With the accelerating pace of developments in the automotive industry, high impact innovations are required to ensure future growth. To shrink time lines and reduce development costs of new vehicles, software tools are increasingly used at Volvo Cars. TriboForm is applied for the door-inner of the all-new Volvo XC90 to achieve these goals for Volvo Cars.
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Volvo Cars has identified that one of the main aspects driving product quality in sheet metal forming is tribology, friction and lubrication. Both in production and in sheet metal forming simulations. To increase the accuracy of sheet metal forming simulations, the TriboForm software is used. A selection of technical case results and business case results considering friction and lubrication modeling in stamping simulations of the Volvo XC90 inner door are described below.
Application of the TriboForm software to the door-inner of the all-new Volvo XC90
The quality of the Volvo XC90 door inner parts is strongly dependent on the friction and lubrication conditions that are acting in the actual production process. For varying production conditions, like stroke rate or cushioning force, the door-inner part can either show severe wrinkling or fracture. See the figure below. Moreover, in the course a production run, these quality issues can either appear or disappear based on the drift of process conditions like tooling temperature during the production run. By changing the production-, tribology-, or lubrication conditions, these quality issues can be prevented.
Although friction is of key importance in the production process, it is currently not considered in detail in stamping simulations. The current industrial standard is to use a constant (Coulomb) coefficient of friction. This limits the overall simulation accuracy. To achieve more realistic simulation results with increased reliability, it is crucial to accurately account for tribology effects in metal forming simulations. For this purpose, the TriboForm software is used in combination with the AutoForm software.
Animation of the time- and location dependent coefficient of friction (from 0.12 to 0.18) using the TriboForm FEM Plug-In in AutoForm.
Door-inner simulation using the TriboForm FEM Plug-In for the ‘production standard’ tribology and lubrication system leading to splits in the product
Door-inner simulation using the TriboForm FEM Plug-In for an optimized tribology and lubrication system leading to a high-quality product
Validation of the simulation results is performed based on door-inner parts taken from the press line in a full-scale production run. The results are presented below for 3 situations:
- Experimentally measured results
- Simulation results using a constant (Coulomb) coefficient of friction in AutoForm
- Simulation results using the TriboForm FEM Plug-In in AutoForm
Validation results: Strain
The experimental strain results show a critical strain distribution, slightly exceeding the Forming Limit Curve (FLC). The simulated strains using a constant coefficient of friction strongly exceed the experimental strain results and do not agree with the experimentally measured results. Finally, the simulated strain results using the TriboForm FEM Plug-In in AutoForm file show a good agreement with the experimental results and demonstrate the improved prediction accuracy of stamping simulations.
Validation results: Draw-in
The experimental draw-in results are strongly dependent on both tribology and an accurate geometrical description of the tools and draw-beads. In the stamping simulations, the real geometry of the production tools have therefore been scanned and implemented in AutoForm. The simulation results show a good correspondence with the experimental draw-in results using the TriboForm FEM Plug-In in AutoForm. A deviation between experimental results and simulation results using a constant coefficient of friction is observed.
Enriched simulation functionalities
TriboForm enriched simulation functionalities by enabling the simulation of:
- The effect of tool temperature and heat-up on friction and product quality in stamping simulations
- The effect of tool coating and sheet coating on product quality and production stability
- The effect of the type of sheet material, lubricant and tooling material used in actual production
The project results demonstrate the improved prediction accuracy of stamping simulations using the TriboForm software with respect to:
In general, this case demonstrate the strong influence of tribology, friction and lubrication conditions on both the part quality and the overall production stability.
More technical results will be presented at the International Deep Drawing Research Group (IDDRG) conference 2016 and available soon.
Optimization of the tribology system (combination of sheet material, lubricant type and tool material) in the production of the Volvo XC90 has put Volvo Cars in the position to increase the stroke rate in production with 50% while maintaining a stable production process and a high product quality (no splits, no wrinkling). This results in:
- Total Cost of Ownership door-inner part at the standard stroke rate: € 8,87*
- Total Cost of Ownership door-inner part at the increased stroke rate: € 7,66*
- At an example production target of 100.000 door-inner products
- The total savings are: € 121.000,- (for a single part, for a single car model)
With multiple critical parts per car model, and an increasing number of car models being developed, the TriboForm software delivers even higher savings. The technical case demonstrates that the TriboForm software empowers its users to quickly understand, simulate and solve tribology-related problems in the metal forming industry. The business case demonstrates that TriboForm enables to shrink time-lines and reduce development costs of new vehicles and results in a high Return On Investment (ROI).
[* ULSAB Cost model stamped parts, Steel association, 2013 ]
For more information, please contact Dr. Ir. J. Hol, CTO.
Courtesy of Volvo Car Group.