The binderless sand casting vacuum process (also referred to as V-process) offers a tremendous amount of freedom to design engineers. It’s one of the near net shaped processes offering close dimensional tolerances without draft, as well as overall thinner walls leading to lighter weight and excellent as-cast surface finish. 

By converting four machined parts from billets, one piece of sheet metal, and one injection-molded part into a one-piece precision sand aluminum casting with V-process, the foundry succeeded in creating tremendous cost savings—$212 per part—as well as reduced weight by eliminating the assembling operation. The one-piece sand casting has no draft, features thinner walls, and offers a variety of better properties.

Part consolidation into a near net shaped casting

•    V-process is a variation of sand casting that uses a vacuum pull to hold the sand in shape instead of a chemical binder. Consequently, binder-related mold gases are not produced and the result is an overall cleaner casting. 

•    The process drapes a thin thermo-plastic film over the pattern, which produces a better surface finish (150 RMS) than conventional sand castings (250-550 RMS); it also allows zero draft with thinner walls.  

•    The process delivers castings approximately twice as accurate as typical sand castings with unlimited pattern life.
Thin wall sections with no draft for lighter weight

•    The wall thicknesses are designed to meet the structural loading requirements. Typically, 2- to 5-degree drafts are added for conventional sand castings, which results in additional 7%–15% weight depending on the feature height with respect to the parting plane.  

•    V-process makes the design process simplified with lightweight solutions because no extra drafts are needed.  Thinner walls have a faster cooling rate, resulting in finer grain and lower secondary dendritic arm spacing (SDAS), which produces better properties!

As-cast versus machined features

The V-process typically restricts the use of cored features and external core placements. However, from a general castability point of view, the proximity of holes to the parting plane, as well as the diameter and depth of the hole features, all factor in to the decision of whether to have holes as-cast or machined out later from the solid casting.