Air Porosity Reduction

WEG is a major electric motor manufacturer in Brazil with captive iron and aluminum high pressure die casting foundries. The die casting foundry was facing a 25 % scrap rate for a two-cylinder compressor. Their client did not accept any porosity on the machined faces of the casting.

Through a design of experiments in the foundry with varying shot velocities and pressures, they were able to reduce the scrap rate to 10%. However, there were still oscillations in the amount of scrap. After two months, they decided to attack this situation with simulation. The first simulation results indicated that the overflows were too small to catch all the entrapped air, and the ingates to the overflows were not properly placed. After the overflows were modified, the scrap rate was reduced to 4 %.

The photo left shows two cylinder compressor casting with porosity due to entrapped air. Original and modified overflow designs show improvements in dealing with entrapped air (right)

In a further step, cooling channels were put in the side cores to increase cooling in the region, aiming to further reduce gas porosity through rapid solidification. This last action brought the scrap rate down to 0.5 %.

Graphic of the evolution of the scrap rate for the compressor component

* Courtesy of WEG Motores, Brazil

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