Diode Laser Cladding Produces High Quality Coatings


A high power direct diode [HPDDL] laser and its unique beam make for a highly efficient tool to use in cladding operations. Laser cladding is performed by melting a pre-placed powder onto a substrate to ensure a bond with minimal dilution, nominal melting and a small heat affected zone. The laser used in the experiment was the Nuvonyx ISL-4000L laser mounted on a Panasonic VR-16 robot. The pre-placed powders chosen for this experiment are ANVAL 410, 156 and C22. 410 and C22 were selected for their superior corrosion resistance. 156 is a general-purpose cobalt hardfacing material. The cladding substrate was ASTM 1018 steel. The dilution of the coatings was analyzed through the use of a Scanning Electron Microscope [SEM]. Through analysis it was discovered that dilution is kept to a minimum, in the range of 0 to .02%. The corrosion resistance and wear resistance was also measured for the appropriate samples. This process is highly advantageous in comparison with competing coating methods such as plasma spraying, arc welding, and other laser sources. The rewards being lower porosity, reduced post-machining, optimum edge detail.


Introduction

As tools for use in industrial applications, HPDDL, also known as semiconductor lasers, are becoming more prevalent.1,2,3 Diode laser technology has been used for a number of years in compact disks, laser printers and laser pointers. Their low cost, high efficiency, and compact design make them an attractive technology in the industrial manufacturing environment. The electrical to optical conversion efficiency of the HPDDL is as high as 55%.

The light emitted at the facet of the laser diode is highly divergent and astigmatic. To make this usable, a lenslet array is close coupled to a two dimensional array of laser diodes. Since the other axis, referred to as the "slow axis," is not collimated and is left to diverge, the final focusing lens will produce a concentrated line of light, which is very useful for large area applications such as cladding. This beam is very uniform, having a nearly tophat intensity profile along the long axis with a guassian profile perpendicular to the line along the short axis. The HPDDL used in this feasibility study employs 4 stacks of 20 bars, which are brought to a line by a single macro lens [Figure 1]. With dimensions of approximately 12.5 mm X <1 mm with a 125 mm focal length lens. With different macro lenses this laser can achieve power densities greater than 200 kW/cm²