Advancement of Cryogenic Science

All Aluminum and aluminum alloy castings have built-in stress due to the shrinkage of the molten metal after it cools in the molds. Some of these stresses can be reduced and in some areas eliminate by good casting design, by the foundry properly incorporating stress risers.

Castings that have to be machined for closer tolerances, flatness and better surface finishes will, in most cases, distort on these surfaces, which in turn affects the tolerances and flatness of the critical areas. This distortion starts when the outer layer is removed by machining.... this outer layer locks in the stresses and when removed, the machined surfaces will de distorted.

What can be done to relive these stresses before machining?
Through the advancement of cryogenic science, it has been discovered and proven that when these castings are treated in a cryogenic chamber at temperatures of 88°F Kelvin (-300°F) at a controlled time/temperature cycle, all internal stresses are relived. These components will now retain a flatness/parallelism here-to-fore not possible.

They will maintain a dimensional stability in their use function far above the non-treated part. This is due to the re-alignment of molecular structure that has been distorted during the casting or heat treating process. When these cryogenically treated castings are machined, there us no distortion on the machined surfaces… if there is a distortion, it is caused by improper machining, dull cutting tools, speeds and feeds being too slow and /or not enough material removed at the first cut.

Source: http://www.300below.com/press/magazine-articles/controlled-dry-cryogenic-process.html