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Comparison and Selection of High-Pressure Casting (HPDC) for Aluminum Alloys with Other Casting Processes

In the global trend of lightweight manufacturing, aluminum alloys, with their excellent specific strength, thermal conductivity, and recyclability, have become core materials in the automotive, aerospace, and consumer electronics industries. Casting, as a crucial step in aluminum alloy forming, directly determines product precision, production costs, and market competitiveness through its process selection. High-pressure casting (HPDC), as one of the mainstream technologies for aluminum alloy forming, has its own advantages and disadvantages compared to Sand Casting and low-pressure casting. This article will systematically compare HPDC from the perspectives of technical characteristics, performance, and applicable scenarios, providing a scientific reference for process selection for global manufacturing practitioners.

I. High-Pressure Casting: A Core Process for Efficient and Precise Mass Production

High-pressure casting of aluminum alloys involves injecting molten aluminum at high speed (typically 10-50 m/s) into a metal mold cavity under high pressure ranging from tens to hundreds of MPa, followed by rapid cooling and solidification. The core advantage of this process lies in its technical characteristics of “high-speed filling and high-pressure feeding,” making it irreplaceable in large-scale production.

From a performance perspective, high-pressure die-Casting Parts achieve dimensional accuracy of CT4-CT6 and surface roughness of only Ra1.6-3.2μm, meeting assembly requirements without complex subsequent machining. Production efficiency is a significant highlight; the production cycle for typical small parts can be controlled within 30 seconds, with a stable output of 60 seconds per part for automotive gearbox housings. Regarding material utilization, high-pressure die-casting yields over 90% of the metal, and the application of recycled aluminum technology further reduces raw material costs.

However, this process also has limitations: gas is easily entangled during high-pressure filling, resulting in a porosity of 3%-5% in the castings, making high-temperature Heat Treatment difficult; simultaneously, the design and manufacturing costs of metal molds are high, typically requiring a production volume of over 100,000 pieces to achieve economic balance. Currently, Tesla’s Berlin factory utilizes ultra-large integrated die-casting technology, an advanced application of high-pressure die-casting, reducing the number of chassis parts in new energy vehicles from 70 to just 1, completely revolutionizing traditional manufacturing methods.

II. Multi-dimensional Comparison of Mainstream Casting Processes and High-Pressure Casting

The differences in the technical principles of different casting processes directly lead to significant differentiations in precision, efficiency, and cost. The following is a comprehensive comparison of high-pressure casting with five mainstream processes, from core characteristics and key indicators to applicable scenarios:

1. Sand Casting: A Low-Cost “Universal Compatible”

Sand casting uses clay sand or resin sand as the mold material, relying on gravity to fill the mold with molten aluminum. It is the most traditional casting process. Its biggest advantage lies in cost control—mold materials are inexpensive, and the cost of a single-piece trial production is only 1/5 of that of high-pressure casting; at the same time, it is highly adaptable to the size and shape of castings, ranging from small parts weighing a few kilograms to engine blocks weighing tens of tons.

Compared with high-pressure casting, sand casting has very obvious shortcomings: dimensional accuracy is only CT10-CT12 grade, surface roughness (Ra50-100μm), requiring additional milling, grinding, and other machining; production efficiency is low and quality stability is poor, with a higher rate of defects such as porosity and sand inclusions. This process is more suitable for new product prototyping, large-scale single-piece production, or general-purpose mechanical parts with low precision requirements, but it cannot meet the precision demands of consumer electronics, high-end automobiles, and other fields.

2. Metal Mold Casting: The Preferred Quality Option for Small to Medium Batch Production

Metal mold casting (permanent mold casting) uses cast iron or steel molds and relies on gravity filling, achieving a balance between cost and quality. Its casting precision (CT6-CT8 grade) and surface quality (Ra6.3-12.5μm) are superior to sand casting. The rapid cooling rate results in a denser microstructure, improving mechanical properties by more than 20% compared to sand casting.

Compared to high-pressure casting, metal mold casting has a significantly slower production cycle (3-5 minutes/piece), and complex internal cavities require sand cores for molding, resulting in insufficient flexibility. Although its mold cost is lower than high-pressure casting, it still requires production volumes of tens of thousands of pieces. This process is particularly suitable for small to medium batch production of structural parts such as automotive wheel hubs and pistons, complementing the mass production advantages of high-pressure casting and the low cost of sand casting.

3. Low-Pressure Casting: A Dedicated Solution for High-Quality Structural Components

Low-pressure casting uses a low pressure of 0.01-0.1 MPa to smoothly press molten aluminum into a mold. The filling process is gentle and turbulent, making it one of the core processes for producing high-quality aluminum alloy parts. Its most prominent advantage is the extremely high density of the castings, with a porosity of less than 0.5%, mechanical properties approaching those of forgings, and the ability to undergo T6 heat treatment for strengthening.

Compared to high-pressure casting, low-pressure casting has slightly lower precision (CT7-CT9 grade), but it is more competitive in fields with extremely high reliability requirements, such as automotive safety components and aerospace structural components. Its main limitation is the large equipment investment and production efficiency, which is only 1/3 that of high-pressure casting. It is suitable for small to medium batch production of high-quality parts, such as high-end automotive cylinder heads and helicopter landing gear components.

4. Investment Casting: The “King of Processes” for Precision and Complex Parts

Investment casting (precision casting) replicates the shape of the part using a wax model, and then uses a ceramic shell as a mold, achieving extremely high forming precision. Its dimensional accuracy can reach CT4-CT6 level, comparable to high-pressure casting, and its parting-free design avoids flash defects. Its complexity far surpasses other processes—from the intricate flow channels of turbine blades to the fine mesh of medical devices, all can be integrally molded.

The core difference between this process and high-pressure casting lies in the production mode: investment casting is a single-piece flow production, with a cycle time of several days and a cost 3-5 times that of high-pressure casting, making it only suitable for small-batch, high-value-added products. In fields such as aerospace sensor housings and precision medical parts, its complex forming capabilities are irreplaceable by high-pressure casting, but it is completely uneconomical in high-volume scenarios such as consumer electronics.

5. Extrusion Casting: A “Cross-Border Solution” for High-Strength Parts

Extrusion casting combines the technical characteristics of casting and forging. After low-pressure filling, a high pressure of 200-400MPa is immediately applied for solidification and feeding, making it a “forging process within casting.” Its castings have a 20%-30% higher tensile strength than ordinary high-pressure castings, a density of up to 99.5%, and the absence of porosity defects allows for comprehensive heat treatment strengthening.

Compared to high-pressure die casting, extrusion casting has lower production efficiency (50-80 seconds cycle time) and higher equipment and mold costs, but it has significant advantages in the field of high-strength safety components. After adopting this process, the wear resistance of Mercedes-Benz V6 engine pistons improved by 30%; key safety components such as automotive steering knuckles and suspension parts are also gradually replacing traditional processes with extrusion casting, forming a high-end complement to high-pressure die casting.

III. Scientific Selection Guide for Aluminum Alloy Casting Processes

The core logic of process selection is “demand matching”—precisely aligning the product’s performance requirements, production volume, and the technical characteristics and cost curve of the process. The following establishes a decision-making framework from four key dimensions:

1. Production Volume as the Primary Basis

– Large-scale production of over 100,000 pieces: High-pressure die casting is preferred. Mold costs can be amortized through scale, and the cost advantage brought by high-speed cycle time is significant. It is suitable for standardized products such as 3C electronic casings and general automotive parts.

– Small to medium-scale production of 1,000-10,000 pieces: Metal mold casting (structural parts) or low-pressure die casting (high-quality parts) is more economical, balancing precision and cost requirements.

1. Small batch/trial production (less than 1000 pieces): Sand casting (low cost) or investment casting (high-precision complex parts) is the optimal solution.

2. Positioning based on product structure and precision requirements:

Thin-walled complex parts (wall thickness ≤ 1.5mm): High-pressure casting is the only choice. Its high-speed filling capability avoids incomplete filling defects, such as mobile phone frames and laptop casings.

Thick-walled structural parts (wall thickness ≥ 5mm): Low-pressure casting or squeeze casting is more suitable. Slow filling and high-pressure feeding can eliminate shrinkage defects, such as engine cylinder heads and aircraft brackets.

Precision complex parts (dimensional tolerance ≤ 0.05mm): Investment casting is preferred, suitable for special products such as turbine blades and medical instrument parts.

3. Limiting the scope based on performance requirements:

General structural parts (no strength reinforcement requirements): High-pressure casting and metal mold casting are both acceptable, selected according to batch size.

High-strength safety parts (tensile strength ≥ 350MPa): Squeeze casting or low-pressure casting, requiring T6 heat treatment.

– Fatigue-resistant parts (e.g., engine pistons): Extrusion casting is the optimal solution, as its dense structure improves fatigue life.

4. Final Decision Based on Cost Budget

Overall cost (mold + single piece + subsequent processing) ranking: Sand casting < Metal mold casting < Low-pressure casting < High-pressure casting < Extrusion casting < Investment casting. When multiple processes can meet the requirements, the total life cycle cost needs to be calculated—for example, although high-pressure casting has higher mold costs, the subsequent processing costs are only 1/10 of those of sand casting, resulting in lower total costs for large-scale production.

IV. Future Trends: Integration of High-Pressure Casting with Innovative Processes

The upgrading needs of the manufacturing industry are driving casting processes towards “high precision, low energy consumption, and integration,” making the integration of high-pressure casting with innovative technologies a significant trend. Vacuum die casting technology reduces the porosity of high-pressure casting to below 0.5%, breaking through heat treatment limitations and has been applied to the production of automotive safety structural components; the application of digital twin technology has reduced the number of trial moldings by 50% for companies like Siemens, significantly lowering development costs.

Meanwhile, derivative technologies such as semi-solid die casting and ultra-large integrated die casting are expanding the application boundaries of high-pressure casting. XPeng Motors uses rheo die casting (a branch of semi-solid processes) to produce motor end caps, achieving a 15% weight reduction while lowering the scrap rate to below 1%. The integrated chassis forming technology driven by L.K.’s 12000T die casting machine further maximizes the economies of scale of high-pressure casting.

Conclusion: There is no optimal process, only the most suitable choice.

The choice of aluminum alloy casting process is essentially the art of matching manufacturing needs with technical characteristics. High-pressure casting, with its core advantages of high efficiency and precision, has built a strong competitive barrier in the field of mass-produced standardized products; while sand casting, investment casting, and other processes are irreplaceable in niche scenarios requiring low cost and high precision.

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