1. 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

2. 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.

3. Specimen and equipment

4. Typical properties of H13

5. Specimen for temperature measurement

6. 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.

7. Effect of Spraying Time on Total Crack Area

8. Effect of Spraying Time on Average Maximum Crack Length

9. Discussion =      =      / 1-
=     
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.

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

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

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

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

14. 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.