Lightweight materials like aluminum alloys have become mainstream due to their superior performance. However, challenges such as heat input control, deformation suppression, and process stability in thin-plate welding pose significant hurdles for traditional welding technologies. Cold Metal Transfer (CMT) welding, with its advantages of low heat input, spatter-free transfer, and intelligent parameter control, offers an innovative solution for battery tray manufacturing.

This article delves into precision control strategies of CMT technology in thin-plate welding for battery trays, analyzing its adaptability, process challenges, and composite application scenarios, aiming to provide theoretical and practical guidance for efficient, high-quality production.

Figure 1: CMT Welding of 104S Energy Storage Battery Liquid Cooling Lower Enclosure

1-Battery Tray Welding Requirements and CMT Adaptability

CMT technology, with its low heat input, spatter-free transfer, and intelligent parameter control, perfectly aligns with the high precision, low deformation, and efficiency demands of battery tray welding.

（1）Core Process Requirements for Battery Tray Welding

a. Material Compatibility and Lightweighting Needs

Battery trays primarily use lightweight aluminum alloys (e.g., 6xxx series, 6061) or carbon fiber composites for high-end models, requiring high strength (60%–70% base material tensile strength) and low density (aluminum alloy: 2.7g/cm³).

Dissimilar Material Joining: For hybrid steel-aluminum structures, thermal expansion coefficient differences must be addressed to minimize deformation.

b. Weld Quality and Performance Metrics

Low Heat Input and Deformation Control: For thin plates (0.3–3mm), deformation must be ≤2mm. Long linear welds require segmented welding or anti-deformation design.

Sealing and Strength: Welds must be fully sealed to prevent electrolyte leakage and pass shear tests (e.g., T/CWAN 0027-2022 standards).

Porosity Control: Aluminum alloy welding is prone to porosity, requiring a porosity rate ≤0.5%.

c. Production Efficiency and Automation Requirements

Batch production demands a welding speed ≥7mm/s, reducing single-tray welding time to 5–10 minutes.

Automated workstations must support dual-station design (simultaneous assembly and welding) and multi-robot collaboration.

（2）Key Advantages of CMT for Battery Tray Welding

a. Precise Low Heat Input Control

CMT reduces heat input by 33% compared to traditional MIG welding by retracting the welding wire to cut off current during droplet short-circuiting, eliminating burn-through risks for ultra-thin plates (0.3mm).

Alternating cold-hot cycles (arc heating-droplet transfer-wire retraction) minimize heat accumulation, controlling deformation to ≤1.5mm (BYD and BAIC case studies).

b. Process Stability and Quality Enhancement

Spatter-Free Welding: Mechanical retraction eliminates droplet spatter, reducing rework.

Porosity Optimization: Using Ar+30%He shielding gas reduces porosity by 50% compared to pure Ar, with pore sizes ≤0.3mm.

High Gap Tolerance: Accommodates assembly gaps up to 1.5mm, lowering fixture precision requirements.

c. Automation Integration and Efficiency Gains

Dual-station workstations (e.g., Taixiang Tech designs) enable parallel welding and assembly, doubling efficiency.

Symmetric robot welding (dual-robot synchronization) with anti-deformation design reduces cycle time to ≤10 minutes.

2-Challenges in CMT Process for Battery Trays

Figure 2: CMT Welding Process Flow

（1）Material Properties and Weld Defect Control

a. Porosity Sensitivity in Aluminum Alloy Welding

Aluminum alloy trays (e.g., 6061, 6063) are prone to porosity due to rapid solidification and hydrogen solubility changes. Shielding gas composition is critical: pure Ar results in ~5% porosity, while Ar+30%He reduces porosity to ≤0.5%. Inductance adjustment (e.g., negative tuning) optimizes molten pool flow, minimizing pore size.

b. Hot Cracking and Composition Segregation

Segregation of Mg, Si, etc., in aluminum alloys can cause grain boundary embrittlement. While CMT’s low heat input reduces HAZ, precise control of welding speed and wire feed is needed to avoid insufficient penetration or localized overheating.

c. Metallurgical Compatibility in Dissimilar Material Welding

Interfaces in Al-steel or Al-composite joints (e.g., crash beams and enclosures) must mitigate brittle phases (e.g., FeAl₃) and Zn vapor interference.

（2）Process Parameter Optimization Challenges

a. Balancing Penetration and Heat Input

Welds must meet T/CWAN 0027 standards for penetration depth (≥0.8mm). CMT’s low heat input may lead to insufficient penetration, requiring arc length adjustment or pulsed current to enhance penetration.

b. Trade-off Between Speed and Stability

Automated lines demand speeds ≥1.2m/min, but high speeds risk arc instability or uneven droplet transfer.

c. Gap Bridging in Complex Welds

Trays often feature large gaps (0.5–1.5mm) or irregular joints (e.g., T-joints).

(3) Compatibility of structural design and manufacturing process

a. Thin plate welding deformation control

The wall thickness of aluminum alloy pallets is usually 2-3mm. The deformation of traditional MAG welding can reach 1.2mm, while CMT welding can reduce the deformation to less than 0.3mm through low heat input. However, it is necessary to cooperate with anti-deformation tooling design and robot symmetrical welding (double-station workstation) to further improve the accuracy.

b. Continuity and sealing of long welds

The length of the sealed weld of the battery tray can reach several meters, and arc breaking or molten pool fluctuations must be avoided. CMT technology ensures the uniformity of the weld through more than 70 arc reignition cycles per second, and the airtightness qualification rate can be increased to 99% with the laser tracking system.

c. Synergy of multi-process composite applications

High-end pallets often use CMT+FSW (friction stir welding) composite process: CMT is used for complex structures (such as the connection between the frame and the bottom plate). FSW is used in high-load areas (such as longitudinal beams) to improve strength. The matching problem of the connection parameters of the two processes (such as preheating temperature and post-weld heat treatment) needs to be solved.

3-Typical application scenarios of CMT process in battery tray manufacturing

(1) Connection of the main structure of the battery tray

a. Frame and bottom plate welding

CMT process is widely used in the connection between the frame and the bottom plate of aluminum alloy battery trays, especially for long welds and thin plates (2-3mm thickness)

b. Connection between beam and bottom plate

In the design of CTP battery trays, due to the reduced number of beams and complex structure, CMT process is used for: High-precision positioning welding: The local connection between the beam and the bottom plate (such as T-joint) needs to avoid insufficient penetration. CMT achieves stable penetration ≥ 0.8mm through digital arc length control (such as Fonis CMT Advanced technology). Multi-material adaptation: If the beam is made of aluminum-magnesium alloy (such as 6061) and the bottom plate is high-strength aluminum, CMT can reduce pores through Ar+He mixed gas protection, while adapting to the thermal conductivity differences of different materials.

(2) Welding of thin plates and complex geometric structures

a. Thin-wall aluminum alloy welding (2-3mm)

The lightweight demand for battery trays promotes the application of thin plates, but traditional MIG welding is prone to deformation. The advantages of the CMT process are:

b. Ultra-thin plate welding: Taixiang Automation uses CMT technology to achieve spatter-free welding of 0.3mm ultra-thin plates for battery tray edge sealing structures.

c. Bridging of special-shaped welds: For special-shaped structures such as internal reinforcement ribs and anti-collision beams of the tray, the CMT Gap Bridging mode can fill the 0.5-1.5mm gap through wire retraction and arc redirection to avoid unfused defects.

d. Welds with high sealing requirements: The sealing of the battery tray is directly related to battery safety. The CMT process ensures it in the following ways:

· Continuous long welds: Using more than 70 arc reignition cycles per second (such as Fronius LaserHybrid technology) to ensure the continuity of several meters of welds, with an airtight pass rate of 99%.

· Low heat input control: Compared with laser welding, CMT has lower heat input, which reduces the thermal impact of molten pool fluctuations on the sealant layer and is suitable for the glue coating process.

(3) Multi-process composite manufacturing scenario

a. CMT+FSW composite process

In high-end battery tray production lines, CMT is often coordinated with friction stir welding (FSW):

Division of labor and cooperation: CMT is used for flexible welding of complex structures (such as frames and special-shaped joints), and FSW is used for high-load areas (such as longitudinal beams) to improve strength. For example, Shanghai Weisheng's automated production line uses a combination of CMT+FSW+CNC to increase the tray production efficiency by 30%.

Process connection optimization: Huashu Jinming's production line adopts a modular design, and achieves seamless connection with FSW through preheating parameter matching (such as local heating to 150°C after CMT welding).

b. Combined with FDS/SPR riveting technology

In the second-generation CTP technology, CMT is coordinated with friction self-tightening (FDS) and self-piercing riveting (SPR) technology: Hybrid connection solution: For example, the load-bearing area of the frame and the bottom plate adopts FSW, while the detachable parts (such as water-cooling plates and insulation layers) are pre-positioned by CMT welding and then fixed by FDS riveting, taking into account both strength and maintenance convenience.