Causes of under casting of die castings

In the production process of die castings, many quality problems will be encountered, that is, as a common quality defect of die castings, under casting is one of the defects. What are the causes of under casting of die castings? The basis analysis is as follows:

During the forming process of die casting, the filling of some parts is incomplete, which is called under casting. When the under cast part is serious, it can be regarded as that the shape of the casting does not meet the requirements of the drawing. In general, under casting is not allowed.

The reasons for under casting are:

1) The filling condition is poor, and the under cast part presents irregular condensed metal;

When the pressure is insufficient and insufficient, and the metal at the moving front solidifies prematurely, it will cause under casting at the corner, deep concave, thin wall (even thinner than the average wall thickness), cylindrical hole wall and other parts.

Mold temperature is too low;

The pouring temperature of alloy is too low;

The position of the inner gate is not good, forming a large movement resistance.

2) The gas is blocked, and the surface of the under cast part is lubricated, but the shape is irregular

Where it is difficult to set up an overflow system, gas accumulation;

When the molten metal moves, the turbulence is violent and the gas is wrapped.

3) Residues in the cavity of plastic mold

Improper coating dosage or spraying method, resulting in local coating deposition.

The splicing gap of formed parts is too large, or the sliding cooperation gap is too large, and the metal runs into during filling. After the casting comes out, it can not be completely brought out and is clamped on the gap. When the kind of sheet metal (the thickness of the metal sheet is the size of the gap) protrudes more than the surrounding mold surface, the protruding height will be changed into the wall thickness of the casting when the mold is closed, so that the future casting will have a penetrating groove (for the wall thickness) there. This penetrating groove becomes a special form of under casting. This under casting phenomenon often occurs in the case of deep cavity composed of inlay.

Insufficient pouring materials (including too thin residual material section).

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