Defects can not be avoided for casting technics, whether it's investment casting or sand casting.
Common defects of investment castings include dross and inclusions, blowholes, shrinkage porosity, shrinkage cracks, cold shuts, hote cracking/hot tearing/hot shortness, miss runs,etc. Such defects will affect the surface roughness and also the strength of the castings. So, all foundries pay lots of costs and time to solve such investment casting defects.
Currently, below methods are widely used to solve or repair the investment casting defects.
1)Before casting, we have to prepare sufficiently.
*Discussing with customer to better the structure of the castings to make it suitable for casting process.
*Improve the gating system to achieve the progressive solidification during casting.
*Control the suitable temperature during casting
*Improve the melting technology to reduce the percentage for air and oxide
*Ensure sufficient casting and add reasonable feeding channels
2)After casting, if the products are with the mentioned defects, we usually repair them as below,
To repair the shrinkage porosity, cracks by weld filling some materials inside the defects. This method is the widely used one. Qualified welds can solve the surface problems and also ensure the strength of the castings. But welding repair require for professional workers, and it takes time and costs to do.Sometime, due to the special material of castings, weld repair might caused more defects on the castings. Then, the casting have to be scraped, thus the production costs is high.
Healant repairing has been used more and more to instead of the tranditional welding repairing. Such metallic healant can be used to repair the castings made from steel, iron, aluminum and bronzes. Such repairing process can avoid to damage the stress of the castings, and solve the problems that might be caused by the welding repairing, thus to save lots of financial loss to increase profits.