Le moulage sous pression est un procédé de fabrication largement utilisé pour produire des pièces métalliques complexes avec une haute précision.. Cependant, ce n'est pas sans défis. Divers défauts peuvent survenir au cours du processus, affectant la qualité, performance, et le coût des produits finaux. Understanding these common problems and their solutions is crucial for manufacturers to improve production efficiency and product quality. Below is a detailed analysis of the key issues in die casting, along with practical solutions.
1. Key Defects in Die Casting: Un aperçu
Before delving into specific problems, let’s first look at a summary of the most common die casting defects, their main causes, and core solutions. This table provides a quick reference for identifying and addressing issues.
| Catégorie de défaut | Main Manifestations | Primary Causes | Core Solutions |
| Stomata and Looseness | Dense shadows in X-ray inspection; exposed pinholes after machining | Trapped air in the cavity (poor exhaust); hydrogen precipitation during solidification | Add serpentine exhaust tanks; use vacuum die-casting; control melting degassing |
| Shrinking Holes and Shrinking Looseness | Concentrated or dispersed shrinkage in thick parts/hot joints | Inadequate replenishment of volume shrinkage during solidification | Extend holding time; increase final pressure; optimize gating system |
| Cracks and Deformations | Thermal cracks in thin-walled parts; distortion of large flat structures | Thermal stress exceeding material strength; uneven cooling contraction | Adjust mold cooling system; increase mold temperature; use arc transitions |
| Mold Sticking and Strain | Rough casting surface; local material shortage; severe mold jamming | High chemical activity of materials (Par exemple, alliages de zinc); poor mold surface or failed release agent | Polish mold cavity; plate hard chrome; use high-temperature release agents |
| Flash and Burrs | Flake-like excess at mold parting surfaces/movable block gaps | Insufficient clamping force; usure; high injection pressure | Check mold wear; increase clamping force; add sealing grooves |
2. In-Depth Analysis of Major Die Casting Problems
Each defect in die casting has unique characteristics and requires targeted solutions. The following sections break down the most critical problems using a cause-effect-solution structure, avec les termes clés mis en évidence pour plus de clarté.
2.1 Stomata and Looseness: Le “Invisible Killers” of Casting Compactness
Stomata (tiny bubbles) et le relâchement (dispersed pores) are among the most stubborn defects in die casting. They are often invisible to the naked eye but can significantly reduce the mechanical properties of parts, such as tensile strength and fatigue resistance.
Qu'est-ce qui les cause?
- During high-speed injection, air in the mold cavity is compressed into a high-pressure zone. If the exhaust channel is blocked or too narrow, this air cannot escape and becomes trapped as bubbles in the casting.
- The metal liquid absorbs hydrogen during melting. As the liquid solidifies and cools, the solubility of hydrogen decreases, causing it to precipitate as tiny pores.
How to solve them?
- Installer serpentine exhaust tanks dans le moule: These tanks have a winding design that increases the path for air to escape, ensuring thorough exhaust.
- Adopter technologie de moulage sous vide: This method actively extracts air from the cavity before injection, reducing air trapping by up to 90%.
- Strictly control the degassing process during melting: Use inert gas (Par exemple, argon) to purge the metal liquid, removing dissolved hydrogen and other gases.
2.2 Shrinkage Defects: Why Thick Parts Fail
Shrinking holes (grand, concentrated gaps) and shrinking looseness (petit, dispersed gaps) are common in thick sections or “hot joints” (areas where multiple metal flows meet and cool slowly). These defects weaken the part’s structure and can lead to leakage in pressure-bearing components.
A comparative look at shrinkage types:
| Taper | Emplacement | Taille | Impact on Performance |
| Shrinking Holes | Thick parts/hot joints | Grand (souvent >1MM) | Severe reduction in compactness; may cause structural failure |
| Shrinking Looseness | Idem que ci-dessus | Petit (généralement <0.5MM) | Gradual loss of mechanical properties; affects long-term durability |
Solutions to prevent shrinkage:
- Extend the temps de maintien of the die casting machine: This allows more metal liquid to flow into the cavity and replenish the space left by solidification shrinkage.
- Increase the pression finale: Higher pressure ensures the metal liquid fills even tiny gaps, reducing the formation of shrinkage.
- Optimize the système de déclenchement: Position the inner gate close to the shrinkage-prone areas so the metal liquid can directly feed these regions. Ajouter rainures de trop-plein to collect excess liquid and assist in replenishment.
2.3 Mold Sticking and Strain: A Nightmare for Production Efficiency
Mold sticking occurs when the casting adheres to the mold surface during ejection, leading to scratches, material loss, or even mold damage. This problem is particularly common with alliages de zinc and other chemically active materials.
What are the warning signs?
- The casting surface becomes rough or has “pull marks” after ejection.
- Local areas of the casting are missing (due to material sticking to the mold).
- In severe cases, the casting gets stuck in the mold, halting production.
How to fix and prevent mold sticking?
- Regularly polish the mold cavity: A smooth mold surface reduces friction between the casting and the mold.
- Plate the mold with hard chrome: This coating increases surface hardness and resistance to adhesion, Extension de la durée de vie.
- Switch to high-temperature resistant release agents: Graphite-based or molybdenum disulfide release agents form a protective layer between the casting and mold, preventing sticking.
- Installer forced ejection mechanisms dans les zones à risque (Par exemple, deep cavities or complex shapes) to ensure smooth part removal.
3. Comprehensive Prevention Strategies for Die Casting Problems
Solving individual defects is important, but a systematic approach is needed to minimize all issues. Below are four key strategies to build a robust die casting process:
- Preliminary Verification with CAE Simulation
Use Computer-Aided Engineering (Cae) software to simulate the filling and solidification process. This predicts potential defect locations (Par exemple, pièges à air, hot joints) before mold production, saving time and cost on revisions.
- Real-Time Process Monitoring
Collect data on injection curves (vitesse, pression) et température du moule en temps réel. Set up control limits for these parameters to ensure the process stays within optimal ranges. Par exemple, if mold temperature drops below a threshold, the system can alert operators to adjust heating.
- Continuous Improvement with FMEA
Conduct Failure Mode and Effects Analysis (FMEA) to review historical defects. Identify root causes (Par exemple, “mold sticking due to infrequent polishing”) and implement corrective actions. This cycle of analysis and improvement reduces defect recurrence.
- Strict Equipment Management
- Regularly calibrate the système d'injection of the die casting machine to ensure accurate pressure and speed control.
- Vérifiez le cleanliness of hydraulic oil: Contaminated oil can cause system malfunctions, leading to unstable injection and defects.
4. Yigu Technology’s Perspective on Die Casting Quality
À la technologie Yigu, we believe that solving die casting problems requires a balance of technical expertise and practical experience. Many defects, such as stomata and shrinkage, are interrelated—improving exhaust to reduce stomata may require adjusting injection pressure, which could affect flash formation. Thus, manufacturers should not focus on single parameters but optimize the entire process based on product structure et Propriétés des matériaux.
We recommend small-batch trials before mass production: Test different process parameters (Par exemple, température du moule, temps de maintien) to find the “point idéal” for each part. En plus, investing in operator training is key—well-trained staff can detect early signs of defects (Par exemple, surfaces rugueuses, refroidissement irrégulier) and adjust the process promptly. By combining advanced technology (like CAE simulation) with hands-on expertise, Les fabricants peuvent atteindre cohérent, high-quality die casting.
5. FAQ: Common Questions About Die Casting Problems
T1: Can vacuum die-casting completely eliminate stomata?
Non, vacuum die-casting significantly reduces stomata (par 80-90%) but cannot eliminate them entirely. Residual hydrogen in the metal liquid or minor exhaust gaps may still cause small pores. Combining vacuum technology with strict degassing during melting is the most effective approach.
T2: Why do cracks often occur in thin-walled die castings?
Thin-walled parts cool faster than thick parts, créer un grand contrainte thermique (due to uneven temperature distribution). When this stress exceeds the material’s strength limit, cracks form. Pour éviter cela, increase mold temperature to slow cooling and use arc transitions (instead of sharp corners) to reduce stress concentration.
T3: How often should I replace the release agent in die casting?
The frequency depends on the release agent type and production volume. For graphite-based release agents, replace them every 4-6 heures (or after 50-100 cycles) to ensure effectiveness. If mold sticking occurs more frequently, check the release agent coverage and adjust the replacement schedule.