Analysis of Ten Defects in Aluminum Die Casting

Die casting is a metal casting process that uses a mold cavity to apply high pressure to melted metal, similar to plastic injection molding. Die casting is particularly suitable for the manufacture of a large number of small and medium-sized castings, so die casting is a widely used one in various casting processes. Compared to other casting techniques, the die-cast surface is more flat and has a higher dimensional consistency. However, non-standard operations and parameters also produce a wide variety of defects.

First, flow marks and patterns

Visual inspection:

On the surface of the casting, there are streaks that are in line with the direction of the flow of the molten metal, and there are clearly visible non-directional lines that are not the same as the color of the metal substrate, and there is no development trend.

The causes of flow marks are as follows:

(1) mold temperature is too low;

(2) Bad sprue design, bad position of the inner gate;

(3) material temperature is too low;

(4) low filling speed and short filling time;

(5) The pouring system is not reasonable;

(6) Bad exhaust;

(7) Spray is not reasonable.

Second, mesh hairy (tortoise crack)

Visual inspection:

On the surface of the die-casting, there are traces of reticular hairlike protrusions or depressions, which continuously expand and extend as the number of die castings increases.

The reason is as follows:

(1) There is a crack in the die casting cavity surface;

(2) The preheating of the die casting mold is not uniform.

Third, cold

Visual inspection:

Die casting surface has obvious, irregular, subsidence linear pattern (with penetration and non-penetration) small and long, sometimes smooth edge of the interface, there may be disconnected under external force.

The reason is as follows:

(1) Two metal streams butt each other, but not completely fused and no inclusion exists, and the two metal bonds are weak;

(2) Pouring temperature or die casting mold temperature is low;

(3) The runner is not in the correct position or the flow path is too long;

(4) The filling speed is low.

Fourth, sinking (dent)

Visual inspection:

There is a smooth dent (like a dish) on the surface of most of the die casting thickness.

The reason is as follows:

(1) Caused by shrinkage

Improperly designed die-casting wall thickness difference is too large;

Improper runner position;

Injection pressure is lower and holding time is shorter;

Die casting mold local temperature is too high.

(2) The design of cooling system is not reasonable;

(3) premature opening;

(4) The pouring temperature is too high.

Fifth, the imprint

Visual inspection:

The trace left by the contact between the surface of the casting and the surface of the die casting mold or the surface of the casting.

The reason is as follows:

(1) Caused by ejection element

The top end of the rod is worn;

The adjustment of the length of the top rod is inconsistent;

Die casting mold cavity splicing part and other parts do not cooperate well.

(2) caused by stitching or moving parts

Inlay part is loose;

Loose or worn parts of the activity;

The side wall surface of the casting is formed by inserts that are interspersed with moving and fixed molds.

VI. Adhesive traces

Visual inspection:

The small pieces and the metal or non-metal are welded to the base part of the metal, and the small pieces are peeled off under the action of the external force. The surface of the casting after peeling is shiny and dark gray.

The reason is as follows:

(1) Metal or non-metal residues on the surface of the die casting mold cavity;

(2) Impregnate impurities on the surface of the cavity when casting.

Layering (skinning and peeling)

Visual inspection or destruction inspection:

There is a distinct level of metal in the casting.

The reason is as follows:

(1) The mold rigidity is not enough. In the molten metal filling process, the template generates jitter;

(2) Crawl phenomenon occurs during the injection process;

(3) Improperly designed sprue system.

Eight, friction ablation

Visual inspection:

Die casting surfaces produce rough surfaces at certain locations.

The reason is as follows:

(1) The position and shape of the in-situ runner caused by the die-casting type (die) are improper;

(2) Insufficient cooling of the molten metal at the inner runner due to casting conditions.

Nine, erosion

Visual inspection:

Die castings or embossings are provided in the local area of the die casting.

The reason is as follows:

(1) Improper setting of the sprue location;

(2) The cooling condition is not good.

Ten, crack

Visual inspection:

The castings were placed in an alkaline solution and the cracks were dark gray. The destruction and cracking of the metal matrix is linear or wavy. The lines are narrow and long, and there is a tendency to develop under the influence of external forces.

The reason is as follows:

(1) The iron content in the alloy is too high or the silicon content is too low; the content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy; the amount of zinc or copper contained in the aluminum-silicon alloy, aluminum-silicon-copper alloy is too high; in the aluminum-magnesium alloy Excessive magnesium content;

(2) The time for leaving the mold is too short and the holding time is short; the wall thickness of the casting has drastic changes;

(3) The local tightening force is too large, and the force is uneven when ejected.