A lot of quality problems may be encountered in die casting production, which are caused by various reasons. The quality problems in production shall be reasonably identified. The root causes shall be found before it is possible to put forward the corresponding feasible improvement measures, so as to continuously improve the quality of castings.
The quality problems, defect characteristics, causes including improvement measures in die casting are described as follows.
In the die casting forming process, some locations of the part are not filled completely, which is referred to as undercasting. When the location has serious undercasting, the shape of castings can be considered as non-conformance to the requirements of the drawings. Usually, it is allowed to have undercasting in parts.
Causes of undercasting:
1) Poor conditions for filling; the location of undercasting has irregular set metal
In case the pressure is insufficient, the forefront of fluid metal solidifies prematurely, which causes angle, deep concave, thin wall (even thinner than average wall thickness) and cylindrical holes in the wall.
B. Crack
The base material of casting is destroyed or disconnected to form a narrow gap in the form of irregular line. Under the action of external forces, it has the tendency to develop. This kind of defect is called crack. On the die casting parts, cracks are not allowed to exist.
Causes of cracks:
1. Structure and shape of casting
2. Poor surface quality and unstable fastening of the molded parts
4. Alloy composition
1) Zinc alloy
A. High contents of harmful impurities like lead, tin and cadmium
B. Insufficient purity
2) Aluminum alloy
A. High iron content, acicular ferrite increased
B. High silicon content in the aluminum silicon alloy
C. High magnesium content in the aluminum magnesium alloy
D. High contents of other impurities increasing brittleness
3) Magnesium alloy
4)High contents of aluminum and silicon
5) Alloy melting quality
A. The melting temperature is too high, resulting in segregation
B. The heating time is too long, resulting coarse grains
C. Too many oxide inclusions
6) Improper operation
A. Too long stay in mold, especially for alloys of high brittleness, such as magnesium alloy
B. Improper coating quantity, resulting in deposits
7) Poor filling, incomplete metal base fusion, insufficient strength after setting, especially prone to locations far from injection gate.
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