company news about Complete Guide to Isostatic Pressing: From Forming Principles to Final Sintering

I. What Is Isostatic Pressing?
Isostatic pressing is an advanced powder forming technology. Its core principle is based on Pascal's Law—pressure applied to a confined fluid (liquid or gas) is transmitted uniformly in all directions. Utilizing this principle, isostatic pressing applies uniform, high pressure from all sides to powder encapsulated within a flexible mold, thereby producing high-performance green bodies with exceptional density uniformity and structural integrity.

Key Differences from Traditional Pressing:

• Die/Mechanical Pressing: Relies on uniaxial or biaxial pressure from rigid dies. Friction against die walls creates density gradients (often denser at the top, less dense at the bottom). The process is affected by uneven temperature and pressure distribution, resulting in larger dimensional tolerances in the final product.

• Isostatic Pressing: Fluid medium applies uniform omnidirectional pressure, completely eliminating frictional effects. This results in excellent density uniformity in the formed product. Uniform stress distribution avoids stress concentrations caused by friction, making the green body less prone to cracking or deformation during drying and sintering. It enables the forming of complex shapes and large components, often with relatively lower operating costs. It also has less strict requirements on powder flowability compared to die pressing, accommodating a wider variety of powder materials.

Isostatic Pressing at Kegu: We primarily utilize Cold Isostatic Pressing (CIP), a mature technology within our operations. It is prominently applied in manufacturing our thermocouple protection tubes. After CIP forming, secondary processing, and sintering, the final products meet all specified customer performance requirements. Currently, we employ isostatic pressing for complex-shaped products and continuously pursue technical improvements to optimize material forming processes.

II. Three Main Types of Isostatic Pressing

1. Cold Isostatic Pressing (CIP)

• Temperature Range: Room Temperature
• Pressure Medium: Water or water-based emulsions
• Pressure Range: 100 - 630 MPa
• Primary Use: Initial forming of powders to create "green bodies" for subsequent sintering.
• Process Characteristics: Relatively low cost, suitable for most ceramic and metal powders, capable of forming complex shapes, and applicable to a wide material range. However, the formed products typically require secondary machining. Production efficiency can be lower, mold design is more complex, and molds are consumables.

2. Hot Isostatic Pressing (HIP)

• Temperature Range: 1000 - 2200°C
• Pressure Medium: Inert gases (e.g., Argon, Nitrogen)
• Pressure Range: 100 - 200 MPa
• Key Advantage: Combines forming and sintering into a single step, directly yielding near-fully dense final components.
• Application Fields: Aerospace turbine blades, biomedical implants, premium tool materials, etc.

3. Warm Isostatic Pressing (WIP)

• Temperature Range: 80 - 450°C
• Pressure Medium: Oil or specialized fluids
• Special Purpose: Handles materials difficult to form at room temperature, such as certain polymers or graphite.
• Technical Position: A complementary technology between CIP and HIP, featuring added temperature control systems which increase equipment complexity.

III. Mold Design: A Key to Successful Isostatic Pressing
Successful isostatic pressing heavily relies on mold material selection and design. At [Company Name, e.g., Kegu], we design custom molds based on client requirements. A well-designed mold plays a critical role in the product forming process. Key points regarding mold design include:

Design Essentials:

1. Material SelectionRubber/Silicone: Flexible, elastic, suitable for complex shapes with high demolding requirements. Low cost and technically mature.

2. Polyurethane: Has become the mainstream trend. By adjusting formulations, a wide range of hardness can be achieved to meet different needs. Offers good resilience, pressure resistance, long service life, and yields smooth surfaces on demolded green bodies. Cost is higher than standard rubber.

3. Metal/Glass Encapsulation: Specifically used for HIP, offering good high-temperature plasticity and sealing properties.

4. Cavity Design Principles

   • Compression Ratio Calculation: Precise control of the powder fill volume to final green body volume ratio (typically around 1.7:1).

   • Shape Adaptability: Allows design of complex internal cavities, curved surfaces, and thin-wall structures.

   • Demolding Considerations: Incorporate appropriate tapers or split structures to facilitate demolding.

5. Sealing System

   • Ensures the pressure medium does not infiltrate the powder under high pressure. Commonly uses O-rings or self-sealing structures.

IV. Detailed Step-by-Step Isostatic Pressing Process

Step 1: Powder Filling & Preparation

1. Fill the flexible mold with precisely weighed powder.

2. Remove air via vibration or vacuum to ensure uniform powder distribution.

3. Seal the mold meticulously to form a complete "powder package."

Step 2: High-Pressure Forming

1. Place the sealed mold into the high-pressure vessel.

2. Inject the pressure medium (oil or water).

3. Activate high-pressure pumps to gradually increase pressure to the set value (e.g., 300 MPa).

4. Dwell Stage: Maintain pressure to allow for thorough particle rearrangement and plastic deformation.

Step 3: Pressure Release & Demolding

1. Execute controlled, slow pressure release (to prevent green body cracking).

2. Remove the mold from the vessel.

3. Peel away the flexible mold to retrieve the "green body."

V. Characteristics of the Final Sintered Product

1. Exceptional Density Uniformity

   • Density variation between different sections can be controlled within 1%.

   • Eliminates risks of deformation and cracking caused by density gradients.

   • Overall density can reach over 99% of theoretical density.

2. Superior Mechanical Properties

   • High strength and toughness: Isotropic, stable, and reliable performance.

   • Excellent fatigue life: Uniform microstructure minimizes stress concentrations.

   • Stable dimensional accuracy: Uniform shrinkage results in minimal distortion.

3. Flexible Shape Capability

   • Can produce complex geometries impossible with traditional pressing.

   • Near-net-shape forming: Significantly reduces subsequent machining allowance and material waste.

   • Particularly suitable for long, tubular, or rod-shaped parts with high aspect ratios.

4. Ideal Microstructure

   • Uniform grain size distribution.

   • High density, with porosity near 0%.

   • Free from internal defects and residual stresses.

5. Final Product Appearance

   • Surface exhibits a uniform, matte sintered finish.

   • Uniform dimensional shrinkage with controllable precision.

VI. Summary of Technical Advantages

VII. Application Fields & Outlook

• Aerospace: HIP is used for critical titanium alloy and superalloy components (turbine disks, blades) to eliminate defects and enhance performance. The ability to process ultra-large, complex components represents advanced national manufacturing capability.

• Medical Implants: HIP is crucial for manufacturing high-performance ceramic joints (hip, knee) from materials like zirconia or silicon nitride, achieving near-perfect density and properties.

• Energy & Environmental: Solid-state batteries use solid electrolytes instead of liquid ones, but poor rigid solid-solid interfacial contact is a major challenge. The isotropic, ultra-high pressure of isostatic pressing is a key process for achieving intimate interfacial contact and enhancing battery performance.

• Tool Manufacturing: Isostatic pressing is a key process in manufacturing wear-resistant parts and cemented carbide cutting tools, offering the core advantage of producing high-density, defect-free parts with uniform properties.

Conclusion: Isostatic pressing technology, through its unique uniform pressure application mechanism, solves the problems of density variation and shape limitations inherent in traditional powder forming. From precise mold design to the strictly controlled pressing process, and finally to the high-performance sintered product, this complete technological chain represents the pinnacle of modern powder metallurgy. With the continuous advancement of materials science, isostatic pressing will undoubtedly play an irreplaceable role in more cutting-edge fields.