Post on 15-Jan-2016
The Effect of Spraying on Thermal Fatigue Cracking
David Schwam, X.J. Zhu and J.F. WallaceCase 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)
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
40 50 60 70 80 90 100 110 120 130 140 150
Time(s)
Die
Temp
erat
ure
(F)
Surface0.08"
surface = 900 F
0.08 = 760 F
Typical Temperature Cycle with 3 Seconds Spraying
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
130 140 150 160 170 180 190 200 210 220 230 240
Time(s)
Tem
pera
ture
(F)
Surface
0.08"
surface = 1182 F
0.08 = 800 F
Typical Temperature Cycle with 8 Seconds Spraying
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
3350 3360 3370 3380 3390 3400 3410 3420 3430
Time(s)
Tem
pera
ture
(F
)
Surface
0.08"
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.