Effect of bulk die temperature on die cavity surface strains in thixoforming of steels

The principal failure mechanism in thixoforming dies is expected to be thermal fatigue, as the mechanical loading on tooling is modest owing to a semisolid feedstock. High process temperatures during steel thixoforming induce high compressive strains at the die cavity surface during slurry injection. The magnitudes of the thermal gradient and strains that develop on the cavity surface are directly linked with the temperature of the die surface immediately before slurry injection. An increase in die bulk temperature from 450 to 550 degrees C reduces the surface to interior temperature differential and thus the surface strains by as much as 30%, a very favourable effect from thermal fatigue point of view.