The optimization of cycle times, die lifetime, microstructures and distortion of castings under the required specifications for component quality and process economy is daily-required practice. In this context, the layout and case-specific optimization of mold temperature control are of outstanding importance. For this task, today, product and process developers have modern mold manufacturing processes and virtual optimization tools at their disposal. These enable high added value from the idea to the series production of a component.
A hydraulic component serves here as an example, which, by design, involves material accumulations and, thus, risks of solidification porosity: a classic in aluminum die casting! It was examined which additional cooling measures in the mold can help to minimize these risks. This involved the comprehensive testing of the small degrees of freedom available.
Figure 1: Porosity in material accumulations is as old as die casting itself. If the problem cannot be avoided by design, effective mold temperature control can help at most.
In the approach chosen in Figure 1, it was possible to increase the cooling of the contour cores in the hydraulic connections without negative effects in other areas. With the aid of the simulation, practically all conceivable cooling variants were calculated in a very short time and evaluated in terms of their effects on the casting and the process in a "virtual test plan".
Figure 2: Test plan of the "virtual DoE": The possible variables of the temperature control (switch-on and switch-off times, flow temperature and flow rate) resulted in 720 conceivable variants, out of which 50 were automatically selected, calculated and evaluated with regard to the achievement of target values for the criteria "solidification time" (due to cycle time), "core temperature gradients" (due to crack risk) and "hot spot" (due to porosity).
The statistical evaluation capabilities of virtual DoE make it possible to determine at a glance early on how sensitive the casting and process are to the different cooling parameters and to determine the best compromise depending on the weighting of the objectives.
Figure 3: The correlation of cooling parameters (below) and target variables (left) shows that the solidification time in the critical casting area, and, thus, the porosity, depends strongly on the start time and the flow rate, but less on the flow temperature. It can also be seen that the flow rate apparently has no influence on the core temperature gradients and, thus, the susceptibility to cracking.
Further potential for efficient temperature control in die casting is provided by three-dimensional, conformal temperature control systems such as can be produced by generic AM processes. They have been state of the art in polymer injection molding for years and are also increasingly gaining attention in die casting.
Early planning is crucial, because conformal temperature control systems and "thermally nimble" molds make the casting process both more sustainable and more cost-effective, while dramatically increasing controllability.