Die Casting Defect Series - Mold Sticking

2025-08-22

Mold sticking phenomenon (mold sticking, adhesion, friction ablation): During the die casting process, the alloy adheres to the core, the cavity partially or even the entire cavity.

The mold sticking defects of electric drive and electronic control housing products not only affect the appearance of the product, but may also cause product leakage due to the destruction of the surface dense layer by the mold sticking, thereby causing the client assembly function to fail.

Defect feature description:

Mold sticking: During the die-casting process, aluminum, magnesium and mold steel are combined together, and the alloy adheres to the core and the local surface of the cavity to form a bonding layer. Even the casting is partially or completely adhered to the cavity. This phenomenon is called mold sticking.

Sticking and stretching: Visual inspection shows that the die-casting alloy adheres to the mold wall (adhesion) and produces traces of stretching, resulting in rough surface, peeling or missing materials of the casting. In severe cases, the casting will be torn and damaged.

Ablation: A rough surface is formed on the surface of a die-cast part in areas with large thickness. The location and shape of the rough surface defect are fixed, and the surface is uneven. It is caused by the molten alloy and the die steel melting and adhering together. Because it occurs under high mold temperature, some people call it ablation.

Cause:

(1) The alloy liquid pouring temperature is too high.

(2) The mold temperature is too high.

(3) The release agent has poor anti-sticking effect, or the spraying amount is too small, or the spraying is uneven and not in place.

(4) The molded surface is rough, has rust scars, and has an inverted demoulding position.

(5) Mold manufacturing problems: the casting radius and demolding slope of the core and local deep cavity are too small.

(6) The runner system is incorrect, especially the ingate position is improper, so that the molten metal directly impacts the core or the wall, causing local overheating of the mold and sticking of the mold, and the die-cast alloy adheres to the mold;

(7) Ablation occurs because the molten alloy is in contact with the mold steel at high temperature for a long time at the gate position of the mold cavity and the thick and heat-concentrated part of the casting. The molten alloy adheres to the mold surface, forming an uneven surface and leaving corresponding marks on the surface of the casting.

Countermeasures:

(1) Properly lower the pouring temperature of the alloy liquid. Lowering the pouring temperature as much as possible is the best way to solve the problem of mold sticking. Therefore, under the premise of ensuring the casting and quality of the product, try to use a low pouring temperature.

(2) Aluminum alloy adheres to the surface of the cavity (especially near the gate), and the mold is locally overheated, causing mold damage. It is necessary to increase mold cooling, set up water cooling on the casting mold, increase the amount of release agent sprayed on the overheated position, and reduce the mold temperature. The mold control temperature should be within the process range of 180~250℃, and the magnesium alloy may be 200~300℃.

(3) Eliminating the rough surface of the cavity, polishing the mold, reducing local surface or hole scratches on the casting, and increasing the casting radius and demoulding angle are also effective avoidance measures.

(4) When there is severe scouring at the gate in the mold cavity and aluminum alloy is adhered, the filling speed can be appropriately reduced, the injection speed can be appropriately reduced to shorten the high-speed injection stroke and reduce the casting pressure.