Numerical Investigation of Keyhole Depth Formation in Micro Welding of Copper with 1030 nm and 515 nm Laser Radiation
The keyhole depth formation in laser micro welding of copper is numerically investigated as a function of feed rate and laser power. The calculations of the keyhole depth are based on an approximate process model for the three-dimensional steady keyhole profile and carried out for laser beams of the wavelengths 1030 nm and 515 nm with equal intensity distributions in the beam waist. It is found that under standard process conditions deeper keyholes are established with the 1030 nm laser when the feed rate is decreased whereas under conditions that minimize the attenuation of the laser radiation by the metal vapor the 515 nm laser leads to an overall more efficient process. Furthermore, the results reveal a different sensitivity of the keyhole depth to feed rate and laser power for both laser beams. Based on model equations and absorption mechanisms, the different behavior towards 1030 nm and 515 nm laser radiation is analyzed. An instructive consideration of the keyhole front in the upper keyhole part is presented and three absorption mechanisms that affect the geometrical form of the keyhole are identified: direct absorption, absorption contributions due to multiple reflections, and radiation attenuation by the metal vapor.