Rubber molds act as a critical, high-elasticity interface in the forming of Er/2024Al alloys, serving as a pressure-transmitting medium that enables the benefits of isostatic pressing. By encapsulating the powder, these molds translate the high pressure of the surrounding liquid uniformly onto the alloy, ensuring the powder is compacted evenly from all directions without direct contact with the hydraulic fluid.
Core Takeaway The primary function of the rubber mold is to convert hydrostatic liquid pressure into a uniform mechanical force that acts on the powder from all sides. This isotropic compression is essential for achieving high density and preventing the structural defects common in directional pressing methods.
The Mechanics of Pressure Transmission
High-Elasticity Encapsulation
The rubber mold serves as a flexible, impermeable barrier between the hydraulic fluid and the Er/2024Al powder.
Because of its high elasticity, the rubber creates a tight seal that moves with the powder as it compresses. This ensures the internal powder remains isolated and undamaged during the process.
Isotropic Force Transfer
In cold isostatic pressing (CIP), liquid pressure can reach up to 300 MPa.
The rubber mold transmits this pressure uniformly from every direction (isotropically). Unlike rigid molds, the rubber does not mechanically restrict the force, allowing the pressure to apply equally to the entire surface area of the component.
Preserving Geometric Precision
Despite the intense pressure, the mold ensures the "green compact" (the pressed powder before sintering) maintains a precise geometric shape.
Upon demolding, the high surface quality of the part is preserved because the elastic mold peels away without adhering to or damaging the compacted alloy.
Achieving Internal Structural Integrity
Particle Rearrangement and Deformation
Under the uniform pressure transmitted by the rubber, the alloy powder particles undergo significant physical changes.
The particles experience rearrangement and plastic deformation, closing voids between them. This leads to extreme density in the final green body, a requirement for high-performance metal-ceramics.
Ensuring Uniform Density
The most critical advantage of this setup is the homogeneity of the internal structure.
Because the rubber allows pressure to hit the powder from all sides, the density of the compact is consistent throughout. There are no "shadowed" areas of low density that might occur in rigid die pressing.
Avoiding Common Forming Pitfalls
The Risk of Uniaxial Pressing
To understand the value of rubber molds, one must look at the alternative: traditional uniaxial pressing.
In uniaxial methods, pressure is applied in only one direction (usually top-down). This often results in density gradients, where the top of the part is denser than the bottom.
Preventing Sintering Defects
Non-uniform density in the green stage leads to catastrophic failures during the subsequent sintering phase.
If the green body is not uniform, it will suffer from non-uniform shrinkage as it is heated. The use of rubber molds in isostatic pressing effectively eliminates this variable, significantly reducing the risk of cracking during sintering.
Making the Right Choice for Your Goal
When determining the forming process for Er/2024Al alloys, consider your quality requirements:
- If your primary focus is Maximum Density: Utilizing rubber molds in cold isostatic pressing is essential to achieve the extreme density required for high-performance applications.
- If your primary focus is Defect Prevention: This method is the definitive choice to ensure uniform internal structure and prevent cracking or warping during the sintering phase.
The use of rubber molds is not merely a containment step; it is the fundamental enabler of uniform densification in complex alloy forming.
Summary Table:
| Feature | Rubber Mold Isostatic Pressing | Traditional Uniaxial Pressing |
|---|---|---|
| Pressure Direction | Isotropic (Uniform from all sides) | Uniaxial (Single direction) |
| Density Gradient | Homogeneous / Uniform | High (Top vs. Bottom variance) |
| Internal Structure | No voids; plastic deformation | Risk of localized low-density zones |
| Sintering Outcome | Uniform shrinkage; low crack risk | High risk of warping or cracking |
| Geometric Quality | High surface precision & integrity | Limited by rigid die friction |
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References
- Tao Qin, Jiukun Zhang. Effect of Erbium Micro-Additions on Microstructures and Properties of 2024 Aluminum Alloy Prepared by Microwave Sintering. DOI: 10.3390/cryst14040382
This article is also based on technical information from Kintek Press Knowledge Base .
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