The basic technological process of die casting is: the liquid metal is first cast at low speed or high speed and filled into the mold cavity of the mold. The mold has a movable cavity surface. It is pressurized and forged with the cooling process of the liquid metal, which not only eliminates the shrinkage defects of the blank, but also makes the internal structure of the blank reach the broken grains in the forged state.

Die casting mold manufacturers say that in die casting production, the most common form of mold damage is crack and crack.
The main causes of mold damage are chemical shock and stress. Stress includes mechanical stress and thermal stress, and the stress is generated from:

1、 In the process of mold processing and manufacturing

1. Quality problems of blank forging

Some molds have cracks after only a few hundred pieces have been produced, and the cracks develop rapidly. It is possible that during forging, only the overall size is guaranteed, while the dendritic crystals, mixed carbides, shrinkage cavities, bubbles and other loose defects in the steel are extended and elongated along the processing method to form a streamline, which has a great impact on the subsequent quenching deformation, cracking, embrittlement and failure tendency in the process of use.

2. Cutting stress generated during turning, milling, planing and other processing

This stress can be eliminated by intermediate annealing.

3. Grinding stress occurs during grinding of quenched steel

Friction heat is generated during grinding, resulting in softening layer and decarburization layer, which reduces the thermal fatigue strength and is easy to lead to thermal crack and early crack. After finishing grinding, H13 steel can be heated to 510-570 ℃ and maintained for one hour every 25mm thickness for stress relief annealing.

4. Stress generated by EDM

A white bright layer rich in electrode elements and dielectric elements is produced on the die surface, which is hard and brittle. This layer itself will have cracks and stress. During EDM, high frequency shall be adopted to minimize the white bright layer. Polishing method must be used to remove it and tempering treatment shall be carried out. Tempering shall be carried out at three-level tempering temperature.

Two, mold processing process
Improper heat treatment will lead to mold cracking and premature scrapping. In particular, only quenching and tempering, no quenching, and then surface nitriding process will lead to surface cracking and cracking after thousands of die casting times. The stress produced during steel quenching is the result of the superposition of the thermal stress during cooling and the structural stress during phase transformation. The quenching stress is the cause of deformation and cracking, and tempering must be carried out to eliminate the stress.

3、 In the process of die casting production
The mold should be preheated to a certain temperature before production. Otherwise, when the high-temperature metal liquid is filled, it will produce chilling, which will increase the temperature gradient inside and outside the mold, form thermal stress, and make the mold surface crack or even crack.

In the production process, the mold temperature rises continuously. When the mold temperature is overheated, it is easy to stick the mold, and the moving parts fail, resulting in the damage of the mold surface. The cooling temperature control system shall be set to keep the working temperature of the die within a certain range.