1、 Thermal fatigue cracking failure
During die casting production, the mold is repeatedly subjected to the action of cooling and heating, the forming surface and its interior are deformed and involved with each other, resulting in repeated cyclic thermal stress, resulting in secondary damage and loss of toughness of the organizational structure, leading to the emergence and continuous expansion of microcracks. Once the crack expands, molten metal is squeezed in, and repeated mechanical stress accelerates the crack propagation.
Therefore, on the one hand, the die must be fully preheated at the beginning of die casting. In addition, in the process of die casting production, the die must be kept in a certain working temperature range to avoid early cracking failure. At the same time, it is necessary to ensure that there are no problems due to internal causes before the mold is put into production and during manufacturing. Because in actual production, most die failure is thermal fatigue cracking failure.
2、 Fragmentation failure
Under the action of the injection force, the mold will initiate cracks at the weakest part, especially the scribed marks or machining marks on the mold forming surface are not polished, or the fine cracks will appear first at the corner clearing of the molding. When there is brittle phase at the grain boundary or the grain is coarse, it is easy to fracture.
The crack propagates rapidly during brittle fracture, which is a very dangerous factor for the fragmentation failure of the die. Therefore, on the one hand, all scratches and machining marks on the mold surface must be polished, even if it is in the gating system. In addition, the die materials used are required to have high strength, good plasticity, good impact toughness and fracture toughness.
3、 Corrosion failure
The commonly used die-casting alloys include zinc alloy, aluminum alloy, magnesium alloy and copper alloy, as well as pure aluminum die-casting. Zn, Al and Mg are more active metal elements. They have good affinity with die materials, especially Al is easy to bite the die. When the die hardness is high, the corrosion resistance is good, while if there are soft spots on the forming surface, the corrosion resistance is unfavorable.
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