Abstract
The digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.
Highlights
Laser welding is a non-contact process for joining both similar and dissimilar materials
This research aims to create an analytical model which allows the choice of pulse width, peak power, pulse energy, welding speed, pulse repetition frequency and beam diameter to obtain the depth of penetration and weld width suitable for micro-joining applications, transferrable between various laser systems
& Average peak power density and specific pulse energy control the material vaporisation rate and heat accumulation, whereas the interaction time controls the weld width. The combination of these parameters simplifies the selection of pulse width, peak power, pulse energy, welding speed, pulse repetition frequency and beam diameter through the application of a new phenomenological model;
Summary
Laser welding is a non-contact process for joining both similar and dissimilar materials. This technique introduces the innovation needed to substitute the traditional tool wearing contact methods, such as mechanical clinching or friction stir welding, improving productivity using ultra-fast scanning devices. It has a good potential in micro-joining due to the high energy density, resulting in a very precise heat input control and high penetration/width ratio when compared to other fusion welding processes [1, 2]. A robust experimental setup is necessary to ensure repetitive and reliable results [6]
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