In aluminum die casting manufacturing, internal porosity is like an invisible killer hidden inside the castings. It not only weakens the product’s structural strength but also is the root cause of leakage and failure in pressure-bearing parts. When an application demands zero leakage, the traditional die casting process often faces significant challenges. This article, through a real-world case study, will provide an in-depth analysis of how CEX Casting uses squeeze casting technology to eliminate the porosity problem for a critical pump casing, successfully meeting its strict zero-leakage standard at 100 PSI.
The root of the problem lies in the physical limitations of traditional die casting processes: high-speed mold filling inevitably leads to air entrapment, while conventional pressures are insufficient to compensate for the volumetric shrinkage of the molten aluminum during solidification. To completely resolve the porosity issue in the pump casing, a breakthrough must be sought from the fundamental point of changing the solidification method of the metal. This is the core reason that CEX Casting chose the squeeze casting process as their solution.
Understanding the Internal Porosity of Aluminum Die Castings
Causes and Classification of Porosity
Internal porosity in aluminum die castings can be primarily categorized into two types based on their causes: air porosity and shrinkage porosity.
The former results from air entrainment during mold filling by the molten aluminum, while the latter is caused by insufficient shrinkage feeding during metal solidification.
In traditional high-pressure die casting, in order to pursue production efficiency, the molten aluminum typically fills the mold cavity at extremely high speeds, which inevitably creates turbulence and entraps air, leading to porosity.
Furthermore, the feeding pressure provided by the process is limited and short-lived, making it difficult to effectively compensate for the volumetric shrinkage during solidification, especially in thicker walls or hot spots, ultimately leading to shrinkage porosity.
Want to know more about the causes and classification of porosity in aluminum die castings? Click here to learn more.
Porosity Challenges in the Pump Casing in This Case Study
The pump casing in this case study is a typical example. It is used in a pump system and requires zero leakage at 100 PSI.
This means that any microscopic porosity can potentially become a critical leak path in the presence of high-pressure fluids. This product was previously produced using traditional die casting.
While reasonably efficient, it consistently failed high-pressure testing, and porosity became a bottleneck restricting its reliability.
Therefore, finding a casting method that could fundamentally eliminate porosity from the forming mechanism became a key breakthrough.
The following figure shows the X-ray inspection image of a pump casing with internal porosity produced by the traditional die casting process:
Pump Casing with Internal Porosity Produced via Die Casting
Using Squeeze Casting to Control Porosity in Aluminum Castings
Facing this industry pain point, CEX Casting, after careful evaluation, decided to abandon the traditional approach of parameter optimization within the traditional die casting framework and instead adopt the more effective aluminum squeeze casting process.
Squeeze casting, also known as liquid die forging, is a hybrid forming technology that combines the advantages of casting and forging. Its core advantages lie in low-speed filling and high-pressure solidification.
Unlike traditional die casting’s jet-like filling process, which can reach tens of meters per second, squeeze casting’s filling process is smooth and slow, fundamentally eliminating turbulence and air entrainment.
Crucially, after the molten aluminum is filled, the equipment will apply a continuous and extremely high mechanical pressure (usually exceeding 100MPa) to the castings that have not yet fully solidified through the hydraulic system.
This pressure acts directly throughout the solidification process, forcibly compensating for shrinkage caused by phase transformation, thereby eliminating the conditions that cause both pores and shrinkage.
This technology was the solution we tailored for this pump casing. The following figure shows the comparison of traditional die casting and squeeze casting processes:
Squeeze Casting vs Die Casting Processes
Key Strategies for Porosity Control and Prevention
After selecting the right casting process, successful implementation still depends on a series of interlinked key strategies. For this pump casing project, CEX Casting implemented the following core control measures:
Mold Optimization and Thermal Management
We redesigned the pouring and venting systems for this 1900-gram pump casing to ensure that the A356.2 molten aluminum fills the mold cavity with a near-laminar flow, fundamentally reducing air entrapment.
Simulation analysis also optimized the mold cooling channel layout, precisely controlling the mold operating temperature within the ideal range of 250°C to 300°C.
This effectively guides the sequential solidification of the casting and directs shrinkage defects to non-critical areas.
Precisely Locking of the Process Window
Stable process parameters are a prerequisite for ensuring quality. Through repeated trials and simulations, we locked the critical process window:
- Stabilizing the pouring temperature of the molten aluminum at 680℃± 10℃.
- Employing a high specific pressure of 90-110 MPa.
- A holding time of no less than 12 seconds.
This combination ensures that the molten aluminum completes solidification compensation under high pressure and comes with a dense internal structure.
The following table shows the critical process parameters of CEX’s squeeze casting process:
|
Process Parameter |
Target Value / Range | Key Function |
|
Molten Aluminum Pouring Temperature |
680°C ± 10°C |
Ensures optimal fluidity while preventing excessive gas dissolution or thermal shock to the die. |
|
Specific Pressure |
90 – 110 MPa |
Applies core densification force to compensate for solidification shrinkage and eliminate shrinkage porosity. |
| Pressure Holding Time |
≥ 12 seconds |
Maintains pressure until complete solidification, providing the necessary duration for internal densification. |
Critical Process Parameters of CEX’s Squeeze Casting Process
Full-Process Quality Monitoring
We have established a comprehensive quality monitoring system from pilot production to mass production.
During the mold trial phase, simulation software is used to predict and mitigate risks.
During mass production, we implement a strict system of first-piece, last-piece, and scheduled spot checks to ensure process stability.
Each batch of pump casings undergoes X-ray sampling inspections. Full batch X-ray inspections are available for critical batches or upon specific customer requirements.
Case Results and Verification
Verified by our strict internal testing process, the pump casing produced by our squeeze casting process has achieved excellent results:
Internal Quality: X-ray inspection result shows that the internal structure of the casting is dense, with no porosity defects found of any size. See figure below:
Porosity Free Pump Casing by CEX Casting
Airtightness Performance: The product has achieved continuous zero leakage through long-term airtightness testing at a pressure of 100 PSI simulating actual working conditions.
The test results show that the performance of the squeeze casting pump casing not only exceeds that of old products manufactured using traditional die casting methods, but also proves the huge advantage of squeeze casting technology in producing parts with high air-tightness requirements.
The picture below is a physical picture of the squeeze casting pump casing:
Squeeze Casting Pump Casing by CEX Casting
Conclusion
The success of this pump casing project fully validates the technical superiority of the squeeze casting process in solving the internal porosity and high-pressure airtightness requirements of aluminum castings.
Compared with traditional die casting, this process fundamentally changes the solidification process of molten aluminum through low-speed smooth filling and continuous high-pressure feeding, making the internal structure of the casting denser and more uniform.
If you are looking for a reliable solution to similar product defects, please contact CEX Casting for a detailed technical evaluation.
Let us work together to transform your design into a truly reliable end product.