Shrinkage Defects (Sink Marks) in Die Casting

Visual Inspection:
Upon examining the surface of thicker sections of die-cast parts, one can observe smooth indentations that resemble the shape of a saucer.

Causes of Shrinkage Defects:

1. Contraction-Induced Issues:
Improper design of the die-cast part leads to significant thickness variations.
Incorrect positioning of the gating system.
Insufficient pressure during the casting process and short holding time.
Overheating in certain areas of the die-casting mold.
2. Inadequate Cooling System Design:
The design of the cooling system plays a pivotal role in the solidification of the molten metal. An inefficient design can lead to uneven cooling, which in turn can cause shrinkage defects.

3. Premature Mold Opening:
Opening the mold too early, before the metal has solidified completely, can lead to sink marks on the part’s surface.

4. Excessive Pouring Temperature:
Using a molten metal temperature that’s too high can exacerbate the shrinkage issue. It’s crucial to maintain an optimal temperature to ensure uniform solidification and minimize casting anomalies.

Recommendations for Avoiding Shrinkage Defects:

To mitigate the risk of shrinkage defects, it’s essential to focus on the design phase. Ensuring uniform wall thickness, optimizing the gating system, and maintaining the right casting parameters can go a long way in producing high-quality die-cast parts. Regularly monitoring and adjusting the process variables, coupled with routine mold maintenance, can further enhance the casting quality and reduce the occurrence of such flaws.