The air tightness of the battery pack is a key factor in ensuring the quality and safety of the battery pack. It is related to the safety, reliability and service life of the battery pack. The air tightness test of the battery pack should be carried out not only during the production process, but also during battery maintenance and inspection.

1-Battery Pack Airtightness Requirements

In actual production, the air tightness of the battery pack must meet the following requirements:

Sealing performance, the battery pack shell, interface and connectors must have good sealing performance to prevent dust, water vapor and other external impurities from entering the battery pack, which can be achieved through welding, sealants, waterproof materials, etc.

Waterproof performance, to prevent moisture from entering the battery, causing short circuits, corrosion and other problems. According to the national standard GB38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles", the sealing performance of batteries and their components should meet the IP67 standard. Most new energy vehicles have higher sealing performance requirements for batteries and their components, and must meet the IP68 standard, that is, the battery pack can prevent water from entering within the specified water depth and submersion time.

Traditional air tightness testing methods include pressure method and immersion method (water test). The immersion method is to immerse the liquid cooling plate in water and observe whether bubbles are generated to judge the sealing.

Liquid Cooling Plate Water Channel Air Tightness Test Tank

Although the IP68 standard is more stringent, in actual applications, the pressure drop method is often used as the main detection method to meet the IP68 requirements by setting appropriate airtightness detection standards. The pressure drop method determines the airtightness of the battery pack by measuring the pressure change inside the battery pack. When performing airtightness testing, multiple parameters need to be paid attention to, such as inflation pressure, inflation time, pressure stabilization time and leakage rate.

                                    Differential pressure basic principle diagram                                             Direct pressure basic principle diagram

2-Analysis of Liquid Cooling Plate Leakage Problem

With the continuous upgrading of market demand for power battery vehicles, battery energy storage systerms, etc., higher energy density and power density battery packs are widely used. Because of the thermal characteristics of batteries, to ensure the stable operation of core equipment such as batteries and improve energy utilization efficiency, liquid cooling technology is one of the mainstream technical routes for energy storage thermal management, and the air tightness test of the liquid cooling system has become a key link.

Liquid cooling plate leakage is a serious problem: the leakage will hinder the normal flow of the coolant, affect the heat dissipation effect of the liquid cooling plate, and reduce the performance of the equipment; the leakage may also cause aging and damage of system components, reducing the reliability of the system; the leakage may also corrode electronic components and circuits, increasing the risk of equipment failure and fire.

Why does the leakage problem still occur after rigorous air tightness testing during the production and manufacturing process of the liquid cooling plate?

Liquid Cooling System Airtightness Test Process

Liquid seepage may be caused by a variety of factors:

l Tiny cracks and defects. Landscape air tightness testing may detect large leakage channels, but tiny cracks and defects may still exist. These tiny cracks may expand under liquid pressure or high temperature environment, causing liquid seepage.

l Coolant surface tension and wettability differences: When the surface tension of the coolant is low, it is easier to penetrate through tiny gaps. If the surface tension design of the liquid cold plate is unreasonable or the coolant is not properly selected, the liquid seepage problem may be aggravated.

Wettability differences: Different coolants have different wettability on solid surfaces. If the material surface roughness of the liquid cold plate is high or there are microstructural defects, the coolant may penetrate more easily.

l Installation or process problems: If the installation process of the liquid cold plate is not fine enough, or there are defects in the welding, connection and other processes, it may also lead to poor sealing and increase the possibility of liquid seepage.

l Environmental conditions: Changes in temperature, especially in high-pressure environments, may affect the permeability of the coolant. Although these environmental factors may not be considered during air tightness testing, in actual operation, temperature fluctuations may cause seal failure.

l Material aging or fatigue: If the material of the liquid cold plate is used for too long, it may age or fatigue, causing its sealing performance to deteriorate, thereby increasing the risk of liquid leakage.

3-Preventive Measures for Liquid Cooling Plate Leakage

l  Improve the design of liquid cooling plate: By optimizing the structure and design of the liquid cooling plate, reduce small cracks and defects, and improve its sealing performance. For example, when welding the module installation beam on the flow channel surface, take anti-leakage measures to avoid coolant leakage.

l Improve the manufacturing process level: In the production process of the liquid cooling plate, high-quality welding processes and materials are used to ensure that the coolant is not easy to penetrate. At the same time, during the assembly process, strictly follow the operating procedures to avoid looseness or incorrect installation.

l Optimize the combination of detection methods to ensure detection efficiency while improving detection accuracy and reducing missed detection rate. The immersion method and pressure drop method are used for air tightness detection, which is simple to operate, economical, and efficient, and is suitable for large-scale routine detection needs. However, the detection accuracy of the two methods is low. The detection accuracy of the pressure drop method is generally a leakage rate of 1×10-4Pa·m³/s, and the accuracy of the detection results is easily interfered by factors such as temperature, humidity, cleanliness, and pressure. Use detection equipment with higher detection accuracy and better effect to increase the detection accuracy to 1×10-6Pa·m³/s, thereby improving the detection effect.

In addition to the preventive measures for the liquid cooling plate itself, it is also necessary to adopt appropriate response strategies in multiple aspects such as coolant selection, seal selection and equipment working environment.

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In heat dissipation design, adopting effective cost-reduction methods can improve the reliability and efficiency of the overall system while reducing unnecessary costs.

1-Derating design  reduces costs

Derating design is a design method that intentionally reduces the electrical, thermal and mechanical stresses that components or products are subjected to during operation. In actual production and use scenarios, the stability of electronic equipment can be improved by reducing the stress borne by components.

Schematic diagram of heat dissipation paths for 2D and 3D packaging

l Reduce working stress: During product design and operation, the working stress of components can be reduced by reducing the workload, controlling the operating frequency, limiting the current and voltage, etc.

l Reduce environmental stress: Reduce environmental stress by selecting appropriate component types, layouts, and packaging forms, such as selecting components with a large temperature margin, or using packaging forms with good sealing to reduce the effects of temperature, humidity, and pressure on components.

l Reliability engineering application: reasonable redundant design, fault detection and isolation, etc., further reduce the failure risk of components.

By reducing the stress on components during operation, their power consumption and heat generation can be reduced. When power devices operate under stress conditions lower than their rated stress, their power consumption and heat generation can be reduced, which helps to improve the energy efficiency and reliability of the system. In the long run, derating design effectively increases the life of components, reduces failure rates, reduces maintenance workload, and thus reduces costs.

2-Optimize layout

The working efficiency of the radiator can be significantly improved through reasonable arrangement of thermal components, and a reasonable component layout strategy can achieve a balance between product performance and cost.

l Distribute heat dissipation components: Disperse components that generate large amounts of heat to reduce the heat load per unit area.

l Location that is conducive to heat dissipation: Place the heating element in a location that is conducive to heat dissipation, such as near a vent or the edge of the device.

l Staggered arrangement: During layout, stagger the heating components with other general components, and try to make the heating components principle temperature-sensitive components to reduce their impact on the heat-sensitive components.

l Improve airflow: By changing the direction design and component layout, the airflow path is optimized, the flow rate is increased, and the heat transfer coefficient is improved.

Spacing recommendations between components

3-Choice of cooling method

As the performance of electronic components improves and the degree of integration increases, the power density continues to increase, resulting in a significant increase in the heat generated by the electronic components during operation. When choosing a heat dissipation method for electronic components, the temperature control requirements mainly include the following aspects:

l Temperature range: Different components have different temperature tolerance ranges. For example, high-performance chips such as CPUs have operating temperature requirements between 85-100°C, while some low-power devices can tolerate higher temperatures, so the cooling system must ensure Components operate within a safe temperature range.

l Temperature control accuracy: In some scenarios with strict temperature control requirements, it is necessary to adopt a heat dissipation solution that can accurately control the temperature to avoid component performance degradation or even damage caused by excessively high or low temperatures.

l Ambient temperature: The heat dissipation effect of electronic equipment not only depends on the heat dissipation capacity of the device itself, but is also affected by the surrounding ambient temperature. The heat dissipation design needs to consider changes in ambient temperature and try to keep the device within a suitable temperature range through heat dissipation means.

l Power consumption and reliability: Some low-power electronic components can use natural heat dissipation when they generate low heat. For high-power consumption equipment, it is necessary to wait for the heat dissipation technology of universities to ensure that it maintains normal performance and prolongs operation under high load. service life.

l Sealing and density: In sealed and high-density assembled devices, if the heat generation is not high, you can rely on natural heat dissipation. When components are densely packed and generate large amounts of heat, more effective heat dissipation technologies such as forced heat dissipation or liquid cooling are needed. Liquid cooling and heat pipe technology are used in scenarios with high power consumption and large heat generation, such as high-power electronic components such as traveling wave tubes, magnetrons, and power amplifier tubes, servers and high-power consumption equipment, and three-electric systems of new energy vehicles. Its unique application advantages.

                    Charging pile air cooling module                                                  Charging pile liquid cooling module

When choosing a cooling method for electronic components, it is necessary to comprehensively consider factors such as heat generation and heat flux, ambient temperature and operating temperature, space constraints and thermal isolation requirements, and cost and feasibility. By using appropriate cooling technology and cooling devices to ensure that components operate at a suitable temperature, the cost of system replacement and maintenance can be effectively reduced. In addition, reusing historical projects is also an effective strategy to reduce development and manufacturing costs and improve reliability.

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Energy storage immersion liquid cooling technology is an advanced battery cooling method that uses the efficient thermal conductivity of liquid to achieve rapid, direct and sufficient cooling of the battery, ensuring that the battery operates in a safe and efficient environment. Its basic principle is to completely immerse the energy storage battery in an insulating, non-toxic liquid with heat dissipation capabilities. This technology uses direct contact between the liquid and the battery for heat exchange, thereby quickly absorbing the heat generated by the battery during charging and discharging, and bringing it to the external circulation system for cooling.

Schematic diagram of the principle of a single-phase immersion liquid-cooled energy storage system

As a key component for carrying the battery pack and ensuring that the battery cells work in a suitable environment, the immersion liquid-cooled energy storage Pack box mainly undertakes functions such as carrying the battery pack and coolant, safety protection, and heat conduction. Therefore, in the design of the box structure, it is necessary to comprehensively consider multiple aspects such as airtightness, cooling efficiency, safety, material selection, and processing technology to ensure efficient, safe, and reliable operation of the system. The box structure design is the basis of the entire liquid cooling system.

1-Unified load

The lower box of the immersion liquid cooling energy storage pack is composed of a bottom plate and side plates. The bottom plate serves as the basic support, while the side plates are fixed around the bottom plate, together forming the main frame of the box. The size of the box is adjusted based on the overall needs and load conditions of the liquid cooling system. In the design of a larger box, an internal partition or process structure can be reasonably set to divide the large space into multiple small spaces, and the uniform load capacity can be improved by increasing the force-bearing area. The internal structure can increase the local load-bearing capacity by adding support ribs and reinforcing ribs, and a load-balancing structure can be set inside the box to balance the load in each corner.

At the same time, in order to reduce the impact of plastic deformation on uniform load-bearing, the processing surfaces of different heights can be designed as the same plane, which can reduce the number of machine tool adjustments and avoid deformation caused by height differences; the width or height of the box can also be increased to disperse the load and reduce deformation.

In addition, the integrated design of the liquid cooling channel and the bottom plate of the box is completed by stir friction welding or laser welding. This design can effectively improve the overall structural strength.

Schematic diagram of the lower box structure of a single-phase immersion liquid-cooled energy storage pack

2-Heat exchange design

Thermal conductivity is an important part of immersion liquid cooling energy storage technology. The design goal is to ensure that the battery can effectively dissipate heat in a high temperature environment, thereby maintaining its performance and safety.

The material of the box should have high thermal conductivity. Commonly used materials are aluminum alloy, copper, and aluminum-based composite materials. The box design also needs to consider the impact of ambient temperature changes. The appropriate thickness of the insulation layer can ensure that the temperature inside the box is within a relatively constant range, thereby improving the overall efficiency of the system.

The structural design of the box directly affects its thermal conductivity. Reasonable flow channel layout ensures that the liquid flows smoothly inside the box and maximizes the contact area, which is the main strategy to improve the thermal conductivity of the box. Multiple flow channels can be set inside the box to increase the coolant circulation path, thereby improving the heat dissipation effect.

               Solution 1:  single item + plate replacement                    Solution 2: single item + box replacement

The liquid cooling system includes a cooling medium, a heat-conducting structure, a liquid cooling pipeline and a supporting structure.

In the first scheme, the same or different types of coolants can be selected to be filled into the liquid cooling plate flow channel cavity and the box cavity respectively, and the two cavities are sealed and not connected to each other. In the box cavity, the coolant immerses the battery module, fully contacts it, cools it without flowing, and absorbs the heat on the battery surface by using the good thermal conductivity of the liquid to reduce the temperature rise. In the liquid cooling plate, the coolant is divided into multiple flow channels in the water inlet manifold and enters the cold plate in parallel, and then converges and flows out in the water outlet manifold, which is mainly responsible for taking out the heat and achieving heat dissipation.

In the second scheme, the coolant with low temperature flows in from the bottom or side, and the coolant with high temperature flows out from the top. The coolant circulates in the battery pack, which can effectively and evenly distribute the heat, improve the overall cooling efficiency, and maintain the consistency of the temperature of the battery cell or battery pack.

In order to further improve the cooling effect, a variety of optimization measures can be taken, such as optimizing the liquid flow and circulation method, selecting a coolant with high heat capacity, and improving the temperature distribution of the liquid. These measures reduce heat buildup and energy loss, ensuring the battery operates in an efficiently cooled state.

3-Sealed design

For liquid cooling pack boxes, the fully sealed design is carried out by adopting advanced sealing materials and structures. The sealing design should not only consider air tightness, but also the sealing of liquid media to ensure that the battery cells are leak-free in all directions.

The design should select the appropriate sealing form and shape according to the specific application requirements, and also consider factors such as the leakage freedom, wear resistance, medium and temperature compatibility, and low friction of the seal, and select the appropriate seal type and material according to the detailed specifications.

In addition, the choice of welding process also has a great influence on the sealing performance. For different materials and thicknesses, choosing the appropriate welding method can effectively improve the quality of the weld to ensure the overall strength and sealing of the system.

Finished picture of the lower box of the single-phase immersion liquid-cooled energy storage pack

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Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Thermal Design

 Use simulation software to analyze the heat dissipation performance of heat sinks and cold plates

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

In a liquid cooling system, the Cold Plate is directly laid at the bottom of the battery or inserted into the gaps between the batteries. After circulating the coolant, it is cooled through a heat exchanger and then circulated back into the system.

The integration of electric vehicle structures can achieve lightweighting, improve space utilization through shared parts, lighten the entire vehicle, enhance endurance, and reduce costs. Based on years of experience in the new energy vehicle industry,Walmate is able to better provide multi in one powertrain components for vehicle manufacturers

New energy vehicles refer to vehicles that use unconventional vehicle fuels as power sources (or use conventional vehicle fuels and new onboard power devices), integrate advanced technologies in vehicle power control and driving, and form advanced technical principles with new technologies and structures.

Structure Design

Stress, load-bearing, and deformation analysis of cold plates and Heatsinks

Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

Clean energy alternative fuel oil：

Climate, environment, resources, energy are closely related to national economy and people's livelihood. Dealing with these related issues well determines whether human society can sustainably develop. Under the pressure of energy shortage and environmental pollution, the two technological routes of energy storage battery vehicles and hydrogen fuel cells have become the main directions for the development of the new energy vehicle industry.

Automotive Light Weighting：

Considering 75 percent of energy consumption is related to vehicle weight, lightweight is an important technological means for new energy vehicles to save energy, reduce consumption, and increase range,

lightweight design is one of the current key drivers to reduce the energy consumption of vehicles. The use of lightweight new materials, structural optimization, and process improvement are the key paths to achieve automotive light weighting.

Thermal Management：

For energy storage electric vehicles, thermal management will become a crucial technology to achieve fast charging and improve range. For hydrogen fuel cell vehicles, water and heat management are key core technologies in the development of fuel cell power systems, which have a decisive impact on the performance, safety, and lifespan of the vehicle's power system.

Generally, external air is used as a heat sink to transfer the heat generated by chip operation to the heat sink through different media and interfaces, and dissipate the heat.

The IGBT power module in the inverter plays a very important role in this process. During the energy conversion process, IBGT will generate a large amount of heat, but when the temperature of IGBT exceeds 150 ℃, IGBT cannot function. Walmate provides various IGBT heat dissipation solutions such as air cooling, single liquid cooling, and phase change.

Product Testing

We offer customized testing procedures to meet our customers’ requirements

Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

Under the requirements of higher system energy density, taking into account factors such as heat dissipation and lightweight cost reduction, Walmate continuously optimizes the production process of battery trays to ensure system safety and reliability while improving cost-effectiveness.

The purpose of a heatsink is to acquire higher heat transfer surface area within a given volume by optimizing the structural shape, thereby improving the heat transfer efficiency from its surface to the surrounding fluid. Through surface treatment and other methods, the effective heat transfer area is increased, achieving enhanced cooling and temperature control.

In applications where volumetric power density and heat flux density requirements are not high, rectangular fin heatsinks are favored by engineers due to their simple structure, reasonable manufacturing cost, and good heat dissipation performance.

Comparision of different heat transfer methods

1- Heatsink Fin Design

The heatsink primarily extends its heat-dissipating surface through the fins, focusing on parameters like fin height, shape, spacing, and the thickness of the substrate.

Plate fin heat sink dimensions

According to the formula, the extended surface area of the heatsink can be calculated as:

The area of a single fin: Af = 2L(h+t/2),
The area between fins: Ab = Lh,
Total heat dissipation area: At = nAf + (n±1) Ab  (n is the number of fins).

Fin sectional view

The primary function of the fins is to increase surface area and improve heat transfer efficiency. The spacing, thickness, and height of the fins are critical factors in determining the number of fins, their distribution, and the expanded surface area.

When the surface area of the heatsink increases, the contact area with the air also increases, making it easier for heat to be dissipated. Engineers can further enhance the expansion area of the heatsink by optimizing the shape of the fins, such as using corrugated or serrated designs.

Although a larger surface area generally improves cooling performance, it is not always true that bigger is better. Whether using natural convection or forced cooling, the spacing between the heatsink fins is a crucial factor that determines the heat transfer coefficient of the air flowing over its surface.

The impact of Fin spacing and height on heat dissipation efficiency

In natural convection, the walls of the heatsink will generate natural convection due to temperature changes on the surface, causing airflow in the boundary layer near the fin walls. If the fin spacing is too small, it will hinder the natural convection process. In forced cooling scenarios, the thickness of the fin boundary layer will be compressed, allowing for narrower fin spacing. However, due to manufacturing methods and the driving force of the power components, the spacing cannot be too small. Therefore, balancing the thickness and height of the fins in actual design is very important.

2-Heatsink Substrate Design

The thickness of the substrate is a significant factor affecting the efficiency of the heatsink. When the heatsink substrate is thin, the thermal resistance to the fins farther from the heat source is larger, leading to uneven temperature distribution across the heatsink and weaker thermal shock resistance.

Increasing the substrate thickness can improve the temperature uniformity and enhance the heat shock resistance of the heatsink, but excessively thick substrates can cause heat accumulation, which in turn reduces thermal conductivity.

Heatsink working principle diagrammatic sketch

As shown in the figure above:

When the area of the heat source is smaller than the area of the base plate, heat must diffuse from the center to the edges, creating a diffusion thermal resistance. The position of the heat source also affects the diffusion thermal resistance. If the heat source is closer to the edge of the heatsink, heat can be conducted away more easily through the edges, thus reducing diffusion thermal resistance.

Note: Diffusion thermal resistance refers to the resistance encountered during the process of heat spreading from the center of the heat source to the edges in heatsink design. This phenomenon usually occurs when there is a significant difference between the area of the heat source and the area of the base plate, requiring heat to spread from a smaller area to a larger area.

3-Connection Process of Fins and Substrate

The connection process between heatsink fins and the substrate typically involves various methods to ensure good thermal conduction and mechanical stability between the two, mainly divided into two categories: integrated molding and non-integrated molding.

In integrated molding heatsinks, the fins and the heatsink substrate are formed as one piece, eliminating contact thermal resistance. The main processes include:

l Aluminum Die Casting: Aluminum ingots are melted into liquid form and then filled into metal molds under high pressure, allowing for the creation of complex fin shapes directly through die casting.

l Aluminum Extrusion: Aluminum material is heated and placed into an extrusion cylinder, where pressure is applied to force it through specific die holes, producing the desired cross-sectional shape and dimensions. Further processing includes cutting and machining.

l Cold Forging: This method allows for the creation of fine, dense fins with a high thermal conductivity material, but the costs are relatively high, and it has better capability for complex shapes compared to aluminum extrusion.

l The material for finned heatsinks can be copper, which has a high thermal conductivity. The fins can be made very thin, and they are directly carved from the substrate using cutting tools. However, when the fins are tall and long, they are susceptible to deformation due to stress.

In non-integrated molding, the fins and the heatsink substrate are processed separately and then joined together through welding, riveting, or bonding processes. The main processes include:

l Welding: The fins and substrate are connected together using solder; this can involve high-temperature brazing or low-temperature soldering. Welding has good thermal conductivity; however, using solder for aluminum substrates and fins requires nickel plating and can be costly, making it unsuitable for large heatsinks. Brazing does not require nickel plating, but the welding costs remain high.

l Riveting: The fins are inserted into grooves in the substrate, which are then pressed together with a mold to tightly hold the fins in place. The advantage of riveting is good thermal conductivity, but there is a risk of gaps and loosening after repeated use. Improving the riveting process can enhance reliability, but costs will also increase, so riveted heatsinks are often used in applications where reliability requirements are not high.

l Bonding: This generally involves using thermally conductive epoxy resin to tightly bond the fins and substrate together, facilitating heat transfer. While bonding uses thermally conductive epoxy resin, its thermal conductivity is significantly lower than that of welding, making it suitable for heatsinks with higher fins and small spacing. It can be used in scenarios where thermal performance requirements are not high.

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The battery storage housing plays a crucial role in energy storage systems, serving essential functions such as load protection, thermal uniformity, electrical installation, and waterproof sealing. With the increasing demands for battery energy density, aluminum alloy materials have become an effective solution to enhance battery system performance due to their higher thermal conductivity and lower density.

The integrated design of flow channels with the housing sidewalls can save welding work in critical load-bearing areas, thereby improving overall structural strength. This design ensures structural safety and stability under various conditions, including static loads, lifting, and random vibrations, while also improving the airtight performance of the housing to some extent. Furthermore, the integrated design helps reduce the number of parts and lower the weight of the housing. Made through extrusion molding, this process has low mold costs, is easy to process, and can be easily modified to meet flexible production needs.

1-Main Types of Aluminum Extruded and Welded Energy Storage Lower Housing

The liquid-cooled lower housing for energy storage typically has a width of 790-810 mm and a height ranging from 40-240 mm, divided into flat and flange types (see below). The length of the liquid-cooled lower housing is related to the capacity of the energy storage product, with common specifications including 48s, 52s, and 104s.

flat tray liquid-cooled lower housing

flanged battery tray liquid-cooled lower housing

2-Structural Form of Aluminum Extruded and Welded Energy Storage Lower Housing

The liquid-cooled lower housing serves as the foundational structure of the entire battery pack, consisting of a bottom plate with flow channels, sealing strips, water nozzles, frames, beams, brackets, and lifting ears, all welded together to form a rectangular frame structure made entirely of aluminum alloy.

Explosive view of the battery lower tray

The liquid-cooled lower housing must possess sufficient load-bearing capacity and structural strength, which imposes high requirements on welding quality, including welding processes, weld grade control, and welder skills, to ensure safety and reliability in actual applications. Liquid cooling technology demands high airtightness for the liquid-cooled housing, including the airtightness of the lower housing and the liquid cooling flow channels. Additionally, the liquid cooling flow channels must withstand the pressure of the coolant flow, necessitating even higher airtightness requirements.

3-Welding Quality Requirements

Generally, the liquid-cooled bottom plate is welded using friction stir welding, and the end caps of the flat liquid-cooled lower housing also employ friction stir welding. Typically, the weld depression for friction stir welding should be ≤0.5 mm, and there should be no detachment or metallic foreign objects that could fall off under vibration conditions.

Liquid cooling flow channels, frames, water nozzles, lifting ears, beams, and accessories are often welded using TIG or CMT welding. Considering the performance requirements of different components, full welding is used for liquid cooling flow channels, frames, water nozzles, and lifting ears, while segment welding is applied to beams and accessories. The flatness of the front and rear battery module beam areas should be <1.5 mm for a single module and <2 mm overall, with frame flatness allowing ±0.5 mm for every additional 500 mm of frame length.

Weld surfaces must be free from defects such as cracks, incomplete penetration, lack of fusion, surface porosity, exposed slag inclusions, and incomplete filling. Generally, the height of the water nozzle weld should be ≤6 mm, and other welds should not extend beyond the lower surface of the housing. The internal welds of the front and rear module beams must not protrude from the inner surface.

The weld penetration must meet relevant standard requirements. For arc-welded joints, the tensile strength should not be less than 60% of the minimum tensile strength of the base material; for laser and friction stir welded joints, the tensile strength should not be less than 70% of the minimum tensile strength of the base material.

Additionally, the welding of the lower housing must meet the airtightness standard of IP67. Therefore, post-welding treatment generally requires the weld slag and seams in the front and rear module beam areas to be ground flat. External welding on the tray should not be ground, and the sealing surfaces at the welds need to be smooth, with no significant height differences from the frame.

Below：Extrusion+FSW battery tray for ESS

We will regularly update you on technologies and information related to thermal design and lightweighting, sharing them for your reference.

Thank you for your attention to Walmate. 

As the power density and heat generation of various electronic and power products continue to rise, heat dissipation faces increasingly severe challenges. Liquid cooling solutions are gradually becoming the mainstream option due to their efficient heat dissipation, low energy consumption, low noise, and high reliability. 

Liquid cooling systems work by attaching cooling plates to battery packs (or other heat sources) and using circulating coolant to carry away the heat generated during operation. This heat is then transferred through one or more cooling circuit heat exchangers, ultimately dissipating the thermal energy of the energy storage system into the external environment.

                    Flanged style battery tray in BESS                                 Cold plate in Solar inverter

As a core component of liquid cooling solutions, the liquid-cooled plate is an efficient heat dissipation component. Its primary function is to remove heat generated by the battery (or other heat sources) through the circulation of coolant, keeping the equipment operating within a safe temperature range. If the channels of the liquid-cooled plate are not clean, it can affect the uniformity of coolant flow. Larger foreign particles can block or impede coolant flow, leading to ineffective heat transfer and consequently impacting the heat dissipation efficiency and overall performance of electronic devices.

Moreover, if impurities remain in the channels, they may damage the oxidation protective film on the metal surfaces, causing corrosion or erosion of the liquid-cooled plate. Additionally, impurities in the channels can lead to poor component contact, potentially causing seal aging or damage, which increases the risk of leakage and affects the long-term stable operation of the system.

1-Cleanliness Requirements for Liquid-Cooled Plate Channels

Current energy storage liquid cooling solutions generally require that no foreign objects, aluminum chips, oil, or liquids are present in the channels. In some cases, specific quality requirements regarding the size of hard and soft particles may be defined.

2-High-Risk Contamination Phases in Liquid-Cooled Plate Manufacturing

During the processing and manufacturing of cold plates, the internal channels and cooling interfaces are particularly vulnerable. The manufacturing processes, including cutting and channel removal, can easily introduce foreign objects such as oil, cutting coolant, and machining chips into the channels. The machining operations occur at the channel entrances, making protection difficult, and once chips enter, they are hard to remove.

(Processing of Liquid-Cooled Plate Components: Channel Removal and Deburring）

After the processing of the cold plate channel, components such as plugs and water nozzles are welded to form closed channels. The channel structure is typically non-linear, which creates blind spots for flushing. After welding, the machining process requires a large amount of cutting coolant for the tools and workpieces, generating significant metal chips. This step is particularly prone to contamination from coolant, chips, and other pollutants, which are difficult to completely remove once they enter.

3-Cleaning and Protection of Liquid-Cooled Plate Channels

To ensure the reliability and performance of liquid-cooled plate components, strict cleaning operations are typically performed. High-pressure water jets are used to flush the internal channels of the liquid-cooled plate to remove any residues, particles, or other impurities. After flushing, the liquid-cooled plate components need to be dried to ensure no moisture remains in the channels.

(Processing of Liquid-Cooled Plate Components:flushing and degreasing）

If the cold plates and other liquid-cooled components are not adequately protected during manufacturing, they are susceptible to contamination from metal chips, oil, cutting coolant, etc., especially during the machining process. The handling process of the cold plates also easily allows foreign objects to enter. Generally, protective measures at the channel entrances are considered in advance, such as dust covers and rubber sleeves for water nozzles.

Thus, cleaning the internal channels of cold plates becomes a necessary measure to eliminate channel contamination and enhance channel cleanliness. In production practice, comprehensive preventive controls should be implemented throughout the process. Based on this, specific contamination control measures should be proposed for particular components and processes to effectively manage the contamination inside the cold plate channels.

Abstract：Hydrogen fuel cells, also known as proton exchange membrane fuel cells (PEMFCs), are widely used in electric vehicle charging stations, automobiles, and other power generation facilities due to their advantages of high efficiency, zero emissions, and zero pollution. Hydrogen fuel cell vehicles emit 3-5 times more heat during operation than traditional fuel vehicles. This article briefly describes the current technology related to hydrogen fuel cell heat dissipation.

1-Working Principle of Hydrogen Fuel Cells

Hydrogen fuel cells release a large amount of heat during operation, among which electrochemical reaction heat accounts for about 55%, irreversible electrochemical reaction heat accounts for about 35%, Joule heat accounts for about 10%, condensation heat and various heat losses account for about 5%. The heat generated by hydrogen fuel cells is approximately equal to the electrical energy they generate. If not dissipated in a timely manner, the temperature inside the battery will significantly increase, thereby affecting its service life.

2-Hydrogen Fuel Cell Heat Dissipations

Compared to fuel powered vehicles, hydrogen fuel cell vehicles have a higher heat generation and a more complex system. At the same time, due to the limitation of the working temperature of hydrogen fuel cells, the temperature difference between hydrogen fuel cells and the outside world is smaller, making it more difficult for the heat dissipation system to dissipate heat. The working temperature of hydrogen fuel cells has a significant impact on fluid flow resistance, catalyst activity, stack efficiency, and stability, thus requiring an efficient heat dissipation system.

Liquid cooling technology is currently the mainstream technology in the application of hydrogen fuel cells in vehicles. It aims to reduce water pump power consumption by reducing system pressure drop, eliminate excess heat in hydrogen fuel cells with the lowest power consumption, and optimize the distribution of circulating working fluid flow channels to reduce internal temperature differences and improve the uniformity of battery temperature distribution.

90% of the heat generated in hydrogen fuel cells is eliminated by the heat dissipation system through thermal conduction and convection, while 10% of the heat is dispersed to the external environment through radiation heat dissipation. Traditional heat dissipation methods include air cooling, liquid cooling, and phase change heat dissipation.

3-Heat Transfer of PEMFC System

3.1 Stack Heat Transfer

After heat is generated inside the PEMFC, it will be transferred between the various components inside the PEMFC and the external environment. The heat transfer inside the fuel cell stack mainly depends on the thermal resistance of each component and the contact thermal resistance between different components. As the gas diffusion layer is the "bridge" connecting the main heat generation component (membrane electrode) and the main heat dissipation component (bipolar plate), its thermal resistance and the size of the contact thermal resistance with other components have a significant impact on the heat transfer performance inside the PEMFC. In addition, the contact thermal resistance between different components can have a significant impact on the internal heat transfer of the fuel cell stack.

3.2 Cooling Liquid Heat Transfer

The cooling methods of fuel cells include air cooling, liquid cooling, and phase change cooling.

The factors that affect coolant heat transfer include the PEMFC stack end, the coolant itself, and the radiator end. The coolant comes into direct contact with the bipolar plate at the end of the PEMFC stack, so the coolant flow channel structure has a significant impact on its heat transfer. In addition, the properties of the coolant itself can also affect the related heat transfer process. Considering the insufficient available space, choosing a coolant with a larger heat capacity can reduce the size of the radiator and improve the thermal management performance of PEMFC. Therefore, the demand for new high-efficiency coolants is becoming increasingly evident.

       The trend towards miniaturization of electronic devices is increasing, while the demand for more functions and higher performance further drives the reduction of external dimensions at various packaging levels, resulting in a rapid increase in power density.

       The miniaturization of equipment originally stems from cost reduction considerations. Cooling solutions directly increase the weight, volume, and cost of the product without any functional benefits, but they provide product reliability.

      Controlling component temperature within a specified range is a common standard for determining the acceptable level of a design, and effective heat dissipation is crucial for the stable operation and long-term reliability of electronic products.

      On the one hand, the result of device miniaturization is a decreasing design margin and a lower tolerance for over design. On the other hand, the overall trend of miniaturization has given rise to increasingly messy and complex geometric models, deepening the close integration of mechanical and electronic components in products. As a result, the flow space is greatly compressed, limiting the range of convective heat dissipation and making the structure of the core material of thermal design - the radiator - more complex.

       Heat sink is the most commonly used heat dissipation strengthening component in electronic device thermal design. Its strengthening principle is to increase the heat exchange area. When designing, it is generally necessary to consider the heat flux density of the heat source, the temperature requirements of the heating components, the internal space size of the product, the installation and appearance design of the heat sink, and other requirements.

     The performance of a heasink is influenced by many factors such as material, geometric dimensions, bottom flatness, thermal resistance, surface treatment, installation and fastening methods, and working environment temperature and humidity.

1.  Heatsink material

      The materials used for heatsinks mainly include aluminum, aluminum alloy, copper, iron, etc. Aluminum is the most abundant metal element stored in nature, with light weight, strong corrosion resistance, and high thermal conductivity, making it very suitable as a raw material for radiators. Adding some metals to aluminum to form aluminum alloys can significantly improve the hardness of the material. Graphite has the conductivity and thermal conductivity of metallic materials, as well as the plasticity similar to organic plastics, and is further applied in fields such as electronics,

communication, and lighting.

2.  Heatsink manufacturing process

The processing technology of radiators mainly includes CNC, aluminum extrusion, shovel teeth, slotting teeth, etc.

       Aluminum extrusion: The aluminum extrusion heat sink heats the aluminum ingot to around 460 ℃, and under high pressure, allows semi-solid aluminum to flow through an extrusion mold with grooves, extruding the initial shape of the heat sink, and then cutting and further processing. The aluminum extrusion process cannot accurately ensure the flatness and other dimensional requirements of the radiator, so further processing is usually required in the later stage.

      Shovel teeth: Shovel teeth are used to cut and straighten long strip shaped metal sheets (usually aluminum or copper alloys) at a certain angle using a shovel tooth machine, and repeat cutting to form a consistently arranged fin structure. Compared to extrusion technology, the advantage of shovel teeth is that they can process heat sinks with higher fin density and higher tooth height ratio.

      Splitting: The processing of slotting heat sink involves inserting the teeth into the heat sink substrate, and connecting the teeth to the substrate through methods such as adhesive welding, brazing, or extrusion; The connection between the teeth and the base of the toothed radiator is very important. If not handled properly, it may form a certain contact thermal resistance, which affects the heat dissipation performance of the toothed radiator.

3. Surface treatment of heatsinks

       Aluminum alloys are prone to oxidation in the air (forming an alumina film), but this natural oxide layer is not dense, has weak corrosion resistance, and is prone to contamination; Based on the requirements of aesthetics, corrosion resistance, and improved heat dissipation performance, metal radiators need to undergo surface treatment. Common surface treatment processes include anodizing, sandblasting, chemical nickel plating, and baking paint.

      Anodization：The principle of anodizing is essentially water electrolysis, which involves placing aluminum or aluminum alloy as the anode in a dielectric solution and using electrolysis to form an aluminum oxide film on its surface. This process is called anodizing treatment of aluminum or aluminum alloy; After anodizing, the surface emissivity of the radiator will increase, and the heat dissipation ability of the thermal radiation will be enhanced; Anodizing can maintain or change the color of aluminum & aluminum alloys, and black anodizing is commonly used for heat sinks.

       Sandblasting：Sandblasting refers to the process of using compressed air as the power and utilizing the impact of high-speed sand flow to clean and roughen the surface of a radiator; By impacting and cutting the surface, this process can not only remove all dirt such as rust on the surface of the radiator, but also exhibit a uniform and consistent metallic luster on the product surface.

       Electroless nickel plating：Chemical nickel plating is a process of depositing nickel alloys from aqueous solutions onto the surface of objects; Its characteristics include high surface hardness, good wear resistance, uniform and beautiful coating, and strong corrosion resistance; Due to the inability of copper and aluminum to be directly soldered, both require chemical nickel plating before using processes such as soldering.

      Baking paint：Baking paint is a high-performance special coating called Teflon added to the surface of a heat sink at high temperatures (280 ℃~400 ℃), which has the characteristics of non adhesion, heat resistance, moisture resistance, wear resistance, corrosion resistance, etc.

       Compared to traditional spray painting techniques, baking paint has advantages in both aesthetics and thermal conductivity. However, heat pipe assembly heat sinks are prone to expansion and deformation due to high temperatures, so low-temperature baking paint is particularly needed during baking.

       As the power to be processed continues to increase, heat sinks begin to be combined with heat pipes, fins and other devices to form higher performance heat dissipation modules, and water-cooled heat sinks with higher heat dissipation efficiency have emerged.

      Abstract：The main heating device in the electronic control system of new energy vehicles is the inverter, which converts the direct current of the battery into alternating current that can drive the motor. During this process, the IBGT in the inverter will generate a large amount of heat. To solve the heat dissipation problem of these devices, this article will introduce the working principle of inverters and advanced liquid cooling heat dissipation technology.

1-The Application of IGBT in the Electronic Control System of New Energy Vehicles

The electronic control system, as the energy conversion unit connecting the battery and the driving motor in new energy vehicles, is the core of motor drive and control. As a device that connects high-voltage batteries and motor power, inverters are responsible for converting direct current energy (batteries, storage batteries) into fixed frequency and voltage or frequency and voltage regulated alternating current (usually 220V, 50Hz sine wave), ensuring the electrical energy conversion of new energy vehicles.

The IGBT power module in the inverter plays a very important role in this process. During the energy conversion process, IBGT will generate a large amount of heat. However, when the temperature of IGBT exceeds 150℃, IGBT cannot function, so air-cooled or water-cooled heat dissipation equipment should be used. The thermal stability of IGBT operation becomes the key to evaluating the performance of electric drive systems.

In addition to the electronic control system, IGBT is also widely used in the onboard air conditioning control system and charging station system of new energy vehicles:

As the core technical component of electric vehicles and charging stations. The IGBT module accounts for nearly 10% of the cost of electric vehicles and about 20% of the cost of charging stations, and its thermal stability becomes the key to evaluating the performance of electric drive systems.

2-IGBT liquid cooling technology

1-Introduction

      Energy storage systems, due to their important role in balancing power grid processes and improving the utilization of new energy, have become the leading force driving global energy development and transformation. Electrochemical energy storage technology is mature, with a short construction period. Power and energy can be flexibly configured according to different application needs, and the charging and discharging response speed is fast, which can be applied in various occasions.

      During the charging and discharging process of energy storage systems, heat is generated. Poor heat dissipation can cause the battery temperature to be too high or the battery temperature difference to be large. In mild cases, it can lead to a decrease in battery life, and in severe cases, it can cause safety issues such as thermal runaway.

      This article is based on a practical project and establishes a thermal fluid simulation model according to the actual size of the battery pack. It analyzes in detail the distribution of pressure, velocity, and temperature in the entire heat dissipation system, obtains the thermal load of the system, and provides structural optimization suggestions for the design of the liquid cooling plate flow channel of the battery pack.

2-Project Overview

  2.1 Environmental Information

2.2Specification information of heat source devices：

2.3 Thermal Conductive Silicone

3-Heat Dissipation Model

A battery pack that uses liquid cooling for heat dissipation, consisting of 72 280AH cells and a liquid cooling plate. The size of the liquid cooling plate is 1570mm in length, 960mm in width, and 42mm in height, with 24 internal flow channels. The heat dissipation model of the battery pack is shown in the following figure:

4-Simulation Results Under The Condition of Inlet Water of 8L/min

The temperature distribution of the battery cells is 18.38-28.77 ℃, with the temperature distribution range of the highest temperature cell being 21.46-26.37 ℃ and the temperature distribution range of the lowest temperature cell being 18.76-26.37 ℃. As shown in Figure (a):

      Temperature distribution of liquid cooled plate: 18.00-21.99℃，as shown in Figure (b)：

The flow resistance is about 17KPa, the pressure profile of the liquid cooling plate is shown in Figure (c), and the velocity profile of the liquid cooling plate is shown in Figure(d):

5-Conclusion

       In this plan, the overall temperature ranges from 18.38 to 28.77 ℃, with a temperature difference of 2.4 ℃ between the highest and lowest battery cells. The overall temperature of the liquid cooled plate ranges from 18.00 to 21.99 ℃, the uniformity of temperature still needs to be optimized, multiple high-temperature areas have appeared.

      Compare the pressure and velocity profile of the liquid cooling plate, the high-temperature area of the liquid cooling plate is mainly distributed in areas with lower pressure and velocity. Based on the layout of the battery cells, it can be seen that the width margin of the liquid cooling plate is relatively large. It is recommended to block the two outermost flow channels of the liquid cooling plate, or appropriately reduce the width of the liquid cooling plate to achieve better heat dissipation effect.

Vehicle and battery energy storage，gain a rapid development opportunity.

And its core component, the power batteries belong to chemical power sources, and they are highly sensitive to temperature, require working in a suitable temperature environment. During the charging and discharging process of power batteries, a large amount of heat is generated due to the internal impedance. Further more, the battery pack is in a relatively enclosed environment. It’s convenient for heat accumulating, arising the temperature , even cause thermal runaway to happen. Therefore, an efficient and safe power battery cooling system has become particularly important.

Currently，there are three battery cooling schemes, respectively as air-cooled, Liquid cooling, direct refrigerant cooling.

The structure is relatively simple and the cost is also low, suitable for scenarios with small battery capacity and low heat dissipation pressure.

In terms of actual usage, liquid media has a high heat transfer coefficient, large heat capacity, and faster cooling speed, so it has a better effect on improving the uniformity of battery temperature.Liquid cooling scheme is currently the mainstream solution.

Direct refrigerant cooling technology can further improve the cooling effect on the battery, but the uniform temperature design of battery evaporators is a technical difficulty. The general requirement is that the temperature difference between the battery cells in the battery system should not exceed 5 ℃ (cooling condition+heating condition). At present, refrigerant direct cooling has not yet become the mainstream design solution in the industry.

To learn more about battery cooling technology and applications, please contact us. Walmate's Battery trays and energy storage liquid pack boxes have become the preferred choice for many new energy vehicle manufacturers, energy storage product manufacturers. At the same time, we also provide professional technical services and look forward to conducting good technical exchanges with you.

      The three major focuses of current new energy vehicle development - safety, lightweighting, and reliability - are closely related to the battery pack, and the battery housing is the load-bearing component of the battery system, which has a significant impact on the collision, energy consumption, and other aspects of the battery pack and even the entire vehicle.

Structure of New Energy Vehicle Battery Pack

1.  Safety of battery pack

   
   

   As the most core component in the three electric systems of new energy vehicles, the battery pack directly affects the main performance indicators of new energy vehicles, and its safety often determines the reliability of the entire vehicle. There are significant safety hazards in the collision of new energy vehicle battery packs. Collision deformation can cause internal battery modules to experience phenomena such as short circuits, open circuits, constant heating, and explosions. The collision resistance performance of the battery pack shell directly affects the safety of the battery module.

    

   The key to battery pack safety design is to reduce the degree of damage to the battery pack during collisions, so optimizing the vehicle collision force transmission path and improving the protective effect of the battery pack shell are the key to design.

   
   

   The current simulation technology is widely used. By establishing a battery pack simulation model, the failure forms in collision, compression, impact, drop and other working conditions are predicted. The system optimizes the shell structure and component dimensions of the battery pack, and conducts multi-objective optimization of battery pack safety to improve safety.

   
   

   2、Lightweighting of battery pack

   
   

   The application of high-strength steel, ultra-high strength steel, aluminum alloys, and composite materials is a necessary link in achieving lightweight of new energy vehicles.

   
   

   Due to the fact that the upper shell of the battery pack does not provide protection and support, but only serves as a sealing and dust-proof function, the upper shell is mainly made of steel plate, aluminum alloy, and composite materials. The lower shell of the battery pack mainly plays a role in supporting the entire battery mass, resisting external impacts, and protecting the battery module in the battery system.

   
   

   The mainstream preparation processes for the lower shell of the battery pack include: extruded aluminum profiles+welding forming, stamped aluminum plates+welding forming, and die cast aluminum+casting forming.

   
   

   Currently, extrusion aluminum profiles+welding forming is a common lower shell manufacturing solution adopted by domestic enterprises. Due to its lower preparation difficulty compared to stamped aluminum lower shells and larger forming dimensions compared to die cast aluminum lower shells.

   
   

   

   Battery Tray( Lower shell of battery pack)

   
   

   Due to the high overlap between the battery pack and chassis of new energy vehicles, the integrated optimization of the chassis and battery pack structure is crucial for the lightweight of new energy vehicles.

   
   

   CTP technology generally assembles battery cells into modules, which are then installed into the battery pack without the need for intermediate modules. Instead, the battery cells are directly integrated into the battery pack, which is integrated into the vehicle floor as part of the vehicle's structural components. CTP technology effectively improves the space utilization and energy density of battery packs, as well as the overall stiffness of battery packs.

   
   

   CTC technology is an advanced version of CTP technology, which directly integrates battery cells into the floor frame, uses the battery pack shell as the upper and lower floor panels, and connects the seat directly to the battery pack cover, achieving a space utilization rate of 63%.

   
   

   CTB technology is an improved version of CTC that retains the crossbeam structure and seat support, with only a portion of the bottom plate replaced by the battery pack cover. The space utilization rate is increased to 66%, and the body structure is more complete, with higher safety.

   
   

   

   
   

   Battery Packaging Configuration Mode

   
   

3. Reliability of battery pack

The entire process of the battery pack shell from service to fatigue failure is: under cyclic loading, fine cracks begin to appear on the surface of the shell, local small fatigue cracks gradually expand, and eventually the instantaneous fracture failure of the parts occurs. Especially, the connection joint of the battery pack housing is a high fatigue failure area. Experimental simulation and optimization of the battery pack casing have become a general approach to improving the reliability design of battery packs.

According to industry requirements, the sealing of the battery pack housing needs to reach IP6K7 level, and even some enterprises need to reach IP6K9K level. Due to the long sealing length of the battery pack casing, usually up to several meters, and the limited sealing design structure, extra attention should be paid to its sealing performance.

1. Basic principles of Friction stir welding(FSW)

After the high-speed rotating stirring head is inserted into the workpiece, it moves along the welding direction. The contact area between the mixing head and the workpiece generates heat through friction, which softens the plasticity of the surrounding metal, due to the movement of the stirring needle, softening layer metal filling the cavity behind the stirring needle.

At present, Friction Stir Welding(FSW) is mainly used for the connection of aluminum, copper, magnesium, titanium and other medium or dissimilar materials.

2. Friction stir welding (FSW) process

At the beginning of welding：Put the shaft shoulder and mixing tools with needle protrusions, which are rotating at high speed, into the welding area of the welded part to be welded. Shaft shoulders can be used simultaneously to prevent material overflow in a plastic state.

During the welding process：The frictional resistance between the stirring head and the welded material generates frictional heat, softening the material and causing plastic deformation, and release plastic deformation energy. When the stirring head is driven to move forward along the interface to be welded, the thermoplastic material is transferred from the front to the rear of the stirring head,And under the forging action of the mixing head shaft shoulder, realize solid phase connection between workpieces.

At the end of welding：Stirring head spin transfer out parts.

Friction Stir Welding Process

3. Technology and characteristics

Small deformation：Materials do not need to be melted, with low heat input and minimal deformation；

High adaptability：Not affected by environmental temperature and humidity, widely adaptable；

Excellent performance：The welding zone forms a dense "forged structure" without bubbles or shrinkage defects；

Environmental protection and safety：The welding process does not produce arcs, smoke, splashes, etc., which is safe, green, and environmentally friendly.

StrengthTest of Friction Stir Welding Joints

Compared with ordinary fusion welding schemes, friction stir 

welding has the following outstanding advantages:

² Belonging to solid-state welding technology, there is no melting of welding materials during the welding process;

² The quality of the welded joint is good, and the weld seam is a fine-grained forged structure without defects such as pores, cracks, and slag inclusions;

² Not limited by the position of the weld seam, it can achieve welding in various forms of joints;

² High welding efficiency, can achieve single pass welding forming within the thickness range of 0.4-100 mm;

² Low residual stress and small deformation in welded parts can achieve high-precision welding;

² High joint strength, good fatigue performance, and excellent impact toughness;

² Low welding cost, no welding process consumption, no need for wire filling and protective gas;

² Welding operation is simple and easy to achieve automated welding.

1.  Application of Friction Stir Welding Technology in Battery Tray Manufacturin

Aluminum alloy has many advantages such as low density, high specific strength, thermal stability, good corrosion resistance and thermal conductivity, non-magnetism, easy forming, and high recycling value, making it an ideal material for lightweight design of battery packs.

At present, the lightweight effect of the aluminum alloy battery tray and plastic top cover scheme is significant and has been adopted by many car manufacturers. The battery tray adopts a scheme of aluminum extrusion profile+friction stir welding+MIG welding, which has low comprehensive application cost, meets the performance requirements, and can achieve the integration of the circulating water channel of water-cooled batteries.

A typical battery tray is mainly composed of an aluminum alloy profile frame and an aluminum alloy profile bottom plate, which are welded together using 6-series extruded profiles, as shown in the following figure:

Aluminum Alloy Battery Tray

Section structure and material:

The frame and bottom plate are made of aluminum alloy extruded profiles, and the materials are generally 6061-T6 (yield strength 240 MPa, tensile strength 260 MPa), 6005A-T6 (yield strength 215 MPa, tensile strength 255 MPa), and 6063-T6 (yield strength 170 MPa, tensile strength 215 MPa). Consider which specific brand to choose based on factors such as cross-sectional complexity, cost, and mold consumption.

Technical difficulties:

The frame and bottom plate are the carriers of the battery module, which requires high strength. Therefore, double-layer cross-sections with cavities are generally selected to ensure strength. The thickness of the bottom plate is generally about 10mm and the wall thickness is 2mm. Less use of single-layer aluminum panels.

The typical cross-section of the frame is composed of multiple cavities, made of 6061-T6 material, with a wall thickness of 2mm at the thinnest point.

The typical cross-section of the bottom plate consists of multiple cavities, including an upper protrusion, which is mainly used for the installation of battery modules. The cross-sectional size is relatively large and the thickness is only 2mm, and the material is generally selected as 6005A-T6.

To learn more about battery cooling technology and applications, please contact us. Walmate's Battery trays and energy storage liquid pack boxes have become the preferred choice for many new energy vehicle manufacturers, energy storage product manufacturers. At the same time, we also provide professional technical services and look forward to conducting good technical exchanges with you.

Solutions：

The bottom plate and bottom plate, as well as the bottom plate and frame, are mainly connected by friction stir welding. The weld strength can reach about 80% of the base material.

The bottom plate profile is stir friction welded with a joint, and the bottom plate is welded with a double-sided butt joint between the bottom plates. Double sided welding has high strength and small deformation.

The double-sided stirring friction welding joint form between the frame and the bottom plate. To reserve enough space for the mixing head, the extension length at the connection between the frame and the bottom plate should be long enough to avoid interference between the frame and the mixing head, and to avoid increasing the size and squeezing difficulty of the frame profile. But double-sided welding has high strength and small deformation, which is also its main advantage.

In recent times, there has been an increased demand for Aluminium Extrusion  in product manufacturing and design. This led to an increase in the demand for a professional and reliable Aluminium Extrusion manufacturer.

In case, you are unaware of this manufacturing process, you are in the right place. In the course of this article, we will talk about Aluminium Extrusion in detail. So, without any further delay, let us get started!

A Guide on Aluminium Extrusion

1-What is Aluminium Extrusion?

It is a process that forces an aluminum alloy material through a die while using some specific cross-sectional profile. The manufacturer uses a powerful ram to pus the aluminum through the die. Due to the intense pressure, the aluminum comes out of t

he die opening.

When the aluminum comes out of the die’s front, it has the same shape as that of the die.  A runout table then pulls out the aluminum. Aluminium Extrusion is easy to understand the process, especially at the fundamental level.

You can link the force applied to push the aluminum via the die’s front as to that of squeezing a tube to get the ingredient out. The substance present inside the tube would take the same shape as the opening of the tube after you apply pressure to it.

So, it means that aluminum shape would depend upon the opening of the die. For round shape, you would require round opening, for square, square opening, and so on.

2-Shapes to be Extruded

You categorize the extruded shapes in three different categories.

a. Solid

Solid shapes do not have enclosed openings or voids. Angle, beam, or the rod are common examples that fall under this particular category.

b.  Hollow

Hallow usually comes with one or more voids. For instance, a rectangular tube or a square tube.

c.  Semi-hallow

These shapes generally have a void that is partially enclosed. For example, the “C” channel having a narrow gap.

3-The Aluminium Extrusion Process

Extrusion is popular among numerous industries including the energy, aerospace, electronics, automotive, architecture, and several other industries. You can achieve even extremely complex shapes by using multiple extrusion processes.

Below, we have explained the Aluminium Extrusion process in ten steps.

Step 1: Preparing and Moving the Extrusion Die

For starters, an Aluminium Extrusion manufacturer would use H13 steel for the machining a round-shape die. Of course, some manufacturers would already have the desired shape. In that case, they would simply pull it out from their warehouse.

The die needs to be preheated between 450 to 500 degrees Celsius. This would not only help maximize the lifespan of the die but at the same it, it would make sure that the metal flows evenly. Once you preheat the die, you can load it into the extrusion press.

Step 2: Heating Aluminum Billet Before Extrusion

The next step is heating the aluminum billet. It is basically a cylindrical solid block of aluminum alloy. Manufacturers extract the billet form a longer log of aluminum alloy material. You should have to preheat this in an oven. The temperature needs to be between 400 to 500 degrees Celsius.

Heating the billet would not melt it completely. However, it would make it malleable enough to yield to the extrusion process.

Step 3: Transferring Extrusion to the Billet Press

Once you heat the billet as required, it would mechanically be transferred to the extrusion press. However, applying a release agent or a lubricant onto the billet is important. This step needs to take place before the loading of the billet into the press.

Also, it is important to apply the same release agent to the extrusion ram. Doing so would ensure that the ram and the billet do not stick together.

Step 4: Pushing the Billet in the Container

After transferring the billet to the extrusion press, it is time for the apply the pressure. The ram would apply around 15,000 tons of pressure to the malleable billet. The application of the pressure forces the billet into the extrusion press’ container.

The material than would expand and gradually fill the container walls.

Step 5: Extruded Material Coming Out of the Die

Even after the material fills the container, the ram is still applying pressure. It means that now the material is pushed against the extrusion die. Due to continuous pressure, the aluminum material would go through the die’s opening.

When it comes out from the opening of the die, it is in the exact shape as that of the die opening. This means, that you have achieved your desired shape so far.

Step 6: Quenching and Runout Table

When the extrusion comes out from the die’s front, a puller holds onto it. This puller is then responsible for guiding it along with the run-out table. The speed of the table would match the speed at which the extrusion is coming out of the press.

With the run-out table movement, the profile is quenched. To ensure its sturdiness, it needs to be cooled uniformly. Aluminium Extrusion manufacturer either uses fans located above the table or they rely on water baths.

Step 7: Extrusion Shearing

After the extrusion has reached its full table length, it is not time to sheared it away from the extrusion process. For this particular purpose, manufacturers use a hot saw. The saw would separate the particular extrusion from the extrusion process.

NOTE: Temperature is an extremely important aspect of the extrusion process. You need to keep a close check on it at every stage of the extrusion process.

Even though you quench the extrusion after it leaves the press, it still requires time to fully cool down.

Step 8: Extrusion Cooling at Room Temperature

After the shearing takes place, it is time to transfer the extrusion from the run-out table to the cooling table. This process would take place mechanically. Now the manufacturer would wait for the profile to reach room temperature before shifting it to some other place.

After they cool down, it is important to let them stretch.

Step 9: Moving Extrusion to Stretcher

Sometimes, there is a certain twisting that occurs in the profile. As a professional Aluminium Extrusion manufacturer, you would have to work on it. In order to correct the problem, you move the table length extrusion on to a stretcher.

Every profile is gripped from both sides. It would mechanically be pulled until it reaches the desired specifications.

Step 10: Sawed According to Specifications  

Now that the table length extrusions are fully cooled and they are straight as well, it is time to transfer them to the saw table.

Here, these extrusions are sawed according to the length. In general, the length ranges from eight to twenty-one feet.

NOTE: The properties of extrusion at this particular stage are similar to that of the T4 temper. After sawing, it is possible to age the extrusion to T5 or T6. In order to do so, you would have to move them to an aging oven.

5-The Final Touches

After the completion of extrusion, it is possible to enhance the properties of the profiles by giving them heat treatments. To enhance the finished look of the extrusions, Aluminium Extrusion manufacturer uses different finish types.

However, these finishes need to be done the heat treatments. To bring the extrusion to their final dimensions, they need to go through different fabrication operations.

（a）Improving Mechanical Properties

It is possible to enhance the tensile strength and stress taking ability of alloys in the 7000, 6000, and 2000 series. In order to get these enhancements, it is important to put the profiles into ovens. These heating treatments would bring the alloys to T5 or the T6 tempers.

（b）Surface Enhancement

There are numerous finishing operations that aluminum profiles would undergo. Surface enhancements not only improve the overall appearance of the aluminum but at the same time, it also improves it corrosion properties.

For instance, when you anodize the aluminum, it would result in the natural occurrence of the oxide layer. Thus, resulting in the thickening of the metal. Also, the process would enhance the corrosion resistance of the profile. In addition, the metal would become more resistant to wear.

Likewise, it would result in a porous surface, it means that the surface would accept different colors. The surface emissivity would be enhanced as well.

There are some other finishing processes available as well. Such as Sandblasting, Powder Coating, Painting, Sublimation,etc.

Summary

Aluminium Extrusion is a process that manufacturers use to create components and parts having certain cross-sectional profiles. To enhance both the properties and appearance of the aluminum, the manufacturer uses different mechanical and surface enhancement processes.

The Aluminium Extrusion manufacturer also uses certain fabrication process to acquire the final dimensions of the product. After all, their objective is to achieve high-quality aluminum parts.

Walmate is absorbed in thermal management for 13 years, we have rich experience in manufacturing and processing heat sinks. To learn more about manufacturing process of heat sinks or look for a heat sinks  supplier or manufacturer, please contact us.