Common Problems with Die Casting Molds

Controlling the surface temperature of die casting molds is very important for producing high-quality die castings. Uneven or inappropriate die casting mold temperature will also lead to unstable casting dimensions, deformation of ejected castings during production, and defects such as thermal pressure, mold sticking, surface depression, internal shrinkage and hot bubbles. When the mold temperature difference is large, it will have different degrees of impact on variables in the production cycle, such as filling time, cooling time and spraying time.

1). Cold lines:

Reason: The temperature at the front end of the molten soup is too low, and there are traces when overlapping.

Improvement methods:

1. Check whether the wall thickness is too thin (design or manufacturing), and the thinner area should be filled directly.

2. Check whether the shape is not easy to fill; the distance is too far, the closed area (such as fins, protrusions) , blocked areas, and small fillets are not easy to fill. And pay attention to whether there are ribs or cold spots.

3. Shorten the filling time. Methods to shorten the filling time:...

4. Change the filling mode.

5. Methods to increase the mold temperature:...

6. Increase the melt temperature.

7. Check the alloy composition.

8. Enlarging the escape channel may be helpful.

9. Adding a vacuum device may be helpful.

2). Cracks:

Reasons: 

1. Shrinkage stress.

2. Cracks due to force during ejection or trimming.

Improvement methods:

1. Enlarging the fillet .

2. Check if there are hot spots.

3. Change the boost time (cold chamber machine).

4. Increase or shorten the mold closing time.

5. Increase the draft angle.

6. Add ejector pins.

7. Check if the mold is misaligned or deformed.

8. Check the alloy composition.

3). Porosity:

Reason: 1. Air is mixed in the molten metal.

2. Source of gas: during melting, in the material pipe, in the mold, release agent.

Improvement method:

1. Appropriate slow speed.

2. Check if the runner turns are smooth and cut Is the area gradually decreasing?

3. Check whether the vent area is large enough, whether it is blocked, and whether it is located at the last filling place.

4. Check whether the release agent is sprayed too much and whether the mold temperature is too low.

5. Use vacuum.

4). Cavitation:

Reason: Due to the sudden decrease in pressure, the gas in the molten soup suddenly expands and impacts the mold, causing mold damage.

Improvement method:

Do not change the cross-sectional area of the flow channel abruptly.

5). Shrinkage:

Reason: When the metal solidifies from liquid to solid, the space occupied becomes smaller. If there is no metal The addition of metal will form shrinkage holes. Usually occurs in the slower solidification area.

Improvement methods:

1. Increase pressure.

2. Change mold temperature. Local cooling, spray release agent, lower mold temperature, etc. Sometimes it only changes the location of shrinkage holes, not eliminates them.

6). Peeling:

Reasons: 

1. Poor filling mode, resulting in molten metal overlap.

2. Mold deformation, resulting in molten metal overlap.

3. Inclusion of oxide layer.

Improvement methods:

1. Switch to high speed early.

2. Shorten filling time.

3. Change filling mode, Gate position, gate speed.

4. Check whether the mold strength is sufficient.

5. Check whether the pin mold device is good.

6. Check whether there is an oxide layer.

7). Ripple:

Reason: The first layer of molten soup cools rapidly on the surface, and the second layer of molten soup flows through and fails to melt the first layer, but has enough fusion, resulting in different structures.

Improvement method:

1. Improve the filling mode.

2. Shorten the filling time.

8). Holes caused by poor flow:

Reason: The molten soup flows too slowly, or is too cold, or the filling The pattern is bad, so there are holes at the joint of the solidified metal.

Improvement method:

1. Same as the method for improving cold lines.

2. Check whether the melt temperature is stable.

3. Check whether the mold temperature is stable.

9). Holes on the parting surface:

Reason: It may be shrinkage or air holes.

Improvement method:

1. If it is shrinkage, reduce the gate thickness or the overflow well inlet thickness.

2. Cool the gate.

3. If it is air holes, pay attention to exhaust or air roll problems.

10). Burrs:

Reason: 1. Insufficient clamping force.

2. Poor mold clamping.

3. Insufficient mold strength.

4. Too high melt temperature.

11). Shrinkage:

Reason: Shrinkage occurs below the surface of the pressed part.

Improvement method:

1. Same as the method for improving shrinkage.

2. Local cooling.

3. Heat the other side.

12). Carbon deposition:

Reason: Release agent or other impurities accumulate on the mold.

Improvement method:

1. Reduce the amount of release agent sprayed.

2. Increase mold temperature.

3. Choose a suitable release agent.

4. Use soft Dilute the release agent with water.

13). Bubbling:

Reason: Gas rolls under the surface of the casting.

Improvement method:

1. Reduce air rolls (same as pores).

2. Cool or prevent low mold temperature.

14). Sticking mold:

Reason: 1. Zinc deposits adhere to the mold surface.

2. Molten soup impacts the mold, causing damage to the mold surface.

Improvement method:

1. Reduce mold temperature.

2. Reduce the roughness of the cut surface.

3. Increase the draft angle.

4. Coating.

5. Change the filling mode.