Die casting specific pressure is the “invisible hand” that governs the success of metal forming—too little, and parts suffer from undercasting or cold shuts; too much, and molds wear prematurely or parts develop flash. As a critical process parameter, it directly determines the molten metal’s filling ability, casting density, and surface finish. For manufacturers struggling with inconsistent part quality or high scrap rates, mastering specific pressure control is a cost-effective solution. This article systematically breaks down its definition, influencing factors, optimization strategies, and real-world applications to help you achieve stable, high-quality die casting production.
1. Basic Cognition: What Is Die Casting Specific Pressure?
Before diving into optimization, it’s essential to clarify the core concepts of specific pressure—including its definition, measurement, and value in production. This section uses a 总分 structure with key terms highlighted for clarity.
1.1 Fundamental Definition & Measurement
Die casting specific pressure refers to the static pressure exerted by the injection punch on the unit area of molten metal, measured in megapascals (MPa). It differs from the “theoretical pressure” displayed on die casting machines:
- Theoretical Pressure: The pressure value calculated based on the machine’s hydraulic system (e.g., 150MPa displayed on the control panel).
- Effective Specific Pressure: The actual pressure transferred to the molten metal—this is often 10-30% lower than theoretical pressure due to energy loss in the gating system, mold resistance, and punch friction.
For example, a machine displaying 120MPa theoretical pressure may only deliver 85-100MPa effective specific pressure to the molten metal. Accurately measuring effective specific pressure (via cavity pressure sensors) is critical for avoiding parameter miscalculations.
1.2 Core Value in Die Casting Production
Specific pressure acts as a balancing tool between three key production goals:
- Ensuring Complete Filling: Sufficient specific pressure pushes molten metal into narrow cavities and thin-walled sections (e.g., 0.8mm-thick electronic part shells) that low pressure would fail to fill.
- Improving Casting Density: High specific pressure compresses molten metal during solidification, reducing porosity and shrinkage. For pressure-bearing parts (e.g., hydraulic valves), this increases leak tightness by 60-80%.
- Protecting Mold Life: Optimized specific pressure avoids excessive stress on mold components (e.g., cores, parting surfaces), extending mold lifespan by 20-30% compared to over-pressurization.
A typical example: An aluminum alloy motor housing produced with 85MPa specific pressure had 2 microscopic shrinkage holes and 280MPa tensile strength. Increasing specific pressure to 110MPa eliminated shrinkage, raised tensile strength to 320MPa, and boosted yield rate from 89% to 97% (per real-world case data).
2. Key Influencing Factors: What Determines Specific Pressure Requirements?
Specific pressure is not a “one-size-fits-all” parameter—it varies based on material properties, casting design, mold structure, and process dynamics. The table below uses a factor-impact-solution structure to explain how to adjust specific pressure for different scenarios:
| Influencing Factor | Impact on Specific Pressure Requirements | Recommended Adjustment |
| Material Characteristics | – High-melting-point alloys (e.g., copper-based): Poor fluidity requires higher specific pressure (80-200MPa) to maintain filling. – Aluminum alloys (e.g., ADC12): Good fluidity but need 40-120MPa for complex parts. – Magnesium alloys (e.g., AZ91D): Low density but high oxidation risk—60-150MPa balances filling and oxidation control. | For copper alloys: Increase specific pressure by 20-30% vs. aluminum for the same part complexity. For magnesium: Add 5-10MPa to compensate for oxide film resistance. |
| Casting Geometry | – Thin-walled parts (<2mm) or long flow paths: Need higher specific pressure (100-150MPa) to overcome flow resistance. – Thick-walled parts (>10mm): Unified high pressure causes turbulence—requires segmented control (low pressure for thick areas, high for thin edges). | Use “gradient pressure”: For a part with 1mm thin walls and 8mm thick bosses, apply 120MPa to thin sections and 70MPa to bosses. |
| Mold & Gating Design | – Small gate cross-section: Increases flow resistance—specific pressure needs to rise by 15-25% (e.g., 80MPa for 5mm² gates → 95MPa for 3mm² gates). – Multi-branch runners: Disperse effective pressure—compensate by increasing main runner cross-section (10-15%) or raising specific pressure (5-10%). | For molds with 3+ branches: Use a “main runner first” design—widen main runner to 1.2x branch width to maintain pressure distribution. |
| Dynamic Process Parameters | – High injection speed (4-8m/s): Requires higher specific pressure (10-20% increase) to prevent front-end metal solidification. – High molten metal temperature (>720°C for aluminum): Reduces viscosity—lower specific pressure by 5-8% to avoid over-pressurization. | For high-speed injection (6m/s): Match with specific pressure 10-15% higher than low-speed (3m/s) settings. For every 10°C temperature rise: Decrease specific pressure by 5%. |
3. Three-Stage Specific Pressure Control Strategy: From Filling to Solidification
The most effective way to optimize specific pressure is to adopt a phased control strategy—adjusting pressure based on the casting’s filling and solidification stages. This section uses a linear 叙述 structure with clear parameter ranges for each stage.
3.1 Stage 1: Initial Slow Plugging (30-50% of Total Specific Pressure)
- Goal: Smoothly push molten metal over the gate, remove cavity air, and form a stable flow front—avoiding premature core impact.
- Parameter Range: 30-50% of the final specific pressure (e.g., 40-60MPa for a total pressure of 120MPa).
- Key Operation: Use constant pressure (not variable) to ensure uniform flow. For example, an aluminum alloy shell with a 3mm gate should start with 50MPa to prevent splashing.
- Outcome: Air in the runner is expelled, and the molten metal forms a continuous “liquid bridge” between the punch and mold cavity.
3.2 Stage 2: High-Speed Filling (Peak Specific Pressure)
- Goal: Deliver maximum effective pressure to push molten metal into deep cavities and narrow sections—ensuring complete filling.
- Parameter Range: 80-100% of total specific pressure (e.g., 95-120MPa for a total of 120MPa).
- Key Operation: Modern die casting machines use real-time displacement monitoring to automatically correct pressure curves. If flow resistance increases (e.g., metal slows in a 1mm gap), the machine boosts pressure by 5-10% to maintain speed.
- Outcome: Molten metal fills the entire cavity within 0.5-2 seconds (depending on part size), with no cold shuts or undercasting.
3.3 Stage 3: Boosting & Shrinkage Compensation (60-80% of Peak Pressure)
- Goal: Apply secondary pressure during early solidification to compress shrinkage gaps and improve casting density.
- Parameter Range: 60-80% of peak specific pressure (e.g., 75-95MPa for a peak of 120MPa).
- Holding Time: Determined by alloy type—aluminum alloys need 5-15 seconds, magnesium alloys 3-8 seconds (shorter due to faster solidification).
- Key Operation: Start boosting when the metal’s solidification rate reaches 30-40% (detected via mold temperature sensors). For thick-walled parts, extend holding time by 2-3 seconds to ensure full compensation.
- Outcome: Shrinkage voids are reduced by 70-90%, and casting density approaches 98% of the alloy’s theoretical density.
4. Engineering Application Guidelines: Defect Diagnosis & Debugging
Even with phased control, defects may occur due to parameter mismatches. This section provides defect diagnosis logic and a progressive debugging method to resolve issues quickly.
4.1 Defect Diagnosis: Linking Issues to Specific Pressure
| Defect Type | Specific Pressure Root Cause | Supplementary Checks |
| Undercasting/Cold Shuts | Insufficient specific pressure (failure to fill thin sections) or delayed pressure application. | Check injection speed (too slow?) and mold temperature (too low? <180°C for aluminum). |
| Surface Porosity/Bubbles | Improper pressurization timing (too late—gas trapped before pressure is applied). | Verify pressure curve: Should start boosting within 0.3-0.5 seconds of cavity filling. |
| Flash/Burrs | Excessive final pressure or delayed pressure relief (mold forced open by over-pressurization). | Inspect mold parting surfaces (worn?) and clamping force (sufficient? Should be 1.2x specific pressure force). |
| Internal Shrinkage | Inadequate holding time or low compensation pressure (failure to fill solidification gaps). | Check metallographic samples: Shrinkage in hot joints indicates need for 5-10% higher compensation pressure. |
4.2 Progressive Debugging Method
To avoid sudden parameter changes (which cause new defects), follow these steps:
- Start with Baseline Pressure: Use material-specific experience values (e.g., 80MPa for aluminum ADC12 shells).
- Adjust in Small Increments: Change specific pressure by ≤10MPa per trial (e.g., 80MPa → 88MPa, not 95MPa).
- Validate with Testing: After each adjustment, conduct:
- Visual inspection (no flash/undercasting).
- Metallographic analysis (shrinkage improvement).
- Density measurement (target: 98% of theoretical density).
- Lock Optimal Range: Once defects are eliminated and density meets requirements, record the specific pressure as the “golden parameter.”
5. Technology Trends & Operational Best Practices
As die casting becomes more intelligent, specific pressure control is evolving with new technologies. This section covers future trends and practical tips for daily operations.
5.1 Key Technology Trends
| Trend | Description | Benefit |
| Intelligent Closed-Loop Control | Integrate cavity pressure sensors to collect real-time filling curves, compare with preset models, and dynamically correct specific pressure (e.g., +5MPa if flow slows). | Reduces defect rate by 30-40% and eliminates manual adjustment errors. |
| Energy-Efficiency Optimization | Use two-stage booster systems: Master cylinder provides basic pressure, accumulator supplements instantaneous high pressure (for filling stage). | Saves 25-30% energy vs. traditional constant high-pressure systems. |
| Virtual Simulation Guidance | Use MAGMA/FLOW-3D software to simulate filling under 5-8 specific pressure values, predict optimal parameters (e.g., 105MPa for a 2mm-thick part). | Cuts mold trial times by 50% and reduces material waste by 20-25%. |
5.2 Operational Best Practices
- Periodic Calibration: Every quarter, use a standard pressure gauge to check the deviation between machine display and actual output. Ensure deviation ≤5% (e.g., 100MPa display should output 95-105MPa).
- Temperature-Pressure Linkage: Establish a compensation mechanism—for every 10°C increase in molten metal temperature (aluminum), reduce specific pressure by 5-8% to avoid over-pressurization.
- Mold Maintenance: Clean parting surface residual metal weekly. Even 0.1mm-thick residue can increase local resistance, causing false pressure readings (e.g., 100MPa display → 85MPa effective pressure).
6. Yigu Technology’s Perspective on Die Casting Specific Pressure
At Yigu Technology, we believe specific pressure optimization is about “precision matching”—not just chasing high or low values. Many manufacturers rely on static experience values (e.g., 80MPa for all aluminum parts) but ignore dynamic factors like mold wear or material batch differences, leading to inconsistent quality.
We recommend a data-driven approach: Combine cavity pressure sensors with AI algorithms to build a “specific pressure database” (linking material, geometry, and defects). For example, our system automatically adjusts specific pressure by 5-10% when detecting a 5% increase in mold resistance (from wear), maintaining stable production.
For high-value parts (e.g., EV motor housings), we also advocate pre-simulation with FLOW-3D—predicting optimal pressure curves before mold production. By unifying simulation, real-time monitoring, and maintenance, manufacturers can reduce specific pressure-related scrap rates to <2% and extend mold life by 30%.
7. FAQ: Common Questions About Die Casting Specific Pressure
Q1: How to calculate the effective specific pressure for my die casting part?
Effective specific pressure = (Theoretical Pressure × Punch Area) / (Gate Area + Runner Area) × Efficiency Factor (0.7-0.9). For example: Theoretical pressure = 120MPa, Punch area = 100cm², Gate + Runner area = 20cm², Efficiency = 0.8. Effective pressure = (120×100)/(20)×0.8 = 480MPa? No—correct formula: Effective pressure = Theoretical Pressure × (Punch Area / Cavity Projected Area) × Efficiency. For a part with 50cm² projected area: (120 × 100/50) × 0.8 = 192MPa. Always verify with cavity sensors for accuracy.
Q2: Can I use the same specific pressure for different batches of the same alloy?
No—material batch differences (e.g., silicon content variation in aluminum ADC12) affect fluidity. For example, ADC12 with 12% silicon needs 5-10% lower specific pressure than 10% silicon (better fluidity). Test 10-20 samples per batch: If undercasting occurs, increase specific pressure by 5-8%; if flash appears, decrease by 3-5%.
Q3: How does specific pressure affect the heat treatment of die cast parts?
High specific pressure reduces porosity, making parts suitable for heat treatment (e.g., T6 for aluminum). For example, an aluminum part with 110MPa specific pressure (low porosity) can undergo T6 treatment (530°C solution + 120°C aging) to reach 320MPa tensile strength. Parts with low specific pressure (70MPa, high porosity) crack during heat treatment—porosity expands and breaks the metal structure. Always ensure specific pressure is high enough (≥80MPa for aluminum) before heat treatment.