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STAR Global Conf. 2012, 19-21 March, Noordwijk Romuald Laqua, Access - - PowerPoint PPT Presentation
STAR Global Conf. 2012, 19-21 March, Noordwijk Romuald Laqua, Access - - PowerPoint PPT Presentation
Simulation of High Pressure Die Casting (HPDC) via STAR-Cast STAR Global Conf. 2012, 19-21 March, Noordwijk Romuald Laqua, Access e.V., Aachen High Pressure Die Casting: Machines and Products Common Materials: Aluminum alloys Magnesium
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High Pressure Die Casting: Machines and Products
Common Materials:
- Aluminum alloys
- Magnesium alloys
- Zinc alloys
- Copper alloys
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HPDC process cycle, horizontal cold chamber machine
Parts considered for simulation
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HPDC process cycle: 1. closing moving die parts
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HPDC process cycle: 2. shot sleeve filled with melt, starting plunger movement
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HPDC process cycle: 3. completed shot
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HPDC process cycle: 4. ejecting and removing solidified casting
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HPDC process cycle: 5. spraying of lubricant, casting cycle finished
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Challenges in HPDC Simulation:
Moving plunger in filling chamber – moving mesh model necessary Thin walled, complicated and large castings – challenging enmeshment and high cell count Multi physics: melt, solid, gas – VoF model with HRIC scheme, combined with surface tension model and correct wetting angle Short pouring times, leading to high fluid velocities – small time steps (~0.1ms) mandatory Extreme pressure ranges from 10 Pa initial cavity pressure up to 1000 bar in melt during solidification – Compressibility model for melt and gas
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Why simulate?
Goals & Objectives of HPDC Simulation: Reduce iterations in tooling development: Cost for one mould insert 50-100k€ Reduce process development time: faster achievement of a stable process window Better process understanding: helpful when negotiate with customers about necessary part design changes Typical defects in high pressure die casting: Misruns: Melt solidifies before filling is completed Cold shuts: Imperfect fusing of molten metal coming together from opposite directions in a mold Porosity: small holes caused by insufficient feeding or dissolved gas Air and oxides inclusions Cold flakes: floating crystals, solidified at shot sleeve walls and transported into cast part
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High Pressure Die Casting – Overview
Features
- Filling Simulation
- Gas is Compressible
- Liquid is Compressible
- Moving Mesh
- Phase Change
- Conjugate Heat Transfer
Simulation
- Shot chamber is half filled with liquid,
plunger follows shot control curve, pushing the fluid into the cavity
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High Pressure Die Casting: shot curve vPlunger=f(t)
Constant velocity until mold is filled, followed by pressure control, up to 1000 bar
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High Pressure Die Casting – Geometry and Mesh
Die parts Shot sleeve Cast Chilled vents (allow air to escape and force melt to freeze)
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Meshing
Structured (extruded) mesh in shot sleeve Polyhedral mesh in cast part and die Cell count: 1.6 million cells in fluid domains 3.6 million cells overall
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Meshing
- Two layers of prism cells on each side of casting-die
interfaces to resolve high temperature gradients
- Water and oil channels are not meshed
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Process parameter setup, additional settings related to HPDC process
Shot sleeve components must be identified: Empty filling chamber Shot sleeve walls Prefilled with melt
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Process parameter setup
Shot curve definition: Enter values or read from file
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Process parameter setup
Pressure curve definition: Enter values or read from file
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Die cycle warm up simulation
Pure thermal simulation over at least 5 casting cycles, including all phases: shot, solidification, die opening, ejection and spraying Final temperature distribution in die is used as initial state for main simulation run with coupled filling and solidification
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Initial temperatures in die and shot sleeve
Cooling cycles in oil and water channels are modelled by applying mean fluid temperatures on channel wall boundaries (channels are not part of computational domain)
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High Pressure Die Casting – Results
Pressure on melt surface Velocity on melt surface
Time = 1.96 seconds Time = 2.05 seconds Time = 2.06 seconds
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Temperature distribution on melt surface during mold filling
Front view Rear view
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Air entrappments in casting after completed shot (2.52 s)
Initial melt temperature = 640°C Initial melt temperature = 680°C
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Animated mold filling process with piston movement
Initial melt temperature = 680°C Tliquidus = 613°C Tsolidus = 555°C
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