Forming and processes. Mikael Schill, Dynamore Nordic AB

Transcription

1 Forming and processes Mikael Schill, Dynamore Nordic AB

2 Agenda Dynaform Optimization Automatic drawbead modeling LS-PREPOST EZ-setup Blank size optimization MAT_UHS recent devolpments Simulation of forming and Welding

3 DYNAFORM V

4 Dynaform - Optimization Dynaform formability includes optimization setup Uses LS-OPT as optimization software Used for friction, blankholder and/or drawbead force optimization

5 Dynaform optimization setup Drawbeads, friction and/or binder forces are automatically identified as variables and can be included in the optimization

6 Dynaform optimization setup Responses and constraints are defined as percentage of elements within a specified FLD-region

7 Dynaform optimization setup LS-OPT input Uses Dynaform and etapost for pre- and postprocessing

8 Drawbead modeling in Dynaform v5.9 Drawbead modeling is moved to the Autosetup in v types of analytical beads exist: Bead Force: Normal and restraining in percent of critical Bead shape: Analytical formulas define normal and restraining force based on bead geometry Load curve: User input of normal and restraining force

9 Drawbead modeling in Dynaform v5.9 By clicking the Geometry Bead button, the analytic beads are transferred to geometric. Dynaform creates both Finite Elements and surfaces of the drawbead which can be exported to CAD. By pressing Line Bead the geometric beads are deleted and converted to analytic drawbeads. This means that geometric beads can be used in an optimization routine

10 LS-PREPOST

11 Pre-processing LS-Prepost A metalforming application denoted EasySetup has been added. The setup includes several different processes which can be arbitrarily chosen to create a metalforming process

12 Pre-processing LS-Prepost Tooling is modeled in closed position Uses *CONTROL_FORMING_AUTOPOSITION. Thus, LS-DYNA positions the tooling automatically and creates the tool movement based on this. This is a great advantage when positioning in a multi-stage forming process. Includes a material database. The process can be identified as either: For feasability only For formability only For springback The user has the possibility to define e.g. tool speed, element size and massscaling based on accuracy requirements

13 BLANK SIZE OPTIMIZATION

14 Motivation To reduce scrap, the part is often trimmed in before the first forming stage. This is typically done with press-hardened parts due to the strength of the material which makes it difficult to trim after hardening. The challenge is then to predict the trimming shape which yields the finished part shape. Can be done in several ways: Manually Tedious, slow Onestep solvers Good for one step processes. Not really applicable for multi-step processes. A good first estimate. Iteratively in LS-DYNA

15 Input file Easiest to do as a simple text input file Nominal part is input as LS-DYNA Keyword file

16 Input file Different number of elements between initial blank and finished simulated part 0=off

17 Input file Relative path to a FE-mesh of the nominal part. This can be done in LS-PREPOST. This does not change between the iterations

18 Input file Relative path to the simulation result. Use the dynain file which contains the deformed mesh

19 Input file Relative path to the initial blank mesh. If adaptivity is used, then use the adapt.msh file which is the finished mesh in original configuration. If adaptivity is not used, then use the FE mesh of the blank

20 Output Run version R7 Takes only a few seconds Output is a new trimcurve as LS-DYNA input format If you are using LSPREPOST as a pre-processor, simply import the new trimcurve and rerun the simulation. If you are using Dynaform or other pre-processor then you might need to convert the trim curve to IGES. This can be done in LSPREPOST

21 Convert trimcurve to IGES Import the file trimcurves.ibo into LSPREPOST Open the keyword manager Right click on the trim curve definition Save geometry as an IGES file

22 Example

23 First simulation with initial guess Nominal part Finished part

24 LS-DYNA input Nominal part Tool mesh of part Simulated part Dynain file from simulation Initial contour/mesh adapt.msh file

25 LS-DYNA output Initial Guess LS-DYNA output First iteration

26 Results iteration 1 Wanted Iteration 1 Error is appr. 0.6 mm

27 Results iteration 2 Wanted Iteration

28 MAT-UHS

29 Modified Start Temperatures User-defined start temperatures for phase transformations Increase of martensite start temperature due to applied stress T st,m = T st,m0 + M sig η σ eq Source: Antretter et al.: The thermo-mechanical response to a general load path of a martensitically transforming steel

30 Effect of Deformation of Austenite Accelerated phase transformation due to plastic deformation of austenite Q R,i ε pl,y = Q Ri c i (ε pl,γ ) F T,f = T st,f T 3 exp Q R,f T F T,p = T st,p T 3 exp Q R,p T F T,b = T st,b T 2 exp Q R,b T T st,msig = T st,m + M sig η σ eq + ΔT m (ε pl,γ ) Time x m = x γ 1 e α T st,msig T

31 Tailored Tempering B-Pillar with different final properties (PhD Thesis P. Feuser, Daimler AG)

32 Tempering Option for Hardness Calculation 1. Automatic detection of holding phase Tavg T crit and t thresh > t sampling 2. Incremental update for hardness of bainite and martensite HV n+1 i = x i n n+1 x HV i n + x i n+1 n x i n+1 h i T i = b, m i x i

33 Tempering Option for Hardness Calculation

34 SIMULATION OF WELDING

35 Simulation of welding Goldak heat source Coupled thermo-mechanic simulations using the implicit solver. New features for modeling weld passes as ghost material New material model denoted *MAT_CWM

36 Heat input The heat input is done using Goldak double ellipsodial heat source. A weld heat input (power) is prescribed along with a movement of the heat source and direction of the weld arc. The type of weld is chosen by using different geometry of the heat source

37 Ghost elements The material in the weld passes uses a special material routine called *MAT_CWM. The material has both a mechanical part and a thermal counterpart *MAT_CWM and *MAT_THERMAL_CWM The element can either be material or Ghost. When the material is Ghost it has the following properties: Low Stiffness No thermal expansion Low specific heat No thermal conductivity When the temperature reaches a specified temperature, material is activated and recieves material properties

38 Material model specifics Apart from the ghost element function, the material model also includes Anneal functionality. Above a specified temperature, all history variables such as hardening and back stress are set to zero. However, the stresses are calculated from equilibrium equations. The material model includes linear hardening whith seamless isotropic/kinematic portions. All properties are temperature dependent

39 Ghost elements Weld arc Temperature Ghost Activated material

40 To summarize Dynaform formability includes an optimization setup which uses LS-OPT as an optimizer Together with the automatic generation of geometric beads, Dynaform can perform optimization using geometric beads. LS-PREPOST has a forming simulation setup denoted EZ-setup which is highly automated LS-DYNA has the possibility to do Blank Size optimization using the keyword *INTERFACE_BLANKSIZE_DEVELOPMENT MAT_UHS has several important improvements: Martensite phase start temperature as a function of stress Modified activation energies caused by austenitic deformation Incremental update of Vickers hardness for tailored tempering simulations New material model for welding simulations denoted *MAT_CWM and *MAT_THERMAL_CWM which includes: Ghost element functionality Annealing

41 Thank you!