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Cold Plate & Welding: Thermal Management

What are the difficulties encountered in current thermal management solutions?

New energy vehicles have increased thermal management requirements for batteries, motors and electronic components compared to conventional vehicles, and this has placed more complex and demanding demands on the thermal management strategy of the system.

In the following we will focus on the thermal management of batteries. The current mainstream technical solutions are air-cooled, liquid-cooled and direct-cooled. As the price of liquid-cooled plates decreases and the safety and performance of the battery becomes more demanding, liquid-cooled has become the mainstream technology for battery thermal management.

Cold Plate & Welding: Thermal Management

Battery thermal management needs to solve three challenges: heat dissipation and heating of the battery cells, temperature balance inside the battery pack and thermal expansion and contraction of liquid-cooled components. An excellent cooling system is the key to solving the challenges, and aluminium alloy liquid-cooled radiators are ideal for cooling the equipment of new energy vehicles.

Liquid-cooled plates: thermal management challenges

Liquid-cooled panels, as the current mainstream battery thermal management method for new energy vehicle manufacturers, have encountered a number of difficulties in their application.

There Are Several Aspects:

1. Design complexity: designers need to have knowledge and experience in fluid dynamics, materials science and heat transfer; and the flow resistance of the coolant side of the plate must not be too high and the temperature uniformity of the surface of the plate must be guaranteed.

2. Manufacturing complexity: Liquid-cooled plates require high precision in the machining of the flow paths and the quality of the materials used, so manufacturing costs are high.

3. Difficulty of maintenance: maintenance requires professional equipment and personnel, which is difficult for some users to afford.

4. Leakage risk: professional protection measures are required to prevent coolant leakage, which may cause serious damage to the interior of the battery.

5. Cooling effect: As the cooling effect is affected by different factors such as flow rate, pressure drop and temperature, the cooling effect is prone to instability.

Liquid coolING plate applications

There are currently four major applications for liquid-cooled panels, namely power battery packs, energy storage battery packs, high heat flow density liquid-cooled heat transfer components and new liquid-cooled heat transfer components. High heat flow density liquid-cooled heat exchange components mainly include inverter heat exchange, IGBT heat exchange and photovoltaic panel liquid cooling, etc.; new liquid-cooled heat exchange components mainly include freeze dryer heat exchange components and chiller heat exchange components, etc.

Liquid-cooled plates can be broadly divided into four categories according to the type of process:

1. Vacuum brazing cold plate (Aluminum Vacuum Brazing Cold plate)
2. Friction stir welding type water-cooled plate (FSW Cold plate)
3. Exposed Tube Cold plate
4. Aluminium / Copper Plate Long Hole Drilled

Liquid cooling panels for new energy electric vehicle battery packs-trumonytechs

Why choose aluminium for liquid-cooled panels?

There are several reasons for choosing aluminium as the main material for liquid-cooled panels:

  1. High thermal conductivity: its thermal conductivity is more than 3 times higher than stainless steel and more than
  2. times higher than copper, so with the same mass, aluminium material has better heat dissipation effect.
  3. Lightweight: aluminium is lighter than other metals, and liquid cooling panels made of aluminium are lighter than other metals.
  4. Corrosion resistance: Aluminium has better corrosion resistance, which makes it possible to use liquid-cooled panels in liquid-cooled environments for a long time.
  5. Easy processing: aluminium is easier to process than other metals.

But aluminium material has some disadvantages in welding, first of all, aluminium material melting point is lower, resulting in a larger heat-affected zone, easy to produce pores and cracks and other related defects; secondly, the oxide film is thicker, need to do some pretreatment measures; finally, the linear expansion coefficient of aluminium material is larger, thermal deformation is more serious, need to take the relevant technology to control the welding deformation.

Liquid Cold Plate Welding Challenge

How to weld the cooling plate?

Liquid cooling plate if the welding quality is not up to standard, the following kinds of problems will occur:

  1. poor quality of the weld: weak strength at the weld, later cracking and leakage will occur;
  2.  reduced heat dissipation: excessive heat will be generated after welding to affect the regional marketing heat dissipation effect;
  3.  decreased thermal conductivity: poor welding quality makes the thermal conductivity of the aluminium material decrease;
  4. Influence material performance: easily cause material deformation, grain growth and other related problems, affecting material performance;

At present, there are three mainstream liquid-cooled plate welding processes: friction stir welding, gas shield welding and vacuum brazing.

  1. friction stir welding has the advantage of high weld strength, high reliability, can be replenished, but the disadvantage is that the profile welding or cause cold plate tampering;
  2. gas shielded welding has the advantages of cheap, good pressure resistance, etc., but requires the addition of auxiliary materials, heat treatment and other operations;
  3.  Vacuum brazing welding seam quality is good, the process is simple, but the cost is higher.

In order to improve the quality of liquid-cooled plates, the staff of Yangchi Technology will select the appropriate welding method, strictly control the welding parameters, test the quality of the weld seam and select the appropriate filler material and shielding gas to make the welding process achieve the best results.

Weld seam qualification by trumonytechs Technology

At the end of the liquid-cooled plate welding process, the following are some of the common inspection methods used in the industry:

  • Visual inspection method: initial judgement of weld quality by observing the appearance of the weld, such as weld integrity, uniformity, cracks, slagging, porosity, etc;
  • Radiographic testing: the use of X-ray or gamma radiation for fluoroscopy or photographic examination of the weld to rank the internal cracks, porosity, etc. of the weld;
  • ultrasonic detection: the use of ultrasonic waves on the weld seam
  • magnetic particle detection: applying magnetic powder after welding and detecting whether the weld is defective by observing the distribution of magnetic powder in the weld;
  • Eddy current detection: using the principle of eddy current induction to carry out the detection.

The staff of Trumonytechs will test the quality of the weld seam after each welding process, picking it according to the actual situation and, if necessary, adopting a combination of methods to ensure the quality of the liquid-cooled plate.

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