Addressing Thermal Cracking Issues in High-Pressure Die Casting Mold Tooling

1. Background

This case involves a set of high-pressure die casting tooling originally designed and manufactured by a previous supplier. Raidymold team was not involved in the initial design and manufacturing phases, but later participated in the process optimization and troubleshooting stage during production.

During extended production, multiple dies began to exhibit varying degrees of surface cracking and localized failure, which negatively impacted tool life and casting stability. Therefore, a systematic analysis was conducted to identify root causes and propose improvement measures.

2. Tooling Performance Overview

A total of four high-pressure die casting tools (A, B, C, and D) were evaluated:

A Tool

• No clear correlation between production cycles and crack occurrence
• Multiple repair records, including welding repair and localized material loss
• Indicates repeated cracking and fatigue-related damage

B Tool

• Over 50,000 cycles in production
• Severe aging and thermal fatigue cracking observed

C Tool

• At 24,420 castings:
  • Severe cracking on the upper core and surrounding areas
• At 33,485 castings:
  • Multiple critical areas on both fixed and moving dies exhibited significant cracking

D Tool

• At 2,976 castings:
  • Initial cracking observed
• At 4,787 and 6,820 castings:
  • Seal groove chipping occurred
• At 19,957 castings:
  • Widespread cracking and material breakage

3. Material and Heat Treatment Assessment

Materials Used

• A / B / C tools: ADC3
• D tool: DIEVAR

Metallurgical Inspection

• Material microstructure complies with:
  • North American standard AS1-9 (raw material)
  • HS1-9 (quenched condition)
• Also meets higher internal standards:
  • AS1-4 (raw material)
  • HS1-5 (quenched condition)

👉 Conclusion:

• No abnormal metallurgical defects
• Material quality meets or exceeds industry requirements

Hardness Evaluation

• Die inserts (core/cavity): 44–46 HRC
• Slides: 46–48 HRC

👉 Analysis:

• Within standard range for large HPDC tooling
• Slide hardness optimized for improved resistance to wear and cracking
• Measured hardness values are consistent with design specifications

4. Root Cause Analysis

4.1 Product Characteristics

The casting features:

• Large volume
• Thick wall sections

👉 As a result:

• Significant heat accumulation during solidification
• Prolonged thermal exposure of the die surface

4.2 Thermal Fatigue Mechanism

During the die casting process, the tooling undergoes repeated cycles of:

1. Molten metal filling (high temperature)
2. Holding and solidification (sustained heat)
3. Spray cooling (rapid temperature drop)

👉 This results in:

• Severe thermal cycling
• Repeated thermal stress loading
• Progressive thermal fatigue accumulation

4.3 Crack Initiation and Propagation

Under continuous thermal stress:

• Microcracks initiate on the die surface
• Cracks propagate due to cyclic stress
• Eventually lead to:
  • Surface cracking
  • Material spalling
  • Localized failure (breakage/chipping)

4.4 Key Conclusion

The primary failure mechanism in this case is thermal fatigue cracking, driven by severe thermal cycling caused by large, thick-walled castings.

5. Material Comparison Insight

• ADC3:
  • Shows relatively stable performance under this high thermal load
  • May offer better resistance to cracking in large-scale tooling applications
• DIEVAR:
  • Known for high toughness
  • However, its resistance to thermal fatigue under this specific condition requires further validation

👉 Conclusion:

Material selection must be aligned with actual operating conditions; no single material can be universally optimal.

6. Improvement Recommendations

To mitigate thermal fatigue cracking, the following measures are recommended:

6.1 Temperature Control Optimization

• Implement mold temperature control systems
• Improve temperature uniformity across the die

👉 Goal: Reduce thermal shock

6.2 Spray Cooling Optimization

• Reduce spray volume
• Optimize spray timing and coverage

👉 Goal: Minimize temperature fluctuations

6.3 Surface Treatment

• Nitriding treatment
• Oxidation treatment

Benefits:

• Improved surface hardness
• Enhanced resistance to crack initiation
• Reduced aluminum adhesion
• Slower crack propagation

6.4 Material Upgrade Recommendation

• Recommended material: Hitachi DAC55

Advantages:

• Excellent thermal fatigue resistance
• High toughness
• Suitable for high thermal load HPDC applications

7. Summary

• Material quality and heat treatment are within acceptable standards
• The primary failure mode is thermal fatigue cracking, not material defect
• Large, thick-walled castings significantly increase thermal load on tooling
• Improving thermal management and surface strength is key to extending tool life

8. FAQ

Q1: What is the main cause of cracking?
A: Thermal fatigue due to repeated heating and cooling cycles during the die casting process.

Q2: Is material the root cause?
A: No. Material testing indicates compliance with standards; material is not the primary cause.

Q3: How can tool life be improved?

• Better temperature control
• Reduced spray cooling intensity
• Surface strengthening (nitriding)
• Use of higher-performance tool steel

Q4: Which material performs better in this case?
A: ADC3 shows relatively better stability in this specific high thermal load condition, but more data is required for a definitive conclusion.

9. Technical Capability Statement (Raidymold)

We, Raidymold Suppliers, possess capabilities in the following areas:

• HPDC tooling failure analysis
• Thermal fatigue mechanism evaluation
• Multi-dimensional optimization (material, process, and surface engineering)
• Practical experience in extending tooling life under high thermal loads
• Providing end-to-end solutions from diagnosis to implementation

👉 Core strength:

Failure Analysis + Engineering Optimization + Industry Experience

If you are looking for a trustworthy die-casting mold supplier, please contact us at Raidymold. We look forward to working with you.