BMW Leipzig plant deploys terahertz technology to transform paint quality control

The Leipzig facility has now introduced a terahertz-based measurement system for plastic exterior components in series production, which is the first application of this technology for exterior plastics in the BMW Group. The system can determine paint layer thickness non-destructively, replacing what had until now been an intrusive and wasteful manual process.

Until now, inspecting paint layer thickness on plastic exterior components required technicians to use scalpels and microscopy – physically cutting into parts to examine them. Beyond destroying the components themselves, this approach meant that deviations from specifications were often only identified at a later stage in the production process, limiting the opportunity to intervene early. It also generated unnecessary material waste a concern at odds with the industry's sustainability ambitions.

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The new system, called "Irys" and developed by technology partner das-Nano specifically for industrial inline inspections, works on a different principle. Sensors mounted on two robots within an existing end-of-line measurement cell are automatically positioned relative to each component. The system then fires terahertz waves at the surface and analyses the time-of-flight of the reflected signal to calculate the thickness of individual paint layers. Measurements take only seconds and achieve accuracy down to the micrometre level, something difficult for manual methods to reliably replicate.

The process has been integrated into the existing production flow. At Leipzig, car production is carried out in four stages – the press shop, bodyshop, paintshop and final assembly – and the plant also manufactures painted plastic components as a distinct operation. It is within this plastics production stream that the terahertz system has been integrated, enabling real-time quality data to be generated without interrupting throughput or sacrificing parts.

The benefits extend beyond simply avoiding waste. Because the system generates objective, reproducible digital measurements at speed, process deviations can be detected and acted upon far earlier than before. The resulting data also feeds into a broader digitalisation drive at the plant, creating a foundation for more sophisticated analysis in the future.

"The combination of higher measurement accuracy, direct process integration and full digitalisation delivers tangible benefits across the entire production chain, strengthening quality, economic efficiency and resource conservation in equal measure," Theiselmann noted.

This latest development follows the introduction of automated surface inspection at Leipzig in 2024 and represents the next step in the plant's roadmap toward a fully digital paintshop for plastic components. Looking ahead, the quality data generated by the terahertz system is expected to be analysed using artificial intelligence to identify deviations earlier, evaluate production trends and continuously refine process parameters supporting the wider BMW iFACTORY concept of lean, green and digital manufacturing.

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The Leipzig plant's role as a pioneer here is significant not just within the BMW Group but across the plastics manufacturing sector more broadly. It is the first BMW site to integrate terahertz measurement into in-house production, and the first facility in the plastics segment to use the technology for inspecting paint layer thickness on plastic components. Following successful piloting and ramp-up, the system is now operational across all component carrier systems and is being extended to cover all colour variants.

There is also potential for wider adoption. The technology is seen as directly transferable to painted body shops and the broader supplier network, meaning the quality and efficiency gains demonstrated in Leipzig could transfer across BMW Group's global production operations.

With more than €5.6 billion invested in the Leipzig site to date, the plant produces around 1,300 cars a day, with a permanent workforce of approximately 6,800 employees turning out the BMW 1 Series, BMW 2 Series Gran Coupé, BMW 2 Series Active Tourer and MINI Countryman for export worldwide.

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