In the production process, die castings will encounter many quality problems, that is, they are common quality defects of die castings. Among them, under-casting is one of the defects, which leads to the cause of under-casting of die-casting parts.
During the forming process of die-casting parts, some parts are not completely filled, which is called under-casting. When the area of ​​under-casting is serious, it can be regarded as the shape of the casting which does not meet the requirements of the drawings. Usually about under-casting is not allowed.
The reasons for the under-casting are:
1) Poor filling conditions, irregular condensed metal in the under-cast part;
When the pressure is insufficient, not enough, and the metal at the front of the activity solidifies too early, causing under-casting of corners, deep depressions, thin walls (even thinner than the average wall thickness), and cylindrical hole walls.
The mold temperature is too low;
The alloy pouring temperature is too low;
The position of the gate is not good and a large resistance to movement is formed.
2) Gas obstruction, surface lubrication of under-cast part, but irregular shape
It is difficult to open the part of the overflow system and accumulate gas;
When the molten metal is active, the turbulence is intense and the gas is wrapped.
3) Residues in plastic mold cavity
Improper use of the coating or spraying method results in localized coating deposition.
The inserting gap of the molded part is too large, or the sliding cooperation gap is too large, and the metal is poured into the filling. After the casting is taken out, it is not completely taken out and presents a sheet-like clip on the slit. When a sheet-like metal (a metal sheet whose thickness is the size of a slit) protrudes more from the surrounding profile, the height of the protrusion is changed to the wall thickness of the casting in the case of clamping. In the future, the casting will have a groove for penetration (for wall thickness). This penetrating groove becomes a special form of under-casting. This under-casting phenomenon occurs mostly in the case of a deep cavity composed of inlays.
Insufficient pouring (including excess material section).
On the vertical die casting machine, when the shot is pressed, the lower punch moves down to make the nozzle opening insufficient, resulting in a series of poor filling conditions.