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Veröffentlichungen:

Haupt, O.; Büsching, C.; Haase M.: Laser cutting using NIR radiation. In: Glass Processing Days, 15.–18. Juni 2007, Tampere

H2B Photonics GmbH, An der Universitat 2, 30823 Garbsen

The use of laser sources in the field of glass cutting is already state of theart in numerous industrial fields of application. Laser radiation has processbased advantages in comparison to conventional production technologies: non-contact, wear-free treatment of sensitive glass products decreases the number of rejects and quality costs, increases the product quality and the productivity of the glass separation process. Precise energy use and good reproducibility open up new economical manufacturing processes. For years, laser beam processing has already been used successfully in the glass industry. Whether for separating blowing caps in the mass production of drinking glasses, or for separating flat glasses in the display glass production, laser processing of glass has established itself successfully in many industrial fields, due to process-based advantages. This publication will specify a modern near-infrared (NIR) laser beam cutting process: the MLBA (Multiple Laser Beam Absorption) process. The author explains the principle of MLBA glass cutting using NIR laser radiation in comparison to mechanical processing and the separation with CO2 laser radiation. Current innovations of the MLBA technology enhance the high potential of laser glass cutting using NIR radiation. The wide range of applications, the high quality level and the high productivity of the MLBA process have already convinced the glass industry – some successful projects have been realized for displays and in the solar market.

Introduction

Glass is an integral component of products from different industries. The variety of applications clearly shows the immense meaning of the material glass. Whether flat glass for architecture applications or for automotive applications. In its value as a functional device, glass has surpassed its role as a basic material for a long time. The need of glass products is growing nearly 4% every year. Due to increasing globalization of the market and the intense competition resulting from this, competition among  the suppliers of glass products or special machines for the treatment of glass will continue to increase in the next few years. A special emphasis can be placed on innovative production processes, which can bring new products, new designs or productivity advantages in relation to the competition on the world market. In the future, the employment of innovative glass processing technologies will increasingly shape the success of the glass industry and will strengthen the position on the world market of glass processing solutions with its technological innovations. Separation of glass plays a substantial role in the refinement of glass products. Whether hollow glass or flat glass, each glass product goes through the process of separation before it is subject to further processes to become a finished product. Frequently, the glass is already provided with functional coatings, before the separation process starts, for example anti-reflection coated glass for the consumer market or ITO coatings for display applications. This means, it is important that the following separation process do not damage the sensitive functional coatings. Conventional separation processes with mechanical tools are coming closer and closer to their limitations. In order to be able to realize the necessary output with high quality standards, expensive diamond cutting tools must be used. The handling of the complex, large one or double layer glass sheets in the automotive industry, which are continually increasing in format and decreasing in thickness, is becoming more and more cost-intensive.

Sensitive glass products, for example with a thickness of d<1mm or functional surface coatings need sensitive production processes. Mechanical scribing and breaking are increasingly meeting their technological limits. Disadvantages of mechanical scratching and breaking are the generation of splinters and microcracks, contamination by cutting oil and mechanical wear. Negative effects such as reduced edge stability or contamination of the glass surfaces have to be eliminated by grinding or polishing and finally cleaning the glass after. Additional costs for postprocessing and the disposal of grinding and polishing agents arise. Beyond that, higher requirements due to increasing  complexity of the glass products call for innovative production processes. For the production of LCD displays, thin ITO coated glasses are connected, before they are filled with LCD material. In mass production of display glass, the double layer glass sheets are becoming larger and larger, so that the handling of the large sized sheets becomes more cost-intensive. An alternative process to conventional glass cutting processes is the separation of thin glasses using CO2 lasers. Here the glass is heated up on the surface by the laser beam at a wavelength of 􀁏=10.6 μm. The heating induces tension in the glass surface. Based on an initial crack, the glass surface cracks due to the cooling with appropriate mediums. The cooling can be guided by using nozzles after the laser beam, shown in fig. 3. The following breaking process then leads to separation of the glass sheets. CO2 laser separation of glass causes no microcracks and almost no glass splinters. This method is also applicable for clean room applications. During the last few years, this process has established itself more and more in the production of display glasses. Excellent edge quality can be achieved and grinding is eliminated [5].

Glass cutting using NIR laser radiation

MLBA glass cutting technology opens up new possibilities for industrial glass processing

A modern process for separating flat glass using NIR laser radiation is the MLBA process: Multiple Laser Beam Absorption. This laser process operates with a wavelength of 􀁏=1030 or 1064 nm. Other than CO2 laser radiation, the NIR laser radiation is absorbed here through the entire glass body. By multiple absorption of the radiation within the glass volume, laser radiation is transformed into heat energy. The hereby generated tension allows to separate the glass with an initial crack in one processing step [1], [2], [3]. The MLBA cutting process does not require additional cooling mediums. Standard industrial NIR laser sources are used, which can also use optical fibers for beam guidance. In this way, flexible integration into industrial production areas is possible. MLBA technology allows also to separate stacked glass layers in one processing step and  eliminates the otherwise common breaking process. Selective cutting of single glass sheets in a multilayer stack is also possible, as usually applied in display glass processing. The cut edge shows highest quality, which equals polished glass edges. In this way, post-processing is often not necessary. MLBA glass cutting can be used for all soda lime glass and many types of borosilicate glass. Presently, the German partner companies H2B Photonics and Rofin/Baasel Lasertech are offering MLBA laser glass cutting solutions for industrial applications. On the international exhibition Glasstec 2006 H2B Photonics and Rofin/ Baasel Lasertech demonstrated new developments on the glass cutting using the disc laser as an innovative NIR laser. Successful industrial projects in Korea and the US have proven great interest of the glass industry in this new future technology.

Industrial NIR laser sources for glass cutting

The disc laser is one of the most innovative NIR industrial laser sources and is currently assuring it�Ls position for a wide range of most different applications. Examples of applications are scribing and drilling of solar cells, welding of polymers and metals via scanner, and most recently also cutting of glass. For material processing, the disc laser shows several benefits which are due to the laser design itself. Excellent cooling qualities of the disc allow an efficient and compact system design. Due to the adjustment of the laser disc, scalability at high output power is possible. High beam quality which is almost independent of the laser power and outstanding scalability – these features allow to provide laser systems operating within a range of only some Watt up to kilo Watt. In this way, almost any applications find their adequate laser source [4], [6]. The technological advantages like consistant power stability make the disc laser the ideal system for cutting of glass. The outstanding dynamic characteristics allow the laser to be integrated in process control systems, so that the laser cutting process can be optimally controlled in the relevant process steps. Coupling several fibers to one laser source allows to realise highly efficient production concepts with several cutting heads. Investment costs for a laser system are thus put in the right perspective. Picture 5 shows the principle operating technique of the disc laser from Rofin-Sinar Laser GmbH in Hamburg. A more costefficient alternative for cutting glass is the Nd:YAG rod laser. Depending on the glass material and the application, the required cutting speed and requirements to the cutting procedure, the decision as to the adequate laser  ource has to be taken as the case arises. NIR lasers are also provided in a lamppumped  version. Lower investment and operating costs are opposed to shorter life time of the pump sources; higher power consumption and lower beam quality. The individual decision is to be taken depending on the application. For cutting all soda lime glass, these lasers are an interesting option.

Current improvements of industrial applications

The MLBA glass cutting technology using NIR laser sources offers several benefits for industrial users. The separation of glass panels with thicknesses of up to 24 mm or two glass sheets in laminated glass panels can be separated in a single pass. High edge quality without cracks and damages increases the bending stability of large glass panels for applications in architecture by a factor of two [2]. What is beneficial for the customer? Glass products cut with MLBA show breakage rates reduced to a minimum. Tab. 1 shows the flexible strength of laser cut glass in comparison to float glass and tempered glass.  The glass separation process using  NR lasers works with thermal induced tension. The process is free of splinters, extremely clean and contact-free. The conventional processing chain (scribing – breaking – grinding – polishing – cleaning) is reduced to “one-stepcutting”. Process times can thus be reduced up to 83%. The increase in productivity is shown in Fig. 8. Current development at H2B Photonics doubles the MLBA cutting speed from 10m/min to 20m/min for float glass (thickness 4mm). Benefits for industrial users lead to first successful projects in the plasma display industry. Applications like cutting of tubes for solar or automotive lighting industry have aroused large interest by industry users. Fig. 9 shows an example of a MLBA basic machine with a working area of 2000x2500mm2 for a generation 8 display sample size [7]. H2B Photonics has developed the MLBA glass cutting process using NIR lasers for tube glass cutting for many glass types based on soda lime glass or alumosilicate glass. The process provides perfect edge quality without any damages of the edge or residual stress inside the glass after separation. The industrial user benefits from less damages during post-processing resulting from increased mechanical or thermal stability of the cut tube glass. Fig. 10 and 11 shows examples of application.

Summary and Conclusion

Comparing laser processes with conventional methods of glass material processing requires to balance reasons of pros and cons. While conventional processing with industry proven machines, fast scribing and automated breaking processes at rather small investment costs appears beneficial, whereas laser processing of glass materials is becoming increasingly interesting for industrial users, due to flexibility, precision, wear-free processing. New possibilities will be opened up for product design and quality. The use of laser technology allows to realise innovative processes, which may lead to dramatically shortened process chains. Enhanced cost-effectiveness and productivity do not only depend on working speeds, but requires a careful analysis of the technical and economic factors of the entire process chain. In this way, the use of laser processes for thermal separation of glass materials cannot only be based on the fact, that the use of expensive tools like diamond cutters can be avoided. Cost-intensive grinding and polishing processes can often be avoided. An evaluation of all pros and cons, frequently clear productivity and competition advantages due to the use of NIR laser processing, clearly justify investment costs for the laser. After evaluating all pros and cons, it is more than obvious that investment costs for a laser system definitely pays off.

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