I. Project Background and Technical Challenges

The brake housing for a certain automobile model is a core safety component of the braking system, required to withstand high pressure, high-frequency vibrations, and extreme temperature cycles (-40°C to 150°C). Brake housings produced by traditional zinc alloy die casting often faced the following issues:

1. Porosity Defects: Gas entrapment during conventional die casting led to high internal porosity rates of 3%-5% in the components. X-ray inspection revealed porosity concentrated around bolt connection surfaces, easily causing leakage during hydraulic pressure tests

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2. Uneven Solidification: Significant variations in brake housing wall thickness (ranging from 2-8mm), combined with insufficient traditional mold temperature control, resulted in shrinkage cavities in thick sections and incomplete filling in thin sections, limiting the yield rate to only 85%

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3. Failure to Meet Mechanical Properties: Porosity and shrinkage defects caused fluctuations in the tensile strength of the parts between 200-240 MPa, below the design requirement of 280 MPa, and also led to deformation after heat treatment

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II. Collaborative Solution: Vacuum Die Casting and In-Mold Temperature Control

1. High-Vacuum Die Casting System Modification

The foundry employed a multi-stage vacuum system to evacuate the mold cavity to an absolute pressure above 90 kPa before injection. Specific measures included:

• Direct Mold Venting Design: Eight vacuum valves were arranged on the parting line, coupled with a sealing structure (parting line flatness ≤0.02mm/m²), ensuring evacuation within 0.5 seconds and reducing oxygen content in the cavity to below 0.1%

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• Real-time Monitoring and Interlock: The vacuum system was interlocked with the die casting machine, utilizing pressure sensors for real-time monitoring to prevent molten metal backflow. This modification reduced gas content in the castings from 15 ml/100g to 2 ml/100g, bringing the porosity rate below 0.5%

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2. Stepped In-Mold Temperature Control Technology

To address uncontrolled solidification sequencing, an active temperature-controlled mold was developed:

• Zoned Heating/Cooling System: Twelve sets of heating cartridges (400W power) and thermocouples were embedded in key mold areas (e.g., gate, thick sections). Software configured temperature gradients: gate zone 415°C, thick wall zone 400°C, thin wall zone 430°C, promoting sequential solidification from the far end of the cavity back to the gate

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• Dynamic Control Strategy: Based on thermocouple feedback, localized cooling channels were triggered when thick section temperature dropped to 400°C to prevent shrinkage porosity, while thin sections maintained higher temperatures to ensure complete filling. Tests showed this approach reduced solidification time by 15% and controlled temperature variation within ±5°C

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3. Process Parameter Optimization

• Injection Pressure and Speed: A strategy combining low-speed filling (0.5 m/s) with high-speed intensification (5 m/s) was adopted to reduce turbulent flow and gas entrapment, utilizing an 80 MPa intensification pressure to compensate for shrinkage

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• Alloy Material Adaptation: A zinc alloy with 3% copper content was selected for its superior creep resistance compared to standard alloys, and a melting temperature of 415°C was used to control oxide slag formation

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III. Quality Improvement Data and Benefit Analysis

1. Significant Defect Reduction

• Reduced Porosity: X-ray inspection showed internal pore size decreased from 0.5mm to below 0.1mm. Hydraulic test pass rate increased from 82% to 99.5%

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• Eliminated Shrinkage: Through mold temperature control, the shrinkage porosity rate in thick sections dropped from 8% to 0.3%. Metallographic analysis of sample sections showed a 40% improvement in microstructure density

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2. Achieved Mechanical Properties

The vacuum die cast parts achieved a consistent tensile strength of 290-310 MPa, with elongation increasing from 3% to 4.5%. They could withstand T5 heat treatment (150°C / 2 hours) without deformation

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3. Economic Benefits

• The increase in yield rate led to an 18% reduction in unit cost. For an annual production of 100,000 pieces, this translated to approximately 2 million RMB saved in scrap reduction.
• Although energy consumption of the vacuum system increased by 12%, the reduction in subsequent processing (e.g., welding repairs) resulted in an overall cost decrease of 15%

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IV. Technology Promotion Value

This case demonstrates the feasibility of combining vacuum die casting with intelligent temperature control for zinc alloy safety components. The solution has been extended to other parts like engine brackets and steering knuckles, establishing a standardized approach for high-integrity die casting (e.g., vacuum >90 kPa, mold temperature gradient control ±5°C). Future integration with AI algorithms for dynamic regulation of vacuum and temperature holds promise for further突破 the yield limitations of large structural components (e.g., battery trays)

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The successful implementation of this technical solution highlights the significant potential of vacuum die casting and precision temperature control in enhancing the performance and yield of zinc alloy die castings, providing an important reference for the production of similarly demanding components.