With the continuous advancement of modern industrial technology, laser cleaning technology is increasingly being used in various fields. In metal surface treatment, fiber laser cleaning, as an efficient and environmentally friendly technology, is gradually becoming the ideal solution for removing contaminants and oxide layers from metal surfaces. Especially for high-temperature oxide layers, fiber laser cleaning demonstrates unique advantages in terms of cleaning efficiency and precision. This article will discuss in detail the principles, challenges, and applications of fiber laser cleaning for removing high-temperature oxide layers.
1. Formation and Impact of High-Temperature Oxide Layers
High-temperature oxide layers refer to the metal corrosion caused by the reaction of metal materials with oxygen at high temperatures. Broadly speaking, high-temperature oxidation includes sulfidation, halogenation, nitridation, and carbonization, which commonly occur during the processing of various industrial metals such as steel, titanium, and aluminum.
2. Challenges in Removing High-Temperature Oxide Layers
In laser cleaning practice, compared to ordinary oxide layers, high-temperature oxide layers present three challenges:
Thickness Differences and Their Impact
The thickness of ordinary oxide layers is generally only tens of nanometers, while that of high-temperature oxide layers can reach micrometers, far exceeding that of ordinary oxide layers, with a thickness difference of up to a thousand times. This significant difference directly leads to a substantial decrease in cleaning efficiency.
Unique Properties of High-Temperature Oxide Layers
Unlike contaminants adhering to the surface of the substrate (such as paint, adhesive, etc.), high-temperature oxide layers are caused by an increase in oxygen defects within the metal substrate. Oxygen defects promote the diffusion of metal atoms, forming a denser oxide layer, which becomes an integral part of the metal substrate. In this case, the binding force between oxygen and carbon atoms that penetrate the metal surface is significantly enhanced, making the cleaning process more difficult.
Challenges to the Laser Cleaning Principle
Laser cleaning is a complex physicochemical process involving surface ablation, decomposition, ionization, degradation, melting, combustion, vaporization, vibration, explosion, and peeling. However, high-temperature oxide layers have stronger high-temperature resistance, making it difficult for ablation and vaporization-based cleaning mechanisms to work effectively, further increasing the difficulty of cleaning. These factors ultimately lead to the fact that the efficiency of laser cleaning for removing high-temperature oxide layers is generally only 1-1.5 m²/h, which cannot meet the efficiency requirements for industrial cleaning.
3. The principle of fiber laser cleaning oxide layer
Thermal Vaporization Effect: When a high-power laser beam irradiates the oxide layer, the local temperature rises rapidly (reaching several thousand degrees Celsius), causing the oxide (such as Fe₂O₃, Al₂O₃) to instantly vaporize or decompose into gas/microparticles, which are then carried away by the airflow. For example, rust on steel surfaces (mainly composed of Fe₂O₃·nH₂O) can be rapidly vaporized under the action of a nanosecond laser, achieving residue-free cleaning.
Plasma Shock Wave: High-energy density laser triggers plasma expansion on the surface of the oxide layer, forming a shock wave that removes hard oxide layers (such as titanium alloy oxide film). This “mechanical peeling” action avoids chemical corrosion and substrate damage.
Substrate Protection Principle: By adjusting laser parameters (such as power density, pulse width), the substrate temperature is kept below the damage threshold (e.g., <300°C for metal substrates), avoiding heat-affected zones (HAZ) or micro-damage.
4. Traditional Cleaning Methods
Previously, methods such as acid pickling, shot blasting, and sandpaper grinding were commonly used to clean oxide layers. However, these methods not only pollute the environment but are also inefficient, labor-intensive, and wasteful of manpower resources.
Fiber laser cleaning removes lubricants, black and colored metal impurities from metal surfaces, resulting in high-quality welds and brazed joints, with visible weld seams after cleaning. It is suitable for cleaning welded surfaces of steel and aluminum as a pre-treatment for welding or post-welding cleaning. It is widely used for brightening various stainless steels, removing various oil stains, rust, oxide scale, weld spatter, etc., restoring the original stainless steel color.
Currently, UMW’s cleaning efficiency for high-temperature oxide layers is a breakthrough in the domestic laser cleaning industry. This laser cleaning process means that a single machine can achieve a cleaning efficiency of 200-300 m²/day, which is an important step towards replacing acid pickling with laser cleaning, demonstrating UMW’s R&D and innovation capabilities.
5. Advantages of Laser Cleaning in Removing High-Temperature Oxide Layers
- Removes oxides and other impurities, improving metal corrosion resistance.
- Optimizes surface conditions before welding.
- Ensures a stable substrate-weld interface.
- No need for media or chemical reagents; the process is dry and clean.
Fiber laser cleaning is considered the most reliable and effective solution due to its advantages: non-abrasive, non-contact, no thermal effect, environmentally friendly, no pollution, and suitability for various materials. It can also address issues that traditional cleaning methods cannot solve.
6. Key Factors Affecting Fiber Laser Cleaning Results
Material Properties
- Metal materials: Steel, aluminum, titanium alloys, etc., have different laser absorption rates, requiring matching wavelengths and power. For example, aluminum has high reflectivity (>90%), requiring higher power (>500W) for effective cleaning; titanium alloys have low thermal conductivity, requiring lower power density (<200J/cm²) to prevent overheating and deformation.
- Non-metallic/composite materials: For example, carbon fiber composites require a suitable wavelength (532nm green laser) and power control to avoid substrate carbonization or delamination.
Oxide Layer Properties
- Thickness: Thin oxide layers (<10μm) can be easily removed with low power (50-200W) and short pulse width (nanosecond). Thick oxide layers (such as rust, hot-rolled oxide scale) require high power (500-2000W) and long pulse width (microsecond) for deep removal through thermal accumulation.
- Density: Loose oxide layers (like rust) are easy to clean; dense oxide layers (like Al₂O₃ film on aluminum) require higher energy density or auxiliary gas (like nitrogen) for enhanced removal.
7. Case Study
- Aerospace industry: In cleaning oxide layers on aircraft engine blades, fiber laser cleaning can completely remove dense oxide films (<50μm) on titanium alloys without thermal damage to the substrate, improving weld quality (reducing porosity to Grade I).
- Automotive Manufacturing: In pre-welding cleaning of automotive body panels, laser cleaning can thoroughly remove oxide layers from steel/aluminum surfaces (thickness <20μm), improving welding yield (reducing defect rate to below 0.02%).
- New Energy Industry: Before coating lithium-ion battery electrodes, laser cleaning can thoroughly remove oxide layers from copper/aluminum foil surfaces (thickness <5μm), ensuring uniform coating and improving battery consistency.
- Cultural Heritage Preservation: In cleaning bronze artifacts, ultra-low power (10-30W) and long pulse width (microsecond level) can precisely remove rust without damaging the artifact, avoiding secondary damage from chemical agents.
8. Advantages Compared to Other Cleaning Methods
- Compared to chemical cleaning: Fiber laser cleaning leaves no chemical residue, avoids substrate corrosion, and is more environmentally friendly (no wastewater).
- Compared to sandblasting: Laser cleaning avoids mechanical contact, preventing surface roughening or subsurface damage, and dust pollution is controllable (99.9% dust collection efficiency with a dust collection system).
- Compared to ultrasonic cleaning: Laser cleaning allows for localized, precise cleaning and is better suited for deep holes and complex structures.
Conclusion
Fiber laser cleaning for removing high-temperature oxide layers is an efficient and environmentally friendly surface cleaning technology with great application potential in metal processing, aerospace, automotive manufacturing, and other fields. While some challenges remain, with continuous technological advancements and decreasing equipment costs, fiber laser cleaning will undoubtedly become a key method for removing high-temperature oxide layers and other contaminants in the future.