| Metallic surface coloring,as a common surface treatment technology,has a wide range of applications in aerospace,ship component manufacturing,biomedical devices,art decoration and other fields.Common metal coloring methods include spark coloring,anodic oxidation coloring,chemical coloring,etc.These traditional metal surface coloring methods have defects such as complicated production processes and poor repeatability,resulting in limitations in industrial applications.As a precise processing method,laser coloring technology mainly utilizes the interaction between laser and metal to present various colors on the metal surface,and the color has the advantages of high glossiness,high saturation,and high stability,which is unmatched by traditional coloring methods.Early research on laser coloring on metallic surface mainly focused on exploring the coloring mechanism and the influence of processing parameters on color changes.In recent years,research on new laser coloring processing technologies and coloring effect control has increased.However,laser coloring technology is still limited in practical applications.For example,there are many laser processing parameters,and multiple parameters cooperate with a long color debugging period.There are deficiencies in flexibility and applicability of the process,and the accuracy,saturation,repeatability,stability and uniformity of prepared colors are still insufficient to meet the application requirements of various industries.To solve the above problems,this thesis has carried out research on the technology and color performance based on laser coloring on metallic surface.Based on the research on the mechanism,process,and coloring quality of nanosecond and ultrafast laser coloring,three new laser coloring process optimization schemes were proposed:rewriting,erasing,and widening color,which make laser coloring technology flexible and applicable.Based on ANN,color prediction can achieve precise color control within a small range of parameters,providing new carriers and means for the application of laser coloring technology in artistic expression.The main work includes:1.Research on the basic theory of laser metal coloringBased on the theory of laser-material interaction,the characteristics of laser and metal material processing and the main factors affecting laser and metal processing were introduced.The double-temperature model of laser and metal material interaction and the analysis of the three mechanisms of coloring on the laser metal surface were discussed,including laser-induced oxidation coloring,periodic structure diffraction coloring,and plasma color excited by metal nanoparticles and nanostructures.Then,the relationship between surface color and process parameters in laser coloring was discussed: laser metal surface coloring is a nonlinear,unstable process affected by multiple parameters coupling.Finally,a finite element model of laser-induced titanium surface coloring thermal simulation was established.The simulation results show that the temperature field of titanium surface laser coloring is controlled by processing parameters and affects the growth of oxide on the titanium surface.Therefore,the color is greatly affected by temperature,and the rapid heating and cooling of the metallic surface temperature can significantly affect the color formation process.Numerical simulations and theoretical analyses produced consistent results,providing theoretical guidance for coloring parameters.2.Experimental study on nanosecond laser metal coloring and quality evaluationA wide range of colors were obtained on stainless steel,titanium alloy,and titanium surfaces based on the metal melting energy threshold.The effects of scanning speed,single-pulse energy,and hatch distance on titanium surface coloring were investigated.Under unchanged conditions,the values of ΔE* and ΔL* increased with the scanning speed increasing.The values of ΔE* and ΔL* decreased with the singlepulse energy increasing,while the brightness of the titanium surface increased with the hatch distance increasing.Subsequently,the coloring mechanism of laser coloring was analyzed.High temperatures generated during the laser metal surface coloring process not only cause surface oxidation but also lead to the melting and re-solidification of the oxide film,resulting in changes in micro-morphology,roughness,and elemental composition.Nanosecond laser metal surface coloring is more complex on titanium surfaces,and the color of the oxide,the morphology of the oxide film surface,and the periodic structure of stripes will all affect the interference coloring of the oxide film.Finally,the coloring surfaces showed good persistence and stability under different conditions.3.Research on ultrafast laser metal surface coloring and quality evaluationHigh-precision color preparation was achieved on titanium by using a 1030 nm picosecond pulsed laser,and the coloring mechanism was characterized and analyzed.The colored surface treated by picosecond pulsed laser showed good persistence and stability under different conditions.Then,the coloring experiments were conducted on stainless steel and titanium surfaces by using a 1064 nm femtosecond fiber laser.The results showed that the color changed greatly with the variation of the incident angle of illumination and the viewing angle,and that multiple samples exhibited phenomena such as burning,unevenness,flying white,and low color saturation.The laser-induced surface stripe structure was uniformly distributed along the laser scanning path.By changing the incident angle of illumination or viewing angle,different colors could be displayed,and the color saturation was increased.4.Research on new technology and parameter optimization of laser metal surface coloringThree basic functions of coloring,erasing,and rewriting were introduced for the multifunctional laser paintbrush.Then,numerical simulations were carried out based on the metal surface ablation during the laser erasing process.The erasing performance of ultrafast and nanosecond pulsed lasers was compared,and it was found that ultrafast pulsed laser had better erasing quality on colored samples.When the ultrafast pulsed laser irradiated the coloring area at a scanning speed of 1500 mm/s,the erased areas showed superhydrophilicity.Subsequently,a method of color expansion based on the nano-particle structure was proposed,and a wider range of colors with higher precision was achieved on an Au-Ti surface using nanosecond pulsed laser.Finally,a model of the relationship between process parameters and colors was established by RSM model to investigate the coupling effects of various parameters on coloring effects,and their parameters were optimized.5.Application research of laser coloring based on ANN and art visual colorimetryA method of using ANN to accurately match the processing parameters and Lab color values in laser metal coloring was proposed,which provides convenient and efficient guidance for fast laser coloring on metal surfaces.Establish the color difference visualization between the predicted value of ANN model and the actual processing color value,and finally draw the traditional face pattern on the titanium surface successfully based on the process parameters predicted by ANN model.Based on art visual colorimetry,traditional cultural elements and colors were summarized and extracted,and then reconstructed and deconstructed to prepare patterns with artistic expression.Laser coloring technology provides a new perspective for artistic expression. |
PDF Full Text Request