Laser Marking Anodized Metal Surface Colour Control
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Solution Overview
Problem
Existing methods for laser marking anodized metal surfaces, particularly aluminum, face issues such as damage to the oxide layer and changes in mark appearance with viewing angle when using nanosecond pulses, which are not commercially viable due to high costs and thermal damage.
Innovation Solution
A method involving a laser system with controlled pulse parameters, including pulse width, repetition frequency, and scanner settings to create high-quality black marks on anodized metal surfaces without damaging the oxide layer, using a combination of spot to spot separation, hatch distance, and multiple line overwriting to achieve desired colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If nanosecond laser pulses are used to create black marks on anodized aluminium, then dark marks can be formed, but the oxide layer is damaged and mark appearance changes with viewing angle
Solution Approach 1:
The patent changes the laser pulse parameters from nanosecond range to picosecond range (10ps or less), which fundamentally alters the interaction mechanism with the anodized surface. This parameter change enables cold processing through multi-photon absorption, avoiding thermal damage to the oxide layer while maintaining dark mark appearance that does not change with viewing angle
Solution Approach 2:
The patent replaces thermal processing mechanisms with optical nonlinear effects (multi-photon absorption). By using picosecond pulses, the processing transitions from thermal ablation to cold ablation, substituting heat-based material removal with direct optical field interactions that preserve the oxide layer structure
2Reliability
If picosecond lasers with pulse widths of 10ps or less are used, then the anodization remains intact and marks do not change appearance, but the equipment cost is higher
Solution Approach 1:
The patent optimizes the pulse width parameter within the picosecond range (specifically 10ps or less) to achieve the threshold for multi-photon absorption dominance. This precise parameter control enables cold processing effects that protect the anodization while using relatively affordable picosecond lasers without requiring more expensive femtosecond systems
3Productivity
If nanosecond lasers are used to create dark marks, then marking can be performed, but thermal damage occurs and processing speed is insufficient for commercial applications
Solution Approach 1:
The patent replaces thermal processing with optical field-based cold ablation using picosecond pulses. This substitution eliminates thermal diffusion and heat-affected zones while enabling faster processing speeds suitable for commercial production, as the nonlinear optical effects occur instantaneously without thermal lag
Solution Approach 2:
The patent uses high-repetition-rate picosecond laser pulses to achieve continuous rapid marking. The periodic pulsed action at picosecond scales accumulates material modification effects efficiently while allowing heat dissipation between pulses, enabling high-speed processing without thermal damage
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables faster and more economical production of high-quality black marks on anodized metal surfaces, reducing thermal damage and maintaining the surface finish, using nanosecond pulsed lasers which are lower in cost compared to picosecond or femtosecond lasers.
Implementation Method 1
Cold processing (such as cold ablation) does not rely on thermal effects to produce the desired processing effect, and therefore has little if any thermal damage surrounding the processed area. Cold processing relies on femtosecond lasers, or picosecond lasers having pulse widths up to around 10ps to 50ps.
Implementation Method 2
Laser light can be used directly to form various colours either within the anodization or in the interface region between the oxide layer that forms the anodization and the aluminium.
Data Source
Figure 1~4
Figure 5~8
Figure 9~10
AI summary
A method for laser marking an anodized metal surface (5) with a desired colour, which method comprises: providing a laser (1) for emitting a laser beam (4) comprising laser pulses having a pulse energy, a pulse width, and a pulse repetition frequency; providing a scanner (2) comprising a first mirror (6) for scanning the laser beam in a first direction (8), and a second mirror (7) for scanning the laser beam in a second direction (9); providing a lens (3) for focussing the laser beam from the laser (2) onto the anodized metal surface (5) to form a spot (31) having a spot diameter and a pulse fluence; providing a controller (11) for controlling the scanner (2) with a control signal (12); marking a plurality of lines (15) separated by a hatch distance (19) on the anodized metal surface to form a desired mark (16) by scanning the scanner (2) while pulsing the laser (1); selecting a scan speed (16), the pulse repetition frequency, and the spot diameter such that the separation (18) between consecutive spots (31) during each scan of the scanner (2) is at least one quarter of the spot diameter; the method being characterized by: overwriting each line (15) more than once; the colour being given by the spot to spot separation (18), the hatch distance (19), the pulse fluence, the pulse width, and the number of times each line is written; and selecting the spot to spot separation (18), the hatch distance (19), the pulse fluence, the pulse width, and the number of times each line is written to form the desired colour.