What's the Deal With Investment Casting,
and How Does It Work?
Step I - Metal Mould/Mold
Wax patterns are destroyed during investment casting, necessitating a fresh wax pattern for each subsequent casting. This instruction is as given at dawangcasting.com. Investment casting requires a mould or die in order to generate the wax patterns unless the volume is very tiny (as is frequent in artistic work or unique jewelry). Consider the predicted shrinkage of the wax pattern, the expected shrinkage of ceramic material that is poured over the wax pattern, and the expected shrinkage of the metal casting itself when determining master die dimensions.
Step II - Production of wax patterns
In all cases, the number of wax patterns required equals the number of castings to be created; each casting necessitates the creation of a separate wax pattern. Hot wax is injected into a mould or die and allowed to harden before being removed from the mould or die. It is possible that cores will be required to build any internal features. The wax pattern that is created is an exact reproduction of the part that will be manufactured. The process is similar to die-casting, with the exception that wax is utilised in place of molten metal.
Step III - Mold Creation
The wax mould has a gating system (sprue, runner bars, and risers). For smaller castings, a tree-like assemblage of wax patterns is linked to a central wax gating system. A pouring cup at the end of the runner bars pours molten metal into the mould. The pattern tree is immersed in a silica slurry. It is dipped several times, each time coating it with additional refractory slurry. The cured refractory layer produces a ceramic shell around the patterns and gating mechanism.
The ceramic shell thickness is determined by the part's size and weight, as well as the metal's pouring temperature. The typical wall thickness is 0.375 inch (9.525 mm). The solid ceramic mould is heated in an oven until the wax melts and drains. A hollow ceramic shell results.
Step IV - Pouring
The ceramic mould is heated to around 1000 – 2000 degrees Fahrenheit. As the mould is heated, it gains more strength, any remaining wax or impurities are removed, and any remaining water in the mould material is evaporated. While the metal is still hot, it is poured into the mould - the liquid metal flows into the pouring cup, via the central gating system, and into each mould hole on the tree. The metal flows readily through the narrow, precise parts of the mould since it has been pre-heated. This method also results in a more accurate casting since the mould and casting will cool and shrink together as a result of the cooling and shrinking.
Step V - Cooling
Following the pouring of the metal into the mould, the metal cools and hardens. Depending on the material that was cast and the thickness of the casting being created, the time it takes for a mould to cool to a solid state varies significantly.
Step VI - Shakeout
Once the casting has solidified, the ceramic moulds will begin to degrade and the casting will be able to be removed. Typically, the ceramic mould is broken apart by hand or with the use of water jets. After being removed from the gating system tree, the individual castings are separated from one another by hand impact, sawing, cutting, burning, or by utilizing liquid nitrogen to split them apart cold.
Step VII - Finishing
To smooth out the component at the gates and remove defects, finishing procedures such as grinding or sandblasting are frequently used in conjunction with each other. Heat treatment may be necessary to harden the finished item, depending on the metal from which the casting was poured. For read more, check out this homepage.