What is a liquid cold plate?
A liquid cold plate is a device that is designed to cool down electronic equipment. It consists of a housing in which a channel has been machined to allow coolant to pass through (for example water), and a cover over the channel. This cover is welded to the housing using the FSW.
Most often these liquid cold plates are made of aluminium, but they can also be made of copper. The advantage of these two materials is their high thermal conductivity.
Cold plate housing
Cold plate cover
Cold plate housing & cover
Cold plate welded by FSW
Liquid cold plate & thermal management
Liquid cold plates are required for customised solutions in industries where small batches are predominant and where perfect thermal management of equipment is essential: rail, wind energy, solar energy, space, aeronautics, data centres, military.
The challenges of thermal management
Cost reduction and mass reduction
Better integration of components, increased heat flux density (W/m²) and the use of lightweight materials (such as aluminium) are required.
Thermomechanical constraints
The cold plate flatness has to be optimized to guarantee a perfect contact with the electronic equipment.
Low coolant pressure drop
The pressure drop has a direct impact on the energy efficiency of systems (pumps consumption).
Coolant quality, safety, and storage
High compatibility between materials and coolant is essential.
A welding technique with many benefits for welding of liquid cold plates
Lower cost
Replacement of vacuum brazing or EBW (electron beam welding).
Higher pressure resistance
Up to 300 bars.
Perfectly waterproof
No porosity.
Excellent thermal conductivity
Metallurgical junction.
Ease of use
Compared to vacuum brazing or EBW.
Comparison of welding techniques for a liquid cold plate
FSW welded cold plate cost
Friction stir welding is the most economical technique in terms of operational cost (machine investment and cover supply) compared to EBW or vacuum brazing.
With the Stirweld FSW head, the investment cost is drastically reduced, and the cover design does not need to be extremely accurate. As a result, the cover can be manufactured by laser cutting which significantly reduces the cost compared to machined covers, which are required for Electron Beam Welding.
Another cost reduction using FSW is the cost of quality control. In the case of friction stir welding, this cost is minimal because:
- There is no risk of sticking or channel collapse (main defects of vacuum brazing),
- It is a solid-state welding process: no porosity (main defects of electron beam welding),
- There is no risk of coolant leaks in service due to a potential crack propagation by cycled fatigue pressure.
Design of friction stir welded liquid cold plate
Design of liquid cold plate cover
The cover dimensions of the liquid cold plate are one of the parameters that influences the welding operation but also the mechanical strength of the welded cold plate. There are two ways to increase the burst pressure strength of the part: to increase cover thickness or to decrease its width.
Friction stir welding parameters
For an efficient and quality FSW welding of your liquid cold plate, several elements must be considered:
- The thickness and width of the cover,
- The definition of the tool path,
- The definition of the dead zone (area of FSW tool exit).
Quality control of the welded liquid cold plate
BURST PRESSURE TEST
Introduction of water under pressure into the channel of the liquid cold plate to mesure the resistance to cracking of the cover.
LEAK TEST
This is the most important test for checking the quality of the welded liquid cold plate.
THERMAL MANAGEMENT
Experimental characterisation of the thermal resistance and pressure drop of the cold plate.
VISUAL TEST
To identify the presence of excessive flash (very common FSW defect), to check if the force applied by the shoulder on the part surface was high enough.
2 essentials reasons led us to choose Friction Stir Welding. First, it’s a good opportunity for us to secure the assembly operations between the sole and the cover, which make up the heat sink. Then, we wanted to use a technology which is simpler and to make the operation more reliable.
FSW technology not only permits to simplify the industrial process, but i’ts also safer and it can lead to significant cost reductions.
X.A – Supplier Development
French electronics group specializing in aerospace, defence, security and land tranport.
FSW OF MACHINED COLD PLATE – THERMAL MANAGEMENT
Technical differences between FSW & Vacuum Brazing
PROS & CONS OF FRICTION STIR WELDING: IMPACT ON DESIGN & MANUFACTURING PROCESS OF A LIQUID COLD PLATE
COMPARISON BETWEEN FSW & VACUUM BRAZING: IMPACT ON COST & SAFETY
Stirweld FSW expertise
With a team of experts in friction stir welding, Stirweld supports you throughout your process for welding of liquid cold plate. Indeed, you can count on Striweld’s design office for:
- Codesign of your liquid cold plate,
- Design & manufacturing of your clampig jig,
- Definition of your welding parameters & quality control,
- Manufacturing of first batches.
Stirweld refers to ISO 25239 – Friction Stir Welding standard throughout the industrial process: weld joint design, welding operator qualification, specification and qualification of welding procedures, inspection & quality requirements.
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