Die cracking is one of the most important life-limiting tool failure mechanisms in high pressure die casting (HPDC). Cracking is caused by thermal shock from sudden heating and then cooling of the die surface. Injection of molten aluminium, transfers heat to the die which results in compressive stresses on the die surface. After the casting has been extracted, the die is sprayed with releasing agent which generates tensile stresses on the surface of the die. These stress fluctuations result in heat check cracking or gross cracking forming on the surface of the die.
Casting simulation software was used to simulate the casting process; metal filling the die cavity, solidification and thermal stresses in the die. For this paper a comparison was made between a simulation analysis and a cracked die slide. When the die cracks due to thermal fatigue, aluminium penetrates into the cracks which results in visual defects being formed in the casting and will further reduce the die-life. The simulation analysis shows a good correlation between the von Mises stress and the minimum principal stresses to the cracks seen on the surface of the die.
The ability to predict the extent of cracking on a HPDC die is vital when designing the die, if the heat check cracking / gross cracking can be reduced by even a small percentage, this will increase the die-life and ultimately reduce the cost of die maintenance throughout the serviceable life of the die, therefore resulting in a more profitable tooling design.