Permanent Mold Casting of Aluminum Alloys

In the entire industry, Aluminum casting in permanent molds of steel and iron is widely used, and aluminum, as well as its alloys, make up the huge majority of permanent mold castings. In permanent molds, several methods are used for aluminum mold casting. This article mostly focuses on permanent mold casting with molten aluminum fed by low pressure, vacuum and centrifugal pressure, gravity, and squeeze casting.

Compared to sand castings, permanent-mold castings cool faster than, giving them a much finer, more uniform microstructure. Mechanical properties are boosted by up to 20%. In comparison, much stronger skin is present in pressure-die-cast parts but has weaker sections of the interior.

The process

Large numbers of dimensionally repeatable parts are produced using Permanent molds that are machined from cast iron or steel. In contrast, investment and sand-cast molds during part removal and die casting are destroyed. This also happens under extremely high pressures when molten metal is injected into dies in aluminum casting factory.

Throughout the industry Aluminum casting in steel and iron is permanent. Consequently, dies must be designed to withstand these pressures which compared to gravity-filled permanent molds drastically boost the cost.

With uniform nonporous microstructures, permanent-mold castings can be made, but on solidification rates and foundry tooling designs, these qualities are highly dependent. Molds must be designed carefully with sprue, vents, and risers.

To help ensure controlled laminar flow of the metal into the mold and adequate feed to all sections of the casting design and placement of sprue and gates are critical. The amount of gas entering the melt is minimized by the laminar flow. In castings inordinate amounts of dissolved gas in the melt produce voids.

For areas of a part that otherwise may become isolated, risers act as reservoirs of metal to supply a constant flow. Compared to thick ones thin sections freeze faster. Thus, to continually feed the cavity carefully placed risers are needed as metal contracts during cooling. Because of this phenomenon in aluminum mold casting projects, the void formed is a casting defect known as shrinkage porosity. At last riser, sprue solidifies resulting in what is denoted as directional solidification.