for more efficient development methods at every stage of the process development chain. In order to decrease the long lead-time for producing a forming tool, sheet-metal-forming simulation was introduced. Even though sheet-metal-forming simulation is widely used in the automotive industry today, there are still challenges to be overcome. Two important examples are the prediction of springback and surface defects. If reliable predictions of these phenomena could be achieved, much money could be saved in reduced lead-times and adjustment costs.



These areas, together with drawbeads, were also highlighted as areas of significant interest when the use of FE simulation was compared to the use of try-out tools. In this evaluation the Production Performance Matrix (PSM) and the Process Correspondence Matrix (PCM) were used. In order to use the achieved information efficiently, a method for efficient information exchange for the FE simulation results was proposed.



The main goal with this project was to find a method for analysis of macro-geometric defects (such as surface defects and springback). Analysis of surface defects involves difficulties in both experimental and numerical assessment. Since the defects are very small and also depend on both position and shape in the classification procedure, it is difficult to find an evaluation system which can detect both small variance in the shape of the surface and classify the defects. Furthermore, the numerical results depend both on the accuracy in the prediction of the forming behavior and the springback. In order to compare the results of the same classification procedure, a method has been developed whereby the surface can be analysed both numerically and experimentally in the same evaluation software. In this way, the classification will be the same and the results will be directly comparable.



Regarding springback, a study of the parameters resulted in the conclusion that the important factors to consider in FE simulations of springback are, among others, to have small elements, low tool speed and good material models. The results were applied to an automotive part, a front side member. The simulations exaggerated the twist but the error was moderate for mild steel and Rephos steel. However, a TRIP steel was also examined and there the deviation was much larger.



In the forming process the flow of material is controlled among other things by drawbeads. The material flow is very important in order to have a correct stress distribution in the formed part, which in turn affects both springback and surface defects. In this work a method for optimising the restraining force (which represents drawbeads in FE simulations) with a small number of iterations has been developed. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Kjellberg, Torsten, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Simulation, Sheet-metal forming, Finite element analysis, Information exchange, Springback, Surface defects, Drawbead, Process analyse, Optimisation, materialteknik, Materiallära, Material technology
pages
180 pages
defense location
Room M:E, M-building, Lund Institute of Technology.
defense date
2004-05-07 10:15
external identifiers
  • Other:ISRN: LUTMDN/(TMMV-1044)/1-168/(2004)
ISBN
91-628-6021-6
language
English
LU publication?
yes
id
d00fb24c-c690-4c44-bba6-6b3b5dd9e1d2 (old id 466962)
date added to LUP
2007-08-09 08:11:29
date last changed
2016-09-19 08:45:18
@misc{d00fb24c-c690-4c44-bba6-6b3b5dd9e1d2,
  abstract     = {Today, shortened lead-times in the automotive industry have dramatically increased the need for more efficient development methods at every stage of the process development chain. In order to decrease the long lead-time for producing a forming tool, sheet-metal-forming simulation was introduced. Even though sheet-metal-forming simulation is widely used in the automotive industry today, there are still challenges to be overcome. Two important examples are the prediction of springback and surface defects. If reliable predictions of these phenomena could be achieved, much money could be saved in reduced lead-times and adjustment costs.<br/><br>
<br/><br>
These areas, together with drawbeads, were also highlighted as areas of significant interest when the use of FE simulation was compared to the use of try-out tools. In this evaluation the Production Performance Matrix (PSM) and the Process Correspondence Matrix (PCM) were used. In order to use the achieved information efficiently, a method for efficient information exchange for the FE simulation results was proposed.<br/><br>
<br/><br>
The main goal with this project was to find a method for analysis of macro-geometric defects (such as surface defects and springback). Analysis of surface defects involves difficulties in both experimental and numerical assessment. Since the defects are very small and also depend on both position and shape in the classification procedure, it is difficult to find an evaluation system which can detect both small variance in the shape of the surface and classify the defects. Furthermore, the numerical results depend both on the accuracy in the prediction of the forming behavior and the springback. In order to compare the results of the same classification procedure, a method has been developed whereby the surface can be analysed both numerically and experimentally in the same evaluation software. In this way, the classification will be the same and the results will be directly comparable.<br/><br>
<br/><br>
Regarding springback, a study of the parameters resulted in the conclusion that the important factors to consider in FE simulations of springback are, among others, to have small elements, low tool speed and good material models. The results were applied to an automotive part, a front side member. The simulations exaggerated the twist but the error was moderate for mild steel and Rephos steel. However, a TRIP steel was also examined and there the deviation was much larger.<br/><br>
<br/><br>
In the forming process the flow of material is controlled among other things by drawbeads. The material flow is very important in order to have a correct stress distribution in the formed part, which in turn affects both springback and surface defects. In this work a method for optimising the restraining force (which represents drawbeads in FE simulations) with a small number of iterations has been developed.},
  author       = {Andersson, Alf},
  isbn         = {91-628-6021-6},
  keyword      = {Simulation,Sheet-metal forming,Finite element analysis,Information exchange,Springback,Surface defects,Drawbead,Process analyse,Optimisation,materialteknik,Materiallära,Material technology},
  language     = {eng},
  pages        = {180},
  title        = {Macro-Geometric Defects, A numerical and experimental study of springback and surface defects},
  year         = {2004},
}