2005 NUMISHEET BENCHMARK # 2 ─ Springback Prediction of a Cross Member ─ The objective of this study is to benchmark springback prediction capability of various software and skills of users on an underbody part mostly dominated by bending effect. This benchmark is provided by DaimlerChrysler Corporation, Chrysler Group in Auburn Hills, Michigan, USA. Chrysler Group leads the benchmark project with the active participation from US Steel Corporation, Ispat Inland Corporation, and Alcoa, Inc. Strain/thickness measurements are conducted by US Steel Corporation, Ispat Inland Corporation and Chrysler Group. Materials and property measurements are provided by US Steel Corporation, Ispat Inland Corporation, and Alcoa, Inc. TOOL GEOMETRY
The simulation process of stamping a cross member panel consists of three operations: forming, trimming and springback. Participants should not move the tooling position in the x-y plane.
1. Forming Lower punch, binder and upper die are illustrated in Figure 1. This tooling geometry is x-z plane symmetry at y=0. Only half of the tooling model and draw bead geometry is provided. Three different blank materials are used for stamping: DP600 (US Steel), DP965 (Ispat Inland) and AL5182-O (Alcoa) all 1.6 mm thick. Total blank holding force: see Table 1. Participants need to use half of the specified holding force in Table 1 if only half of the tooling geometry is used in the simulation.
Binder Travel: 100 mm, see Figure 2.
Initial blank setup position: see Figure 3.
Tool moving direction: | Lower Punch: stationary | | | Upper Die: moving (-z direction) | | Binder: moving (-z direction) | | | |
Table 1. Total blank holding force | Material type of blank | Total blank holding force (+z direction) | DP600 | 1068 kN (120 English Ton) | DP965 | 1281 kN (144 English Ton) | AL5182-O | 400 kN (45 English Ton) |
In this benchmark, participants can use either physical beads or line beads in forming simulation. The information of physical bead geometry and bead center lines (see Figure 4) is provided in the Nastran mesh file and IGES file. Line Bead forces should be calibrated from the following bead section profiles (see Figure 5 and Table 2). The interbead transitions start at the specified Y coordinate in Figure 4 and have a length of 15 mm towards the symmetry line at Y=0.
Table 2. Parameters of draw bead section (unit: mm) | Bead | H1 | H2 | H3 | W1 | W2 | R1** | R2** | A | 2.7 | 1.6 | 6.1 | 12.5 | 1.0 | 4.5 | 4.5 | B | 1.9 | 1.6 | 6.1 | 12.5 | 1.0 | 4.5 | 4.5 | C | 0.16 | 1.6 | 6.1 | 12.5 | 1.0 | 4.5 | 4.5 | D | -0.88* | 1.6 | 6.1 | 12.5 | 1.0 | 4.5 | 4.5 | * Negative value indicates the center of R1 is above the upper binder surface | ** R1 and R2 are equivalent bead radii |
2. Trimming Trim line, illustrated in Figure 6 as the edges, is provided in the Nastran mesh file and IGES file. 3. Springback
Boundary conditions (BCs) for springback analysis are shown in Figure 7. In addition to the x-z plane symmetric BC, BCs are applied at two points (A & B) to eliminate rigid body motion. The coordinates of these two points on the lower punch surface are shown in Figure 7. Files for simulation Geometry data are represented by Nastran mesh format & IGES. Nastran File: The blank and tools are described by triangular and quad elements. Trim line and bead center lines are described by line elements (CBAR elements). All the tools are at home position. All data is in the NASTRAN file cross_member.nas. IGES File: Only the upper die surfaces and bead geometry are provided in the IGES files. Participants need to offset the surfaces 1.76mm to obtain the lower punch portion and offset 1.6mm to obtain the binder surfaces. The female bead surfaces also need to be offset by 1.6mm. The initial blank profile, bead center lines and trim line are indicated by lines. All data is in the file cross_member.iges. Material Property Files: Standard properties are listed on the worksheet and additional information is provided in case that participants want to use more sophisticated material models. Data for this benchmark are in the following 3 Excel spreadsheets. BM2_DP600.xls BM2_DP965.xls and BM2_AL5182.xls BENCHMARK REPORT The due date for benchmark submission is listed on the website. All results are to be reported using the benchmark report template that is included in the download (BM2_Report_TMP.xls). Instructions for participating in the benchmark is provided in the file Report_Filing_Instructions.pdf. A total of 24 distributions and 21 data values are required for completion of Benchmark 2. Note that the 21 data values (7 for each material listed in items 1 and 2) are to be reported on the second worksheet in the spreadsheet and the 24 distributions (8 for each material listed in items 3 and 4) are to be reported in two separate worksheets for each material. The following information is requested for each material on the appropriate worksheet: Maximum total upper die force(kN) for full model during forming. Data values: 1. Blank draw-in (mm) ( ) after forming at Sections I, II and III (see d1~d6 in Figure 8). The draw-in measurement starts from binder closure and bead set. Data values: 6. Strain distributions (true major strain on top surface, true minor strain on top surface, true thickness strain) inside trim line at Sections I and IV after forming (see Figure 9). Strains must be dimensionless, not in units of percent. Recover strain values versus arc-length distance from specified reference points C and D (“zero” points) in Figure 9. On the front side from the reference points, the arc-length distance is defined as negative. Distributions: 6. Section profiles of sheet blank at Sections I and IV before and after springback. Distributions: 2.
It is critical to update the number of points used in each of the 24 distributions in ROW 10 of the appropriate columns and worksheets. 
Figure 8. Draw-in measurement at Sections I, II & III. |
Figure 9. Strain measurement and springback section profiles at Sections I & IV. |
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