Electric Vehicles (EVs) have become a pivotal direction in the transformation of the automotive industry. Since EVs rely on batteries for propulsion, the battery tray plays a critical role in ensuring the normal and safe operation of the battery system. Currently, there are three common types of battery trays: steel battery trays, die-cast aluminum battery trays, and extruded aluminum battery trays. Among these, extruded aluminum battery trays are the most highly regarded.
Compared to steel trays, choosing aluminum offers numerous advantages, such as lower density and lighter weight for the same volume, which helps conserve energy. Aluminum also possesses excellent corrosion and weather resistance, allowing it to withstand harsh external environments. Furthermore, its superior machinability and plasticity effectively reduce production costs. When compared to die-cast aluminum trays, extruded aluminum designs are more flexible and easier to modify or refine. The diversity of dimensions and wide range of applications for extruded aluminum trays are also unmatched by die-cast alternatives. Consequently, extruded aluminum battery trays are widely used across various fields.
Overview of Automotive Battery Trays
The battery pack is the core energy source of an EV, providing driving power for the entire vehicle. As the carrier for battery modules, the battery tray is vital for the safety and protection of these modules. An EV battery tray primarily consists of a lower tray and an upper cover. The battery lower tray typically features a friction stir welded (FSW) structure made of aluminum alloy profiles. Its main structural components include the bottom plate, frame, and mounting brackets , with welding serving as the primary connection method. The tray must not only exhibit excellent vibration resistance, mechanical shock resistance, and squeeze resistance to protect the battery from damage during external collisions or compression, but also meet an ingress protection rating of at least IP67 (as per GB/T 4208-2017), along with salt spray corrosion and high-low temperature shock test requirements.
Material for Automotive Battery Trays
Developing electric vehicles (EVs) is an effective way to address environmental pollution and energy issues. In a pure EV, the battery pack accounts for approximately 30% of the vehicle’s curb weight, while the battery lower tray represents about 20% to 30% of the pack’s weight. Therefore, lightweight and cost-effective structural design and manufacturing of the lower tray can effectively reduce EV costs and increase driving range.
6XXX series aluminum alloys are ideal for aluminum battery trays because they are not prone to stress corrosion cracking and offer excellent weldability. By utilizing rational structural design of the profiles, material usage can be reduced while ensuring structural rigidity and strength. Combined with Computer-Aided Engineering (CAE) simulation, the cavity structure and wall thickness can be optimized. This allows for the verification of safety performance—including durability under vibration, impact resistance, and lateral squeeze resistance—enabling better lightweighting without compromising safety.
Structure of Aluminum Battery Trays
Aluminum battery trays are constructed from extruded aluminum profiles, which are joined via welding to form a complete integrated frame structure. Sheet metal is used in certain areas to serve as sealing plates for the profile cavities. Fasteners include hexagonal rivet nuts, press-fit studs, and M12×1D or M8×1.25D wire thread inserts.
The main components of an aluminum battery tray include the bottom plate, left/right side beams, front/rear side beams, and module mounting beams. The four side beams utilize three different L-shaped profile cross-sections, which are more conducive to welding with the bottom plate. Two module mounting beams are positioned above the weld seams between the bottom plate and the front/rear side beams, serving as support surfaces and connection points for the battery modules. Multiple hexagonal rivet nuts are installed along the upper flange of the tray to connect the upper cover and form a sealed space. A fire extinguisher mounting base, composed of a bracket and press-fit studs, is welded to the inner side of the front side beam. Six M12×1D wire thread inserts are uniformly distributed on the outer bottom of the tray to secure the tray to the vehicle. Additionally, six M8×1.25D wire thread inserts are installed on each of the two module mounting beams to connect three side-by-side battery modules.
Battery Tray Process and Production
Aluminum battery trays are mostly fabricated by welding machined aluminum extrusions. The structure comprises a bottom plate and a frame. The bottom plate is usually formed by splicing 2 to 4 aluminum extrusions using Friction Stir Welding (FSW). The frame is typically composed of 4 to 6 aluminum profile beams welded together using methods such as MIG (Metal Inert Gas), TIG (Tungsten Inert Gas), or CMT (Cold Metal Transfer). The bottom plate and frame are then joined using FSW, MIG, TIG, or CMT to form the battery tray assembly. The cross-sectional design of the extrusions must account for CAE simulation results, extrusion feasibility, and the chosen connection methods.
To minimize welding deformation, welding simulation technology is used beforehand to predict outcomes and optimize welding sequences and parameters. Specialized welding jigs and fixtures are designed to ensure dimensional accuracy and assembly precision, which reduces production costs, shortens cycles, and improves efficiency.
Quality of the tray is ensured through a rigorous testing suite: weld quality inspection, dimensional accuracy via Coordinate Measuring Machines (CMM), sealing performance via airtightness testing equipment, corrosion resistance via environmental chambers, and rigidity/strength via vibration, shock, and squeeze test rigs. Only by completing these tests can the performance and quality of the tray be guaranteed.
Processes for Automotive Battery Trays
Raw aluminum extrusions undergo sawing to reach the approximate length of individual parts or are directly sawed to shape. After machining and grinding, the individual parts are completed. The overall processing for an aluminum battery tray includes sawing, laser cutting, machining, grinding, assembly/fit-up, welding, airtightness testing, press riveting, blind riveting, and adhesive bonding.
Individual Part Machining
All individual parts must undergo CNC machining to meet dimensional tolerances. Sheet metal is processed via laser cutting, which offers high efficiency and meets the requirements for non-precision assembly. Profiles are processed via CNC sawing, which is efficient, cost-effective, and accurate enough for most applications. For complex features or high-precision areas, 3-axis CNC machining centers are utilized. The quality of individual parts directly affects the assembly precision, dimensional tolerance, flatness, and surface finish of the final battery tray.
Assembly
The assembly precision between parts significantly affects subsequent welding quality and is a key factor in meeting sealing requirements for the aluminum battery tray. Specifically, the fit-up between the bottom plate’s water ports and sealing blocks is decisive for the welding of the cooling channels. The tray’s airtightness depends on the assembly and welding of the front, rear, and side beams. Excessive gaps between parts can make welding impossible, while poor clamping of weak sections can lead to severe thermal deformation, affecting dimensions. During assembly, parts are laid flat on a multi-functional platform, secured with fixtures, inspected for initial dimensions, and tack-welded to prepare for final welding.
Welding
Once the assembly dimensions are verified, tack welding is performed at key stress points to secure the parts and minimize deformation during the final full welding process. This final stage is the “closing” step that ensures the aluminum battery tray’s sealing integrity. Any welding defect at any location can result in a failure during airtightness testing.
Airtightness Testing
Airtightness testing is divided into two parts: water channel testing and tray body testing. During water channel testing, quick-connect fittings are used to pressurize the channels to approximately 400 kPa. The tray is fully submerged in a water tank for 3 minutes. The presence of continuous bubbles indicates a failure, while no bubbles indicate a pass. During tray body testing, a leak detector is used to pressurize the interior to 3,500 ± 500 Pa. After the stabilization period, a 60-second test is conducted; a pressure drop of no more than 38 Pa is considered a pass.
Integral Machining
Features requiring high geometric tolerances such as the module mounting surface flatness of 0.3 mm, upper hexagonal hole position of 0.5 mm, and bottom flatness of 0.5 mm—cannot be guaranteed if features are machined on individual parts before welding due to cumulative errors, assembly deviation, and welding deformation. Instead, integral machining after welding is employed to meet these precision requirements.
Riveting
Riveting includes blind riveting and press riveting. In blind riveting, a rivet gun installs hexagonal rivet nuts onto the upper flange of the aluminum battery tray for subsequent bolted connection with the upper cover during final assembly. In press riveting, a press machine uses the plasticity of the aluminum profile to join steel press-fit studs with aluminum brackets, suitable for attaching small components to the main tray body.
Dimensional Inspection
Inspection is conducted through manual measurement and CMM. Linear dimensions are checked by quality inspectors using calipers and tapes, while geometric tolerances like position and flatness are verified via CMM.
Bottom Plate Water Port Sealing
As the circulation path for coolant, the quality and sealing of the bottom plate are critical to the processing of the aluminum battery tray. The bottom plate is formed by assembling and welding sealing blocks to the profile base. The multiple cavities within the extruded profiles serve as cooling channels. One end of the profile connects the non-communicating inlet and outlet, while the other end seals the ports to allow the cavities to communicate. This creates a loop, flowing from the inlet, through the cavities, and out the outlet—to effectively cool the battery.
How Getzshape Can Help
Getzshape delivers high-quality custom CNC machining, sheet metal fabrication, electrical discharge machining, die casting and more. Leveraging advanced equipment and strict quality control, we ensure accuracy and on-time delivery for prototypes to large production runs. As your end-to-end manufacturing partner, we streamline sourcing, machining, post-processing, and logistics.
