ActFast: TWI and partners develop real-time fibre-optic monitoring for laser welding


TWI has been working alongside Swedish fibre-optic cable specialists, Coherent, and automotive manufacturer, Sodecia SA, to develop ActFast, a real-time fibre-optic cable-based process monitoring system for laser welding.

The last 15 years have seen a significant increase in the use of high-power laser welding for automotive fabrication. However, despite the operational and financial benefits offered by laser processes, there remains a need to detect weld defects quickly, reliably, and cost-effectively. The ActFast project aims to address this by providing an innovative solution based on both existing and newly developed sensors able to offer fast algorithm process monitoring.

The sensors developed for the project reflect a range of visible, UV and infrared wavelengths back to the process head from the work-piece in order to detect changes indicative of misalignments, weld defects, and the contamination or damage of optics.

The four types of sensor include:

1.       Photodiodes, to detect intensities and wavelengths of radiation inside the connector using ultraviolet, visible light and infrared wavelengths

2.       ΔT sensors, to measure the difference in temperature between the inlet and outlet cooling water to the connector. A rise in coolant temperature indicates an increase of losses inside the connector, with the sensor capable of measuring temperature changes as small as 0.01°C

3.       Absolute temperature, to gain status information about the general condition of the connector

4.       Humidity sensor, which gives information about the environmental climate inside the connector.

The ActFast project not only seeks improvements in detection speed, accuracy, and real-time data processing, but also sees the development of a database for system calibration and teaching based on information generated from test samples with zero defects and other samples with known, deliberately introduced defects. ActFast also compares the results of the fibre-optic cable with the technological and economic factors from other existing laser welding monitoring and control solutions.

The benefits of the system include the sensors being integrated to the interlock circuitry so that the laser source can be shut down in the case of unexpected behaviour, thereby reducing the risk of damage to expensive optical components. In addition, ActFast will offer process monitoring through a closed-loop interface between the sensors and the laser controller to improve weld quality and minimise scrappage and rework.

Offering quick and accurate alignment of the optical components, without the need for external equipment, the project will also record raw data for each work-piece for future improvements and offline analysis.

While the project initially examines sensory capabilities in relation to automotive components specified by project partner Sodecia, Coherent expects to investigate the use of ActFast in other industries, including aerospace and power generation.

With the ActFast project entering its closing stages, final results are expected to be shared at the end of 2018.

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