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1Formation of a weld joint using laser radiation with different
pulse shapes
E. Surmenko1*, P. Ustinov1, T. Sokolova1, D. Bessonov1
1- Yuri Gagarin State Technical University of Saratov, 77 Polytechnicheskaya st., 410054, Saratov, Russia
The temporal shape of the laser pulse has a significant effect on the dynamics of surface heating during laser welding [1]. Modern laser technological set-ups allow varying the pulse shape in a wide range.
The aim of the study is to determine the optimal conditions for laser welding of thin sheet metal plates by changing the shape of the laser radiation pulse. The paper describes the sequence of study stages, including determining the optimal pulse duration, its energy, shape and repetition rate.
The weld was modeled on plates of 29NK material (Kovar, ASTM F15, UNS K94610, Fe-29Ni-17Co). Laser processing was carried out on the LRS-50 installation (LLC EDB "Bulat"): Nd:YAG-laser, pulse duration 0.2-20 ms, pulse repetition rate 0.5-100 Hz. The obtained weld spots and joints were examined with microscopes. The elemental composition of the joint and its changes under various welding modes were determined by the LIBS-method. The following welding modes were studied in various parameter combinations: pulse repetition rate 1 and 5 Hz, pulse duration 5 ms, 10 ms and 15 ms, pulse shapes 1 - triangular with amplitude increase, 2 - triangular with amplitude decrease, 3 - rectangular (Fig. 1). The energy input was changed by the voltage supplied to the pump lamp, from 200 to 240 V. To compare the obtained data, the value of the "speed" of change in the joint width with a change in energy input V (^m/V) was introduced.
1 2 3
Fig. 1. Laser welding pulse shapes.
It was found out that, for both repetition rates 1 Hz and 5 Hz, the following distribution is characteristic.
Pulse 1: the joint width steadily increases with increasing of pulse duration at all pump voltage; the speed of increase in the joint width with increasing pump energy increases with increasing pulse duration (the longer the pulse, the faster the heating).
Pulse 2: the joint width also steadily increases at all pump voltages with increasing of pulse duration, but the speed of increase in the joint width with increasing pump energy decreases with increasing pulse duration (the longer the pulse, the slower the heating). Pulse 3: the joint width steadily increases with increasing pump. The maximum speed of joint width growth with increasing energy input is observed at a pulse duration of 5 ms, and then decreases with increasing pulse duration to 15 ms.
Rectangular pulse 3: the joint width steadily increases with increasing pump voltage, remaining less than with Pulse 1. The speed of joint width increase, when increasing pumping energy, increases within the measurement accuracy, remaining less than with Pulse 1 (about 80%).
LIBS-study of the joint centerline composition was performed for pulses 1 and 2 with different combinations of repetition rates and durations. It was found out that the depletion and enrichment trends for the same elements are almost similar in different modes. But Ti demonstrated different behavior with different pulse shapes.
[1] L.Ya. Min'ko, A.N. Chumakov, Yu.L. Chivel, Effect of the laser pulse shape on the formation of plasma near absorbing targets, Quantum Electronics, 11:11, pp. 2241-2245, (1984).
