In die casting, what causes "cold shuts"?

"Cold shuts" in die casting are defects that occur when two flows of molten metal do not completely fuse together, leading to an incomplete joint where the metal solidifies. This phenomenon is primarily caused by insufficient flow of the molten metal, which results in cooler areas meeting at the joint that have solidified before the two sections can properly combine.

In the context of this question, the correct answer, which refers to a lack of fusion at the joint, highlights the mechanical and thermal dynamics involved in die casting processes. For a successful casting, maintaining proper temperature and ensuring that the molten metal adequately flows and fills the mold is essential. If the flow is interrupted or insufficient, cold shuts arise, indicating that the processes of melting, pouring, and flowing were not adequately managed.

While other factors like lack of metal flow, solidification shrinkage, and excessive flash can affect the casting quality, they do not directly lead to the occurrence of cold shuts in the same manner as the absence of proper fusion at the joint. Each of these factors relates to different types of defects or issues but does not epitomize the specific cause of cold shuts.