What Are the Key Precautions for Die-Casting Processing of Aluminum Parts?

Aluminum die casting is widely used in automotive, electronics, and aerospace industries due to its lightweight, high strength, and cost-effectiveness. However, the process involves multiple complex links—from material selection to post-treatment—and any oversight can lead to defects like porosity, cracks, or undercasting. To ensure stable production and high-quality aluminum parts, manufacturers must master critical precautions throughout the workflow. This article systematically breaks down key considerations in each stage, providing actionable guidance to avoid common pitfalls.

1. Material Selection: Match Alloy to Part Function

Choosing the right aluminum alloy is the foundation of successful die casting. Different alloys have unique properties, and mismatching alloy to part function can cause premature failure or performance issues. Below is a comparative table of commonly used aluminum alloys and their application precautions:

Core Tip: For parts with mixed requirements (e.g., heat resistance + toughness), conduct small-batch trials first. For example, an EV battery frame may need A356 for heat resistance but require adjusting copper content to enhance strength—test 50-100 samples to verify performance.

2. Mold Design & Manufacturing: Avoid Structural Hidden Dangers

Mold design directly affects part quality and production efficiency. Poor mold structure often leads to defects like flash, shrinkage, or difficult ejection. The following are key precautions organized by mold component:

2.1 Shrinkage Compensation: Ensure Dimensional Accuracy

Aluminum alloys shrink during solidification—ignoring this leads to undersized parts. Follow these rules:

• General Compensation: Apply an average shrinkage rate of 1.6%-1.8% for most aluminum parts. For example, a part with a designed length of 100mm should have a mold cavity length of 101.6-101.8mm.
• Zonal Compensation: For complex structures (e.g., ribs, bosses), adjust compensation rates:
• Add 0.2mm to rib thickness (e.g., 3mm rib → 3.2mm mold cavity) to prevent shrinkage-induced thinning.
• Reduce compensation to 1.2%-1.4% for thin-walled areas (<2mm) to avoid overfilling.

2.2 Gating & Exhaust Systems: Prevent Porosity and Undercasting

• Gating System:
• The cross-sectional area of the main runner should be 15%-20% larger than the gate sleeve entrance to reduce flow resistance. For example, if the gate sleeve entrance is 20mm², the main runner should be 23-24mm².
• Inner gate thickness = 40%-60% of part wall thickness (typical 3-5mm). A 5mm thick part needs an inner gate of 2-3mm—too thin causes premature solidification; too thick leads to excess material.
• Exhaust System:
• For deep-cavity parts (depth >50mm), use three-stage exhaust (main exhaust groove + auxiliary exhaust needle + vacuum valve) to fully remove trapped air.
• Total exhaust cross-sectional area ≥ 1/3 of inner gate area. If the inner gate is 30mm², exhaust area should be ≥10mm² to avoid air entrainment.

2.3 Ejection Mechanism: Protect Part Integrity

• Ejector Pin Spacing: ≤Φ8mm for general parts; ≤Φ5mm for thin-walled parts (<1.5mm) to prevent deformation. For a 100mm×100mm thin-walled cover, arrange at least 9 ejector pins (3×3 grid).
• Ejection Force Calculation: Account for expansion pressure (aluminum expands 2-3% when heated) and friction coefficient (0.15-0.2 for aluminum-mold contact). Use the formula: Ejection force (kN) = Part weight (kg) × 8-10 (safety factor).

3. Process Parameter Control: Stabilize Production Quality

Aluminum die casting is sensitive to process parameters—small deviations can cause major defects. Focus on the following critical parameters with specific control ranges:

3.1 Temperature Control: Balance Fluidity and Solidification

3.2 Injection & Pressurization: Avoid Turbulence and Shrinkage

• Injection Speed: 0.5-1.2m/s. For complex parts (e.g., 5G filter cavities with narrow grooves), use stepped speed increase (0.5m/s → 0.8m/s → 1.0m/s) to prevent splashing.
• Pressurization Build-Up Time: 3-8 seconds. Extend to 10 seconds for stress-bearing parts (e.g., automotive suspension brackets) to ensure full compaction.
• Special Processes:
• Vacuum Die Casting: Cavity vacuum >90kPa reduces porosity to <1%—suitable for pressure-resistant parts (e.g., hydraulic cylinders).
• Oxygenated Die Casting: Inject pure oxygen into the cavity to reduce inclusions by 70%—ideal for parts requiring high surface quality (e.g., smartphone frames).

3.3 Holding & Cooling: Ensure Dimensional Stability

• Holding Time: 10-25 seconds. Add 2 seconds for every 1mm increase in gate thickness. A 5mm gate needs 18-20 seconds of holding time to compensate for shrinkage.
• Cooling Time: 8-20 seconds. Use cooling inserts (e.g., copper inserts with water channels) to shorten cooling time by 30% for thick-walled parts, improving production efficiency.

4. Defect Prevention & Response: Troubleshoot Common Issues

Even with strict control, defects may occur. The table below lists typical defects, their causes, and immediate solutions:

5. Post-Treatment & Quality Control: Ensure Final Performance

Post-treatment and inspection are the last lines of defense against defective parts. Follow these precautions:

5.1 Post-Treatment Processes

• Precision Machining:
• CNC milling allowance: 0.3-0.5mm per side (0.8mm for complex surfaces with curved shapes).
• Use PCD (polycrystalline diamond) inserts to improve tool life by 3-5 times compared to carbide inserts—critical for high-volume production.
• Surface Strengthening:
• Micro-arc Oxidation: Achieve film thickness of 15-25μm; ensure salt spray test >2000 hours for corrosion-resistant parts (e.g., marine components).
• Composite Coating (Ni-P/PTFE): Apply double coating for parts requiring wear resistance (e.g., sliding bearings) to reduce friction coefficient by 40%.
• Defect Repair:
• Argon arc welding: Current ≤90A, interlayer temperature <150°C to avoid thermal cracks.
• Metal penetrant impregnation: Use low-viscosity impregnants for small pores (<0.1mm) to ensure leak tightness.

5.2 Quality Inspection Standards

• Dimensional Inspection: Use CMM (Coordinate Measuring Machine) for key dimensions (CTQ, Critical to Quality) with tolerance ≤±0.15mm.
• Mechanical Performance: Tensile test requires σb≥320MPa, δ≥2% for structural parts.
• Leak Detection: Helium mass spectrometry ensures leakage rate <1×10⁻⁶mbar·L/s for pressure-bearing parts (e.g., EV water-cooled plates).
• Internal Defects: X-ray real-time imaging meets ASTM E446 Level B to detect internal porosity and inclusions.

6. Yigu Technology’s Perspective on Aluminum Die-Casting Precautions

At Yigu Technology, we believe that aluminum die-casting success lies in “precise control + systematic prevention.” Many manufacturers focus only on process parameters but ignore early-stage DFM (Design for Manufacturability) reviews—for example, designing parts with sharp corners that inevitably cause cracks. We recommend establishing a cross-departmental DFM team (including design, mold, and process engineers) to identify manufacturability issues before mold production.

For mass production, we advocate SPC (Statistical Process Control) to monitor key parameters (mold temperature, injection speed, cooling time) in real time—this reduces defect rates by 40-50% compared to manual monitoring. Additionally, for high-end parts like aerospace servo valve housings, combining vacuum die-casting with selective laser cladding (for local reinforcement) balances precision and performance. By integrating these precautions into every stage, manufacturers can achieve a yield rate of over 98% for aluminum die-cast parts.

7. FAQ: Common Questions About Aluminum Die-Casting Precautions

Q1: Can I reuse aluminum scrap from die casting, and what precautions should I take?

Yes, but the proportion of return material should be controlled within 30% to avoid increasing impurity content. Before reuse, remove surface oxides and oil stains by shot blasting; preheat scrap to 150-200°C to eliminate moisture. Mixing return material with new ingots in a 3:7 ratio maintains alloy performance stability.

Q2: How to prevent mold sticking during aluminum die casting?

First, ensure mold preheating temperature is ≥180°C (cold molds increase adhesion). Second, use high-temperature resistant release agents (e.g., graphite-based) and apply a uniform film (thickness 5-10μm) to the cavity. Third, polish the mold cavity to Ra≤0.8μm—rough surfaces increase friction and sticking risk.

Q3: What are the precautions for packaging and transporting aluminum die-cast parts?

• Anti-Rust Protection: Impregnate with LZ-301 anti-rust oil (oil film thickness 3-5μm) to prevent oxidation during storage.
• Physical Protection: Use pearl cotton for corner protection and EPE foam padding between layers to avoid collision scratches.
• Environmental Control: Maintain relative humidity ≤60% and temperature -20~45°C during transportation—avoid extreme temperatures that cause thermal deformation.