Applications for laser cleaning

The laser is becoming the most preferred method for surface cleaning of materials.

Fig1 Web

ALEX FRASER

From manufacturing plants and medical labs to the automotive, aviation, and steel fabrication industries, the laser is becoming the most preferred method for surface cleaning of materials.

Although the use of lasers in cutting, drilling, and welding applications is well known, its current adaptation in industrial cleaning applications is relatively new and unexplored.

This current application of lasers came as a result of the need for a nonhazardous, nonabrasive cleaning method that could be used as a substitute in applications where chemical, manual, and abrasive blasting methods were formerly used.

Benefits of using lasers in cleaning applications

Key problems presented by conventional cleaning methods include negative environmental impact and wear on the substrate. Abrasive blasting systems created significant amounts of waste and damaged delicate surfaces, while the use of chemical solvents resulted in potentially hazardous vapors and liquid waste products.

This led to the adaptation of laser technology in surface cleaning applications. Due to its many benefits, laser cleaning is now the most effective method of removing unwanted matter from the surface of materials.

Currently, there is a wide array of pulsed laser cleaning and de-coating systems used in various applications ranging from removing vulcanizing residue from tire molds and engraving surfaces by ablation to stripping insulation from conductors and de-coating paint from delicate surfaces.

Some of the many benefits of using lasers in surface cleaning applications include:

  • Automated and nonrandom cleaning method
  • Reduced amount of waste products
  • Increased safety
  • No need for chemicals or blasting media
  • Nonabrasive and noncontact cleaning process

Laser cleaning applications

Surface profiling and rust removal in steel fabrication. Laser cleaning is also an effective and efficient method for removing rust and scale from metallic materials. Rust and scale are contaminants that form on metal surfaces as a result of natural or artificial processes. When metals are exposed to moisture, they react with water to form ferrous oxides, resulting in rust. This rust degrades the quality of the metal, making it unsuitable for use in various applications.

Fig1 Web

(Source: worldsteel Image Library)

On the other hand, scales form on metal surfaces as a result of heat treatment processes and its oxide discolors the metal surface, preventing any subsequent finishing operations.

Removing these unwanted surface deposits requires the execution of descaling processes to provide smooth surfaces for prefinishing and finishing processes such as electroplating.

Conventional rust removal and descaling operations involve the use of physical methods such as blasting, polishing, scraping devices, extra blows, and wire brushes. Chemical methods such as alkali descaling and acid descaling (pickling) can also be used for scale removal. However, these methods are very abrasive and result in environmental pollution and damage to the substrate metal.

To avoid these disadvantages, laser cleaning has become the preferred method for rust removal and descaling operations. The rust/scale is removed by directing a laser beam with high peak power and repetition rates on the rusted layer.

The laser must be fired in short pulses to avoid damage to the substrate being worked on. The rust rapidly absorbs the energy of the laser beam, resulting in increased temperature levels. Once the temperature is sufficiently high, the rust melts and eventually vaporizes.

Using pulsed fiber lasers is the preferred option since it provides greater control over power, wavelength, and pulse duration, allowing the rust/ scale to vaporize without any damage to the underlying material.

The laser cleaning process can also be applied to surface profiling. Before protective coatings can be applied to fabricated steel parts for preservation and protection from corrosive action, their surfaces must be clean and free from all contaminants.

Surface profiling/preparationentails the removal of all contaminants from the surface of steel parts in preparation for protective coating applications. These contaminants include oil, grease, scale, hydrates and oxide layers, shop-primer, etc. For any subsequent processes, the bars, wires, and profiles must also be free from these contaminants.

Since fiber laser cleaning uses a nonabrasive, noncontact approach without the involvement of solvents, chemicals, or abrasive media, it is ideal for surface profiling and rust/scale removal. The cleaning process can be conducted on a small or large scale and can be automated. Laser cleaning is an environmentally friendly and cost-effective way to remove rust and prepare the surfaces of rolled steel products and fabricated steel parts for protective coating.

Anode assembly cleaning. The aluminum smelting industry uses carbon blocks as "sacrificial" anodes in the production of primary aluminum. The quality of the anode has an impact on the environmental, economic, and technological aspects of aluminum production. A small percentage of cell power is devoted to overcoming the electrical resistance of prebaked anode.

Fig2 Web

(Source: Flickr)

The presence of dirt and other contaminants will increase the anode's electrical resistance, resulting in the consumption of more cell power. The presence of contaminants also reduces the lifespan of the anode by increasing its rate of consumption during the smelting process. From the standpoint of efficiency, it is necessary to clean and remove all surface contaminants from anode assemblies before they are used in aluminum smelting operations.

In addition, anode assemblies are valuable tools that can be reused, but only after executing a thorough and careful treatment of its main components—under specific conditions.

Laser cleaning meets the specific conditions under which anode assemblies can be treated for reuse. It can be used in the following applications:

  • Removal of residue from carbon butts
  • Cleaning of cathode bars
  • Removal of contaminants and dirt from thimbles and stub rods

Adhesive bonding preparation for metals. To increase process stability, surface adhesion, and better seam quality, the surface of the metallic materials to be joined must be prepared before the application of welding and other joining techniques.

Without the necessary groundwork, joints and seams become susceptible to degradation, increased wear, and catastrophic failure. Laser cleaning can be used to prepare surfaces before they are joined, resulting in excellent bond strength quality for improved corrosion resistance and durability.

Laser cleaning is suitable for adhesive bonding preparation since it removes oxides and other contaminants such as grease and oxides that reduce the strength of adhesive bonds. It is particularly suitable for applications involving curved or flat surfaces or parts with certain limitations for highly complex 3D geometries.

One of the major benefits of laser cleaning is the ability to fine-tune its power and wavelength for precise modification of metals such as magnesium and aluminum to be used for microstructuring purposes. It also endows materials with very high resistance to corrosive elements, ensuring stable, long-lasting adhesive bonding.

In recent times, there is an increased use of adhesive bonds in structural design applications in place of conventional joining techniques such as riveting and welding. This is attributed to the many advantages of adhesive bonding over conventional techniques.

These advantages include uniform stress distribution, corrosion reduction, structure lightening, vibration attenuation, and acoustic insulation. However, these benefits can only be achieved if the surfaces to be bonded are prepared, degreased and carefully cleaned.

Laser cleaning is ideal for such applications since it carefully removes oils, rust, protective coatings and other contaminants resulting from shipping without harm to the underlying substrate.

Pretreatment for brazing and welding. Laser cleaning has also proven effective in pretreatment applications for welding and brazing. Before aluminum and steel materials are used for welding purposes in shipbuilding, precision tool manufacturing, automotive, and other related industries, their surfaces must first be prepared.

Laser weld preparation is one of the many applications of laser cleaning and helps to remove ferrous and nonferrous metals, lubricants, and other contaminants from metal and aluminum surfaces in preparation for high-quality welds. It also ensures smooth and pore-free brazed seams.

When used in pretreatment processes for welding and brazing, laser cleaning does the following:

  • Thorough removal of shop-primer, hydrates, and oxide layers
  • De-greasing and de-oiling

Apart from welding and brazing preparation, lasers can also be used to remove weld residues such as residual flux and oxide materials as well as thermal stains from finished weld joints. This cleaning method is particularly beneficial for stainless steel parts since laser light suspends grain boundaries, ensuring that weld seams are passivated—thus increasing corrosion resistance.

The benefits of using laser cleaning in welding and brazing pretreatment applications include:

  • Adjustable wavelengths and power for precise treatment of joining surfaces over a wide range of material thicknesses
  • No damage to the underlying substrate—that is, the galvanized layers of sheet steel

Partial decoating. Laser cleaning is particularly effective in applications that require the partial removal of paint or coatings from finished surfaces. It can be used on virtually all surface types, whether chemically anodized, oxidized, or organic. Laser cleaning can be used to de-coat solar panels and remove paint in the automotive and aerospace industries while maintaining the integrity of the primer substance.

In de-coating applications, fiber lasers are the preferred option. They obviate the need for masking by precisely removing the layer of coating in the specified area, thus eliminating some of the challenges inherent in partial de-coating applications. Lasers can be used in:

  • Precise treatment for functional and design surfaces
  • Creating Faraday cages and continuity contacts for the aerospace industry
  • Partial removal of paint for electromagnetic compatibility
  • Produce bond points for wire connections
  • Strip coating in the electronics and automobile industry

Laser cleaning is highly effective in situations where critical weld seams on painted structures/parts must be de-coated for inspection purposes. The laser removes the coatings without the need for hand or power tools, abrasives, or chemicals that can hide the problem areas and cause further damage to the surface.

Selective paint removal. Selective paint removal represents one of the many applications of laser cleaning. In the automobile and aerospace industry, it is sometimes necessary to remove the top layer of paint while maintaining the primer. This is often the case when the top weathered coatings on vehicles need to be thoroughly removed before the application of a new paint finish.

Fig3 Web

(Source:Laserax)

Since the top layer of paint is physically and chemically different from the underlying primer, the power and frequency of the laser can be set to a frequency that only removes the top layer of paint.

The primer remains intact since the laser has no mechanical, chemical or thermal effect on it. This ensures the maintenance of the primer's corrosion resistance ability. When bare metal-to-metal contact is required for electrical continuity between parts, the laser cleaning process is preferred since it saves time and materials while improving the quality of the finished surfaces.

Conclusion

The possibilities of using lasers for polishing, surface cleaning, and coating removal is rapidly gaining traction. Depending on its application, the pulse frequency, fluence, and wavelength of the laser must be precisely chosen for cleaning, polishing, and ablation of the target materials. This is necessary to prevent any form of damage to the substrate material.

However, the laser cleaning technique is being used mostly for small parts and structures. There is a huge possibility for the technology to be adapted for cleaning large surface areas and huge equipment/structures. With current advancements being made in the field, this is sure to become a possibility in the not too distant future.

ALEX FRASER is vice president and CTO at Laserax, Quebec, QC, Canada; laserax.com.

More in Home