During die-casting production, the mold is repeatedly subjected to the action of stimulating heat and heat, and the forming surface and its interior are deformed, which are involved in each other and cause repeated cyclic thermal stress, resulting in damage to the structure and loss of toughness, causing the occurrence of microcracks and continuing to expand. Once the crack is enlarged, the molten metal is squeezed in, and repeated mechanical stress causes the crack to accelerate. For this reason, on the one hand, the mold must be sufficiently preheated at the start of die casting.
First, thermal fatigue crack damage failure
During die-casting production, the mold is repeatedly subjected to the action of stimulating heat and heat, and the forming surface and its interior are deformed, which are involved in each other and cause repeated cyclic thermal stress, resulting in damage to the structure and loss of toughness, causing the occurrence of microcracks and continuing to expand. Once the crack is enlarged, the molten metal is squeezed in, and repeated mechanical stress causes the crack to accelerate. For this reason, on the one hand, the mold must be sufficiently preheated at the start of die casting. In addition, the mold must be kept in a certain operating temperature range during the die casting process to avoid early crack failure. At the same time, it is necessary to ensure that the internal factors before and during the production of the mold are not problematic. Due to actual production, most mold failures are thermal fatigue crack failure.
Second, fragmentation failure
Under the action of the injection force, the mold will crack at the weakest point, especially the scribing marks or electromachining marks on the molding surface of the mold are not polished, or the fine cracks will appear first at the clear corners of the molding. When the grain boundary has a brittle phase or a coarse grain, it is easily broken. The crack propagates rapidly during brittle fracture, which is a dangerous factor for the failure of the mold. For this reason, on the one hand, scratches, electric machining marks, etc. on the mold surface must be polished, even if it is in the pouring system, it must be polished. In addition, the mold material used is required to have high strength, good plasticity, impact toughness and fracture toughness.
Third, dissolution failure
Commonly used die-casting alloys are zinc alloys, aluminum alloys, magnesium alloys and copper alloys, as well as pure aluminum die-casting. Zn, Al, and Mg are relatively active metal elements, and they have good affinity with mold materials, especially Al is easy to bite. mold. When the hardness of the mold is high, the corrosion resistance is good, and if the molding surface has a soft point, the corrosion resistance is disadvantageous.
