Compensating springback in CAD die surfaces
Achieve enormous time savings in die tryout with global surface morphing
The elastic properties of the sheet metal cause springback after the forming of sheet metal parts. This is ordinarily compensated in the sheet metal die, so that the part is initially formed to an "incorrect" geometry and then springs back to yield the desired geometry. While mechanical compensation, introduced by grinding the die, results in an enormous time expenditure, the approved sheet metal die geometry can be arrived at far more quickly through the implementation of deformation technology in the CAD surfaces.
In CAD-based forming, morphing rules are used that result either from a simulation system, from measurement results, from scanned sheet metal parts, or from experience. Tebis morphs all the affected individual surfaces completely automatically, compensating for springback. The qualitative surface properties such as segmentation, polynomial degree, and transitions are optimally adjusted for the deformation. Analysis functions indicate adherence to the morphing rule and to the quality of the formed surfaces.
Less correction grinding in tryout ensures enormous time savings.
All morphing measures in Tebis are reproducible and can be optimized. Anyone starting out with CAD-based springback compensation learns more with each project, resulting in continuous reductions in correction grinding expenditure. When defining the deformation, the user subdivides the surface data set in three areas:
- Area without morphing because there is no springback (green)
- Area with morphing because springback has to be compensated here (blue)
- Transition area (yellow)
The user assigns a separate tolerance to each of these areas. This describes the maximum deviation that can be assumed by the surface result from the exact morphing rule.
The morphed CAD surfaces can be used immediately in active surface design (see Active surface design) and in die design.
Global morphing of CAD surface models based on morphing rules
Tebis offers several options for defining the morphing rule. All morphing rules can be combined together.
From simulation systems:
FEM systems specializing in the simulation of sheet-metal deformation simulate springback and provide compensation rules, such as with two triangular meshes. Tebis uses these and automatically morphs the affected area of the active surface of the die.
If the expert knows how the sheet metal springs back and how it must be deformed, the morphing rule is created in Tebis with a substitute surface pair (visible in the background) that represents the desired morphing. Rules can also be specified with vectors and rotation.
From measurements on the sheet metal part:
Tebis takes the measuring points determined on the test part with springback, calculates the distances from the desired part, and automatically compensates the CAD surfaces in the die.
From scanned sheet-metal parts:
The comparison between the scanned sheet-metal part and the CAD surfaces of the die indicates where springback is occurring. The meshes from the scanning process are used to define the morphing rule. Also, Scanned sheet-metal parts can be quickly and easily reverse engineered to surfaces in Tebis (see Tebis reverse engineering).
Morphing of outer skin surfaces based on results from forming simulations:
The predictions regarding springback are imported in Tebis through interfaces to simulation systems, and the CAD surfaces are automatically morphed. The better the original surfaces are, the better the morphed resulting surfaces will be. Tebis offers an extensive function package for the analysis and optimization of CAD surfaces before and after deformation.
Morphing sheet-metal parts based on measuring points:
Tebis takes the measuring points determined on the test part with springback, calculates the distances from the desired specified part, and automatically compensates the entire sheet-metal part.
Your benefits from the springback-compensated active surfaces:
- Less grinding work and fewer correction cycles in tryout ensure enormous time savings.
- All morphing steps for compensating springback are reproducible and can be optimized. You learn with each project and become better over time.
- You have short calculation times.
- All morphing rules can be combined together.
- The morphed CAD surfaces can be immediately used in active surface design and in die design.
Our new department structure, as well as the Tebis solution for morphing and the Tebis analysis and optimization functions, enabled us to get correction grinding under control. We scored in all areas: Parts got to the machine faster, CAD data and NC programs could be updated faster, and surface quality was even better.
Florian Schulze, head of the competency center for milling data, Volkswagen AG
What used to take a week, we can now accomplish in a single day using Tebis Morphing, and the need for manual reworking has gone down.
Björn Wind, Team Leader for work preparation and NC manufacturing, Merima Präzisions-Werkzeugbau GmbH
Challenges in Sheet Metal Draw Die Manufacturing: Perfect interaction between the virtual and real world
Tebis active surface preparation includes compensation of sheet-metal thinning, incorporation of pressure surfaces, and free design of negative radii. Specialized functions enable programming without virtual wall thicknesses, resulting in the disappearance of visible edges and steps in the die surface. Compensation for press deflection and die deformation can be simply integrated with corresponding overbending rules.
Advances in sheet metal forming: End-to-end automation in the context of Industry 4.0
Tebis has developed functioning software-supported processes specifically for die manufacturing to enable the production of top-quality class-A surfaces and to automate the manufacturing of small parts. Both processes verifiably reduce manufacturing expenditure thanks to standardization and the integration of individual manufacturing knowledge.
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