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Item type:Publication, Access status: without files , Laser cutting of carbon fibre reinforced plastics of high thickness(2016-02-15); ; ; ; Laser cutting of CFRP is an interesting, wear-free alternative to conventional cutting of CFRP with increasing production volumes of CFRP-parts, especially in the automotive and aerospace industries. Cutting CFRP with laser has been investigated by several research groups but was usually limited to thin structures. This paper deals with a new approach to enable laser cutting of CFRP parts with a thickness above 6 mm.Based on a remote cutting approach, experiments were conducted in order to generate high process speeds and reduce heat affected zones to around 200 μm. It was found that laser cutting may be applied to thicknesses around 6 mm while keeping the width of the cut in the size of the focal spot, before shadowing effects prevent the laser from penetrating deeper into the material. When even thicker laminates need to be cut, parallel passes may be used to widen the cut, and enabling the laser focus to follow into the cut kerf. With the latter approach, CFRP with a thickness of up to 13 mm has been cut.Publicationtype: Journal Article116 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Laser cutting of carbon fiber-reinforced plastic with an absorber transparent for visible spectrum(2015-08-01); ; ; ; Mass production of carbon fiber-reinforced plastic parts has lately started in the automotive industry. Due to no abrasive wear in combination with a high degree of automation and ability for 3D processing, laser remote cutting is a suitable method for machining purposes in this context. In the automotive environment, solid-state lasers are favored because optical waveguides may then be used. In turn, the low absorption of the radiation of such lasers in the matrix material presents a drawback in terms of comparatively large heat affected zones (HAZ) and flaking at the cutting kerf. This paper deals with the question, if a laser absorbing additive can be used to enhance the absorption within the matrix material, while the optical properties in the visible spectrum are kept. For this purpose, an additive known from laser transmission welding has been added to the matrix material. Cutting experiments have been carried out while varying concentration of the additive. The investigations show that a significant reduction of the mean HAZ of 25% and the standard deviation (1 σ) of 56% can be achieved by adding 4% w/w of the additive to the resin. In addition to that, the flaking behavior can be avoided. Compared to adding soot particles, the optical properties of the laminate do not change in the visible spectrum, leaving the fiber textile visible.Publicationtype: Journal Article103 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigations on the process strategy of laser remote cutting of carbon fiber reinforced plastics with a thickness of more than 5 MMLaser cutting of CFRP becomes an issue since production volumes of CFRP-parts in automotive and aerospace industry are increasing. This paper deals with the process strategy of the remote cutting approach and its adaptively to laminates with a thickness greater than 5 mm. The strategy is varied in 3 different approaches in order to maximize the cutting depth while keeping the heat affected zone at minimum. The experiments have shown that the cutting depth is a linear function to the number of passes up to a certain depth, dependent on process speed and laser power. When changing the strategy to parallel passes, to avoid shadowing the laser beam as well as retracing the focus, the cutting depth can be increased up to 13 mm while the HAZ stays around 200 µm.Publicationtype: Conference Paper57 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Laser cutting of carbon fiber reinforced plastic using a 30 kW fiber laser(2015-02-01); ; ; ; Today, industrial usage of carbon fiber reinforced plastic (CFRP) is steadily increasing, with an amount of 67 000 ton/yr ["Carbon fibers and carbon fiber reinforced plastics (CFRP) - A global market overview," Report, Research and Markets Ltd., Dublin, Ireland, 2013]. Products such as the Boeing 787 and Airbus A350 in the aerospace sector, as well as the BMW i3 from the automotive industry consist of more than 50% of CFRP in their structural weight. At the same time, these products also have comparatively high production volumes, e.g., >10 000 cars/yr in the case of the BMW i3 ["BMW undertakes global launch of i3 EV," see http://www.ihs.com/products/global-insight/industry-economic-report.aspx?id=1065981621, May 20, 2014]. Therefore, a higher degree in automation and cost-efficiency is needed in production. Due to the highly abrasive carbon fibers, conventional machining processes result in short tool life and high costs. Therefore, laser cutting of CFRP as a wear-free alternative has lately become the focus of several research groups. Two different approaches are commonly chosen: cutting by short- and ultra-short pulsed laser systems to reach a process regime of cold ablation and cutting with continuous wave (cw) lasers at high cutting speeds. For the latter approach, it has already been shown that by increasing power and cutting speed, the heat affected zone (HAZ) can be reduced due to less time allowed for heat conduction [Bluemel et al., "Laser machining of CFRP using a high power laser - Investigation on the heat affected zone," in Proceedings of 15th European Conference on Composite Materials, Venice, Italy (2012)]. Graf and Weber introduced a perpendicular heat flow model, calculating that the required intensity to cut 2 mm of CFRP with a HAZ of 10 μm using a cw laser is 109W/cm2. The required cutting speed is 8.3 m/s [T. Graf and R. Weber, "Laser applications from production to machining of composite materials," in Proceedings of EALA, Bad Nauheim, Germany (2012), pp. 289-299]. In this paper, experiments using an ultra-high power fiber laser system of 30 kW to cut CFRP laminates are presented. Although it is not possible to fully achieve the intensities proposed by Graf and Weber, the intensities of approx. 108W/cm2 of the setup still allow for a practical validation of the CFRP cutting at very high laser power. Due to the high intensities, high cutting speeds per laser pass are necessary. A special experimental setup is chosen with a rotational movement of the specimen, reaching a feed rate of 85m/s. The heat affected zone was considerably reduced to 78μm with the 30kW system, 10% lower than with a 5kW system under comparable conditions. Although today no scanner systems are available that could handle these high intensities at such high cutting speeds, the experiments still show that processing of CFRP with cw laser systems at highest power has a potential in order to reduce the heat damage to the material.Publicationtype: Conference Paper139