What Are the Most Common Problems in the Die Casting Process and How to Solve Them?

La pressofusione è un processo di produzione ampiamente utilizzato per produrre parti metalliche complesse con elevata precisione. Tuttavia, non è privo di sfide. Durante il processo possono verificarsi vari difetti, influendo sulla qualità, prestazione, e il costo dei prodotti finali. Comprendere questi problemi comuni e le relative soluzioni è fondamentale per i produttori per migliorare l’efficienza produttiva e la qualità del prodotto. Di seguito è riportata un'analisi dettagliata delle principali problematiche legate alla pressofusione, insieme a soluzioni pratiche.

1. Difetti chiave nella pressofusione: Una panoramica

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.

2. Analisi approfondita dei principali problemi di pressofusione

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 struttura, con i termini chiave evidenziati per chiarezza.

2.1 Stomi e scioltezza: IL “Assassini invisibili” della Compattezza del Getto

Stomata (tiny bubbles) e scioltezza (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?

• Install serpentine exhaust tanks nello stampo: These tanks have a winding design that increases the path for air to escape, ensuring thorough exhaust.
• Adottare 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 (PER ESEMPIO., argon) to purge the metal liquid, removing dissolved hydrogen and other gases.

2.2 Difetti di ritiro: Perché le parti spesse falliscono

Shrinking holes (grande, concentrated gaps) and shrinking looseness (piccolo, 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:

Solutions to prevent shrinkage:

1. Extend the tempo di trattenimento of the die casting machine: Ciò consente a più liquido metallico di fluire nella cavità e di riempire lo spazio lasciato dal ritiro da solidificazione.
2. Aumenta il pressione finale: Una pressione più elevata garantisce che il liquido metallico riempia anche i più piccoli spazi vuoti, riducendo la formazione di ritiro.
3. Ottimizza il Sistema di gating: Posizionare la porta interna vicino alle aree soggette a ritiro in modo che il liquido metallico possa alimentare direttamente queste regioni. Aggiungere scanalature di troppopieno per raccogliere il liquido in eccesso e favorire il rifornimento.

2.3 Attaccamento e deformazione della muffa: Un incubo per l’efficienza produttiva

L'adesione allo stampo avviene quando il pezzo fuso aderisce alla superficie dello stampo durante l'espulsione, leading to scratches, material loss, or even mold damage. This problem is particularly common with leghe di zinco 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, fermare la produzione.

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, estendendo la vita della muffa.
• 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.
• Install forced ejection mechanisms in high-risk areas (PER ESEMPIO., deep cavities or complex shapes) to ensure smooth part removal.

3. Strategie di prevenzione complete per i problemi della pressofusione

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:

1. Preliminary Verification with CAE Simulation

Use Computer-Aided Engineering (CAE) software to simulate the filling and solidification process. This predicts potential defect locations (PER ESEMPIO., air traps, hot joints) before mold production, saving time and cost on revisions.

2. Real-Time Process Monitoring

Collect data on injection curves (velocità, pressione) E Temperatura della muffa in tempo reale. Set up control limits for these parameters to ensure the process stays within optimal ranges. Per esempio, if mold temperature drops below a threshold, the system can alert operators to adjust heating.

3. Continuous Improvement with FMEA

Conduct Failure Mode and Effects Analysis (FMEA) to review historical defects. Identify root causes (PER ESEMPIO., “mold sticking due to infrequent polishing”) and implement corrective actions. This cycle of analysis and improvement reduces defect recurrence.

4. Strict Equipment Management

• Regularly calibrate the injection system of the die casting machine to ensure accurate pressure and speed control.
• Controlla il cleanliness of hydraulic oil: Contaminated oil can cause system malfunctions, leading to unstable injection and defects.

4. La prospettiva di Yigu Technology sulla qualità della pressofusione

Alla tecnologia 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 E Proprietà materiali.

We recommend small-batch trials before mass production: Test different process parameters (PER ESEMPIO., Temperatura della muffa, tempo di trattenimento) to find the “punto debole” per ogni parte. Inoltre, investing in operator training is key—well-trained staff can detect early signs of defects (PER ESEMPIO., superfici ruvide, uneven cooling) and adjust the process promptly. By combining advanced technology (like CAE simulation) with hands-on expertise, I produttori possono ottenere coerenti, high-quality die casting.

5. Domande frequenti: Domande comuni sui problemi di pressofusione

Q1: Can vacuum die-casting completely eliminate stomata?

NO, vacuum die-casting significantly reduces stomata (di 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: Why do cracks often occur in thin-walled die castings?

Thin-walled parts cool faster than thick parts, creating large stress termico (due to uneven temperature distribution). When this stress exceeds the material’s strength limit, cracks form. Per prevenire questo, increase mold temperature to slow cooling and use arc transitions (instead of sharp corners) Per ridurre la concentrazione di stress.

Q3: 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 ore (or after 50-100 cicli) to ensure effectiveness. If mold sticking occurs more frequently, check the release agent coverage and adjust the replacement schedule.