Quality Evaluation Of Laser Coloring On Metal Surface And Research On Color Barcode Marking Technology

Laser coloring on metal surface is a new coloring process that produces different colors on the metal surface by irradiating the metal surface with laser.Laser coloring does not need special coatings,and has the advantages of non-contact and flexible processing,which has attracted extensive attention in recent years.However,there is still a long way to go to realize the industrial application of laser coloring on metal surfaces.This is because the coloring effect is extremely sensitive to laser parameters and material characteristics during the interaction between laser and metal materials.Uniformity and repeatability have always been two challenging topics in the field of laser coloring.For this reason,Research of laser coloring on surfaces of Ti-6A1-4V alloy using Nd:YAG nanosecond laser is carried out in this paper.The main factors affecting the stability and non-uniformity of laser coloring are mainly studied,the causes of non-uniformity of laser coloring are explored based on thermophysical field,and improvement measures are proposed,and laser marking of color two dimensional barcode is realized.The main contents are as follows:The main laser parameters that affect the stability and uniformity of laser coloring are studied.A laser coloring evaluation method based on HSI(Hue-Saturation-Intensity)color space is proposed.By analyzing the distribution of laser coloring samples in HSI color space,the coordinates of main color and the proportion of main colors are determined as evaluation indexes to describe the stability and uniformity of samples.The effects of laser current,repetition frequency,scanning speed and line spacing on colors laser-marked on surfaces of titanium alloy were studied.The experimental results show that the laser can stably produce yellow,orange,red,purple,blue,gray and other colors on the surface of titanium alloy,of which yellow and blue colors are relatively easy to produce with a wide range of parameters.The color produced under low repetition frequency and high current have good uniformity.A theoretical and a computational simulation model of the interaction between laserand materials are established,and the causes of non-uniform samples in laser coloring are analyzed.Based on the heat conduction theory,a theoretical model of the interaction between laser and metal is established,and a computer simulation model is established based on COMSOL Multiphysics finite element analysis software to obtain the temperature field distribution generated by laser irradiation on the surface of the material.By analyzing the distribution characteristics of temperature field and comparing the color distribution of non-uniform samples,it is found that the non-uniform coloring phenomenon is mainly affected by the highest temperature accumulated in the heat affected zone of different laser scanning tracks.For the same reason,under the condition that the processing parameters are unchanged,changing the size of the processing area will also change the coloring effect.In order to improve the non-uniform coloring phenomenon,two improvement measures,temperature control during processing and scanning path planning,are designed.Experiments prove that the methods are effective.The laser marking technology of direct part marking based on color two dimensional barcode is studied,and the processing of color direct part marking is successfully realized.Based on the Data Matrix barcode,a color Data Matrix barcode based on quaternary is designed by converting binary information into quaternary information.Three colors of orange,red and blue,which have good stability and uniformity in the experimental study of laser coloring on TC4 titanium alloy surface.and the background color of titanium alloy,are selected as the four color units of the color two dimensional barcode to express quaternary information and form the color two dimensional barcode.During processing,because the marking parameters of different color modules are different,a plurality of marking files are established according to the distribution ofdifferent color units of the color Data Matrix barcode.and marking operations are respectively carried out.The problem of color stability in multi-module coloring was found and improved during processing.In order to test the laser marking quality of color two dimensional barcode,further information extraction experiments are carried out on the laser marked color two dimensional barcode samples.A set of image processing methods,such as binarization,mathematical morphology processing,edge extraction,corner detection,projection transformation correction,color unit clustering are used on the sample images.The extraction of color Data Matrix barcode quaternary information is successfully realized.Furthermore,it is reduced to ordinary Data Matrix barcode through binary conversion.The content of the color symbol is consistent with that the original Data Matrix barcode by comparison,which proves that laser coloring is feasible for color two dimensional barcode.Since there is no color two dimensional barcode marking software in the existing laser marking system,a color two dimensional barcode laser marking auxiliary software is designed to store color information formed by various metals under the action of laser into a database.During marking operation,the corresponding color two dimensional barcode is generated according to the content of the marking and split according to different color units.At the same time,the processing parameters of the corresponding color stored in the database are invoked and the marking files of different color modules are generated for the selection and use of laser marking operation.The design of this software is easy to operate,which is helpful to form a complete color laser marking system.