Casting Simulations with STAR-Cast Julian Gänz, CD-adapco
Need for Casting Simulation Processes Market Overview [Mio tons] Permanent Mold Tilt – Casting 13,6 38,16 Grey Iron 9 Low Pressure-Casting Ductile Iron High Pressure Die 19,4 Steel Non Ferrous alloys Casting Continuous Casting From Modern Casting “ 2010 world census casting production” ... Lost Mold Sand Casting Material Cost/tonne [$] Relative Precision Casting 550 1 Carbon Steel Centrifugal 830 1,51 Cast Iron Bridgeman Aluminium/alloys 2220 4,0 ... Titanium /alloys 17 000 30,9
Need for Casting Simulation • Variety of processes and materials Call for advanced casting processes • Sophisticated geometries • Simulation can help to meet the different and often contradicting demands – Requirements • Mold filling with solidification • Defect Prediction 100000 120000 150000 • Design tool From Austin Group 2002 12000 30000 Tool Cost [$]
Strategic Partnership • Best of both worlds – Provide state of the art of casting simulation solution by combining the engineering experience of two companies which have a long-standing track record in providing CAE solutions and casting processes for over 25 years – Established casting solution STAR-Cast
STAR - Cast • First released in 2009 • Dedicated design and engineering tool for the casting engineer • Core -Capabilities • Multiphase • Resolution of the molten flow and filling front • Model phase change • Dedicated material database • Dedicated User Interface • STAR- CCM+’s state of the art meshing
The Process • Speaking the language of the casting engineer • Quickly adaptable to simulation needs • Any given CAD data • 3D-CAD Modeller Geometry • VOF • Isothermal- gating design • Fluid /Solid Interfaces Filling • Thermal - cooling/ solidification • Appropriate meshing models • Particles/ erosion Mesh • Progress of Solidification • Adapt to simulation goal • Influence on flow Solidification • Expandable • Misruns and cold shut Physics • Transient Postprocessing • Piston Motion • Criteria functions, defect analysis • Tilting Motion Post • Rotation processing
Industrial Challenge - Materials • A dedicated Material Database is available in STAR-Cast, pooling all relevant material information for the casting engineer
Industrial Challenge - Solidification • Mushy / Slurry Zone – Transition from liquid to solid leads to partially solidified areas – Carman Kozeny approach • Solid - Flow Stop – Complete stop of flow in solidified areas Solid Mushy Liquid f L = 0.0 f L = 0.3 f L = 1.0
Industrial Challenge - Defect Prediction • Deduct additional information about the solidification process and the overall quality of the cast • Gather Temperature gradients, cooling rates and local solidification times • Compute criteria functions, such as Niyama or G/v criterion • Estimate porosity characteristics centre line porosity Ref: f: Ac Acces ess, s, ST STAR AR-Cast ast 1.10 10
Industrial Challenge - Porous molds • Phase selective wall porosities for VOF- Phases – Capture the venting effect of a porous mold, core ( i.e. Sand, Investment mold) Calibrated porosity Porosity to low
Industrial Challenge - Complexity • Multi region problem ... – Complex Geometry – Fluid Cavity – Surrounding Air – Different solids ( mold, cooling iron ..) ... Meshing requirements: – Easy surface repair – Multi region Volume meshing – Prism layers – Cell count effective meshing in thin areas
Investment Casting: Shell generation • For precision casting – Dipping a wax model into a ceramic based slurry – Ceramic slurry dries and builds the mold for the casting – Wax is removed in an autoclave Automatic shell mold generation
Investment Casting: Shell generation • Shell mold generator – Mimics a manufacturing process – Based on local curvature Investment Casting
Investment Casting • Challenges in Investment Casting – Thin-walled components with designs at the limit of producibility – Late design freeze, thus shorter development cycles – New materials – New processes Courtesy of Access e.V.
Investment Casting • Answers Engineers are seeking – Sensitivity analyses for process parameters, running and gating system – Geometrical parameter studies – Enhancement and conservation of raw materials and reduction of overall manufacturing cost
Example of a mould-filling optimization Crucible Sprue cup Initial setup Optimized setup Courtesy of Access e.V. & CD-adapco
1 Example of a mold-filling optimization 7 Non-optimized Optimized Simulations show that in a non-optimized distributor the liquid metal keeps rotating in the distributor for a longer time before entering the sprue
Investment Casting • What kind of Defects are of relevance for Investment Castings: • Misruns • Porosity • Freckles • Stray grain formation • Segregation • Hot tearing
1 Predictions of misruns in a gravity-cast LPT blade 9 Inlet Runner Blade Sprue Shell Mould Polyhedral Volume Mesh Schematic diagram of the process
Comparison of simulation and casting trials Magnitude of velocity Gravity casting, Access Temperature TechCenter Courtesy of Access e.V. & Value of secondary dendrite arm spacing was obtained from microstructure measurements CD-adapco
DS/DX Castings: Stray Grain Formation • Stray grains form when corners of the part solidify and there is no connection to the main solidification front. Marked corner will show a stray grain
Looking ahead • Enhance accuracy, robustness and ease of use for a wider range of casting processes • Include further solidification models – Ductile Iron, Grey Iron – Composite castings • Next STAR-Cast release: » Fully Based on STAR-CCM+
STAR-Cast embedded in STAR-CCM+ : v8.02 • Latest solver and meshing capabilities • Modern and easy handling • All the physics to carry out casting simulations – Material Database – Shell mold generator – Defect prediction • Add on module to STAR-CCM+
STAR-Cast embedded in STAR-CCM+: 8.04 • Dedicated mesher for investment casting – Automated Region generation – Prism Layer + Embedded Thin Mesh in thin areas • Streamlined Workflow • Simple set of input variables
STAR-Cast embedded in STAR-CCM+ : Outlook • Process driven GUI for casting applications: – New approach to STAR-CCM+ – GUI adapts to the selected casting process – “Best Practices” are stored – High level of automation – Guide the user through process
STAR-Cast embedded in STAR-CCM+ : Outlook • Concept • Expose only required functionalities • Use casting terminology • Shorten the learning curve • “Conditions”: reusable • Input is stored in an XML file
Casting Simulations with STAR-Cast Julian Gänz, CD-adapco
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