For the other process variables, corresponding virtual Designs of Experiments were conducted, too. These led to the following fundamental insights:
In the area analyzed, the diameter of the cooling channels has no influence on the tool life. Explanation: The average die temperature does not change, resulting in the maximum stresses both during spraying and during filling/solidification not changing either.
The temperature of the cooling medium has a considerable influence on the tool life. This effect can be explained by the fact that the die is on average colder with colder cooling agents. This, in turn, leads to a reduced thermal shock during spraying and, thus, to lower tensile stresses. The temperature increase of the die surface during filling/solidification, however, remains approximately the same, which means that the level of compressive stresses is also almost identical. Overall, the stress range decreases with lower cooling agent temperature (see Figure 5).
Reducing the pouring temperature minimizes both the tensile stresses during spraying and the compressive stresses during filling/solidification, thus increasing the tool life. This can be explained as follows: Reducing the casting temperature leads to a reduction of the average die temperature. This results in a smaller thermal shock during spraying. Likewise, the temperature gradient during filling/solidification is also reduced due to the colder melt.
The variation of spraying, in turn has shown that intermittent spraying of smaller amounts causes smaller tensile stresses in the die surface than one single, intense spray stroke.