Method for laser marking an anodized metal surface with a desired colour

Abstract

A method for laser marking an anodized metal surface () with a desired color, which method comprises: providing a laser () for emitting a laser beam () comprising laser pulses having a pulse energy, a pulse width, and a pulse repetition frequency; providing a scanner () comprising a first mirror () for scanning the laser beam in a first direction (), and a second mirror () for scanning the laser beam in a second direction (); providing a lens () for focussing the laser beam from the laser () onto the anodized metal surface () to form a spot () having a spot diameter and a pulse fluence; providing a controller () for controlling the scanner () with a control signal (); marking a plurality of lines () separated by a hatch distance () on the anodized metal surface to form a desired mark () by scanning the scanner () while pulsing the laser (); selecting a scan speed (), the pulse repetition frequency, and the spot diameter such that the separation () between consecutive spots () during each scan of the scanner () is at least one quarter of the spot diameter; the method being characterized by: overwriting each line () more than once; the color being given by the spot to spot separation (), hatch distance (), the pulse fluence, the pulse width, and the number of times each line is written; and selecting the spot to spot separation (), the hatch distance (), the pulse fluence, the pulse width, and the number of times each line is written to form the desired color.