Professor Wang, Huazhong University of Science and Technology
Laser cleaning principle, process and application analysis
Professor Wang from Huazhong University of Science and Technology shared his report on the topic of "Laser Cleaning Principles, Processes and Application Analysis".
Professor Wang introduced the history of the development of laser cleaning technology, which was first proposed by Schawlow. A. L in 1965, and Huazhong University of Science and Technology first studied the process and mechanism of YAG pulsed laser in stripping paint from aluminium plates and cleaning the rubber layer on the surface of tyres in 2000. Laser cleaning can be widely used for rust removal, oil removal, paint removal, stripping of coatings (galvanised, aluminised, protective coatings etc.), removal of oxide films from alloys (aluminium alloys, titanium alloys, copper alloys), pre-treatment before welding and post-welding cleaning. Professor Wang made a specific introduction to the typical application cases of laser cleaning for everyone. For example, laser cleaning before brazing the side surrounds of the body-in-white roof is necessary, without cleaning before welding, the surface of the weld is prone to porosity defects; Using laser cleans rust prevention oil before gear welding, the oil on the surface of the workpiece was thoroughly cleaned after laser cleaning, and the original machined knife marks on the surface of the gear were still clearly visible, proving the non-destructive nature of the cleaning. In addition, from the point of view of economic benefits, according to the annual output of 1 million sets of gears, the use of laser cleaning instead of ultrasonic cleaning can save 1.16 million - 1.96 million yuan.
For the future development trend of laser cleaning technology, Professor Wang believes that there are three aspects: 1. cross, that is, the process, mechanism and equipment development direction will cross; 2. popularization, laser cleaning is penetrating all walks of life; 3. standardization, the urgent need to enhance the volume of industry, through the modularization of laser cleaning technology to change the status quo of non-standardization, modularization after the realization of large-scale production, reduce costs and improve cost performance. The modularization will lead to mass production, lower cost and higher cost performance.
Ms. Zhang, PhD, JPT Technical Director, Nanyang Technological University, Singapore
Pioneering and Prospects of Fiber Lasers in Laser Cleaning
Ms. Zhang, Technical Director of Shenzhen JPT Photoelectric Co., Ltd. shared the main parameters of single mode/multi-mode/multi-mode combined beam/composite spot lasers, the application mechanism and characteristics of different spot modes with the theme of "Pioneering and Prospects of Fiber Laser Technology in Laser Cleaning" from the perspective of laser light source.
Ms. Zhang focused on MOPA fiber laser for introduction, the MOPA fibre laser works on the principle of main oscillation amplification, with an electrically modulated semiconductor laser as the seed source, amplified by a fibre amplifier, characterised firstly by independent pulse width modulation and repetition frequency; secondly by a wide range of adjustable pulse widths and a wide range of adjustable re-frequencies.
In additional, in terms of spot distribution, the multi-mode laser spot distribution is similar to the flat-top spot distribution. When comparing the Gaussian spot with the flat-topped spot, the Gaussian beam has a high central energy density and a low edge energy density, while the difference between the central and edge energy densities of the flat-topped beam is small. Both Gaussian and homogenised spots have different applications, but if the energy density in the centre of the Gaussian spot is too high, the substrate may be damaged during cleaning. Therefore, levelling spots can better alleviate the problem of substrate damage and improve processing efficiency and results.
Ms. Zhang also went through specific single-mode laser cleaning, multi-mode laser cleaning, and compound cleaning cases. Take single-mode laser rail cleaning as an example, the railway track is composed of high manganese steel, containing a large number of carbon elements and manganese elements, its anti-wear, pressure resistance, high hardness, the accumulation of rust on the rail erosion leads to uneven rail surface to produce bumps, while affecting the train to receive signals which leads to failure, the use of CL single-mode series lasers can be very good to achieve the removal of the rust layer. The use of CL multi-mode series lasers, on the other hand, does not harm the substrate, has a long depth of focus and is better suited for precision mould cleaning.
In the case of composite cleaning, composite light source cleaning compared to pure pulse cleaning efficiency is faster, pulse laser cleaning in the material heat dissipation is fast, composite cleaning allows the material to maintain a high temperature state, to assist pulse cleaning effect. But the composite light source cleaning process is relatively large heat accumulation, therefore, cleaning thicker rust, paint layer, if the substrate damage requirements are not high, the pursuit of high efficiency can be preferred to the composite light source.
