The simplest measure was to reduce the length of the entire gating system, which was forcing the casting to bend. The main process restriction was an increased danger for cold shuts during filling and some porosity in heavy sections, since the intention was to also remove the feeders. This design change was demonstrated to be effective by reducing the casting distortion from 1.4 mm to 0.8 mm. The simulation with MAGMASOFT® also showed that the new gating system led to an increased yield without compromising the casting quality.
During the study, high stress values also were detected in the central ribs of the casting. Removing the ribs completely relieved the casting stresses. Discussions with designers showed that 15 years ago the ribs were introduced only for manufacturing reasons, to make the casting “less sensitive” to distortion. The ribs had no functional purpose. In fact, the “stiffening” of the casting generated more problems because it increased the potential for cracks. Consequently, the casting was redesigned without the interior ribs, avoiding the stresses and reducing the component’s, and hence the engine’s, weight.
Samples produced with the new gating system were machined using the new magnetic fixation system without any problems caused by distortion.