Common Defects of Investment Casting from jccasting's blog

Since investment casting involves a complex process, there is no shortage of opportunities for error. When certain undesirable irregularities in the metal casting process cause defects, the fabricator can decide whether these defects are tolerable, repairable or need to be eliminated entirely. However, the nature of the defect must be clearly understood before making a decision. In addition, the location, appearance, size and shape of the defect must also be considered. These investment casting defects fall into the following categories:

Hot tear or shrinkage crack

Hot tear defects can occur when the ceramic shell mold restricts the shrinkage of the molten metal during solidification or cooling. This usually looks like a jagged crack with an irregular path. Manufacturers often modify investment casting designs to address this issue.

Inclusions

These are classified as negative defects and appear as small, round, angular or irregular pits and are usually due to foreign non-metallic particles within the casting. They can also be surface cavities or depressions of various shapes and sizes with traces of refractory material. One possible cause of inclusions could be cracks in the wax pattern allowing ceramic fragments to enter the cavity.

Misrun

Poor pouring is a negative defect that can occur when the mold cavity is not completely filled with molten metal. This usually happens when the shell is too cold, the metal is too cold, or the filling rate is too slow.

porosity or gas

This can manifest itself as air pockets forming within the investment casting during cooling. Since liquid materials tend to contain large amounts of dissolved gas, these materials outgas as they solidify.