Because many castings need internal cavity structure, the mold can not be directly extracted from the inside of the casting, so it is impossible to create a cavity.
At this time, a core with internal cavity structure is necessary, which can be cleaned from the inside of the casting after the casting is formed and broken by heating.
This increases the casting cost. But it is better to make a part by dividing it into two or more parts and then making it into one part by welding and grinding.
It saves a lot in cost, and the structure is integrated, more stable and firm.