SPRINGBACK

 

The QS/SPRINGBACK GUI (as shown in Figure 8.1.10) allows the user to easily setup a springback analysis.

 

Figure 8.1.10 The QS Springback GUI

 

TOOL DEFINITION GUI

Allow the user to define a deformed blank.  Selecting the TRIM BLANK button to carry out the trim operation, the user has to read in the trim curve. By default, the deformed blank is assigned automatically as BLANK after the file (in DYNAIN format) is read into the eta/DYNAFORM database.

 

BLANK PARAMETERS

Define blank material and properties.

 

CONTROL

The user can either select the single or multi-step implicit method. The single-step implicit method is the default setting. If it does not provide converged springback results, the user may select the multi-step implicit method for the springback analysis.

 

The coarsen control can be activated to combine the refined mesh prior to springback analysis. The function allows the eta/DYNAFORM solver to combine neighbouring elements that have an difference of normal angle of less than a given angle (default is 8º). Coarsening blank mesh can reduce computational noise, and therefore helps the springback simulation to converge.

 

CONSTRAINT

Enable the user to select appropriate constraint points to prevent rigid body motion during springback analysis.

 

IMPLICIT PARAMETERS

Define parameters for springback analysis. The dialog box is shown in Figure 8.1.11. For detailed information about each parameter, refer to the LS-DYNA User’s Manual.

Figure 8.1.11 The Implicit Parameters dialog box

 

 

8.1.3.1 THE QUICK SETUP/SPRINGBACK PROCEDURE

 

Following is the procedure for setting up a springback analysis using QS/SPRINGBACK:

 

1.       Read in the blank results.

The blank results are obtained from a draw simulation. They are output as a DYNAIN file after each draw simulation. The user may read in the DYNAIN file by selecting BLANK from the QS/SPRINGBACK tool GUI and then selecting IMPORT MESH from the DEFINE BLANK dialog box.

 

2.       Trim the blank.

If no trim operation is involved, the user may skip this step and continue with Step 3. Refer to Section 9.8.5 for more information about blank trimming.

 

3.       Define blank parameters.

The user needs to define the initial blank material and thickness. The blank parameters are required for the solver to perform initialization prior to springback analysis. These blank parameters should be similar to the blank parameters used in the draw simulation.. After the initialization, the thickness, stress and strain stored in the DYNAIN file will be used as the initial blank parameters.

 

4.       Select type of implicit method and coarsen options.

 

5.       Define implicit parameters.

There are no appropriate default implicit parameters which are good for all springback applictions. The user needs to adjust implicit parameters accordingly.  Refer to the LS-DYNA User’s Manual for a detailed explanation of all the implicit parameters following the listed cards.  NOTE: control cards list different solver versions.

 

6.       Control rigid body motion.

The user needs to define appropriate constraints on the blank to eliminate the six rigid body motions. This is done by using the SPRINGBACK CONSTRAINT option in the IMPLICIT PARAMETER dialog box (Figure 8.1.11).  eta/DYNAFORM will prompt the user to select the contrained nodes.

 

For most applications, 3 constraint nodes are recommended for springback analysis. The chosen 3 constraint nodes should be well separated from each other and away from the edges and flexible areas in the part.  The first constraint node will lock the three translation degrees of freedom and define the reference point in the springback model.  The springback displacement is zero at the first constraint node. The second constraint node will lock the Y- and Z- translation, while the third constraint node eliminates the translation in Z-direction. For detailed information about springback analysis, contact eta/DYNAFORM’s Technical Support at support@eta.com.