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How to Adjust a Laser Marking Machine to Fix Whitening and Yellowing
When using a laser marking machine, you might encounter issues where the markings appear whitish or yellowish. This not only affects the aesthetic quality of the mark but can also reduce the overall product quality. Below is a detailed analysis of the causes and methods for adjusting these issues.
# Causes of Whitening and Yellowing
1. Power Setting is Too High: One of the main reasons for yellowing is an excessively high laser power setting. High power causes the material's surface to overheat, leading to carbonization or oxidation, which results in a yellow color.
2. Marking Speed is Too Slow: A slow marking speed means the laser dwells on the material's surface for too long. This excessive heat exposure can cause the material to yellow.
3. Material Properties: Some materials are more prone to whitening or yellowing when exposed to a laser. For example, if the parameters for marking stainless steel are not set correctly, an oxidation layer can form, leading to a color change.
4. Aging Laser Source: An aging laser source can lead to unstable power output, which negatively impacts the marking quality. An older laser might generate too much heat at high power settings, causing the material's surface to turn yellow.
# Adjustment Methods
1. Reduce Power: If your markings are yellowing, try lowering the laser power. Generally, reducing the power to 50-70% can effectively lessen the yellowing effect. For metals like stainless steel, a power setting of 50-80% is recommended to create a clear mark without generating too much heat.
2. Increase Marking Speed: Increasing the marking speed to 500-800 mm/s reduces the time the laser spends on the material's surface, preventing excessive heat buildup and subsequent yellowing. While the speed can be lowered for detailed marks, it's best to increase it for large-area markings to minimize heat accumulation.
3. Adjust Pulse Frequency: The pulse frequency significantly influences the marking color. Higher frequencies (e.g., 80-100 kHz) are suitable for lighter marks, while lower frequencies (e.g., 20-50 kHz) enhance the heat accumulation effect, making them ideal for darker marks. If your marking is coming out whitish, you can try lowering the frequency to around 30 kHz.
4. Optimize the Material Surface: Before marking, ensure the material's surface is clean and free of any oxidation layers. For metals like stainless steel, you can perform sandblasting or chemical pre-oxidation to improve the marking quality. Using the appropriate materials and surface treatment processes can also help reduce whitening and yellowing.
5. Use a Suitable Laser Source: If your equipment is old or the laser source's performance has degraded, consider replacing the laser or performing comprehensive maintenance on the machine. For applications requiring colored markings, a MOPA fiber laser marking machine can be used, as it allows for a wider range of colors by adjusting pulse width and frequency.
6. Test Marking: After adjusting your parameters, it's crucial to perform a test mark on a scrap piece of material or in an inconspicuous area. Check if the color effect meets your expectations. By testing multiple times, you can find the optimal combination of parameters.
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# Summary
The issue of laser marking appearing whitish or yellowish is usually caused by excessive power, a slow marking speed, or specific material properties. You can effectively improve this issue by lowering the power, increasing the marking speed, adjusting the pulse frequency, and optimizing the material's surface. If the problem persists, it's best to consult your equipment's user manual or contact the manufacturer's technical support. Regular maintenance and replacing an aging laser source can also improve marking quality and extend the equipment's lifespan.
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