Why Red and Blue Lights are Commonly Used in Battery Welding Visual Inspection, but Not White or Green?

In the field of battery manufacturing, particularly for welding processes, visual inspection plays a crucial role in ensuring the quality and reliability of the finished product. During battery pack assembly, welding involves high precision, and detecting defects such as cracks, spatter, or misalignments is essential. Among various light sources used for inspection, red and blue lights are commonly chosen, while white and green lights are less frequently used. This article explores the reasons behind the preference for red and blue lights in visual inspection systems for battery welding.

1. Light Spectrum and Material Interaction

Red and blue light are preferred due to the way they interact with the materials used in battery welding. These materials, typically metallic surfaces like aluminum and copper (used in busbars and tabs), have specific reflective and absorbent properties at different wavelengths of light.

- Red Light:

Red light has a longer wavelength and is less scattered, which allows for better penetration and highlights surface imperfections on shiny or reflective surfaces. It is particularly effective in detecting surface oxidation, scratches, or deformation in metals used for battery welding.

- Blue Light:

Blue light has a shorter wavelength and tends to create high contrast, making it easier to detect fine surface details, such as small cracks or weld defects. It also reduces the impact of ambient lighting, improving the clarity of defects during inspection.

2. High Contrast for Surface Inspection

The main objective of visual inspection in battery welding is to identify defects that could affect battery performance, such as misalignment, incomplete fusion, or overlapping welds. The high contrast generated by red and blue light makes it easier for cameras and optical sensors to distinguish these defects clearly.

- Red and blue lights create sharper images with better definition. They highlight surface abnormalities, making it easier for automated visual inspection systems (with machine vision) to detect these defects.

- White light, on the other hand, contains a broad spectrum of wavelengths, leading to less contrast when it interacts with the metal surfaces. It could potentially wash out fine details, making it more challenging to detect subtle defects.

3. Optimal Light for Cameras and Sensors

In welding visual inspection, cameras or sensors equipped with specific filters are used to capture the light reflected from the surface of the welded components. These sensors are optimized for certain wavelengths, and the blue and red light wavelengths are particularly effective for enhancing sensor sensitivity and improving image sharpness.

- Red light enhances sensor sensitivity for detecting larger surface defects or thermal distortion in battery components.

- Blue light, with its ability to detect fine surface defects and increase image resolution, is ideal for capturing minute details like cracks or spatter.

4. Avoiding Color Interference

Using green or white light can lead to color interference due to the reflective nature of metals. These light sources are more prone to reflections that alter the color accuracy and make it harder to identify small defects. In addition, the green wavelength might have issues with certain types of materials used in battery components.

- Green light is less effective in creating the desired contrast needed to highlight defects, especially on metallic surfaces. It also does not provide the necessary clarity needed to inspect the weld joints or busbar connections.

- White light has a broad spectrum that can wash out details, leading to less precise detection of issues. This makes it harder for inspectors to distinguish between subtle differences, especially when viewing small or intricate welds.

5. Better Detection for Automated Systems

In automated visual inspection (using machine vision or AI-based algorithms), the precise wavelengths of red and blue light contribute to faster and more accurate detection of defects. These automated systems rely on contrast differentiation to detect issues, and these two colors are ideal for distinguishing between different materials and identifying tiny surface flaws.

- Red and blue lights also enhance the accuracy of automated inspection, ensuring higher-quality welds and safer battery packs.

6. Why Not White or Green?

While white light and green light may work in some applications, they don’t offer the same level of precision and contrast needed in battery welding visual inspections. Their inability to highlight defects as effectively as red or blue lights makes them less suitable for ensuring the high standards required in battery manufacturing.

Conclusion

The use of red and blue light for visual inspection in battery welding is primarily due to their optimal interaction with metal surfaces, high contrast capabilities, and their ability to enhance sensor sensitivity. These wavelengths help highlight defects such as cracks, misalignment, and poor fusion, ensuring high-quality and safe battery production. White and green light, while useful in some scenarios, don’t offer the same level of precision and can lead to reduced contrast, making them less ideal for this particular application. As the demand for high-performance batteries continues to grow, laser welding combined with advanced visual inspection technologies will play a critical role in ensuring battery pack quality and safety.