damage
During die-casting production, the mold is repeatedly subjected to the effects of cold shock and heat, and the molding surface and its interior are deformed, which involves each other and repeatedly cyclic thermal stresses, resulting in damage to the structure and loss of toughness, causing the appearance of micro-cracks and continuing to expand Once the crack expands, molten metal squeezes in, and repeated mechanical stress accelerates the crack. For this reason, on the one hand, the mold must be fully preheated at the beginning of die casting. In addition, the mold must be kept within a certain operating temperature range during the die casting process to avoid early cracking failure. At the same time, it is necessary to ensure that the internal factors before the mold is put into production and during manufacturing do not cause problems. In actual production, most of the mold failures are thermal fatigue cracking failures.
Fragmented
Under the action of injection pressure, the mold will crack at the weakest point, especially the scribe marks or electrical machining marks on the molding surface of the mold have not been polished, or the micro-cracks will appear first in the clear corners of the mold When there is a brittle phase or coarse grains in the grain boundary, it is easy to break. However, the crack propagation is very rapid during brittle fracture, which is a very dangerous factor for the fracture of the mold. For this reason, on the one hand, all scratches and electrical machining marks on the mold surface must be polished, even if it is in the pouring system, it must also be polished. In addition, the mold materials used are required to have high strength, good plasticity, good impact toughness and fracture toughness.
Dissolution
As mentioned above, the commonly used die-casting alloys are zinc alloys, aluminum alloys, magnesium alloys and copper alloys, as well as pure aluminum die-casting. Zn, Al, Mg are more active metal elements, and they have better affinity with mold materials. Especially Al is easy to bite. When the hardness of the mold is high, the corrosion resistance is good, and if there are soft spots on the molding surface, it is detrimental to the corrosion resistance.
There are many factors that cause the mold to fail, and there are external factors (such as the temperature of the casting, whether the mold is preheated, the amount of spray coating, whether the tonnage size of the die casting machine matches, the pressure of the die casting is too high, the speed of the gate is too fast, the cooling Water opening is not synchronized with the production of die-casting, the type of casting material and the composition of Fe, the size and shape of the casting, the wall thickness, the type of paint, etc.). There are also internal factors (such as the metallurgical quality of the mold itself, the forging process of the blank, the rationality of the mold structure design, the rationality of the design of the pouring system, the internal stress generated during the processing of the mold machine (electrical processing), the heat treatment process of the mold, including Various requirements for precision and finish, etc.). If the mold fails early, it is necessary to find out which internal or external causes for future improvement. However, in actual production, the dissolution is only a local part of the mold. For example, the part (core, cavity) directly eroded by the gate is prone to dissolution, and the sticky mold of aluminum alloy is prone to occur in the soft hardness.