What are the reasons and preventive measures for the cracking of aluminum alloy die casting mould after a period of production?
The temperature of the mold in the die casting process is high (preferably additional cooling system).
It is unreasonable to spray the mould in the die casting process.
The mold heat treatment is not ideal, mainly for hardness (hardness should not be less than 47HRC).
The steel material is not good.
Early cracks are usually caused by the high temperature of forging and forging, which is an irredeemable defect.Therefore, it is necessary to strictly control the forging temperature in the manufacturing process.
In the case of about 10,000 molds, the mold should pay attention to the stress of tempering. The crack is the performance of the stress concentration, which can be used to remove the stress repeatedly, which can increase the die life.
There are several reasons for the cracking of aluminum alloy die casting mold after a period of production.
The mold temperature is high and the stress is too high.
The hardness of the mold is too high.
To prevent the crack of die-casting mould and improve the service life of die, the following points should be made.
The heat treatment requirements of the die casting mold forming part (moving, die-casting kernel and core) are required: the hardness must be 43-48hrc (SKD61 or 8407 is optional for materials).
The mould should be fully preheated before die casting production. The function is as follows.
A. Make the mould achieve a better thermal balance, so that the casting solidification speed is uniform and favorable to pressure transfer.
B. Maintain the fluidity during filling of die casting alloy, have good molding and improve casting surface quality.
C. Reduce preproduction defects and improve die casting productivity.
D. Reduce the thermal stress of the mold and improve the service life of the die.
Die preheating temperature: aluminum alloy is 180-300 ° 0, zinc alloy is 150 ~ 200 ℃.
(3) new mold in production after a period of time, the accumulation of the thermal stress is the direct cause of cracks of cavities, in order to reduce the thermal stress, and put into production after a certain time of cavities and slider should be to eliminate the thermal stress of tempering treatment.
Aluminum alloy: the first tempering <2000 mode, the second tempering <10000 mode, the third tempering <30000 mode;Zinc alloy: first tempering <10000 mode, second tempering <20000 mode;Third tempering <50000 mode.
Aluminum alloy die-casting die under heavy work alternating stress, which must be from the mold material, design, processing, heat treatment and operation aspects pay attention to get long mould life, the following considerations is to improve the die life.
1. High quality molding material.
2. Reasonable design of mold wall thickness and other mould dimensions.
Try to use inserts.
4. Use as many corners as possible under possible conditions.
6. The distance between the cooling channel and the surface and the corner must be large enough.
5. Stress should be tempered after rough machining.
7. Heat treatment is correct and quenching must be fast enough.
8. Thoroughly polish and remove EDM metamorphic layer.
9. The type surface shall not be highly polished.
10. The mould surface shall be treated with oxidation.
11. If nitrogen is selected, the layer should not be too deep.
12. Preheat the mold to the recommended temperature in the correct way.
13. Start casting 5 ~ 10 pieces should use slow hammer head speed.
14. Reduce the temperature of aluminum liquid as much as possible under the premise of obtaining qualified products.
15. Do not use excessive aluminum injection speed.
16. Ensure that the mold is appropriate cooling, cooling water temperature should be kept in 40 ~ 50 ℃.
17. Temporary shutdown should be made to the best of the mold and reduce the cooling water, so as to avoid the thermal shock of the mold when the machine is turned on.
18. When the model surface is at the highest temperature, the coolant should be closed.
19. However, a lot of spray mold.
20. Stress tempering after a certain number of die-casting.
A. The main reason is that the temperature is too high, and it is recommended to control the temperature at any time during the die-casting process.
B. Pay attention to the preheating of the mold to prevent thermal fatigue (cracking is mainly caused by thermal fatigue).
C. Pay attention to die processing, preferably with machining center, if necessary. After electroprocessing, the grinding and polishing process should be increased.
D. Pay attention to the maintenance of the mould (stress tempering).
E. It is recommended to use ASSAB8407 material with high life requirement, and the hardness of die casting mould should not be higher than 50HRC.