Analysis of Damage to Aluminum Alloy Die Casting Dies

Analysis of Damage to Aluminum Alloy Die Casting Dies

In the production of aluminum alloy die-casting, the common ways of mold damage are crack marks and cracking. Stress is the primary cause of mold damage.

In the production process of die-casting

1 Mold temperature

Before production, the mold should be preheated to a certain temperature. Otherwise, when the high-temperature metal liquid fills the mold, it will undergo quenching, causing an increase in the temperature gradient between the surface and inner layers of the mold, forming thermal stress and causing the surface of the mold to crack or even crack.

During the production process, the mold temperature occasionally rises. When the mold temperature becomes too hot, it is easy to cause mold sticking, causing moving parts to fall off and damage the surface of the mold.

A cooling temperature control system should be set up to ensure that the mold task temperature is within the necessary limits.

2 alloy filling

Metal liquid filling at high pressure and high speed will inevitably cause severe impact and erosion on the mold, resulting in mechanical and thermal stress. During the impact process, the metal liquid, impurities, and gases will also have complex chemical effects on the surface of the mold, accelerating the occurrence of erosion and cracks. When the metal liquid is wrapped with gas, it will first expand in the low-pressure area of the mold cavity. When the gas pressure increases, an inward explosion occurs, pulling out the metal particles on the surface of the mold cavity and forming damage, resulting in cracks due to cavitation.

3 Mold opening

During the process of core pulling and mold opening, mechanical stress may also occur when certain components undergo deformation.

4 Production process

In the production process of every aluminum alloy die casting, due to the thermal exchange between the mold and the molten metal, the surface of the mold undergoes periodic temperature changes, causing periodic thermal expansion and contraction, resulting in periodic thermal stress. If the surface of the mold is subjected to compressive stress due to heating during pouring, and after the mold is opened and ejected from the casting, the surface of the mold is subjected to tensile stress due to cooling. When this alternating stress cycles repeatedly, the accumulated stress inside the mold increases. When the stress exceeds the limit of the data, cracks appear on the surface of the mold

2、 Rough forging issues

Some molds only produce a few hundred pieces and show crack patterns, and the cracks develop quickly. It is possible that during forging, only the external dimensions are covered, while loose defects such as dendritic crystals, mixed carbides, shrinkage holes, and bubbles in the steel are elongated along the processing method, forming a streamline. This streamline has a significant impact on future quenching deformation, cracking, brittle cracking, and failure tendency during use.

The cutting stress that occurs during final machining such as turning, milling, and planing can be eliminated through central annealing.

Grinding stress occurs during the grinding of quenched steel, friction heat occurs during grinding, softening layer and decarburization layer occur, which reduces the thermal fatigue strength and easily leads to thermal cracking and early cracking. After precision grinding, H13 steel can be heated to 510-570 ℃ and subjected to stress relief annealing at a thickness of every 25mm for one hour.

4. Stress occurs during electrical discharge machining. There is a white bright layer on the surface of the mold, which is rich in electrode elements and dielectric elements. It is hard and brittle, and this layer itself will have cracks and stress. During electrical discharge machining, a high frequency should be used to reduce the white bright layer to a small size. Polishing methods should be used to remove it and tempering treatment should be carried out. The tempering should be carried out at a three-level tempering temperature.

3、 Mold disposal in progress

Improper heat treatment can lead to mold cracking and premature scrapping, especially when using only quenching and tempering without quenching, followed by surface nitriding process. After several thousand die casting cycles, surface cracking and cracking may occur.

The occurrence of stress during steel quenching is the result of the superposition of thermal stress during the cooling process and structural stress during phase transformation. Quenching stress is the cause of deformation and cracking, and tempering is necessary to eliminate stress.

Precision machining