Die Spray Cooling Model
Between shots in high pressure die casting, spray robots traverse the open die with banks of nozzles that apply lubricant and coolant to the die surface. This spray cooling step is one of the most important thermal management tools available to the die caster. Where the spray lands, how long it is applied, and which areas are blocked by die geometry all have a direct effect on die temperature distribution, hot spot behavior, and ultimately casting quality and die life.
The Die Spray Cooling Model in FLOW-3D CAST simulates the spatial variation in spray cooling across the die surface during thermal die cycling simulations. Rather than applying a constant heat transfer coefficient to the entire cavity, the model explicitly computes the cooling effect of each spray nozzle, accounting for nozzle position and movement, spray cone geometry, die surface shape, and blockage effects. This produces a realistic, spatially varying temperature distribution that reflects the actual spray process.
How the Model Works
The model uses a ray tracing algorithm to compute the spray area on the die surface in real time as the spray robot moves. For each nozzle and die surface element, the model determines whether the element is within the spray cone, whether it is blocked by die geometry, and whether it receives spray from multiple overlapping nozzles. Areas blocked from the spray receive only the ambient heat transfer coefficient; areas sprayed by multiple nozzles receive the highest applicable heat transfer coefficient.
Nozzles are grouped into banks, each with its own spray cone characteristics, coolant properties, and on/off control schedule. The translational and rotational movement of the spray robot arm is defined as a time-dependent motion table, allowing the full traversal path to be captured accurately.
Heat Transfer Coefficient Calculation
Two methods are available for defining the spray cooling heat transfer coefficient (HTC), giving engineers flexibility based on the data available to them.
Dependency-Based Method
When the spatial variation of the HTC is known from measurement or prior CFD analysis, it can be expressed as a base HTC multiplied by factors that account for spray distance, spray angles, and other spatial dependencies. These factor functions can be defined as constants or tabular data, and can be linked to external files for ease of management across multiple nozzle configurations.
Spray Medium Properties Method
When spatial HTC data is not available, the model can compute the heat transfer coefficient directly from spray medium properties. The calculation is based on the energy exchange between the spray and the die surface, accounting for the spray nozzle flow rate, coolant density and evaporation temperature, spray cone geometry, spray distance, and spray angles. A calibration efficiency coefficient (default 0.75) can be adjusted to match experimental temperature measurements. This method makes the Die Spray Cooling Model practical for foundries that do not have access to detailed spray characterization data.
Modeling Capabilities
The Die Spray Cooling Model in FLOW-3D CAST supports:
- Ray tracing computation of spray area on the die surface, updated continuously as the robot moves
- Blockage detection based on die surface shape and spray angle
- Overlap handling for areas covered by multiple spray nozzles
- Multiple nozzle banks with independent spray characteristics, coolant properties, and on/off schedules
- Time-dependent robot arm motion (translational and rotational) defined as a motion table
- Two HTC calculation methods: spatial dependency functions or spray medium properties
- Nozzle database for storing and reusing characterized nozzle properties across simulations
- Spray area visualization output for validating nozzle positioning and robot path
- Total spray time and total heat removed per unit area for postprocessing
- Integration with Thermal Die Cycling for multi-cycle die temperature analysis
- Part-by-part spray treatment schedules with options for spraying, cleaning, and coating defined independently per die component
- Slider motion support, with cooling channels and heating elements moving with sliders during the spray stage
Case Study: Structural Vehicle Component
A case study was carried out using a large, thin-walled structural vehicle component to demonstrate the importance of simulating die spraying explicitly rather than assuming a uniform heat transfer coefficient. The simulation used five thermal die cycles, each consisting of four stages: solidification, ejection, spray cooling, and dwelling.
Three thermocouples were placed in the ejector die to monitor temperature at different locations: one in the casting area, one outside the cavity where spray cooling occurs but no metal contact is made, and one at the biscuit, which acts as a hot spot. Comparing the thermocouple histories from the simulation against measured data demonstrated that the Die Spray Cooling Model produces significantly more accurate temperature predictions than a constant HTC approach, particularly at locations where spray geometry and blockage effects are significant.
Spray area during spray cooling. Simulation courtesy of Audi AG.
Die surface temperature at the fifth cycle of spray cooling. Simulation courtesy of Audi AG.
Applications
The Die Spray Cooling Model is used in HPDC process design and optimization for:
- Optimizing spray robot paths and nozzle bank configurations to eliminate hot spots
- Evaluating the effect of spray duration, flow rate, and nozzle positioning on die temperature balance
- Designing spray protocols for large, complex dies where geometry blocking is significant
- Validating spray cooling designs against thermocouple measurements before production
- Supporting die life analysis by predicting thermal fatigue from temperature gradients
- Reducing cycle time by identifying the minimum spray duration needed to achieve target die temperatures