One. Causes of damage to the die-casting production mol […]
One. Causes of damage to the die-casting production mold:
In die casting production, the most common form of mold damage is cracking and cracking. Stress is the main cause of mold damage. Thermal, mechanical, chemical, and operational shocks are sources of stress, including mechanical and thermal stresses, which are generated by:
1. In the mold manufacturing process
(1) Quality problems of rough forging. Some molds produce cracks only when they are produced in a few hundred pieces, and cracks develop rapidly. It is possible that only the outer dimensions are ensured during forging, and the loose defects such as dendrites, inclusions, shrinkage cavities, and bubbles in the steel are stretched and elongated along the processing to form a streamline, which is quenched in the future. Deformation, cracking, brittle cracking during use, and failure tendency have a great impact.
(2) Cutting stress generated during final machining such as turning, milling, planing, etc., which can be eliminated by intermediate annealing.
(3) Grinding stress occurs during hardening of hardened steel, friction heat is generated during grinding, softening layer and decarburization layer are generated, thermal fatigue strength is reduced, and thermal cracking and early cracking are easily caused.
(4) EDM produces stress. The surface of the mold produces a white bright layer rich in electrode elements and dielectric elements, which is hard and brittle. This layer itself has cracks and stress. EDM should use a high frequency to minimize the white bright layer, must be polished and removed, and tempered, and tempered at the tempering temperature.
2. During the heat treatment of the mold
Improper heat treatment will cause the mold to crack and be prematurely scrapped. In particular, only quenching and tempering, no quenching, and surface nitriding will occur. Surface cracking and cracking will occur after several thousand die castings.
The stress generated during quenching of steel is the result of the superposition of thermal stress during cooling and the structural stress during phase change. Quenching stress is the cause of deformation and cracking, and tempering must be performed to eliminate stress.
3. In the process of die casting production
(1) Mold temperature. The mold should be preheated to a certain temperature before production. Otherwise, when the high temperature molten metal is filled, chilling occurs, which causes the temperature gradient of the inner and outer layers of the mold to increase, forming thermal stress, causing the surface of the mold to crack or even crack.
During the production process, the mold temperature is continuously increased. When the mold temperature is overheated, the mold is easily generated, and the moving parts are broken, resulting in damage to the mold surface. The cooling temperature control system should be set to keep the working temperature of the mold within a certain range.
(2) Filling type. The metal liquid is filled with high pressure and high speed, which will inevitably cause severe impact and erosion on the mold, thus generating mechanical stress and thermal stress. During the impact process, molten metal, impurities, and gases also create complex chemical interactions with the mold surface and accelerate corrosion and crack generation. When the metal liquid is wrapped with gas, it will first expand in the low pressure region of the cavity. When the gas pressure rises, inward blasting occurs, and the metal dots on the surface of the cavity are pulled out to cause damage, and cracks are generated due to cavitation.