The Challenges of Laser Welding Batteries

The Challenges of Laser Welding Batteries

In the production of electric vehicle (EV) batteries, welding the interconnections between cells is often a major bottleneck. Each module requires hundreds, or sometimes thousands, of micro-welds that must be meticulously inspected for quality and safety—there's absolutely no room for error. Given the critical safety standards for lithium-ion batteries, especially in passenger cars, the precision and reliability of the welding process are paramount.

At HUIYAO, we offer efficient and thoughtful service tailored to these complex challenges.

Battery manufacturers face an immense challenge: they need to ramp up production while maintaining rigorous quality standards. While laser welding is celebrated for producing high-quality welds at rapid speeds, integrating this technology into EV battery production lines brings its own set of unique hurdles. To overcome these, EV manufacturers must collaborate with experts in laser technology and automation to ensure success. Key objectives include:

• Achieving a high yield of >99.999% good welds;

• Maintaining fast production rates, such as completing one module every minute.

Key Challenges in Laser Welding for EV Battery Production

1. Clamping Must Be Adaptable to Optimize the Laser Process

2. Vision Systems Must Be Precise Without Compromising Speed

3. Laser Process Development is Essential

4. The Welding Machine Needs to Be Kept Clean

5. Everything Must Be Calibrated

6. Manual Module Inspection is Still Necessary

7. In-Process Monitoring Must Be More Reliable

• Real-Time Weld Monitoring

• Automated Testing Techniques

8. Weld Rework Must Not Slow Down the Line

9. The Complete Journey: Design, Prototyping, Pre-Production & Full-Scale Production

1. Clamping Must Be Adaptable to Optimize the Laser Process

4 SCARA robots being used simultaneously for dynamic clamping

As with all welding processes, laser welding requires clamping to ensure a zero gap between the current collector and the poles. However, the complexity increases in EV battery production lines.

The clamping system must be adaptable to account for the following variations that naturally occur during production:

• Variations: During manufacturing, battery modules are rarely perfect. Variations in the positions of cells and busbars can affect the clamp’s effectiveness. To ensure precision, the clamping system must adjust to these variations at each individual weld position.

• Design Changes: Battery designs are constantly evolving. If the positioning and height of welds are altered, the clamping system must be adaptable to these design changes.

• Multiple Products: With multiple production models, the clamping system must easily adapt to changes in model types to avoid slowing down the line.

Failure to address these adaptations could lead to quality issues or delays due to clamping adjustments.

Two common approaches to clamping in battery welding are:

• Dynamic Clamping: Mounted on actuators, gantries, or robot arms, dynamic clamping tools offer maximum flexibility on all axes. When paired with vision systems, they can automatically adjust for localized deviations and adapt to design changes or multiple part models. Robot arms, in particular, offer the fastest operation.

• Clamping Plates: Clamping plates apply pressure across all welding positions at once. While faster, this method lacks flexibility, making it difficult to accommodate deviations. This requires designing modules with tighter tolerances, which can be more challenging to manufacture.

The key difference between dynamic tooling and static plates lies in the available space for clamping tools. Dynamic clamping offers more flexibility by allowing larger tools to accommodate cell-to-cell variations, whereas static plates are restricted by the space available.

At HUIYAO, we use dynamic clamping to achieve more than 99.999% good welds. Given its slower pace, we’ve employed SCARA robots to keep the laser welding process moving efficiently. These robots, each carrying a clamping tool, can independently prepare the next weld while another is being completed.

With SCARA robots, we can also accommodate:

• A fume extraction nozzle mounted on the robot arms to remove dust and fumes near the welding area;

• An air blower to direct contaminants toward the extraction nozzle;

• A shielding gas (e.g., argon) delivered directly to the welding zone when needed.

2. Vision Systems Must Be Precise Without Compromising Speed

The XYZ measurements of multiple cells

Accurate vision systems are crucial for detecting small variations in cell positioning and adapting the laser welding and clamping processes accordingly.

A good vision system for battery welding should meet the following criteria:

• X-Y-Z Measurements: The system must be capable of determining the exact position of each cell. X-Y measurements ensure proper clamping and welding, while Z measurements (height) ensure that the laser is focused and the clamping is precise. Methods like 3D stereoscopic vision and OCT measurements are commonly used.

• Speed: Vision analysis must occur quickly to avoid slowing down the production cycle.

• High Resolution: Precise measurements are necessary to adapt the laser process and clamping to tight tolerances.

• Lighting: Uniform lighting is essential to ensure that vision cameras can detect all zones clearly without misinterpreting elements.

• Field of View: A wide field of view allows for simultaneous measurement of multiple cells, speeding up the vision process.

• Module Integrity: The system must validate the positioning of busbars and other components to prevent welding on improperly assembled modules.

While some systems analyze one cell position at a time for the highest resolution, this approach adds valuable seconds to the process, causing bottlenecks when scaling up production. In our solution, we analyze groups of cells at once, gaining up to 50 ms per cell. This approach optimizes the laser's uptime without compromising weld quality.

3. Laser Process Development is Essential

Laser welding for batteries is far more complex than traditional welding applications, like car frames. Each application demands a unique and advanced approach, making it impossible to rely on predefined processes.

The laser process must be meticulously developed and optimized for each specific use case, with factors like spot size, scan speed, wobbling, and power requiring careful control.

Some of the key challenges during laser process development include:

• Sensitive Components: Excessive heat from the laser can cause severe damage to batteries, leading to short circuits, explosions, or permanent damage. The laser parameters must be carefully controlled to minimize heat and ensure precision.

• Weld Characteristics: Welds must meet the necessary strength specifications, including peel and shear strength, while also ensuring proper penetration depth.

• Electrical Resistance: Minimizing electrical resistance in welding joints is critical to prevent heat buildup during charge cycles, optimizing battery range and heat management.

• Aging: Long-term performance is crucial, so aging tests are required to validate the durability of the welds over time.

4. The Welding Machine Needs to Be Kept Clean

An extraction system installed just under the clamping system to capture fumes, dust, and spatter close to the laser welding process

Maintaining cleanliness in the laser welding machine is vital to preserving weld quality. Dust, fumes, and spatter can cause several critical problems:

• Short Circuits: Contamination on electrical components can result in short circuits and thermal runaways.

• Thermal Lensing: Contaminants on the protective window can cause thermal lensing, distorting the laser beam and compromising precision.

HUIYAO’s systems include integrated filtration systems that ensure the work area remains clean. These systems remove dust and fumes during the welding process and prevent thermal lensing and unwanted power losses, all while maintaining the machine's integrity for higher productivity.