Laser cladding for application of wear resistant coatings

So far direct diode lasers are not very common for laser cladding applications in the field of surface protection, remanufacturing and rapid prototyping, since they have a low beam quality and usually a rectangular or line shaped spot with a short working distance. However, their extreme compact size, ease of operation, high wall plug efficiency and lower investment and running costs makes them very interesting for laser cladding, especially in an industrial environment. In this study a diode laser coating process for cladding of oil drilling equipment is presented, which was developed a the Fraunhofer Center for Coatings and Laser Applications. In order to develop a simple and cost efficient system for laser cladding, a direct diode laser was modified to match the required beam profile. In the first attempt to increase the working distance and to scale the focus size, one lens of the focusing optics was removed. To further increase the spot size, the laser beam was defocused below its focal plane. In a second step the laser spot was made square in the focal plane by readjusting the diode stacks inside the laser head. Thereby it was also possible to achieve a relatively smooth intensity distribution. To obtain the needed spot size of approximately 6x6 mm(exp 2), a lens with 300 mm focal length was used. Thus the process could be run in the focus of the laser, which has a specified spot geometry. The result was increased stability of the cladding process with a large parameter window. Porosity free and near crack free nickel based coatings with a high content of globular WC were applied to metal surfaces of oil milling equipment. Besides the process description, an example of laser integration into a 3-axis milling workstation is presented