Process Sensor for Laser Welding

WELDCHECK 4.1 is an established product of Lessmüller Lasertechnik that allows automated monitoring of laser welding using emitted process light. The system is able to reduce test costs and production time. The photodiode-based WELDCHECK offers quality assurance and documentation of pulsed or continous-wave laser welding processes in industrial scale production.

Real-time data evaluation and detection of weld faults is combined with external fieldbus data. The compiled data serves as basis for optimization of the manufacturing processes.

  • Real-time monitoring of welding process
  • Real-time data evaluation and detection of weld faults combined with external fieldbus data
  • Wide monitoring spectrum (from 320 nm to 1650 nm)
  • For welding with cw or (optional) pulsed lasers
  • Simple integration into conventional laser heads through the standard C-mount camera port or directly into the laser source
  • Easy operation and setup
  • QS solution for various laser welding processes and different materials
  • Small, robust, lightweight, easy maintenance, and cost-effective design system



The WELDCHECK 4.1 SYSTEM consists of an optical unit and an electronic unit. WELDCHECK 4.1 SENSOR is a receiver of the system in the  visible and infrared wavelength range. WELDCHECK 4.1 EVA is an evaluation unit of system containing interfaces for fieldbus & office communication. Despite full performance, it is the world's smallest and easiest device and can fit into almost any laser or laser head.


When welding with a solid-state laser the process creates secondary radiation, produced by a liquid weld pool and metal vapour. There, the WELDCHECK evaluates the secondary radiation. The intensity of this radiation corresponds the volume of the molten metal.

WELDCHECK's function is to recognise the weld faults in real-time by means of secondary radiation evaluation.

The results are compared in real time with reference welds. If the system detects the devation from the norm, the weld fault is immediately indicated. The tolerance limits are flexible and adjustable.

Fault indication in LLT-Client-Software

Fault indication in LLT_Client-Software


Detectable faults (application-dependent)

  • Laser energy deviations
  • Contaminated optics and protection glass
  • Deviated focus position
  • Large gaps 
  • Positioning fault
  • Alteration of the laser penetration depth
  • Contaminated surface
  • Seam breakthrough


ModSets for adaption to various laser processing optics 





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