Research On Multi-heads CO₂Laser Texturing Technology Based On Beam Modulation By Polygon Scanning

Cold-roll steel sheet is widely used in automobile, appliance, construction and decoration industry, and the requirement for its forming ability and painting quality is also increasing. The surface quality of cold-roll steel sheet is controlled through surface texturing of cold roll whose micro organizations of surface will be printed into the surface of steel sheet during the rolling process. Comparing with the SBT(shot blast texturing) and EDT(electrical discharging texturing) technology, research shows that laser texturing is more precise, clean and uniform, meanwhile its textured roller has longer working duration and the laser texturing cold roll steel sheet has both good forming and painting quality, thus can be used as vehicle and appliance outer panel. However, the efficiency of single-head laser texturing is not sufficient to meet the requirement of large cold-roll enterprise. In order to shorten the texturing time, the surface crater density of single-head laser texturing is usually low and thus has compromised the quality of cold roll steel sheet, which in turn affect the application of laser texturing technology. In order to solve the problem of low efficiency of single-head laser texturing, a multi-heads CO2laser texturing technology based on pulse beam modulation by polygon scanning is proposed. The major content of this thesis is as following:(1) The principle of modulation of a high power continuous laser into several high repetition pulse lasers by polygon scanning is introduced, and the repetition rate is up to30kHz.(2) By using "Embed fundamental Gaussian beam", the distribution of light intensity of the focusing spot on the output plane is derived and the transmission and focus of pulse beam through the optical system is analyzed. The focusing spot is constantly on the move outside the focusing plane while the roller is rotating, and the condition for synchronization is discussed. Therefore, round texturing crater can be obtained instead of elliptical ones which will influence the of steel sheet surface uniformity.(3) Multi-heads texturing system parameters are determined according to the requirement of texturing condition. The design parameters of focusing lens and rotating polygon are discussed and the influence of flying optics on the focusing spot is analyzed. A geometrical optical model is introduced to simplify the analysis of synchronization between focusing spot and roller surface to determine the appropriate off-focus parameters.(4) The influence of texturing parameters such as laser power and pulse width on surface roughness and surface topography parameters are studied through laser texturing experiments. Metallographic analysis and hardness tests are performed on the textured surface of roller, and the average hardness is above HV800.(5) The practice of two-heads CO2laser texturing device is introduced and the device possesses features such as low cost, stability and high efficiency. The fluctuation of roughness of textured roller surface is between±0.2μm and meets the requirement of roller surface uniformity.