Analysis Of 10 Defects In Aluminum Die Casting

Die casting is a kind of metal casting process, which is characterized by using the mold cavity to apply high pressure to molten metal, similar to plastic injection molding.

Die casting is especially suitable for manufacturing a large number of small and medium-sized castings, so die casting is the most widely used casting process.

Compared with other casting technologies, the surface of die casting is smoother and has higher dimensional consistency.

However, nonstandard operation and parameters will also produce many kinds of defects.

1. Flow marks and patterns

Appearance inspection:

There are streaks on the surface of casting which are consistent with the flow direction of molten metal

There are obvious non directional lines with different colors from the metal substrate, and there is no development trend.

Flow marks and patterns

The causes of flow marks are as follows:

1) The mold temperature is too low;

2) The runner design is not good, and the gate position is not good;

3) The feed temperature is too low;

4) Low filling speed and short filling time;

5) The gating system is unreasonable;

6) Poor exhaust;

7) Spray is unreasonable.

2. Turtle crack

Appearance inspection:

On the surface of the die casting parts, there are the marks of convex or concave-like reticular hair, which expand and extend with the increase of die casting times.

Turtle crack

The causes are as follows:

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

2) The preheating of die casting die is uneven.

3. Cold isolation

Appearance inspection:

The surface of the die casting has obvious, irregular and depressed linear lines (penetrating and non penetrating) with small and narrow shapes. Sometimes the joint edge is smooth, which may break under the action of external force.

Cold isolation

The causes are as follows:

1) The two metal flows butt with each other, but they are not completely fused and there are no inclusions between them, and the bonding force of the two metals is very weak;

2) The pouring temperature or die casting temperature is low;

3) The runner position is not right or the flow path is too long;

4) Low filling speed.

4. Indentation

Appearance inspection:

There are smooth dents (such as discs) on the surface of most of the thick parts of the die casting.

Indentation

The causes are as follows:

1) Caused by contraction

  • The design of die casting is improper and the wall thickness difference is too large;
  • Improper runner position;
  • The injection ratio is low and the holding time is short;
  • The local temperature of the die casting die is too high.

2) The design of the cooling system is unreasonable;

3) The mold was opened too early;

4) The pouring temperature is too high.

5. Impression

Appearance inspection:

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

Impression

The causes are as follows:

1) Caused by ejecting element

  • The end face of the ejector rod is worn;
  • The adjustment length of the ejector rod is inconsistent;
  • The splicing part of the die casting die cavity does not fit well with other parts.

2) Caused by splicing or moving parts

  • The inlay part is loose;
  • Loose or worn moving parts;
  • The sidewall surface of the casting is formed by inserts interpenetrating the moving and fixed molds.

6. Adhesion marks

Appearance inspection:

Under the action of external force, small flakes are peeled off, and some of the peeled castings are bright or dark gray.

Adhesion marks

The causes are as follows:

1) There are metal or nonmetal residues on the surface of die casting die cavity;

2) When pouring, impurities are brought in first and attached to the surface of the cavity.

7. Delamination (peeling)

Appearance inspection or damage inspection:

There are obvious layers of metal in the part of the casting.

Delamination

The causes are as follows:

1) The rigidity of the mold is not enough, and the template shakes during the filling process;

2) In the process of injection, the punch crawls;

3) Improper design of runner system.

8. Friction ablation

Appearance inspection:

The surface of die casting has rough surface in some places.

Friction ablation

The causes are as follows:

1) The position, direction and shape of the ingate caused by the die casting die are not proper;

2) Because of the casting condition, the molten metal in the ingate scours violently and the cooling of the part is not enough.

9. Erosion

Appearance inspection:

There are pockmarks or convex lines in the local position of die casting parts.

Erosion

The causes are as follows:

1) The position of ingate is improper;

2) The cooling condition is not good.

10. Crack

Appearance inspection:

When the casting is put in alkaline solution, the crack is dark gray. The failure and cracking of the metal matrix are linear or wavy, and the grain is narrow and long, which has a development trend under the action of external force.

Crack

The causes are as follows:

1) The results show that the content of iron is too high or the content of silicon is too low; the content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy; the content of zinc or copper in Al Si alloy and Al Si Cu alloy is too high; the content of magnesium in Al Mg alloy is too high; the content of copper in Al Si alloy and Al Si Cu alloy is too high;

2) The results show that the mold retention time is too short, the holding time is too short, and the wall thickness of the casting changes sharply;

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

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