In situ synchrotron observation of the vapor capillary geometry in laser welding of copper with 1030 nm and 515 nm laser beam sources

Abstract

Laser welding as a tool for manufacturing highly precise parts for electronic and electro mobility components is gaining worldwide importance. The precise control of energy input is one paramount challenge of welding highly reflective materials with high thermal conductivity such as copper and its alloys. Laser beam wavelengths in the visible range show an increase in absorptivity from < 5% (1030 nm) to ≥ 40% (515 nm) on copper at room temperature and open new options in material processing technologies. This paper presents the in situ observation of laser welding processes on Cu-ETP and CuSn6 with laser beam sources of 1030 nm and 515 nm wavelength using synchrotron radiation at DESY Petra 3 Beamline P07 EH4. The influence of laser power from 1 kW up to 4 kW and feed rates from 50 mm/s up to 500 mm/s on vapor capillary geometry and dynamics with same focal diameters is compared. For the investigations, a synchrotron beam of 2x2 mm2 in size with a photon energy of 89 keV is used for investigation. The material samples are analyzed by means of material phase contrast method to show boundaries between solid, liquid, and gaseous material phases. It is found, that both welding processes show a different geometry of the vapor capillary. A different sensitivity to changes of the feed rate of the welding process is observed. The vapor capillary of the 1030 nm welding process tends to be more sensitive on feed rate changes while showing an overall better weld seam quality. When welding with 515 nm, comparatively higher feed rates lead to better welding results.

In Situ Synchrotron Investigations of Beam Diameter Influence on Vapor Capillary Formation during Laser Beam Welding of Copper Alloy with a Blue Laser Beam Source

“…In addition to the wavelength as a variable for the power absorbed in the material, the angle of incidence of the laser radiation in the vapor capillary also plays a decisive role for the absorption. Studies have already been carried out using synchrotron radiation as an analysis tool for the incident angle α when welding with 515 nm and 1030 nm wavelengths [14]. Accordingly, the formation of the front angle and the vapor capillary depth when varying laser power and feed rate with a laser of 445 nm will be examined.…”

“…Building on these publications, the goal of this work is to compare laser welding of CuSn6 with two different focal diameters at a wavelength of 445 nm and to analyze the welds with in situ synchrotron experiments. Several publications in the state of the art describe the visualization of the internal process dynamics in the material using synchrotron radiation [14][15][16]. The latest studies on in situ phase-contrast videography to describe the dynamics of the vapor capillary during welding of copper with a wavelength of 445 nm were published by Heine [17].…”

Towards an Understanding of the Challenges in Laser Beam Welding of Copper – Observation of the Laser-Matter Interaction Zone in Laser Beam Welding of Copper and Steel Using in Situ Synchrotron X-Ray Imaging

“…In addition, it was stated that multiple reflections have an increased effect in the case of infrared laser radiation, as the absorptivity for 1030 nm is lower compared to the wavelength of 515 nm, becoming particularly visible when investigating the capillary in width direction, where a decisive bulge was found in the lower keyhole area [26]. The authors in [42] performed porosity analysis in CuSn6 weld seams for same processing parameters for 515 and 1030 nm laser sources using in situ synchrotron observation. The green laser beam was observed to lead to a higher porosity, which is more evenly distributed over the entire capillary depth.…”