FSW Liquid Cold Plates for OEM Thermal Projects

Friction Stir Welded (FSW) Cold Plates: Complete Engineering & Manufacturing Guide

Modern power electronics, EV batteries, and industrial inverters generate extreme heat in increasingly compact footprints. To maintain reliability, you need a cooling technology that combines high thermal performance, structural integrity, and leak-free construction — without excessive cost or complexity.

That’s exactly where friction stir welded (FSW) cold plates excel. Using a solid-state welding process instead of brazing or fusion, FSW cold plates deliver strong joints, clean internal channels, and excellent thermal conductivity.

1. Understanding Friction Stir Welding (FSW)

What Is Friction Stir Welding?

Friction Stir Welding is a solid-state joining process used primarily for aluminum alloys. A rotating tool with a specially shaped pin and shoulder plunges into the joint between two workpieces and moves along the seam.

Friction generates heat, softening the metal around the tool. The plasticized material flows and forges together as the tool moves forward. Once the weld cools, it forms a defect-free joint with high mechanical strength and no melting.

Why FSW Matters for Cold Plates

Because FSW does not melt the material:

• There are no voids, cracks, or flux residues.
• Distortion and porosity are minimized.
• The weld maintains the base material’s conductivity and corrosion resistance.

This makes FSW ideal for liquid cold plates, where precision sealing, internal cleanliness, and consistent thermal contact are critical.

2. What Is an FSW Cold Plate?

An FSW cold plate is a liquid-cooled thermal management component made by friction stir welding two or more aluminum plates containing machined coolant channels. The welded structure becomes a sealed cooling assembly that transfers heat from electronic components into the circulating liquid.

Core Structure

• Base plate: Machined with flow channels or grooves.

• Cover plate: Forms the top surface, welded to the base using FSW.

• Ports/fittings: Connect the coolant inlet and outlet.

• Machined surfaces: Provide flat contact for power modules or battery cells.

Why It’s Popular

• Fully recyclable and eco-friendly manufacturing (no flux or filler metals).
• Excellent thermal conductivity due to solid-state bonding.
• Lower cost compared to vacuum brazing or laser welding.
• Ideal for high-volume automotive and industrial cooling plate production.

3. FSW Cold Plate Manufacturing Process

Step-by-Step Overview

1. CNC machining of coolant channels and surface features on the base plate.
2. Cleaning and degreasing to remove contaminants.
3. Alignment and fixturing of the cover plate.
4. Friction Stir Welding along the channel perimeter using a rotating tool.
5. Leak testing (usually helium or pressure testing).
6. Surface finishing and flatness machining.
7. Assembly of fittings, plugs, and optional anodizing or coating.
8. 3.2 Tool Design and Control

FSW parameters — such as tool rotation speed, traverse speed, and plunge depth — directly affect weld quality. For cold plates, controlling heat input is vital to maintain flatness and dimensional stability.

Automation

Modern manufacturers use robotic FSW systems with CNC control to ensure repeatable weld seams. This allows mass production of consistent, leak-free cold plates for OEM customers.

4. Thermal and Mechanical Advantages

High Thermal Conductivity

Since no filler metal is used, the joint remains metallurgically continuous. That ensures uniform heat flow across the weld zone — a major advantage over bonded or soldered joints.

Leak-Free Construction

FSW produces a solid-phase bond with no internal porosity, resulting in cold plates that easily withstand pressures above 6–10 bar, depending on wall thickness and design.

Structural Strength

The weld area retains nearly the same mechanical strength as the parent aluminum, allowing lightweight yet robust cooling structures.

Environmental Friendly

Unlike brazing, FSW uses no flux, filler metal, or vacuum furnace, reducing both environmental impact and production energy.

Cost Efficiency

Lower energy consumption and shorter cycle times make FSW plates cost-competitive for large-scale production, particularly in the EV battery cooling and industrial electronics sectors.

5. Design Considerations for Engineers

Designing an FSW cold plate requires balancing thermal, hydraulic, and mechanical performance.

Channel Geometry

The coolant path should maximize surface contact while maintaining manageable pressure drop. Common designs include:

• Serpentine channels for even heat distribution.
• Parallel flow channels for low flow resistance.
• Manifolded paths for multiple component cooling zones.

Flow Rate and Pressure Drop

Select pump capacity and coolant viscosity carefully. Excessive flow velocity increases erosion risk; too little flow causes thermal gradients.

Flatness and Surface Finish

After welding, the plate’s mounting surface is precision-milled to maintain flatness typically within ±0.05 mm, ensuring minimal thermal interface resistance.

Material Selection

Most FSW plates use 6061-T6 or 6063 aluminum alloys for good machinability and corrosion resistance. For special applications, marine-grade or anodized alloys may be specified.

Sealing and Porting

Ports are usually threaded or brazed inserts. O-ring grooves may be added for modular systems.

6. Comparison with Vacuum Brazed Cold Plates

In short, if you need cost-effective, strong, leak-tight aluminum cold plates, FSW is often the best choice. For extreme heat density or multi-metal assemblies, vacuum brazing remains superior.

7. Testing and Quality Control

Non-Destructive Inspection (NDI)

Ultrasonic or X-ray testing detects internal voids or lack-of-bond defects in weld seams.

Pressure & Leak Testing

Each finished plate undergoes helium leak or hydrostatic pressure testing to ensure joint integrity.

Dimensional Verification

CMM or laser scanning verifies flatness, weld depth, and tolerance compliance.

Thermal Performance Testing

Plates are tested under operational flow and heat load to confirm pressure drop and temperature rise within spec.

8. Maintenance and Service Life

FSW cold plates are low-maintenance, but proper system care extends longevity:

• Use filtered coolant (≤20 µm filtration).
• Maintain correct glycol concentration to prevent corrosion.
• Flush and inspect annually for deposits.
• Avoid coolant freezing or cavitation.
  With good coolant hygiene, service life can easily exceed 10–15 years.

9. Key Advantages Summary

FAQs

1. What is the FSW method?

Friction Stir Welding (FSW) is a solid-state welding process that joins materials without melting them. In FSW, a rotating tool is used to generate frictional heat, which softens the material. The tool’s pin stirs the material together, creating a strong weld. This method is mainly used for aluminum and other metals that are difficult to weld with traditional methods. FSW results in high-quality welds with fewer defects, making it ideal for industries like aerospace and automotive.

2. How does the Friction Stir Welding process work?

In the FSW process, a specially designed tool with a rotating pin is placed at the joint of two pieces of material. As the tool rotates, it creates friction and heat, softening the material without reaching its melting point. The rotating pin moves along the joint, mixing the softened material together and forming a solid bond. The heat generated by the tool is controlled to ensure a clean weld, which avoids problems like warping or distortion.

3. Is Friction Stir Welding better than brazing?

Friction Stir Welding is often considered better than brazing for certain applications because it produces stronger, more durable welds. Unlike brazing, which involves melting a filler material, FSW joins materials directly, without any filler. This creates a more reliable bond and minimizes the chances of defects. FSW is also more suitable for high-stress applications, such as in aerospace and automotive industries, where strength and reliability are critical. However, brazing might still be preferred for joining dissimilar materials or for lower-temperature applications.

4. What are our products used for?

Our products are mainly used in data center servers, graphics cards, power (ultra-high voltage, flexible DC, new energy), rail transportation (high-speed rail and urban rail transit), 5G communication, and IoT industries.

5. What can we do currently?

We can design and manufacture liquid cooling plates for high-power, high-heat- flux density chips. Our company has specialized equipment and processes such as friction stir welding, vacuum brazing, instantaneous liquid phase diffusion welding, laser welding, and flame welding, as well as specialized testing equipment for thermal resistance, flow resistance, and sealing. We also have 3D modeling and CAE and CFD simulation capabilities.

6. What are we currently researching and developing?

We are currently researching and developing high-power, high-heat-flux density liquid cooling plates, pump-drive two-phase cooling systems, high thermal conductivity composite materials, and spray jet direct cooling systems, among other high-power, high-heat-flux density cooling technologies.