Quelles sont les principales précautions à prendre lors du traitement par moulage sous pression de pièces en aluminium?

Le moulage sous pression d'aluminium est largement utilisé dans l'automobile, électronique, et les industries aérospatiales en raison de sa légèreté, haute résistance, et la rentabilité. Cependant, le processus implique de multiples liens complexes – de la sélection des matériaux au post-traitement – ​​et tout oubli peut conduire à des défauts comme la porosité, fissures, ou sous-casting. Pour garantir une production stable et des pièces en aluminium de haute qualité, 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. Sélection des matériaux: 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 (par ex., résistance à la chaleur + dureté), conduct small-batch trials first. Par exemple, 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. Conception de moules & Fabrication: Avoid Structural Hidden Dangers

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

2.1 Compensation du retrait: 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. Par exemple, a part with a designed length of 100mm should have a mold cavity length of 101.6-101.8mm.
• Zonal Compensation: For complex structures (par ex., côtes, bosses), adjust compensation rates:
• Add 0.2mm to rib thickness (par ex., 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. Par exemple, 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), utiliser 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 Mécanisme d'éjection: 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 broches d'éjection (3×3 grid).
• Ejection Force Calculation: Account for expansion pressure (aluminum expands 2-3% lorsqu'il est chauffé) et friction coefficient (0.15-0.2 for aluminum-mold contact). Use the formula: Force d'éjection (kN) = Part weight (kilos) × 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 Contrôle de la température: Balance Fluidity and Solidification

3.2 Injection & Pressurization: Avoid Turbulence and Shrinkage

• Vitesse d'injection: 0.5-1.2MS. Pour pièces complexes (par ex., 5G filter cavities with narrow grooves), utiliser stepped speed increase (0.5m/s → 0.8m/s → 1.0m/s) to prevent splashing.
• Pressurization Build-Up Time: 3-8 secondes. Extend to 10 secondes for stress-bearing parts (par ex., automotive suspension brackets) to ensure full compaction.
• Special Processes:
• Coulée sous vide: Cavity vacuum >90kPa reduces porosity to <1%—suitable for pressure-resistant parts (par ex., vérins hydrauliques).
• Oxygenated Die Casting: Inject pure oxygen into the cavity to reduce inclusions by 70%—ideal for parts requiring high surface quality (par ex., cadres de smartphones).

3.3 Holding & Refroidissement: Ensure Dimensional Stability

• Holding Time: 10-25 secondes. Add 2 seconds for every 1mm increase in gate thickness. A 5mm gate needs 18-20 seconds of holding time to compensate for shrinkage.
• Temps de refroidissement: 8-20 secondes. Use cooling inserts (par ex., copper inserts with water channels) to shorten cooling time by 30% pour pièces à parois épaisses, 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 & Contrôle de qualité: Ensure Final Performance

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

5.1 Post-Treatment Processes

• Usinage de précision:
• CNC milling allowance: 0.3-0.5mm per side (0.8mm for complex surfaces with curved shapes).
• Utiliser 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 (par ex., composants marins).
• Composite Coating (Ni-P/PTFE): Apply double coating for parts requiring wear resistance (par ex., 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

• Contrôle dimensionnel: Use CMM (Machine de mesure de coordonnées) for key dimensions (CTQ, Critical to Quality) with tolerance ≤±0.15mm.
• Performances mécaniques: 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 (par ex., 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

Chez Yigu Technologie, we believe that aluminum die-casting success lies in “contrôle précis + systematic prevention.” Many manufacturers focus only on process parameters but ignore early-stage DFM (Conception pour la fabricabilité) reviews—for example, designing parts with sharp corners that inevitably cause cracks. We recommend establishing a cross-departmental DFM team (y compris la conception, moule, and process engineers) to identify manufacturability issues before mold production.

Pour la production de masse, we advocate CPS (Contrôle statistique des processus) to monitor key parameters (température du moule, injection speed, temps de refroidissement) in real time—this reduces defect rates by 40-50% compared to manual monitoring. En plus, 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?

Oui, 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?

D'abord, ensure mold preheating temperature is ≥180°C (cold molds increase adhesion). Deuxième, use high-temperature resistant release agents (par ex., graphite-based) and apply a uniform film (thickness 5-10μm) to the cavity. Troisième, 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.