How Does Laser Cleaning Affect Surface Roughness and Cleanliness?

Laser cleaning utilizes the characteristics of laser beams such as high energy density, controllable direction, and strong convergence ability to destroy the binding force between the contaminant and the substrate or directly vaporize the contaminant to remove contaminants, thereby reducing the bonding strength between the contaminant and the substrate, and thus achieving the effect of cleaning the surface of the workpiece. When the contaminant on the workpiece surface absorbs the energy of the laser, it quickly vaporizes or expands instantly due to heat to overcome the force between the contaminant and the substrate surface. Due to the increase in heat energy, the contaminant particles vibrate and fall off the substrate surface. Laser cleaning can change the grain structure and orientation of the substrate surface without damaging the substrate surface, and can also control the surface roughness of the substrate, thereby enhancing the comprehensive performance of the substrate surface. By adjusting the laser parameters for different materials, the roughness and cleanliness of the material surface can be affected to maximize the cleaning effect.

Understanding Surface Roughness and Cleanliness

Understanding surface roughness and cleanliness helps us understand the impact of the laser cleaning machine on the material surface.

Surface Roughness

Surface roughness refers to the roughness of the machined surface of parts with small spacing and small peaks and valleys. It is usually defined as the small distance (wave distance) between two wave peaks or two wave valleys. In general, the wave distance is within 1mm or less. It can also be defined as the measurement of micro-contours, commonly known as micro-error values. In engineering, surface roughness is defined as the small local deviations of the surface from the nominal shape. These deviations may be caused by manufacturing processes (machining, casting, etc.) or may occur naturally (oxidation, corrosion, etc.). These local surface irregularities can have a significant impact on the function and performance of engineering surfaces.

Surface Cleanliness

Surface cleanliness refers to the degree to which specific parts of parts, assemblies and complete machines are contaminated by impurities. It is expressed by the quality, size and quantity of impurity particles collected from specified characteristic parts using specified methods. The “specified parts” mentioned here refer to characteristic parts that endanger product reliability. The “impurities” mentioned here include all impurities that remain in the product itself, are mixed in from the outside, and are generated by the system during the design, manufacturing, transportation, use and maintenance of the product.

Effect of Laser Cleaning on Surface Roughness

Cleaning Mechanism

Laser cleaning mechanisms can be roughly divided into two types: ablation and thermal effect. Ablation refers to the evaporation or decomposition of impurities on the surface of the material under the action of the laser. Laser cleaning does not produce thermal effects on the material itself. The thermal effect of laser cleaning refers to the thermal effect of impurities under laser irradiation, thereby being removed. The following are their specific principles.

Ablation

Each material has a specific ablation threshold based on its molecular bonds, and this threshold is different from other materials. When the laser hits the surface, its energy heats up and vaporizes or ablates the contaminants that are present. When the laser beam interacts with the surface, it vaporizes or ablates the unwanted material. This means that the intense heat generated by the laser causes the contaminants to evaporate or break down. This ablation process creates shock waves. The sudden expansion and heating of the contaminants creates shock waves that quickly remove them from the surface. These shock waves act as a strong push to effectively separate and eject the unwanted material.

Thermal Effects

The thermal effect on the laser cleaning machine refers to the process in which the laser cleaning machine focuses the laser beam and irradiates a high-energy-density beam onto the target surface. After the dirt, coating, or oxide on the surface absorbs the laser energy, it converts the energy into heat energy. After absorbing the laser energy, the surface of the material will heat up rapidly, forming a high-temperature area. This high temperature can cause the dirt or coating to loosen, decompose, or volatilize, thus facilitating subsequent physical removal. The thermal effect directly affects the effect of laser cleaning. High temperature can accelerate the decomposition and evaporation of dirt, making the cleaning process more thorough and efficient. At the same time, the thermal effect can also improve the roughness and adhesion of the surface, making subsequent cleaning and processing easier. In laser cleaning, the impact of the thermal effect needs to be controlled and optimized to ensure that no damage to the material or surface is caused. By adjusting the laser power, pulse duration, repetition frequency and other parameters, the size and depth of the thermal effect can be precisely controlled to adapt to different cleaning needs and material types. In summary, the thermal effect on the laser cleaning machine refers to the use of heat energy generated by laser energy to help accelerate the removal of dirt during the cleaning process.

Laser Parameters

Laser cleaning can change the grain structure and orientation of the substrate surface without damaging the substrate surface, and can also control the surface roughness of the substrate, thereby enhancing the comprehensive performance of the substrate surface. When applying laser cleaning technology, it is necessary to select appropriate laser parameters to achieve the best cleaning effect. Here we mainly discuss the effects of pulse duration, smoothness, spot size and beam quality on surface roughness.

Pulse Duration

Shorter pulse duration: Short-pulse lasers (such as nanosecond lasers) often allow more precise control of the release of energy, thereby reducing the thermal impact on the substrate. This short pulse helps reduce thermal diffusion and overheating of the material surface, thereby reducing damage to the substrate and the increase in roughness. In this case, the laser energy is mainly concentrated on the contaminants and can more effectively remove surface contamination without significantly changing the microstructure of the substrate surface.
Longer pulse duration: Longer pulses (such as microseconds or longer) may cause greater heat diffusion, thereby increasing the heat-affected area on the substrate surface. This may cause the formation of a molten layer, vaporization or ablation on the material surface, leading to an increase in surface roughness. Long pulses may also cause excessive material removal or uneven thermal effects, thereby increasing surface roughness.

Pulse duration plays an important role in laser cleaning. In practical applications, we need to find the most suitable pulse duration through experiments to meet specific material processing requirements.

Pulse Smoothness

High pulse smoothness: means that the energy output of the laser pulse is more uniform and stable, which usually reduces the thermal impact and local over-removal in the surface treatment of the material, and obtains a smooth surface and lower roughness.
Low pulse smoothness: may lead to unstable pulse energy, resulting in uneven heating of the material surface, more molten layers or vaporization, and increased roughness.

In general, high pulse smoothness can reduce surface roughness.

Spot Size

For applications that require high precision and delicate processing (such as micromachining or precision cleaning), a smaller spot size will be more suitable.
For large-area cleaning or processing (such as removing large areas of rust or pollution), a larger spot size may be more effective.

The spot size has a great influence on the surface roughness. In practical applications, we need to find the appropriate spot size through experiments to meet the specific material processing requirements.

Beam Quality

High beam quality: High beam quality means that the divergence angle of the laser beam is small and the energy distribution is uniform, which can provide more consistent processing results, reduce local overheating and melting, and thus reduce surface roughness. Higher beam quality helps to achieve more precise processing, can process small structures and features, and further reduce roughness.
Low beam quality: Low beam quality may cause uneven energy distribution of the laser beam, resulting in larger spot size and more heat-affected area, which may lead to uneven surface treatment and higher roughness. Low beam quality affects the accuracy and detail performance of the processing, and increases the defects and roughness in the surface treatment.

In practical applications, the beam quality and its related parameters are adjusted through experiments to find the most suitable settings to achieve the ideal surface roughness. High-quality beams are more likely to obtain low roughness.

Material Properties

During the laser cleaning process, the characteristics of the material itself have a significant impact on its surface roughness, which is mainly reflected in the following aspects.

Thermal Conductivity

High thermal conductivity: Materials with high thermal conductivity can diffuse laser-induced heat from the laser action point to the surrounding area more quickly, reducing local heat accumulation. This can reduce the degree of local melting and vaporization, thereby reducing surface roughness. The high thermal conductivity of the material helps to distribute the laser energy more evenly and reduce surface unevenness caused by thermal gradients.
Low thermal conductivity: Materials with low thermal conductivity can cause laser energy to concentrate in the surface area of the material, resulting in a larger heat-affected zone. This can cause local melting, vaporization, or ablation, thereby increasing surface roughness. Low thermal conductivity materials may also produce greater thermal stress, causing material deformation or cracking, further increasing roughness.

Absorption Coefficient

High absorption coefficient: A high absorption coefficient means that the material can effectively absorb laser energy, thereby improving the local heating effect. Appropriate energy absorption helps to effectively remove contaminants, but too high absorption may cause excessive heating and increase roughness. A high absorption coefficient generally improves cleaning efficiency and makes contaminants more thoroughly removed, which helps to achieve a smoother surface, provided that the thermal effect is controlled.
Low absorption coefficient: Materials with low absorption coefficients absorb lasers poorly, which may result in the laser energy not being effectively used to remove contaminants or surface treatment, reducing the cleaning effect and may require more energy or longer processing time. Low absorption coefficients may result in poor cleaning results and incomplete removal of contaminants, which affects surface quality and roughness.

The thermal conductivity and absorption coefficient of materials have a significant impact on the surface roughness in laser cleaning. Understanding and considering these characteristics can help optimize the laser cleaning process and adjust laser parameters to achieve the desired surface quality.

Effect of Laser Cleaning on Surface Cleanliness

Selective Pollutant Removal

Laser cleaning can remove various types of contaminants from the surface of various materials, achieving a cleanliness level that cannot be achieved by conventional cleaning. It can also selectively clean contaminants on the surface of materials without damaging the surface of the materials. Laser cleaning is highly efficient and saves time.

Cleaning for Specific Contaminants

Laser cleaning can precisely control laser parameters such as wavelength, pulse duration and energy density to effectively remove specific types of contaminants. For example, by adjusting the laser wavelength and energy density, rust, oil, coatings or other contaminants can be specifically cleaned. This selective removal capability enables laser cleaning to remove contaminants in a targeted manner without damaging the substrate, thereby improving surface cleanliness.

No Residual Waste

Contaminants in the laser cleaning process are usually directly gasified or evaporated, reducing the waste residue problem common in traditional cleaning methods. Because contaminants are quickly converted into gas under the high energy of the laser, the amount of waste generated by laser cleaning is small and easy to handle. This feature helps ensure that the surface after cleaning is clean without worrying about the impact of chemical residues or solid waste on the surface cleanliness.

Maintaining Substrate Integrity

Laser cleaning machines are suitable for a wide range of applications in various fields. They can effectively clean a variety of contaminants and coatings while maintaining the integrity of the substrate.

Non-Destructive Cleaning

Laser cleaning is a non-contact cleaning technology that does not require mechanical contact or wear, and can effectively reduce physical damage to the substrate. The laser beam can accurately act on the contaminant layer without causing direct wear or scratches on the substrate, thereby maintaining the original surface state of the substrate and ensuring the substrate integrity and surface cleanliness during the cleaning process.

Minimum Heat Affected Zone

During the laser cleaning process, high-precision control of the laser beam minimizes the heat-affected zone. By properly controlling the laser pulse duration and energy density, the heat can be concentrated on the contaminants without having a significant impact on the substrate. This can avoid deformation, melting or other thermal effects on the substrate surface caused by heat diffusion, further ensuring the cleanliness of the surface after cleaning.

Optimizing Surface Roughness and Cleanliness for Laser Cleaning

Material Properties and Compatibility

Material type: Understand the physical and chemical properties of the material to be cleaned, including melting point, thermal conductivity, reflectivity, absorption coefficient, etc., in order to select the appropriate laser type and parameters.
Compatibility analysis: Evaluate the compatibility of the material with the laser cleaning process to ensure that the laser will not damage the material or change its surface properties.

Laser Parameter Optimization

Laser wavelength selection: Select the appropriate laser wavelength according to the absorption characteristics of the material to improve cleaning efficiency and effect.
Power and energy density: Adjust the laser power and energy density to ensure that contaminants can be effectively removed without damaging the material itself.
Pulse width and frequency: Optimize the pulse width and frequency of the laser to achieve the best cleaning effect and surface roughness control.
Scanning speed and overlap rate: Adjust the scanning speed and overlap rate of the laser beam to ensure uniform cleaning and improve surface finish.

Process Validation and Quality Control

Experimental verification: Process verification is carried out under laboratory conditions to find the best cleaning solution by testing different parameter combinations.
Quality inspection: Use optical microscopes, scanning electron microscopes (SEM) and other inspection methods to evaluate the surface roughness and cleanliness after cleaning.
Standardized process: Establish standard operating procedures and quality control standards to ensure the repeatability and consistency of the cleaning process.
Feedback and improvement: Continuously optimize and adjust the cleaning process based on quality inspection results and actual application feedback.

Operator Training and Skills Development

Training plan: Develop a detailed training plan for operators to ensure that they understand the basic principles of laser cleaning and equipment operation.
Skill improvement: Help operators master the skills of laser parameter adjustment and process optimization through practical operation and technical exchanges.
Safe operation: Train operators to identify and prevent possible safety hazards and ensure the safe use of laser equipment.
Continuing education: Regularly organize technical updates and training courses to keep the operator’s skill level in sync with technological progress.

Summarize

Laser cleaning is an efficient and environmentally friendly surface treatment technology that can effectively improve the surface roughness and cleanliness of materials. High-quality laser cleaning effects can be achieved by understanding material properties, optimizing laser parameters, and applying advanced surface analysis techniques. In industrial production, continuous process improvement and enhanced operator training will further enhance the application value of laser cleaning.

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Choosing the right laser cleaning machine can help optimize power consumption and achieve high operational efficiency. Working with a trusted supplier ensures access to advanced technology, tailored advice and ongoing support. At AccTek Laser, we offer a comprehensive range of laser cleaning equipment designed to meet a variety of industrial needs. Our experts can help you choose the most energy-efficient model and configuration, taking into account factors such as material type, thickness and production volume. We also offer cutting-edge features such as high-efficiency laser generators, intelligent cooling systems and energy management software to maximize performance and minimize energy use. In addition, our team provides regular maintenance services and technical support to keep your equipment at peak efficiency. By partnering with us, you can achieve significant energy savings, reduce operating costs and enhance your sustainability efforts. If you have any questions, please contact us in time, AccTek Laser is committed to providing every customer with perfect laser solutions!

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