1.What are the principles and effects of laser engraving?
Galvanized steel sheets are primarily composed of two layers:
1. Surface layer: zinc (galvanized layer).
2. Base material: cold-rolled steel sheet.
During laser engraving, by precisely controlling the laser energy and scanning speed, the zinc layer can be vaporized and removed from a specific area without causing deep damage to the underlying steel substrate. Because zinc is silvery-white and the steel substrate is gray-black, removing the zinc layer reveals the gray-black substrate, creating a clear black-white contrast.
Light engraving: Only the zinc layer is removed, revealing the gray-black steel substrate. This is the most common and desired effect, providing good contrast and minimal impact on corrosion resistance.
Deep engraving: Excessive laser energy can not only vaporize the zinc layer but also melt portions of the steel substrate. This can result in:
The marking color may become lighter (molten steel will reflect light).
Microscopic slag and unevenness may form.
Severely impairing the corrosion resistance of the area.
2.How to choose a laser?
Fiber laser: This is the preferred option. Fiber lasers (wavelength approximately 1060nm) have a very high absorption rate for metal materials and are particularly well-suited for materials like galvanized sheet metal. They offer advantages such as high beam quality, high precision, high speed, and low maintenance.
CO2 lasers: This can also be used, but their absorption rate for metals is relatively low, requiring higher power, and they are more prone to slag generation. Their edge quality may not be as good as that of fiber lasers.
3.How to optimize parameters?
Power: Medium to low power is required. Excessive power can burn through the zinc layer and damage the steel substrate.
Speed: Scanning speed should be fast. High speed combined with appropriate power can vaporize the zinc layer rather than melt it, resulting in crisp, clean edges.
Frequency: Adjust the frequency appropriately to find the "sweet spot" that effectively removes the zinc layer without overheating.
Fill spacing: The distance between fill lines should be appropriately set. Too close together will cause heat accumulation, while too sparse will result in incomplete fill.
4.What are the main challenges and problems?
Zinc Vapor and Spatter: Zinc has low melting and boiling points (boiling point approximately 907°C). During laser irradiation, zinc vaporizes rapidly, potentially carrying molten zinc particles with it. These particles condense and form difficult-to-remove zinc slag around the engraved area, affecting both aesthetics and cleanliness.
Surface Reflection: The galvanized sheet's smooth surface has high reflectivity, which reflects some of the laser energy. Therefore, the equipment must be well protected.
Corrosion Damage: This is the biggest application limitation. The engraved area loses the sacrificial protection of the zinc layer, making it a potential starting point for rust. This should be carefully considered if the product is used in a highly corrosive environment.
Heat-Affected Zone: The heat generated by the laser can cause microstructural changes in the zinc layer at the edge of the engraving, potentially slightly affecting its performance.
5.What is the summary of advantages and disadvantages?
Advantages:
Permanent: The mark is permanent and cannot be easily erased.
High Precision: Capable of engraving very fine QR codes, barcodes, text, and complex patterns.
Non-Contact: No physical pressure or deformation is applied to the sheet material.
High Efficiency: High engraving speed, suitable for in-line marking on automated production lines.
Environmentally Friendly: No consumables such as ink are required, making the process clean.
Disadvantages:
Localized loss of corrosion resistance: The engraved area is susceptible to rust.
Complex process debugging: Parameters must be repeatedly tested for different zinc layer thicknesses and surface conditions (e.g., smooth finish, no spangles, etc.).
Potential spatter: Impacts the aesthetics and cleanliness of the mark.
Equipment Investment Cost: A high-quality laser marking machine is a significant investment.