What are the reasons for the lack of casting of die castings

Update:30 Apr 2021

In the production process of die-casting parts, many quality problems will be encountered, that is, as a common quality defect of die-casting parts, under-casting is one of the defects. What are the reasons for the under-casting of die-casting parts? According to the analysis as follows:

During the forming process of die-casting parts, Magnesium die casting parts  some parts are not filled completely, which is called under-casting. When the lack of casting is serious, it can be regarded as the shape of the casting does not meet the requirements of the drawing. Generally speaking, undercasting is not allowed.
The reasons for undercasting are:img_e5951

1) Poor filling conditions, irregular condensed metal in the undercast part;
When the pressure is insufficient, insufficient, and the metal at the front of the activity solidifies prematurely, under-casting occurs in corners, deep recesses, thin walls (even thinner than the average wall thickness), and cylindrical holes.

The mold temperature is too low; the alloy pouring temperature is too low; the position of the inner gate is not good, forming a large movement resistance.

2) The gas is obstructed, the surface of the under-casting part is lubricated, but the shape is irregular. The part where it is difficult to set up the drainage system, the gas accumulates; when the molten metal is active, the turbulence is violent and envelops the gas.
3) There are residues in the plastic mold cavity. Improper amount of paint or spraying method causes local paint deposition.

The inlay gap of the molded part is too large, or the sliding cooperation gap is too large, and the metal enters during filling. After the casting is released, it cannot be completely taken out and appears to be sandwiched in the gap. When the sheet-like metal (the thickness of the metal sheet is the size of the gap) is more convex than the surrounding molding surface, the height of the protrusion is changed to the wall thickness of the casting when the mold is closed, so that Future castings will create grooves that penetrate (in terms of wall thickness) there. This penetrating groove becomes a special form of undercasting. This kind of under-casting phenomenon mostly occurs in the case of a deep cavity composed of inlays.

On a vertical die-casting machine, when injecting, the lower punch moves down to make the nozzle orifice insufficient, resulting in a series of poor filling conditions.