10 DEFECTS ANALYSIS IN DIE CASTING

10 DEFECTS ANALYSIS IN DIE CASTING

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Die casting is a metal casting process characterized by the use of a mold cavity to apply high pressure to melted metal, similar to injection molding of plastic.

Die casting is particularly suitable for the manufacture of a large number of small and medium-sized castings, so die casting is the most widely used of all kinds of casting processes. Compared to other casting techniques, die casting provides a flatter surface and a higher degree of dimensional consistency. However, non-standard operations and parameters can also create a wide variety of defects.

1. Flow marks and patterns

Appearance inspection:

There are stripes on the surface of the casting consistent with the flow direction of the metal liquid, and there are obviously visible non-directional lines which are different from the color of the metal matrix, and there is no development trend.

The causes of flow marks are as follows:

1) The mold temperature is too low;

2) Poor sprue design and poor internal gate position;

3) The material temperature is too low;

4) Low filling speed and short filling time;

5) Unreasonable casting system;

6) Poor exhaust;

7) Unreasonable spray.

2. Reticulated hairy wing (turtle crack)

Appearance inspection:

There are raised or depressed marks like reticulated hair on the surface of the die casting parts, which are continuously expanded and extended with the increase of the number of die casting.

The causes are as follows:

1) There are cracks on the surface of die casting cavity;

2) Uneven preheating of die casting mold.

3. Cold insulation

Appearance inspection:

Die casting surface has obvious, irregular, sinking linear lines (there are two kinds of penetration and not penetration) small and long shape, sometimes the transition edge is smooth, there is the possibility of disconnection under the action of external force.

The causes are as follows:

1) The two metal flows are butted with each other, but they are not fully fused and there is no inclusion in them, and the binding force of the two metal flows is weak;

2) Casting temperature or die casting temperature is too low;

3) The sprue position is not correct or the flow is long;

4) Low filling speed.

4. Shrinkage (indentation)

Appearance inspection:

There is a smooth indentation (like a disc) on the thickest surface of the die cast.

The causes are as follows:

1) Improper design of die castings caused by shrinkage and too large wall thickness difference; Improper gate position; Low injection ratio, short holding time; The local temperature of the die is too high.

2) Unreasonable cooling system design;

3) Die opening too early;

4) Pouring temperature is too high.

5. Dented Surface

Appearance inspection:

The marks left by the contact between the casting surface and the die casting cavity surface or the step marks on the casting surface.

The causes are as follows:

1) The ejector rod end face is worn by the ejector element; Inconsistent length of push rod adjustment; The cavity splicing part of the die casting model does not fit well with other parts.

2) Loosening of the Mosaic part caused by splicing or moving part; Loose or worn movable parts; The side wall surface of the casting is formed by inserts interspersed between moving and fixed molds.

6. Adhesion Traces

Appearance inspection:

Small flake and metal or non-metal and metal matrix part melting, under the action of external force peeling off small flake, after peeling off the surface of the casting some shiny, some dark gray.

The causes are as follows:

1) There are metallic or non-metallic residues on the surface of the die casting model cavity;

2) When pouring, the impurities are first brought into the cavity surface.

7. Layering (clipping and peeling)

Appearance inspection or damage inspection:

There are distinct layers of metal in parts of the casting.

The causes are as follows:

1) The rigidity of the mold is not enough. In the process of filling with metal liquid, the template jitter occurs;

2) The punch crawls in the process of injection;

3) Improper gate system design.

8. Frictional ablation

Appearance inspection:

Die castings produce rough surfaces at certain locations.

The causes are as follows:

1) Improper position direction and shape of the inner gate caused by the die casting mold (die);

2) The cooling of the intense scouring of metal liquid in the inner runner caused by casting conditions is insufficient.

9. Erosion

Appearance inspection:

There are pitting or convex lines at local locations of die castings.

The causes are as follows:

1) Improper setting of the inner gate position;

2) Poor cooling conditions.

10. crack

Appearance inspection:

When the casting is placed in alkaline solution, the cracks appear dark gray. The damage and cracking of metal matrix are linear or wavy, and the grain is narrow and long, which tends to develop under the action of external force.

The causes are as follows:

1) Iron content is too high or silicon content is too low; The high content of harmful impurities reduces the plasticity of the alloy. Al-si alloy and al-si copper alloy contain too much zinc or copper. Aluminum magnesium alloy contains too much magnesium;

2) The mold retention time is too short and the pressure retention time is short; There are drastic changes in casting wall thickness;

3) The local wrapping force is too large, and the force is uneven during ejecting.

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