Causes analysis and improvement methods of fissure marks in die casting

Posted on : March 24, 2022 By  GREFEE

To learn more problems and preventions of die casting, click to check it out.

What is fissure mark?

The casting surface has protrusions or sinks which look like hairs. It enlarges and spreads as the number of die casting times increases.

What the causes of fissures?

1.The marks caused by the crazing of the cavity surface. The heat conduction around the in-gate area is most concentrated, at which the friction force is largest. The degree of molten metal erosion is highest, and the sudden change of cold and hot is the most serious. It is also the area that is most likely to generate stress concentrated, so it is easy to produce thermal cracking, then forms crazing. 

2.Improper mold material or improper heat treatment process.

3.The temperature difference of die casting mold is big.

4.Pouring temperature is too high and the mold is not preheated

5.The cavity surface is too rough.

6.The metal flow speed is fast and flushes right against the mold cavity

7.The die casting mold wall is thin or with sharp corners.

8.The mold cavity surface local area is welded and hasn’t removed the welding stressing in time.

How to improve the fissures on the die casting mold surface?

1. Check the production mold times and records of stress-relief treatment. Uses mold according to the maintenance protocols to manage stress relief in time. Adds points cooling or uses insert block at the positions where are easy to have fatigue crazing. In production, it should be aware of the spray painting of this area and enhance the forced cooling. 

2. Checks the material content of mold and mechanical performance. Selects suitable mold material and heat treatment technique.  

3. Through the analysis of simulated temperature field to find the temperature imbalances areas in the cavity. Sets spot cooling or spot heating structure to maintain the balance of cavity temperature. In the production, the balanced temperature can be obtained by spraying the mold release agent.

4. Evaluate by the liquid alloy thermoprobe and mold thermoprobe. Try to lower the alloy pouring temperature. The mold must be preheated to the required range before die casting.

5. Uses roughness tester to test the level of cavity surface roughness. Polishes the cavity surface to the required range, and Ra value should not exceed 0.2.

6. The mold surface is easy to find sinks in high-speed areas. Under a good molding condition, properly lowering the filling speed of liquid metal to change its filling direction.

7. The casting surface is evidently brightening on thin wall position. Modifies the mold structure.

8. Check the mold production mold times. The welding area has crazing earlier and quite easily. The mold should be welded properly.

Key inspection positions of die casting products：

Generally, the fissures are in the sealing groove or the edges of the mold.

How does fissure affect the products?

it mainly affects the appearance, airtightness of sealing sloth, and working life.

How to evaluate whether a product with fissures is qualified or not?

1. The fissure of casting surface can be removed by the blasting or grinding.

2. Not applicable to these areas:

a  .the heat sink groove of baking  paint side, hard to remove.

b. the fissure is in sealing groove, hard to remove, or the fissure sinks after grinding, affects the sealing groove finish.

c.the mold degradation further causes corrosion spots. The sealing groove is not allowed to have fissures.

Improve the fissures issue:

The checking marks result from the fissures on mold. Many factors contribute to mold fissures, like sharp corners, small R, unqualified steel material, or improper heat treatment. All these factors will affect the quality and working life of the mold.

GREFEE uses ASSAB high-quality steel in the long-life die casting mold. In the long term relationship, not only as our high-quality supplier, but ASSAB also provides advanced steel heat treatment service. We have 20 years of experience in the die casting industry, so no matter it is mold material or an aluminum alloy material or since alloy material, GREFEE will select the best supplier with materials that conform to international standards. Contact us now for professional die casting project plans!

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