There will always be defects in die cast tooling. Is there any way to prevent them before defects happen? Therefore, it is important to understand the features and causes of defects in order to find solutions.
1. Casting blowholes
The blowholes are the holes that exist on the surface or inside of the casting. They are round, oval or irregular in shape. Sometimes several holes form an air mass, and the skin is generally in the shape of peers.
2. Casting shrinkage cavities
The shrinkage cavity is a kind of rough surface hole existing on the surface or inside of the die cast. The slight shrinkage cavity consists of many scattered small shrinkage cavities, namely the shrinkage porosity. The crystalline grains in the shrinkage cavity or the shrinkage porosity are coarse.
3. Casting slags
Slags are open or dark holes on the casting, holes are completely or partially filled with molten slags and they have irregular shapes. It is not easy to find small dot flux slags, smooth holes appear after the slag is removed. And they are generally distributed in the lower part of the pouring position. Near the inner runner or at the dead corner of the casting, the oxide slag is mostly distributed on the surface of the die cast near the inner runner in a network. It is sometimes in the form of flakes, or irregular clouds with wrinkles, or in the form of flake interlayers, or exists in the inside of the casting in the form of clusters. With the oxide inside in it, it often breaks from the interlayer when it is broken, which is one of the main causes of cracks of the casting.
4. Casting cracks
The appearance of the crack is a straight or irregular curve. The surface of the hot crack fracture is strongly oxidized and becomes dark gray or black without metallic luster. And the surface of the cold crack fracture is clean with a metallic luster. In general, the external cracks of the casting can be seen directly while the internal cracks can only be seen by other methods. Cracks are often associated with defects such as shrinkage porosities and slags. They mostly occur on the inside of the sharp corners of the casting, and at the junction of thick and thin sections as well as the hot joint area between the casting riser and the casting.
5. Sand inclusions
Relatively regular holes are formed on the surface or inside of the casting, and the shapes are consistent with the shape of the sand grain. The sand grains that are inlaid on the surface of the casting can be seen when they are just out of the mold, and the sand grains can be taken out from it. When multiple sand inclusions exist at the same time, the surface of the casting is in the shape of orange peels.