With the hot tear criterion, critical areas can be identified early on. The calculation is based on a stress calculation that considers both the casting and the die. This makes the calculation very time-consuming, even if significant computing power is available. To reduce the calculation time for an optimization of the casting layout, in this case a modified coo-ling for an existing casting, Martinrea Honsel has developed a methodology that also allows the qualitative risk assessment for areas prone to hot tearing using a greatly simplified model . The transferability of the results of this optimization is then verified using the conventional hot tear prediction (which is based on a full stress calculation).
The starting point for optimization in this case was a crankcase in which hot tearing occurred reproducibly during prototype production as a low pressure die casting. The position of the hot tear can be reproduced using a MAGMASOFT® stress simulation (Fig. 3).
The simplified hot tear criterion (SHC) defined by Martinrea Honsel evaluates the differences in the solidification time in the region where the hot tear occurs and the solidification time of the area influenced by cooling. The criterion can be generated and evaluated using evaluation areas in MAGMASOFT® with a so-called “user-result”.
As a variable for the systematic optimization of the process conditions, the time at which cooling is activated was chosen. The optimization objectives were to minimize the SHC as well as the porosity.