Presentation on theme: "Catastrophic Failure of Die Material"— Presentation transcript:
1Catastrophic Failure of Die Material Gross CrackingCatastrophic Failure of Die MaterialSteel whose acceptance criteria falls out of the NADCA recommendation (was prior to first quarter 2006)Charpy impact fracture toughness levels are below recommended specs of NADCA , Chrysler or GM spec. (above 10 ft lbs.)Incorrect annealed microstructure and excessive banding.Improper or poorly performed heat treatment procedures. Happens far too often.
2Steel Acceptance Criteria and Heat Treatment Crucial to Tool Life (live link) Recommended reading: NADCA publication ##229 (2006) “Steel & Heat Treatment Acceptance Criteria ”Cost $80 through NADCAClick this link: NADCA PublicationThe number one cause of premature die failure is poor steel and poor heat treatment
3Ideal Steel Attributes Resistance to thermal fatigue cracking – low coefficient of thermal expansion, high thermal conductivity, high hot yield strength, temper softening resistance, high creep strength, and adequate ductilityResistance to gross cracking – high fracture toughness, high yield strength, and proper heat treatmentResistance to soldering - high thermal hardness, high resistance to thermal softening, low solubility in molten aluminum, and good oxidation resistanceBreakout and pitting are influenced by improvements in die filling conditions. Lubrication and intrinsic barriers are necessary to prevent soldering due to aluminum and iron interaction.
4Combination of thermal and mechanical Gross CrackingCombination of thermal and mechanicalCracks frequently occur at low temperature or in die steels with low fracture toughness.Usually initiate from deep thermal cracks near cooling lines.Can be avoided by good die design, right material, proper heat treatment, proper SPC.Preheating to min 335 degrees F raises fracture toughness to almost twice as high as that at room temperature.
5Rule of thumb hardness Relationship to Fatigue Failure High Rockwell hardness*Prone to gross cracking(lowers toughness)Low Rockwell hardnessProne to heat checking46-47RcLarger tools usually are heat treated to lower rockwells to prevent gross cracking while small tooling, with detail, are treated to higher rockwells to prevent heat checking.A higher hardness of 48-51Rc common for smaller dies vacuum quenched at a high cooling rate. A Lower hardness of 44-46Rc preferred for larger dies.Breakout and pitting are influenced by improvements in die filling conditions. Lubrication and intrinsic barriers are necessary to prevent soldering due to aluminum and iron interaction.
6Exceptions to the rule of thumb with newer die steels For large tooling that have difficulty achieving high cooling rates, consider the newer steels with better toughness.These steels allow a higher hardness of 49-50Rc with the same cooling rate of H-13 without the risk of gross crackingLarger tools usually are heat treated to lower rockwells to prevent gross cracking while small tooling, with detail, are treated to higher rockwells to prevent heat checking.
9to relieve surface stresses in Die Casting Dies Other recommended readingto relieve surface stresses in Die Casting DiesRecommended reading: NADCA publication #531 (May 2007) “Users Guide for Relieving Stresses in Die Casting Dies”Cost $60 through NADCA – Pages 17-21Click this link: NADCA PublicationCompressive Stress and Tensile are constantly in opposition to one another. Softening or annealing of the tool can also happen as the die is cycled during production runs.