How High-Pressure Die Casting and Mold Technology Are Reshaping Automotive Body Manufacturing Amid the New Energy Vehicle Lightweighting Wave

Introduction: The "Must-Have" of Lightweighting and Opportunities for Die Casting in the Electric Era

With the explosive growth of the global new energy vehicle (NEV) market, range anxiety and energy efficiency improvement have become the industry's most pressing core challenges. Lightweighting, as one of the most direct and effective methods to boost driving range and cut energy consumption, has evolved from a "nice-to-have" feature into an absolute industry necessity.

Industry statistics show that fueled by the NEV boom, the global die casting market is projected to reach approximately $185.6 billion by 2025. As leading automakers including Tesla, BYD and Volkswagen ramp up adoption of large integrated aluminum castings (also known as "gigacasting" in the industry) to replace traditional steel stamping-and-welding structures, high-pressure die casting technology and its underlying mold development and manufacturing capabilities have become the decisive factor in the success of this "lightweighting revolution."

High-Pressure Die Casting: From "Component Manufacturing" to "Body Structure Reshaping"

Aluminum alloys have become the material of choice for automotive lightweighting due to their low density, high specific strength and excellent corrosion resistance. In conventional manufacturing, a complex body structure requires dozens or even hundreds of stamped parts welded together—a process that is not only labor-intensive and costly, but also limits further weight reduction.

Breakthroughs in high-pressure die casting technology, particularly the emergence of large integrated die casting processes, have completely disrupted this traditional model.

1. Process Advantages: Reshaping Structures, Reducing Costs and Increasing Efficiency

The core of high-pressure die casting lies in "high pressure" and "high speed". Molten aluminum alloy fills the mold cavity at extremely high injection specific pressure (typically 30-150 MPa, with 80-120 MPa commonly used for large body structural parts) and very high velocity, then solidifies under pressure. This process delivers significant benefits:

• Integrated design: Structures that originally required dozens of components can now be die-cast in a single piece, drastically reducing part count and assembly operations. For example, a complete rear floor assembly can be consolidated from over 70 parts into just 1-2 parts through one-shot forming with a large die casting machine. Through this integration, the rear floor assembly can achieve 20%-30% weight reduction while increasing body torsional stiffness by 10%-15%.
• High dimensional accuracy: Die castings achieve dimensional tolerances of IT11~IT13 or better, with excellent surface finish. They require little to no machining before assembly, and material utilization rates exceed 90%.
• Superior mechanical properties: Molten metal solidifies under high pressure, resulting in a dense microstructure and fine grain size. Its tensile strength is 20%~35% higher than that of traditional sand casting, providing more reliable mechanical support for body structural components.

2. Material Adaptability: Selection of Key Aluminum Alloy Series

To meet NEV requirements for high-ductility, high-strength structural parts, selecting the appropriate aluminum alloy grade is critical. For instance, certain 6-series aluminum alloys (such as 6463) produce a mirror-like surface after anodizing, and offer good formability and corrosion resistance, making them ideal for exterior components.

For large integrated body structural parts, heat-treat-free aluminum alloys (such as the AlSi10MnMg series) have become the industry mainstream. These alloys can achieve mechanical properties equivalent to T6 heat-treated materials in the as-cast state, eliminating the deformation and cost issues associated with heat treatment, and are a key technology enabling mass production of ultra-large castings. For other body structural parts, higher-performance alloys enable even greater lightweighting benefits.

Die Casting Molds: The Core "Tool" That Determines Die Casting Success

If the die casting machine is the "stage," then the die casting mold is undoubtedly the star player. Without a high-performance, long-lasting mold, it is impossible to produce consistent, high-quality die castings.

Large structural part die casting molds are typically manufactured from H13 hot work tool steel (North American standard) or 1.2344 steel (European standard), achieving a hardness of HRC 44-48 after vacuum quenching and tempering. For high-volume production molds, PVD coatings (such as CrN, AlTiN) are also applied to improve surface hardness and thermal fatigue resistance.

In the production of large NEV structural parts, mold design and manufacturing face unprecedented challenges.

1. Precision Design of Gating and Venting Systems

The mold's parting surface design directly determines the casting's ejection direction and dimensional accuracy. Design must follow fundamental principles: ensuring the casting remains on the moving mold half after opening for easy ejection; and facilitating optimal layout of the gating, overflow and venting systems to ensure smooth metal flow and prevent air entrapment.

• Gating system: The cross-sectional area of the ingate must be precisely calculated based on the casting geometry to ensure molten metal fills the cavity at the optimal velocity and flow pattern, avoiding direct impact on cores to minimize kinetic energy loss and mold erosion.
• Overflow and venting systems: Properly designed overflow wells and vent slots are essential. They effectively remove trapped gas and cold, contaminated metal from the cavity, which is critical for eliminating casting defects such as porosity and flow marks. In thin-walled complex structural parts, poor venting design will directly cause a sharp increase in scrap rates.

2. Mold Temperature Control and Thermal Balance

During die casting, mold temperature is another core variable that impacts both casting quality and mold life. Excessively high mold temperatures cause metal soldering (sticking) and casting distortion; too low temperatures lead to misruns and cold shuts.

Therefore, molds require internal heating and cooling systems to maintain thermal balance, ensuring the mold operates within the optimal temperature range during continuous production. For aluminum alloy die casting molds, the working surface temperature is typically controlled at 180-240°C, while large integrated structural part molds require zoned temperature control technology, with local maximum temperatures not exceeding 280°C. Proper thermal balance control can extend the life of large structural part molds from 100,000 shots to over 200,000 shots, significantly reducing per-unit production costs.

From "Castability" to "Post-Processing": Full-Stack Technology Ensures Quality

A high-quality die casting is not determined by the casting process alone.

1. Casting structure design: Die casting processability must be considered from the earliest design stages. For example: avoiding excessively thin mold sections that cause premature failure; optimizing undercut features to simplify core-pulling mechanisms; and ensuring adequate draft angles. These design optimizations significantly extend mold life and ensure casting precision.
2. Surface treatment and corrosion resistance: Exposed chassis components or battery pack housings typically require surface treatments such as anodizing or chemical conversion coatings. The rare earth bohmite layer process, for example, shows promising application prospects due to its non-toxic, environmentally friendly nature and excellent corrosion resistance. For components exposed to corrosive environments, rigorous salt spray testing (such as GB/T 10125-2021, equivalent to ISO 9227:2017) is a necessary validation step.
3. Clean production: Throughout the surface treatment process—whether pre-treatment (degreasing, acid etching) or post-treatment (passivation, sealing)—processes and chemicals must comply with environmental standards and automotive restricted substance requirements (such as GB/T 30512-2014, aligned with EU ELV Directive 2000/53/EC) to ensure green, compliant products.

Advanced Processes: Enabling Superior Casting Integrity

As quality requirements for die castings continue to rise, advanced derivative processes of high-pressure die casting are becoming new technological frontiers.

• High-vacuum die casting: By creating a high vacuum (<10 mbar, with industry-leading levels reaching <5 mbar) in the mold cavity, porosity defects are significantly reduced. This allows castings to undergo T6 heat treatment without blistering, resulting in higher strength and ductility to meet the stringent requirements of safety-critical structural parts.
• Local squeeze technology: For localized thick hot spots in castings, shrinkage cavities and porosity are effectively eliminated through feeding with local squeeze pins, typically applying a pressure of 100-200 MPa. This improves internal casting quality, particularly for components with high airtightness requirements.
  

Conclusion: Deep Technical Expertise Is the Cornerstone of Industrial Upgrading

Amid the NEV lightweighting wave, high-pressure die casting technology and mold development capabilities together form the two core engines driving innovation in automotive body manufacturing. From forming large integrated structural parts to high-performance die casting of complex thin-walled components, every technological breakthrough relies on precise control of process parameters, in-depth understanding of mold thermal balance, and accurate application of material properties.

As market demands for casting strength, ductility, airtightness and heat treatability continue to increase, advanced processes such as high-vacuum die casting and local squeeze technology are shifting from "optional extras" to industry standards. All of this ultimately returns to the fundamental link of mold design and manufacturing—superior molds are the cornerstone of consistent casting quality and sustained production efficiency.

In the future, the automotive lightweighting race will increasingly test companies' comprehensive capabilities in technical depth and system integration. Only by finding the optimal balance between mold development, process optimization and large-scale manufacturing can companies gain a sustainable competitive edge in the global market.