Laser Transmission Welding of Thermoplastics Using Local Laser Beam Modulation
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Neuware - The results described in the preset work show for the first time for the polymer welding that through the use of laser modulations a reduction of the Heat Affected Zone, and therefore a reduction of the thermal load in both joining partners is possible, without losses in the weld seam strength. The evenly distributed laser energy in the joining area leads to a reduced depth of the weld seam compared to the conventional contour welding of polymers. Based on this aspect the experiments described in Chapter 6.3.2 indicate that the welding of parts with reduced material thickness, for applications where plastic parts with high requirements on the surface finish have to be joining, can be welded without any appearance of the weld seam on the visible surfaces. Therefore, a significant material saving of about 33% can be considered. Furthermore, the reduced thermal load of the joining partners enables the welding of fine structures without thermal deformation of these structures. Especially among the biomedical applications there is a variety of products with microfluidic channels that have to be hermetically sealed, usually by welding a plastic foil or cover on top of them. Such microfluidic channels with walls having a thickness smaller than 0.5 mm require a minimal thermal input in the welding area in order to avoid the deformation or the collapse of these fine structures. The possibility to control the size and shape of the HAZ make the welding of polymers using local beam modulations a strong candidate for such applications. The welding results discussed in the present work indicate that concerning the weld seam strength and gap bridging ability the new welding approach reaches a similar performance as the other already established laser welding process variants. For all the investigated materials the same weld seam strength as previously reported in the literature can be achieved through the welding using local laser beam modulation; as shown in Figure 76. However, the presented results indicate that in the low laser power range (at the lower limit of the process window) a superior result can be achieved compared to the conventional contour welding. In this region of the characteristic curve, under identical processing conditions (e.g. identical laser power and feed rate) the homogeneous melting of a thin material layer at the welding interface across the weld seam width enables a higher weld seam strength compared to the conventional contour welding (Figure 81, bottom). In this way the new welding approach enables the widening of the process window and contributes to the increase of the process robustness. A similar effect is expected at the upper limit of the process window where the laser beam modulations and the homogeneous energy input in the welding area across the weld seam width could avoid the thermal damage of the material in the middle of the weld seam, typical for this region of the characteristic curve. In this way the process window could be extended in both directions enabling a more robust and reliable process. Intensive investigations within large scale international projects are currently focused to determine the possibility to extend the process limits in this direction by using laser local beam modulation and alternative approached derived from this process (e.g. using optical components to shape the laser beam intensity profile in order to achieve a similar energy distribution in the welding area as for the welding with local beam oscillations). Concerning the gap bridging ability of the new process proposed within the present work it can be concluded that for spot diameters lower than 2w0= 0.200 mm and reduced oscillation amplitudes the process instability will increase. The reason can be found in the high laser intensities resulting in the welding area for highly focuses laser beams (I= 105 - 106 W/cm2), which will lead to the nearly instantaneous thermal damage of the material in the areas with. Bookseller Inventory # 9783844020816
Title: Laser Transmission Welding of Thermoplastics...
Publisher: Shaker Verlag Aug 2013
Publication Date: 2013
Book Condition: Neu
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