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In the field of metal forming, the choice of casting process directly impacts product quality, production costs, and efficiency. Among these, gravity casting and high-pressure die casting are two widely used techniques, yet many clients often struggle with decision-making when faced with these options. This article will delve into the principles, advantages, disadvantages, and applicable fields of both processes to help you quickly identify the most suitable casting solution.

I. Process Principle: The Core Difference Between Two Casting Methods

The principle of gravity casting is relatively straightforward. It relies on the natural flow of molten metal under its own gravity to fill the cavity of a metal mold, followed by cooling and solidification within the mold. The entire process requires no additional pressure, as the flow of molten metal is primarily guided by gravity and the structure of the mold cavity, resulting in a relatively gentle forming rhythm.

High-pressure die casting is entirely different, as it injects molten metal at high speed (typically under 10-150MPa pressure) into a steel mold, using intense pressure to force the metal to rapidly fill the cavity and solidify while maintaining pressure. This "high-pressure, high-speed" characteristic enables the metal to solidify in an extremely short time, which is the most fundamental difference between it and gravity die casting.

II. Key Performance Indicators Comparison: Pros and Cons at a Glance

Cost variance

• Mold cost: Gravity casting molds have a relatively simple structure and are mostly made of cast iron, with costs typically ranging from 50,000 to 200,000 yuan. High-pressure casting molds must withstand high pressure and are often made of high-strength alloy steel, requiring high processing precision, with costs reaching 300,000 to 2 million yuan.

2. Production efficiency

Gravity casting has a slower production cycle, with single-piece production times typically ranging from 15 to 60 seconds. In contrast, die casting features faster metal liquid filling speeds (up to 10-50 meters per second), resulting in shorter cycles and greater suitability for high-efficiency mass production, particularly in automated production lines.

3. Product Precision and Surface Quality

• Dimensional accuracy: Gravity casting typically achieves a precision of CT6-CT8 (tolerance range approximately 0.1-0.3mm); high-pressure casting, due to the pressure effect, results in tighter contact between the molten metal and the mold, achieving a precision of CT4-CT6 (tolerance range approximately 0.05-0.1mm).

• Surface quality: Gravity casting typically has a surface roughness of Ra 6.3μm with minor shrink marks, while die casting offers a smoother surface with roughness down to Ra 1.6μm, requiring less post-processing.

4. Material Properties

Gravity casting results in slower cooling of molten metal, leading to more uniform crystallization, higher density, and superior mechanical properties (such as strength and toughness), making it suitable for parts that need to bear loads. In contrast, high-pressure casting involves rapid cooling, which can trap gases in the molten metal, forming pores that reduce material strength. Additionally, heat treatment is generally not feasible (as pores would expand and cause deformation).

3. Applicable Fields: On-demand selection is key

Typical scenarios of gravity casting

• Small and medium-sized batch production with an annual output of less than 50,000 pieces, such as customized mechanical parts.

• Stress-bearing structural components requiring heat treatment strengthening, such as engine cylinder heads and hydraulic valve bodies.

• In fields with rapid product iteration and frequent mold changes, the initial investment risk can be reduced.

Advantageous Areas of High-Pressure Die Casting

• Ultra-thin wall parts (such as shells with a thickness of 1-3mm), complex-shaped components, such as phone frames and laptop casings.

• Large-scale mass production scenarios with annual output exceeding 100,000 pieces, such as automotive transmission housings and motor end covers.

• Products requiring high dimensional accuracy and surface quality, with minimal need for post-processing.

IV. Industry Application Examples

In the automotive industry, integrated body castings are produced through high-pressure die casting, which significantly reduces assembly costs by enabling efficient mass production and forming complex structures. Meanwhile, components such as diesel engine cylinder heads, which must withstand high temperatures and pressures, are typically manufactured via gravity casting to ensure adequate strength and sealing.

In the field of industrial equipment, the housing of hydraulic pumps must withstand the impact of high-pressure hydraulic oil, relying on the high density achieved through gravity casting. Meanwhile, motor end covers, due to their large production volumes and moderate precision requirements, are more suitable for high-pressure casting.

In the field of new energy, vacuum die casting (an improved variant of high-pressure casting) is commonly used for energy storage battery housings to balance sealing performance and mass production efficiency. For heat dissipation substrates of photovoltaic inverters, which require excellent thermal conductivity and structural strength, gravity casting is the preferred choice.

V. Conclusion

Gravity casting and high-pressure casting are not about "which is better," but "which is more suitable." The choice must consider factors such as production scale, cost budget, product structure, and performance requirements: for small to medium batches, load-bearing parts, and those requiring heat treatment, gravity casting is preferred; for large batches, high precision, and complex thin-walled parts, high-pressure casting offers greater advantages. Making reasonable decisions based on actual needs ensures both quality and a balance between cost and efficiency.

Yongkang Zhonghuan has the production capacity to manufacture 5,000 tons of aluminum alloy parts, equipped with over 300 production and testing facilities. From mold customization to casting and machining, we provide one-on-one tailored services. We supply the highest-quality aluminum castings and services to clients worldwide, serving industries such as automotive, construction machinery, marine and offshore, new energy, and compressors