Simulation models for development of components with tailored material properties

Transcription

1 CHS Theme Day at Volvo Cars, Simulation models for development of components with tailored material properties Professor Mats Oldenburg Luleå University of Technology Presentation outline: - The press hardening process - Process modelling - Components with tailored material properties - Challenges and opportunities

2 Press hardening from innovation and research in Luleå to a global technology Background Manufacturing of ultra-high strength steel components Thermo-mechanical process Boron alloyed steel Simultaneous forming and quenching Innovation from Luleå, Sweden, 40 years ago. Cooperation between the university and the iron works NJA (now SSAB) Industrialized by Plannja Hardtech (now Gestamp Hardtech) Today the globally dominant technology for weight reduction of vehicle structures

3 Research: Process modelling Interactions involved in the thermo-mechanical forming process Advanced automotive applications Structural components with distributed tailored mechanical properties 1 - Deformation dependent thermal boundary conditions 2a - Mechanical properties depend on temperature 2b - Thermal expansion 3a - Latent heat due to phase transformations 3b - Thermal properties depend on microstructure 4 Microstructure evolution depend on temperature 5a - Mechanical properties depend on microstructure evolution 5b - Volume change due to phase transformations 5c - Transformation plasticity 6 - Phase transformations depend on stress and strain Side rails B-pillar Other structural components

4 Research: Process modelling Maximum springback = 0.29 mm (negative, scaled 20 times) Results final component Martensite Measured and calculated forming force (Åkerström, Oldenburg: Numerical simulation of a thermo-mechanical sheet forming experiment, Numisheet 2008, Interlaken)

5 Tailored properties - process modelling Tool model for studies of pressing sequence Steady state condition - temperature histories Formation of martensite Formation of ferrite

6 Industrial application example, Gestamp Hardtech Tooling compensation for cooling deformation of a tailored property component - Volvo XC90 A-pillar inner reinforcement - Initial deformation range -2.4 to 3.3 mm - Cooling deformation compensation in one step - Production tool design based on simulation results - Component within tolerances (+/- 1 mm) with only minor further adjustments of the production tool Out of plane cooling deformation Martensite content Range -2.4 mm (blue) to 3.3 mm (red) Range 0.0% (blue) to 99.9% (red)

7 Paradigm shift - Component and structure design include design of material properties that govern final performance - The complete process chain is taken into account during technology development - Technology developments creates new demands on accuracy in material and process modelling - New demands on material and process modelling when performance simulations are directly linked to process simulation results

8 Challenges and opportunities - Short term: - Improved microstructure models that takes different types of ferrite, bainite and martensite into account => better prediction of material properties and performance - Model development for new steel grades and manufacturing processes - Accurate prediction of strength, deformation and failure properties based on process simulations - Long term: - Accurate prediction of fatigue properties based on process simulations - Material development based on simulation models, taking the complete process chain into account

9 Example of cooperation between research and industrial development Industrial partner Failure modelling and simulation Component function analysis Crash simulation and test Wear modelling and simulation Process simulation Tailored material properties Analysis of hot stamping PROCSIM II PROCSIM III PROCSIM IV IMCOR DYNSYS OPTUS Hot LOWHIPS OPTUS OPTUS II OPTUS III TiFORM I, II CHS Failure modelling LTU, Solid Mechanics FFI Tool Wear Diecond

10 Laboratory resources Materials testing machines and Split-Hopkinson pressure bar From quasi-static to high-speed (VHS) (20 m / s).

11 Laboratory resources High Speed Test (VHS) of car structure component 15 m/s (54 km/h), max. 15 velocity m/s (54 = km/h) 20 m/s, max. force = 100 kn

12 Laboratory resources High Speed Test (VHS) of car structure component 15 m/s (54 km/h), max. velocity = 20 m/s, max. force = 100 kn

13 Measured force Measured velocity

14 Laboratory resources High speed, high temperature strain field measurements using Digital Speckle Photography, notched specimen Fast video camera, frames/sec, at 512x512 resolution Boron steel sheet, heated to 900 DegC, fast cooling to 800 DegC, initial strain rate 200 /sec

15 Laboratory resources Impact mechanics Tensile testing of Inconel 718 at high temperatures and strain rates High temperature compressive testing in Split Hopkinson Pressure Bar True stress [MPa] Strain rate ~900 1/s o C 1000 o C o C True strain True stress [MPa] Strain rate ~4400 1/s o C 1000 o C 1100 o C True strain

16 Laboratory resources Hot tensile test at 800 DegC austenite phase Austenitisation at 900 DegC for 3 minutes, fast cooling to 800 DegC, strain rates = 1, 10, 50 and 200/sec Engineering stress strain curves

17 6th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS The sixth international conference on hot forming and press hardening where arranged by Luleå University of Technology, University of Kassel and AIST in Atlanta, Georgia, USA, 4-7 June, 2017.

18 7th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS The seventh international conference on hot forming and press hardening where arranged by Luleå University of Technology in Luleå, Sweden, 2-5 June, 2019.

19 Gestamp 2017 CHS Temadag

20 Background Failure prediction at Gestamp Development of the OPTUS model started in 2005 Cooperation with Ford Forschungszentrum Aachen (FFA), Volvo cars & Luleå university of technology Features that were considered lacking in models available in commercial software Mesh size regularization Capturing thickness dependent fracture elongation for shells Gestamp

21 The OPTUS model DD = AA ll tt 2 ee BB εε pp εε 0 1, εε pp εε 0, σσ = σσ(1 DD) A = Material parameter B = Material parameter l = Characteristic element size t = sheet thickness εε 0 = localization threshold strain Gestamp

22 The OPTUS model Summary a) 0-2,5-1,5-0,5 0,5 1,5 2,5 x/t L 0 0,05 0,1 0,15 εε pp The predicted fracture strain is a function of stress state, mesh size and sheet thickness. Overall behavior is regularized with respect to mesh size Handles several sheet thicknesses without modification of input data Longitudinal coordinate Gestamp

23 Failure prediction with reference to manufacturing history Thermo-mechanical forming analysis Air cooling during transfer Forming and quenching Post cooling to obtain final shape, thickness and microstructure Mapping Field variables Material properties / phase content Failure parameters geometry/ thickness Crash analysis Force-displacement response Deformed geometry Area with failure Gestamp

24 Failure prediction with reference to manufacturing history Approach based on mean-field homogenization Gestamp

25 Rear side rail example Mesh division into property groups Flow curves and fracture properties of each group estimated with the MFH method Rear side rail example Gestamp

26 Rear side rail example Gestamp

27 Working for a Safer and Lighter Car Gestamp 2017 Gestamp 2017