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Ragnar Larsson, Professor Johan Ahlström, Ph D

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1 Ragnar Larsson, Professor Johan Ahlström, Ph D
MCR - Chalmers University of Technology Dept. of Applied Mechanics/Materials and Manufacturing Technology Gothenburg, Sweden Håkan Sterner Volvo Cars Engine Process Development CDS-id = hsterner MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

2 Measured out-of-roundness (OOR)
Picture shows OOR before machining at 5 positions Circles are reference lines The outer curve = the upper part of cylinder - oval! The inner curve = the lower part of cylinder - square! MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

3 Improved Quality and reduced Costs
Problem: High residual stresses arise during casting of engine blocks with liners of cast iron due to differences in thermal expansion. Unwanted out-of-roundness (OOR) during machining of cylinders. Targets: A working model for prediction of form distorsions due to residual stress Improved Quality and reduced Costs Improved future cylinder block design MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

4 Simulate the casting process with preliminary material models
Approach/Methods: Simulate the casting process with preliminary material models Material analyses and implementation into better material models Improved calculations of distortions and residual stresses after casting Measure residual stresses Measure machined parts Simulate the machining process Compare results Compare results MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

5 The full FE-model, block and liners
The block is high-pressure die-cast from aluminium (blue) Liners of cast iron (orange) ca elements MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

6 High-pressure die-casting of blocks
Cast iron liners are fixed into the die Aluminium melt (AlSi9Cu3) is pressed into the die; filling time 130 ms Ejected after 25 s; temperature ca 350°C Air cooling at pallets, according to fig. (ca 1 h cooling to 50°C) Trimming and grit blasting MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

7 Preparations before mechanical computation
Thermal computation - cooling by convection Assumptions of the relative values of the film coefficients h Adjustment of absolute levels to match the measured cooling rate DOF: ca CPU-time: < 1 h Compensation for thermal contraction Red = high convection MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

8 Mechanical computation
Done in steps: Thermal contraction and generation of residual stresses, reading the temperature field from the thermal simulation (down to ca 50 °C) Residual cooling in one step down to 20°C (no relaxation at low temp.) Preliminary machining simulation: top/bot surfaces, oil tube, crank case ventilation Preliminary machining simulation: liners and water slots between cyl. Ca DOF Ca 30 CPU hours MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

9 Material volumes removed in steps 3-4
ca elements ca elements MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

10 Computed vs measured OOR after cooling near the top plane
von Mises stress Deformations magnified 20x OOR, cyl. 2 – 4 x-direction y-direction Computed rnom – 0.2 mm rnom mm Measured rnom mm MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

11 von Mises stresses in the block
After step 2 After step 4 After step 3 MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

12 Improve the material model for the aluminium. Master’s thesis running:
Future work Improve the material model for the aluminium. Master’s thesis running: tensile testing of block material at different temperatures and strain rates. material models are evaluated and calibrated (efficient models) Improve the material model for the cast iron. Data available through cooperation with Volvo AB. Implement direction-dependent friction between liner and block Residual stress measurements at Volvo Powertrain Improved modelling of machining Compare results between computations and measurements MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

13 Thank you for your attention!
MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

14 Preliminary material model
MERA-programmet/programkonferensen , projekt: , Ragnar Larsson/Tillämpad mekanik, Chalmers

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