(1) Temperature of mold is high during die casting production process (it is best to add a cooling system).
(2) Mold release agent is unreasonably sprayed during die casting production process.
(3) Heat treatment of mold is not ideal, mainly hardness (hardness should not be less than HRC-47).
(4) Mold steel material is not good, it is recommended to use 8407 or refined H13
Early cracking is generally due to high forging temperature of blank forging (commonly known as overburning). Overburning is an irreparable defect, so starting temperature during blank manufacturing process should be strictly controlled. Same is true for quenching process. And heating time should be strictly controlled to prevent decarburization. After material is selected, it is heat treated. Pay attention to stress relief after a certain amount is produced. There is also a reasonable design. Try to avoid stress concentration and pay attention to size of R angle. At about 10,000 mold times, mold should pay attention to tempering and stress relief. Internal stress concentration processing residual stress is not removed. Thermal stress in the die casting process is not well removed. In short, cracking is manifestation of stress concentration. Multiple tempering can be used to remove stress so that life of mold can be increased.

 

(1) Mold temperature is too high and stress is too large
(2) Use 8407, skd61 for mold core material
(3) Hardness of mold heat treatment is too high
(4) Regular maintenance, 5k times tempering, 15k times tempering, 30k times tempering

1. Heat treatment requirements of molding parts (moving, fixed mold core, core) of die-casting mold must be HRC43~48 (material can be SKD61 or 8407)
2. Mold should be fully preheated before die casting production. Its functions are as follows:
2.1 Make mold achieve a better thermal balance, make casting solidification speed uniform and conducive to pressure transmission.
2.2 Maintain fluidity of die-cast alloy during filling, have good formability and improve surface quality of casting.
2.3 Reduce pre-production defects and improve die casting productivity.
2.4 Reduce thermal alternating stress of mold and increase service life of mold.

3. After new mold is produced for a period of time, accumulation of thermal stress is directly cause of cracks in mold core. To reduce thermal stress, mold core and slider after a certain period of production should be tempered to eliminate thermal stress.
Specific production modes that need to eliminate thermal stress are as follows:

Aluminum alloy die casting mold withstand tremendous alternating working stress, must pay attention to all aspects of molding materials, design, processing, heat treatment and operation to get a long mold life. Following are 25 tips to make mold reach a long life:

 

1. High-quality molding materials
2. Reasonable design of mold wall thickness and other mold dimensions
3. Try to use inserts
4. Select the largest possible corner R under possible conditions
5. Distance between cooling water channel and profile, corner must be large enough
6. Stress relief and tempering should be done after rough machining
7. Heat treatment is correct, quenching and cooling must be fast enough
8. Thoroughly polished to remove EDM metamorphic layer
9. Profile cannot be highly polished
10. Mold surface should be oxidized
11. If nitriding is selected, infiltration layer should not be too deep
12. Preheat mold to recommended temperature in correct way
13. Start to die-cast 5～10 pieces and use slow hammer speed
14. Under premise of obtaining qualified products, try to reduce temperature of molten aluminum
15. Don't use too high aluminum injection speed
16. Make sure that mold is properly cooled, and temperature of cooling water should be maintained at 40~50℃
17. Temporary shutdown, mold should be closed as much as possible and amount of cooling water should be reduced to avoid mold being subjected to thermal shock when it is restarted
18. When model surface is at the highest temperature, coolant should be turned off
19. Not too much spray release agent
20. After a certain number of die-casting, stress relief and tempering
21. Main reason is that temperature is too high, it is recommended to use a thermometer to control temperature at any time during die casting process (recommended temperature for aluminum alloy die casting <650)
22. Pay attention to preheating of mold to prevent thermal fatigue. (Cracks are mainly caused by thermal fatigue)
23. Pay attention to mold processing, it is best to use a machining center to complete, if there is a need for electrical processing, after electrical processing, grinding and polishing procedures should be added.
24. Pay attention to maintenance of mold (stress relief and tempering)
25. It is recommended to use ASSAB 8407 material for molds with high life requirements. It is recommended that hardness of die-casting molds should not exceed 50HRC.