Measurement of core temperature through semi-transparent polyamide 6 using scanner-integrated pyrometer in laser welding

Abstract

Predicting the core temperature during welding is an ambitious aim in many research works. In this work, a 3D-scanner with integrated pyrometer is characterized and used to measure the temperature during quasi-simultaneous laser transmission welding of polyamide 6. However, due to welding in an overlap configuration, the heat radiation emitted from the joining zone of a laser transmission weld has to pass through the upper polymer, which is itself a semi-transparent emitter. Therefore, the spectral filtering of the heat radiation in the upper polymer is taken into account by calibrating the pyrometer for the measurement task. Thermal process simulations are performed to compare the temperature field with the measured temperature signal. The absorption coefficients of the polymers are measured, in order to get precise results from the computation. The temperature signals during welding are in good agreement with the computed mean temperature inside the detection spot, located in the joining area. This is also true for varying laser power, laser beam diameter and the carbon black content in the lower polymer. Both, the computed mean temperature and the temperature signal are representing the core temperature. In order to evaluate the spatial sensitivity of the measurement system, the emitted heat radiation from both polymers is calculated on basis of the computed temperature field. Hereby it is found, that more than 90 percent of the detected heat radiation comes from the joining area, which is a crucial information for contact-free temperature measurement tasks on semi-transparent polymers.

Progress and perspectives of in-situ optical monitoring in laser beam welding: Sensing, characterization and modeling

“…The results indicated that the use of infrared radiation could be a promising tool for the temperature detection and weld quality control. Another work [55] has been reported a 3D-scanner with integrated pyrometer was designed to real-time monitor the temperature during quasi-simultaneous laser transmission welding of polyamide 6. By changing the laser power, the laser beam diameter and carbon black content in the lower polymer, the temperature information was acquired under different welding conditions.…”

Recent advances in laser welding for joining polymeric components

“…The addition of particles or other materials can also be carried out to purposely alter the properties of the laser welded materials, changing their response to the laser radiation (Schmailzl et al 2020). This is useful, for example, in applications based in transmission laser welding processes, as described in Section 2 of this document.…”

Laser welding of thermoplastics: An overview on lasers, materials, processes and quality

“…Laser power [28,29,31,33,34,35,37,12,46,41,43,62,63,88,89,50,52,53,54,55,56,57,64,65,6,70,71,72,82,83,101,102,114,112,73,58,90,91,75,109,59,117,105,120,116,84] Welding speed [28,29,31,33,37,12,46,…”

“…This technique enables not only the development of a nondestructive technique to control the welding process, but also facilitates the part and process design as well as quality check in mass production. Schmailzl et al [90] used a 3D-scanner with integrated pyrometer to measure the temperature during quasi-simultaneous LTW of PA6 taking into account the spectral filtering of the laser radiation in the semi-transparent emitter upper polymer. Process simulations were performed to compare the temperature field with the measured temperature signal.…”