Coupled Thermomechanical Strain Life FEA for Large Format Gigacast Tray Molds
Coupled thermomechanical strain-life FEA predicts thermal checking and insert fatigue life in gigacast tray molds using non-linear elastoplastic plasticity models.
Liquid Aluminum Thermal Shock
Meaning
Instantaneous heat transfer from a molten alloy to a cooler steel surface creates an extreme temperature gradient within the first few millimeters of the tool. Managing liquid aluminum thermal shock is necessary to prevent the surface of the die from cracking prematurely. The metal enters the cavity at temperatures exceeding six hundred degrees Celsius which causes the tool surface to expand rapidly against its colder interior.
This rapid expansion creates a localized zone of high compressive stress that can exceed the yield strength of the steel.
Stress Gradient
Internal tension develops because the outer layer of the steel tries to expand while the core remains rigid. This liquid aluminum thermal shock cycle repeats with every shot in the die casting process. The magnitude of the stress depends on the temperature difference and the speed of the injection.
Surface Damage
Heat checking is the most common outcome of this repeated expansion and contraction. Small cracks form in a spider web pattern during liquid aluminum thermal shock and eventually grow into deeper fissures. These defects transfer to the surface of the cast part and increase the need for post processing.
Tool Protection
Preheating the die and using thermal lubricants mitigates the severity of the initial contact. Careful management of liquid aluminum thermal shock involves keeping the tool within a specific temperature window to reduce the delta. Applying ceramic coatings can also provide a barrier that slows the rate of heat transfer.