Factors That Affect Die Casting Die Life Yulong Zhu Ryobi Die Casting Inc. (USA) David Schwam, Xuejun Zhu, John Wallace Case Western Reserve University

Materials Related Design Related Process Related Sharp Features Surface Finish Internal Cooling Lines Location Steel Composition Steel Processing Heat Treatment Process Related Die Preheating Temperature Cycle Lubricant Spray

Background Many variables, including these listed on the previous slide, act simultaneously to affect die life. In a production environment it is difficult to separate these variables and to determine their relative weight. Objective Quantify the effect of die lubricant application on die temperature and die life: timing, duration and pressure using the immersion test.

Specimen and equipment

Specimen for temperature measurement

Chemical Composition of H13 Steel Mn, % Cr, % V, % Mo, % S, % P % H13 0.40 1.0 0.35 5.25 1.5 0.001 0.020

Typical temperature recording without any spray (36s cycle time, no spray)

Typical temperature recording with 3 seconds spray (36s cycle time, 60 psi) Spray

Typical temperature recording with 8 seconds spray (36s cycle time, 45 psi) Spray

Typical temperature recording with 13 seconds spray (36s cycle time, 45 psi)

Typical Temperature Cycle with 30 Seconds Cycle Time Note: min. temperature 370oF 30s cycle time: 3s traveling down, 7s immersing, 2s traveling up, 14s dwelling, 3s spraying and 1s air blowing

Typical Temperature Cycle with 36 Seconds Cycle Time Note: min. temperature 300oF 36s cycle time: 3s traveling down, 7s immersing, 2s traveling upper, 14s dwelling, 3s spraying, 1s air blowing and another 6 dwelling

Effect of Spraying Time on Cracking Behavior Longer spraying times depress the lows in cycle temperature, while increasing the ΔT (=Tmax-Tmin), causing more cracking.

Effect of Spraying Pressure on Cracking Behavior Higher spraying pressures can overcome the vapor blanket at higher temperatures, increasing the cooling and the temperature extremes. More cracking can be expected.

Effect of Cycle Time on Cracking Behavior Longer cycle time leads to more cracking if the temperature drops more.

Chemical Composition on Cracking Behavior Die Steels wt.% Si wt. % Mn Cr V Mo S P Heat Checking Resistance Gross Cracking Resistance P. G. H13 0.40 1.00 0.35 5.25 1.50 0.001 0.025     H11 0.38 5.20 1.20 <0.005 <0.02   Dievar 0.20 0.50 5.00 0.60 2.30 0.002 0.02  KDA-1 0.21 0.42 0.51 1.85 0.01 TQ1 0.43 1.90 QRO90 0.37 0.30 0.63 2.46 0.84 2.22 0.015  RPU 2.80 Die steels with slightly lower vanadium, silicon and carbon but higher molybdenum content seem to provide longer die life in many applications.

Effect of Chemical Composition on Basic Properties Die Steels Washout Indentation Temper Resistance Hot Yield Strength Ductility Toughness Hardenability P. G. H13     H11  Dievar KDA-1 TQ1 QRO90 RPU All modern die steels, when properly processed, will offer satisfactory performance in “routine” applications. Some will outperform others in demanding applications. The steel with the best combination of properties for the specific application will provide best die life.

Effect of Quench Cooling Rate on Microstructure Fast cooling rates(1,2) produce martensitic structures while avoiding grain boundary carbides and pearlite.

Effect of Quench Cooling Rate on Microstructure and Fracture Toughness

Effect of Quench Cooling Rate on Cracking Behavior Faster cooling rates during quenching provide better thermal fatigue resistance.

Effect of Hardness on Cracking Behavior Higher hardness usually provides better thermal fatigue resistance.

CONCLUSIONS Excessive spray will significantly reduce the die life. Longer cycle time led to more cracking if the temperature dropped more. Chemical composition of the steel can affect die life. Die steels with slightly lower vanadium, silicon and carbon but higher molybdenum content seem to provide longer die life in many applications. Proper heat treatment including optimized austenitizing temperature and time, fast quench cooling rate and higher hardness usually provide better thermal fatigue resistance. Whenever practical, thermal control by internal cooling is preferable to aggressive external spraying from a die life standpoint.

ACKNOWLEDGEMENTS This research work is supported by DOE funds provided through by ATI SMARRT program. NADCA and the members of Die Materials Committee approved this work and provided background. This work was performed at the Department of Materials Science and Engineering, Case Western Reserve University. The contribution of DOE, ATI, NADCA, and Case Western Reserve University are hereby acknowledged. This publication was prepared with the support of the U.S. Department of Energy (DOE), Award No. DE-FC36-04GO14230.