Research On Laser Transmission Welding Of Thermoplastic

More and more people are highlighting laser transmission welding of thermoplastic because of so many advantages, such as excellent welding quality,easy to control,available for micro-welding( weld less than 500μm)and so on, especially thermoplastic parts in automobile industry , laser transmission welding is the first choice in those fields. However, there are few domestic study on this research subject, which results in huge gap between domestic and foreign study on theory,industrialization and patents. Therefore, starting research on laser transmission welding of thermoplastic has significant meaning to this subject.Fist of all, a heat flow model in welding process is established for PP (Polypropylene) and HDPE (High Density Polyethylene). A conclusion can be obtained from the model that welding materials temperature change AT depends on laser power P,beam diameter on the material D,welding velocity V,welding time t,ratio of absorption of material a_T,material densityρ, so the model provides very important theoretical basis for determining influencing factors.Secondly, experimental scheme is plotted for welding experiments, which includes choosing laser equipment,welding materials,welding method,additives,designing new fixture specially for laser transmission welding and designing welding experiments scheme with Orthogonal Experimental Design.At the end of the paper, tensile and section tests are conducted for experimental samples in order to investigate the influence of welding factors on welding quality. And the influence of welding factors on tensile strength and welding seam size is analyzed, which indicates subsequence according to influence for PP is welding velocity,laser frequency,cooling time,fixture pressure,beam diameter on the material,laser power; subsequence for PP is welding velocity,laser power,cooling time,beam diameter on the material,laser frequency,fixture pressure. Welding velocity has most influence on welding seam quality for both PP and HDPE. Experimental results indicate that low welding velocity can obtain high quality welding generally. This paper presents detailed analysis on black welding seam and fake fracture in the course of welding and testing, finding high laser power density can result in coking on samples' faces and that fake fracture appears when welding seam is not even. Besides, the optimized welding parameters are determined using Range Method, and welding quality is compared when both two kinds of additives are used, and experimental results indicate that black coating is better than black films for welding.