# The Effect of Spraying on Thermal Fatigue Cracking David Schwam, X.J. Zhu and J.F. Wallace Case Western Reserve University NADCA DMC February 20, 2007.

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The Effect of Spraying on Thermal Fatigue Cracking David Schwam, X.J. Zhu and J.F. Wallace Case Western Reserve University NADCA DMC February 20, 2007

Main Role of Die Spraying Facilitate casting release Prevent soldering Cool the die Sprays of water-based lubricants are commonly used in high pressure die casting to provide both lubrication and cooling of the dies.

Specimen and equipment

Typical properties of H13

Specimen for temperature measurement

Parameters of the test Total cycle time of 36 seconds (3 seconds stroke down, 7 seconds immersion, 2 seconds stroke up, 14 seconds dwell, 3-13 seconds water spraying, one second air blowing and another 6 seconds dwell before stoke down). Air pressure is 45 psi and the estimated spraying rate is 1.25 ml/second.

Effect of Spraying Time on Total Crack Area

Effect of Spraying Time on Average Maximum Crack Length

Discussion  =      Where δ is the thermal stress, α is the linear thermal coefficient of expansions, E is the elastic modulus and ∆T is the temperature change. For biaxial condition the stress is given by:  =      / 1-  Where is Poisson’s ratio. Larger  lead to higher the thermal stresses.

Typical Temperature Cycle with no Spraying (internal water cooling only)  surface = 900 F  0.08 = 760 F

Typical Temperature Cycle with 3 Seconds Spraying  surface = 1182 F  0.08 = 800 F

Typical Temperature Cycle with 8 Seconds Spraying  surface = 1226 F  0.08 = 700 F

Typical Temperature cycle with 13 seconds Spraying  surface = 1058 F  0.08 = 820 F

Conclusions As anticipated, the die lube spray has a significant effect on thermal fatigue cracking. Increasing the spray time increases both the total crack area and the average maximum crack length. This indicates that aggressive application of die lubricant spray will significantly reduce the die life.

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