In the process of die-casting production, the forming conditions of die-casting die parts are very bad. They are subject to repeated effects of mechanical abrasion, chemical erosion and thermal fatigue.
1) The metal liquid enters the die cavity under high pressure and high speed, which produces intense friction and impact on the surface of the die cavity, and causes erosion and wear on the surface of the die.
2) Slag is unavoidable in the process of casting. Slag has complex chemical effect on the surface of forming parts. Compounds of aluminium and iron, like wedges, accelerate the formation and development of cracks in die casting dies.
3) Die-casting die factories show that thermal stress is the main reason for surface cracks of die-casting parts. In each production process, besides being scoured by high-speed and high-pressure metal liquid, the surface of die-casting parts also absorbs the heat released by metal during solidification and generates heat exchange. In addition, because of the heat conduction of die material, the temperature of the surface layer of the forming parts rises sharply, and there is a great temperature difference between the surface layer and the inner layer, which results in the internal stress. When the metal liquid fills the cavity, the surface of the cavity first reaches high temperature and expands, while the inner layer has low temperature and relatively small expansion, which results in compressive stress on the surface. After opening the mould, the surface of the cavity contacts with air and is chilled by compressed air and paint, which results in tensile stress. This alternating stress increases with the continuation of production. When it exceeds the fatigue limit of the die material, plastic deformation will occur on the surface layer of the die and cracks will occur.
In order to maintain the durability of the surface and prolong the service life of the die-casting die, the die-casting die factory must use the die reasonably and maintain the die regularly.