Die casting is a widely used manufacturing process for producing complex metal parts with high precision. Sin embargo, it is not without challenges. Various defects can occur during the process, affecting the quality, actuación, and cost of the final products. 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: Una descripción general
Antes de profundizar en problemas específicos, Veamos primero un resumen de los defectos más comunes en la fundición a presión., sus principales causas, y soluciones centrales. This table provides a quick reference for identifying and addressing issues.
| Defect Category | 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 (P.EJ., aleaciones 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 | Fuerza de sujeción insuficiente; desgaste del molde; 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 estructura, con términos clave resaltados para mayor claridad.
2.1 Stomata and Looseness: El “Invisible Killers” of Casting Compactness
Stomata (tiny bubbles) and looseness (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.
What causes them?
- 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?
- Instalar serpentine exhaust tanks en el molde: These tanks have a winding design that increases the path for air to escape, ensuring thorough exhaust.
- Adoptar vacuum die-casting technology: 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 (P.EJ., argón) to purge the metal liquid, removing dissolved hydrogen and other gases.
2.2 Shrinkage Defects: Why Thick Parts Fail
Shrinking holes (grande, concentrated gaps) and shrinking looseness (pequeño, 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:
| Tipo | Ubicación | Tamaño | Impact on Performance |
| Shrinking Holes | Thick parts/hot joints | Grande (a menudo >1milímetros) | Severe reduction in compactness; may cause structural failure |
| Shrinking Looseness | Same as above | Pequeño (generalmente <0.5milímetros) | Gradual loss of mechanical properties; affects long-term durability |
Solutions to prevent shrinkage:
- Extend the tiempo de espera de la máquina de fundición a presión: Esto permite que fluya más líquido metálico hacia la cavidad y reponga el espacio dejado por la contracción por solidificación..
- aumentar el presión final: Una presión más alta garantiza que el líquido metálico llene incluso los huecos más pequeños., reduciendo la formación de contracción.
- Optimizar el sistema de activación: Coloque la puerta interior cerca de las áreas propensas a encogerse para que el líquido metálico pueda alimentar directamente estas regiones.. Agregar ranuras de desbordamiento para recoger el exceso de líquido y ayudar en la reposición.
2.3 Mold Sticking and Strain: A Nightmare for Production Efficiency
La adherencia del molde ocurre cuando la pieza fundida se adhiere a la superficie del molde durante la expulsión., lo que lleva a rayones, perdida material, o incluso daños por moho. Este problema es particularmente común con aleaciones de zinc y otros materiales químicamente activos.
¿Cuáles son las señales de advertencia??
- La superficie de fundición se vuelve rugosa o tiene “marcas de tirar” después de la expulsión.
- Faltan áreas locales del casting. (debido al material que se pega al molde).
- En casos severos, la pieza se atasca en el molde, detener la producción.
Cómo arreglar y evitar que el moho se pegue?
- Regularmente pulir la cavidad del molde: Una superficie lisa del molde reduce la fricción entre la pieza fundida y el molde..
- Placar el molde con cromo duro: Este recubrimiento aumenta la dureza superficial y la resistencia a la adhesión., Extender la vida útil del moho.
- Cambie a agentes desmoldantes resistentes a altas temperaturas: Los agentes desmoldantes a base de grafito o disulfuro de molibdeno forman una capa protectora entre la pieza fundida y el molde., evitando que se pegue.
- Instalar mecanismos de expulsión forzada en zonas de alto riesgo (P.EJ., cavidades profundas o formas complejas) para garantizar una extracción suave de las piezas.
3. Estrategias integrales de prevención de problemas de fundición a presión
Resolver defectos individuales es importante, 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 (P.EJ., trampas de aire, hot joints) before mold production, saving time and cost on revisions.
- Real-Time Process Monitoring
Collect data on injection curves (velocidad, presión) y temperatura del molde en tiempo real. Set up control limits for these parameters to ensure the process stays within optimal ranges. Por ejemplo, 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 (P.EJ., “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 injection system of the die casting machine to ensure accurate pressure and speed control.
- Revise el cleanliness of hydraulic oil: Contaminated oil can cause system malfunctions, leading to unstable injection and defects.
4. La perspectiva de Yigu Technology sobre la calidad de la fundición a presión
En la tecnología 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 y propiedades del material.
We recommend small-batch trials before mass production: Test different process parameters (P.EJ., temperatura del molde, tiempo de espera) to find the “punto” for each part. Además, investing in operator training is key—well-trained staff can detect early signs of defects (P.EJ., superficies ásperas, enfriamiento desigual) and adjust the process promptly. By combining advanced technology (like CAE simulation) with hands-on expertise, Los fabricantes pueden lograr consistente, high-quality die casting.
5. Preguntas frecuentes: Preguntas comunes sobre problemas de fundición a presión
Q1: ¿Puede la fundición al vacío eliminar completamente los estomas??
No, vacuum die-casting significantly reduces stomata (por 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.
Q2: ¿Por qué suelen aparecer grietas en piezas fundidas a presión de paredes delgadas??
Thin-walled parts cool faster than thick parts, creating large estrés térmico (due to uneven temperature distribution). When this stress exceeds the material’s strength limit, cracks form. Para evitar esto, increase mold temperature to slow cooling and use arc transitions (instead of sharp corners) para reducir la concentración de estrés.
Q3: ¿Con qué frecuencia debo reemplazar el agente desmoldante en la fundición a presión??
The frequency depends on the release agent type and production volume. For graphite-based release agents, replace them every 4-6 horas (or after 50-100 ciclos) to ensure effectiveness. If mold sticking occurs more frequently, check the release agent coverage and adjust the replacement schedule.