8 Décembre 2015
Advanced industrial lasers have evolved well beyond simple cutting and welding applications. Laser technology now offers an industrial de-coating and surface cleaning solution that is cost effective as well as responsive to environmental concerns. From the automated cleaning of molds to precise de-coating to oxide removal, laser surface treatments are proving to be an attractive option to traditional labor-intensive methods.
In the past decade laser paint removal and cleaning systems have generated significant interest as a viable alternative to conventional cleaning and paint removal technologies.fiber laser marking machine Research on mobile, reliable, and powerful laser systems for cleaning and paint removal operations began in the late 1980s with the modification of welding or cutting lasers into laser systems for surface preparation. This approach did not meet the requirements for surface preparation, which are significantly different than for cutting and welding.
In the early 1990s, research took place around the world for more efficient, reliable laser systems for surface preparation work. It took another few years to develop the technology from experimental laboratory systems to dependable systems capable of use in day-to-day industrial operations. Today, a wide variety of industries have adopted laser systems for a range of surface preparation tasks. Applications include mold cleaning, paint removal, joining pretreatment, oil and grease removal, and many more.
The laser generates a directed and monochromatic beam of light which typically is tightly focused to create high power density. At the focal point, the energy of the intense laser beam will be absorbed by the contamination or paint layer, thermally incinerating or sublimating the target material, such as paint or contamination (see FIGURE 1). These processes will, in combination with the resulting micro-thermal shockwave,fiber laser marking machine remove the target material as long as the target material is able to absorb the incident laser energy. The better the target material absorbs the energy, the faster it can be removed.
Color, chemical composition, and thickness of the target layer all have a direct impact on the effectiveness of the process. The removal process automatically stops once a metal, or otherwise relatively reflective, substrate is reached.
Reflective surfaces do not generally readily absorb the laser energy.
Any residual heat transfer into the substrate material can be a critical factor.
To minimize this effect, many laser equipment manufacturers use pulsed laser sources. The beam intensity (laser power per beam spot) is a critical parameter for the heat transfer into the substrate material. Very short laser pulses with a pulse duration of only a few nanoseconds (ns) in combination with a very small focus diameter (0.02 in) or longer pulses in the millisecond (ms) range with a larger focus diameter (0.2 in) result in a minimal heat transfer into the substrate material. Under normal operating conditions and with the right process parameters, damage to the substrate material can be avoided.
The heat transfer factor of continuous-wave laser systems is much higher and might result in substrate temperatures that will damage the substrate. Test results with a handheld pulsed Nd:YAG laser with an average laser power of 500W (peak power of more than 400kW) on an aircraft aluminum sheet resulted in maximum substrate temperatures of 170 °F.
Pulsed laser systems generate laser power levels well beyond the average power of the laser source.fiber laser marking machine A pulsed 150W solid-state laser will generate a peak pulse power of more than 160kW. This high peak power and the above mentioned beam parameter result in a power intensity removing many target materials with acceptable production rates.
Currently, there are three different kinds of laser sources available for
surface preparation works. The main difference is the laser beam generation and the resulting beam delivery configuration.