Damage to the
Die casting production, die again and again by the chilling effect of thermal forming surface and its internal deformation, with each other and appear repeatedly cyclic thermal stress, lead to structure damage and loss of resilience, cause the emergence of micro cracks, and continue to expand, once the crack expand, fluid diapir and molten metal, and repeated mechanical stress to accelerate the extension of crack. 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 mold must be kept in a certain working temperature range to avoid early cracking failure. At the same time, to ensure that the mold before production and manufacturing internal causes do not occur problems. In actual production, most die failure is thermal fatigue cracking failure.
Under the action of injection force, the mold will crack at the weakest point, especially the streaking trace or electrical processing trace on the molding surface has not been polished, or the forming Angle will be the first fine crack, when the grain boundary there is a brittle phase or coarse grain, that is, easy to fracture. The rapid crack propagation during brittle fracture is a very dangerous factor for the fracture failure of the die. For this reason, on the one hand, all scratches and electrical processing marks on the surface of the mold 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, impact toughness and fracture toughness.
Previously mentioned, commonly used die casting alloys are zinc alloy, aluminum alloy, magnesium alloy and copper alloy, but also pure aluminum die casting, Zn, Al, Mg are more active metal elements, they have a good affinity with mold materials, especially Al easy to bite the mold. When the mold hardness is higher, the corrosion resistance is better, and the forming surface if there are soft spots, the corrosion resistance is not good.
There are many factors that lead to mold failure. Both external (case whether pouring temperature, mould preheating, water-based paint spraying quantity of how many, size matches, high pressure die casting, die casting machine tonnage gate open not too fast, cooling water and die casting production synchronization Fe casting material, the type and composition of high and low, casting dimension shape, wall thickness, size, coating type, etc.). There are also internal factors (such as the metallurgical quality of the material of the die itself, the forging process of the blank, the rationality of the structure design of the die, the rationality of the pouring system design, the internal stress generated by the die machine (electrical machining), the heat treatment process of the die, including various matching accuracy and finish requirements, etc.). If there is an early failure of the mold, it is necessary to find out what internal or external causes are for future improvement. However, in the actual production, the dissolution is only in the local part of the mold. For example, the parts directly washed by the inner gate (core and cavity) are prone to the dissolution phenomenon, and the aluminum alloy sticky mold is easy to appear in the soft hardness.