The Flow Mapping Unit (FMU) is an innovative diagnostic system developed by Air Liquide Innovation Campus Paris to improve the understanding and control of protective gas flow in Laser Powder Bed Fusion (L-PBF) additive manufacturing systems. As metal additive manufacturing continues to expand toward larger build volumes and increasingly demanding applications, gas flow management has become a critical factor influencing process stability, part quality, and manufacturing reliability. The FMU was created to address a significant industry challenge: the lack of detailed and reliable tools capable of characterizing gas flow behavior throughout the entire build chamber.

In L-PBF processes, the protective gas atmosphere serves several essential functions. It prevents oxidation, maintains a safe inert environment, and removes process by-products such as metallic fumes, condensates, and spatter particles generated during laser melting. These particles can travel at extremely high velocities and, if not efficiently extracted, may interfere with the laser beam, contaminate the powder bed, and create defects such as porosity, inclusions, or reduced mechanical performance. While many systems rely on basic flow measurements at a limited number of locations, actual gas flow behavior inside manufacturing chambers is often highly complex and non-uniform.

The FMU provides a unique solution by enabling high-resolution three-dimensional mapping of gas velocity across the entire build volume. The system consists of a modular three-axis robotic platform specifically designed to operate inside confined additive manufacturing chambers. Using a lightweight rack-and-pinion mechanical structure driven by low-voltage stepper motors, the platform can precisely position measurement probes throughout the chamber while minimizing interference with the gas flow being studied.

A major strength of the innovation is its versatility. Unlike fixed sensors integrated into specific machine designs, the FMU can be adapted to different machine configurations and build volumes. This universal and modular architecture allows the same platform to be used across multiple L-PBF systems, providing a standardized approach to flow characterization. The system can investigate large build areas exceeding 1000 × 1000 mm and perform measurements at multiple heights above the build platform, producing detailed velocity maps that reveal complex flow patterns and previously undetectable low-velocity regions.

The FMU supports two complementary measurement technologies: Pitot tube probes, which provide robust pressure-based velocity measurements, and hot-wire anemometry (CTA), which offers highly sensitive velocity measurements in applications where space constraints are more demanding. Measurements are automated through dedicated software controlling the robot motion and data acquisition process. Thousands of measurement points can be collected during a fully autonomous campaign lasting between 10 and 15 hours, and in some cases more than 50 hours. Operators can monitor and control the process remotely via a local Wi-Fi connection without opening the chamber, preserving test integrity and maintaining hermetic conditions.

The innovation has already demonstrated significant industrial value. FMU measurements have identified critical areas where gas velocity falls below 0.3 m/s, creating so-called “dead zones” that allow process ejecta to accumulate. This information has been used to redesign gas diffuser systems and improve gas shield homogeneity across production platforms. Such optimizations directly contribute to improved process stability, enhanced part quality, and reduced defect rates in additive manufacturing.

From a sustainability perspective, the FMU supports more efficient operation of L-PBF systems by helping manufacturers optimize gas distribution and improve process consistency. Better flow control reduces the likelihood of defective builds, minimizing material waste, energy consumption, and machine downtime associated with failed production runs. Its adaptable structure also allows deployment across multiple machine types without requiring dedicated equipment for each installation.

The FMU has reached Technology Readiness Level 7 (TRL 7) and has been successfully deployed in operational industrial environments. Protected through Air Liquide proprietary technology and patent WO2023179948A1, the system represents a significant advancement in process monitoring for Powder Metallurgy and additive manufacturing.

Overall, the Flow Mapping Unit provides the first practical solution for comprehensive three-dimensional characterization of gas flow inside L-PBF machines. By enabling precise validation and optimization of protective gas systems, it supports improved material integrity, process understanding, machine qualification, and part quality, making it a valuable tool for the next generation of metal additive manufacturing technologies.