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What Is Metal Casting？

What Is Metal Casting

Metal casting is the process of pouring molten metal into a mold whose cavity corresponds to the shape and dimensions of the desired part. Once the metal cools and solidifies, it forms a casting blank or finished component.

This technique has been a cornerstone of modern manufacturing, from automotive to aerospace, due to its flexibility in forming complex shapes and high-strength components.

Defining Metal Casting

Definition:
Casting is a method of producing parts by pouring liquid metal into a mold cavity that matches the shape and size of the final part. After cooling and solidification, the desired metal part or casting is obtained.

Main Characteristics:

• Low yield rate: Metal casting often has a relatively low finished product rate compared with machining.
• High scrap rate: Errors in pouring, cooling, or mold design can easily lead to defective parts.
• High dust level: Traditional sand casting in particular produces dust and fumes, requiring proper ventilation and safety management.

Despite these challenges, casting remains indispensable because it can produce shapes and sizes that machining alone cannot achieve.

The Core Principle: Molten Metal Filling

Filling process:
The process of molten metal filling the mold cavity is called filling (or mold filling).

Filling ability:
It refers to the ability of molten metal to completely fill the mold cavity and produce a casting with a clear and complete shape.

Factors affecting filling ability:

1. Metal fluidity – how easily the molten alloy can flow through the mold channels.
2. Casting conditions – including:
   • Pouring temperature
   • Filling pressure or head pressure

Conditions for successful mold filling:

• Mold material: Must have sufficient permeability and strength.
• Mold temperature: Especially for sand molds, temperature should not be too low; a slightly higher mold temperature reduces the temperature difference and helps the alloy fill completely.
• Mold gases: Proper venting is essential to allow trapped air to escape.

A Real Experience: From Metal to Mold

Many years ago, when I walked into a foundry as a beginner, the air was thick with the smell of molten metal and burnt sand. It was not the most pleasant start, but it revealed something profoundly captivating.

Over the years, I realized that companies select casting methods not merely based on cost but on how each process aligns with their performance goals. Choosing between sand casting, die casting, or investment casting can determine the success of an entire production run.

In a typical foundry, the casting process begins long before the metal is melted. It starts with mold design—whether a sand mold, ceramic mold, or metal die—based on production volume and product complexity.

Once molten aluminum, iron, or steel reaches the optimal pouring temperature, it is carefully poured into the mold cavity. What happens next decides the final quality:

• Cooling rate
• Solidification pattern
• Air venting and gas escape

All of these factors have a direct effect on the mechanical strength and surface finish of the casting.

Experimental Findings – Temperature and Mold Design

Through years of testing with different alloys and mold compositions, I discovered that temperature control and gating system design are often the most overlooked yet critical factors.

• Even a small temperature deviation can cause porosity or internal voids.
• Poor air venting leads to surface defects and uneven solidification.

Precision in pouring temperature and mold preparation often separates a flawless casting from a costly rejection.

Key Takeaways

Conclusion

Metal casting may appear simple—pouring liquid metal into a mold—but in practice, it is a scientifically precise process involving metallurgy, thermodynamics, and materials engineering.

Understanding filling behavior, temperature control, and mold design allows manufacturers to improve yield, reduce defects, and enhance product reliability.

Metal casting remains not only a manufacturing method but a bridge between raw material and engineered precision, continuously evolving with modern technologies and sustainability goals.