This article will explore the process of laser cleaning technology in the context of cleaning metal surfaces, including how it works and why it is advantageous.
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What is laser cleaning technology?
Light amplification by stimulated emission of radiation (laser) is a monochromatic, coherent electromagnetic source that propagates in a straight line with negligible divergence. Lasers are currently used in a variety of material processing applications in the manufacturing sector, ranging from surface cleaning to nanofabrication.
Laser cleaning represents a non-destructive, non-contact cleaning method that allows the removal of surface contaminants from most material in a controlled manner using a laser beam. Thus, laser cleaning machines are gradually becoming the equipment of choice for the containment removal/cleaning process.
The appropriate laser type and optimal settings differ for each cleaning application. The laser output parameters can be varied on a large scale in the laser cleaning method. Thus, specific laser output parameters can be selected based on the material/contaminant to be removed.
Steam cleaning and dry cleaning are the main types of laser cleaning methods used to remove surface contaminants. Dry laser cleaning involves powder laser heating of a dry solid surface, while vapor laser cleaning involves powder laser heating of the solid surface in the presence of a liquid layer.
Dry laser cleaning becomes evaporative cleaning when the energy of the incident laser pulse is increased. Although this technique is simple, dry cleaning is less effective compared to steam cleaning and requires a higher laser intensity. Also, dry laser cleaning can cause damage to the metal surface.
How laser cleaning technology works
Laser cleaning is primarily a form of laser ablation that occurs when a material deposited on a surface or layer of material is removed using a laser beam. Laser rust removal on steel and other materials is based on the laser ablation process.
However, laser ablation of material only occurs when the energy of the incident laser beam is greater than the ablation threshold of that material. Each material has a specific ablation threshold based on its molecular bonds, and the threshold differs from other materials.
Thus, one material can be ablated in a highly selective manner during laser cleaning without affecting the other material when the difference between the ablation thresholds of two materials is large enough.
For example, the ablation threshold of rust is significantly lower compared to the threshold of steel or aluminum, which allows the use of laser cleaning machines to completely vaporize the rust without damage the underlying steel.
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Although pulsed and continuous laser beam cleaning processes can be used to effectively remove a layer, the speed of the process varies depending on the laser beam used for cleaning.
The pulsed laser beam is more efficient and offers a faster removal rate compared to the continuous laser beam. In addition, the use of a pulsed laser beam can prevent overheating of the underlying metal.
Advantages and disadvantages of laser cleaning technology
Laser cleaning is environmentally friendly, consumable-free and requires no chemicals or solvents, as this method only uses a laser beam to vaporize a layer. In addition, laser cleaning machines do not pose any risk to operators, as these machines are designed to meet all safety standards.
Other important advantages of using laser cleaning technology include high productivity, lack of mechanical damage to the surface and remotability. Therefore, laser cleaning is the safest method currently available to remove rust. However, the difficulty in discriminating the ablation thresholds between the substrate and the contaminant layer is a major disadvantage of this technology.
Types of laser cleaning systems
Robotically controlled solid-state lasers used in tire mold cleaning showed higher cleaning speed compared to conventional abrasive cleaning methods. Similarly, a neodymium: yttrium aluminum garnet (Nd: YAG) laser cleaner was recently used to clean railroad sheets. Nd:YAG lasers improve the flexibility of the cleaning process and are more reliable and free from operational failures compared to other lasers.
Large surfaces are laser cleaned using transversely excited atmospheric pulsed carbon dioxide (CO2) lasers with power outputs of several kilowatts. The 10.6 µm laser output length of these lasers makes them suitable for cleaning metal substrates, as metals highly reflect this laser wavelength, ensuring removal of only organic contamination. However, achieving uniform energy distribution is difficult in high-power CO2 lasers.
Main industrial applications of laser cleaning technology
Laser cleaning is typically used for rust removal and surface profiling in steel fabrication, anode assembly cleaning, adhesive bond preparation for metals, pretreatment for welding and brazing strong, partial uncovering, selective removal of paint and removal of dirt from metal mold surfaces.
New studies on laser cleaning technology
In a study published in the journal MATEC Web of Conferences, researchers experimentally investigated the effect of different key laser parameters, such as the number of passes and scan speed, on the removal depth and properties of the surface, such as surface profile, hardness and roughness, after laser cleaning.
A moving pulsed laser beam was used to irradiate the rusted mild steel samples. The removal depth increased with increasing laser power and number of scans and decreased with increasing scan speed. The surface was deformed and discolored after laser cleaning at higher powers and lower laser speeds.
The final surface roughness and surface profile after laser processing depended on the laser scanning patterns. Thus, the surface roughness values of the laser cleaned parts were not related to the initial surface roughness values before laser cleaning.
In addition, the surface hardness increased significantly after laser treatment. The microhardness values varied with the laser beam scan path, indicating changes in the microstructure due to laser cleaning.
Single passes at higher velocities resulted in a very clean surface, while multiple passes resulted in random changes in surface topology at lower velocities and specific changes in topology at higher velocities.
In summary, unconventional laser cleaning technology has emerged as an environmentally friendly and simple method and a suitable alternative to conventional cleaning processes to increase the effectiveness and quality of metal surface cleaning.
More from AZoM: Improving the effectiveness of laser heat treatment with laser beam profiles
References and further reading
Hirmaz, MS (2019). Laser cleaning of metal surfaces: a review. International Journal of Scientific Research and Engineering, Volume 10, Number 7. ISSN 2229-5518. https://www.ijser.org/researchpaper/Laser-Cleaning-of-Metal-Surfaces-A-Review.pdf
Marla, D., Singh, RK, Narayanan, V. (2018). Laser cleaning for rust removal in mild steel: an experimental study on surface characteristics. MATEC Web of Conferences221, 01007. https://doi.org/10.1051/matecconf/20182210100