Results and Discussions Figure 1 shows a schematic of an MCC mini-bar. The MCC mini-bar has eight emitting points soldered onto a macro-channel cooler. The optical procedure for every mini-bar consists of three steps: fast axis collimation, beam symmetrizing with beam transformation systems, and slow axis collimation. The spot widths and divergence angles of the fast and slow axes for each emitting points were 3.2 mm, 6 mrad and 2.6 mm, 6 mrad, respectively (Fig. 4). Every four mini-bars with the same wavelength were mounted in a stair-step manner (Fig. 5), leading to the formation of a simulated beam spot with a 7 mm×6 mm field-shape distribution (Fig. 6). Then, all emitting units were coupled theoretically into a fiber with core diameter of 200 μm and numerical aperture of 0.22 using polarization and wavelength multiplexing, as shown in Fig. 7. In the experiment, a fiber-coupled module comprising 16 MCC mini-bars (eight of 915 nm and eight of 976 nm) achieved an output power over 800 W and wall-plug efficiency of 45% under macro-channel cooling with industrial water (Fig. 8). Furthermore, the lasing beam from 19 fiber-coupled modules was coupled by a 19×1 fiber optic combiner into a 1 mm optical fiber (Fig. 10), achieving a maximum output power over 15 kW (Fig. 11) and spot size of 165 mm×25 mm (Fig. 12).
With the increase in wind turbine equipment volume, the scale and performance requirements of wind turbine bearings are increasing. This is a significant challenge for the production and manufacturing of large-scale wind turbine bearings. In recent years, high-power lasers have been applied for the processing of workpieces such as crane-main and worm-shaft bearings. Therefore, high-power lasers, while serving as quenching light sources, are expected to solve the surface hardening of large-scale wind turbine bearings, enabling the development of large-scale wind turbine bearing technology. After CO2 and solid-state lasers, high-power diode laser systems have gained substantial interest in laser quenching for metal materials because of their high wall-plug efficiency, high reliability, long lifetime, relatively low investment costs, small footprint, and high absorption efficiency. Currently, high-power diode laser sources have achieved an output of over ten thousand watts in many countries, particularly in the USA and Germany. However, domestic development has been relatively slow. In this scheme, a novel method of 19 fiber-coupled laser modules, one of which is coupled with 16 macro-channel cooling (MCC) mini-bars, is used to develop a 15-kW fiber-coupled diode laser-quenching light source.
Aiming at the practical application of laser quenching in the production of large-scale wind turbine bearings, a 15-kW fiber-coupled diode laser-quenching light source was designed. First, 16 MCC mini-bars with linear array beam shaping, eight of 915 nm and eight of 976 nm, were used by adopting a space/polarization/wavelength beam combination to obtain a high-power fiber-coupled module with an optical fiber with core diameter of 200 μm and numerical aperture of 0.22. Under cooling with industrial water, the high-power fiber-coupled module achieved a continuous output power of over 800 W and high wall-plug efficiency. Then, the laser beams from the 19 fiber-coupled modules were coupled by a 19×1 fiber optic combiner into a 1 mm optical fiber. Finally, the intensity distribution of the lasing beam spot was further homogenized using the microlens array combined with the focusing lens. In addition, the performance of the fiber-coupled module was analyzed in our simulations and experiments.
In this study, a high-power and high-efficiency fiber-coupled module is demonstrated by adopting a space/polarization/wavelength beam combination composed of 16 MCC mini-bars, eight of 915 nm and eight of 976 nm. Under macro-channel cooling with industrial water, an output power of over 800 W and wall-plug efficiency over 45% are demonstrated for a fiber with core diameter of 200 μm and numerical aperture of 0.22. Then, the lasing beams from the 19 fiber-coupled modules are coupled by a 19×1 fiber optic combiner into a 1 mm optical fiber. A better homogenized intensity distribution of the light spot is achieved using a microlens array combined with a focusing lens. The results show a maximum output power over 15 kW and spot size of 165 mm×25 mm, satisfying the power required for quenching the bearing raceway surface of a large wind turbine spindle.
