Plastics play an important role in almost every facet of our lives and constitute a wide variety of products, from everyday products such as food and beverage packaging, over furniture and building materials to high-tech products in the automotive, electronics, aerospace, white goods, medical and other sectors.

To join plastic to metal a laser based two-step laser process is described. The first process step is the laser micro structuring of the metal surface to create microstructures with undercut grooves. The subsequent transmission joining process allows a selective heating of arbitrary component geometries and the local control of the joining temperature. Both parts are brought into direct contact prior to welding. The plastic part is melted and expands into the microstructures through the external clamping pressure. The joining results due to micro cramping after setting. The long term stability of the joining is described.

Different types of laser sources can be used for polymer welding. By the principle of laser transmission welding the wavelength of the laser is one of the most important criteria when selecting a laser source as the optical properties of the polymers are depending on the wavelength. Up to date white material cannot be welded to each other. The results show that by analysis of the optical properties, especially the absorption and the scattering coefficient and adaption of the laser wavelength the process limits can be extended.

For many applications especially in electronics laser welding but also in medical device manufacturing is the dominating joining technology. The main advantages are the non-contact and vibration-free energy input, the precise control of the deposited energy and thus the related reproducibility and low thermal load of the parts. The decreasing costs for laser source and beam guiding system are enhancing these advantages and make laser welding even more competitive compared to other joining technologies.

Joining of dissimilar materials is gaining more and more importance especially in the automotive industry. The latest international initiatives concerning the average fleet CO2-emissions are forcing manufacturers to reduce fuel consumption and exhaust gas output. This can mainly be achieved by reducing the weight of the vehicles. New methods for weight optimization have been enabled by material selections adapted to local strength requirements. While plastics are characterized by low density, low price, and literally unlimited shaping, metals can withstand distinctly higher mechanical loads. Hybrid components combine the contradictory characteristics of plastics and metal and thus can lead to advantageous construction part properties. As a result, light and concomitantly stiff components can be produced. The need for joining these dissimilar materials without using additional material such as adhesives or primers is a central challenge. A new approach to overcome the problems of state-of-the-art technologies is using laser radiation to ablate the metal surface in order to create microstructures with undercut grooves. When the above placed plastic is melted with laser radiation or induction joining, the material expands into these structures through external clamping pressure and after setting the joining results due to microclamping. In this paper, the influence of different microstructure geometries and the process parameters of this innovative approach are presented and discussed in detail.

Hybrid components combine the contradictory characteristics of plastics and metal and thus can lead to advantageous construction part properties. As a result light and concomitantly stiff components can be produced. Therefore, the need for joining these dissimilar materials is a central challenge.A new approach to overcome the problems of state-of-the-art technologies is using laser radiation to ablate the metal surface in order to create microstructures with undercut grooves. When the above placed plastic is melted with laser radiation or induction joining, the material expands into these structures through external clamping pressure and after setting the joining results due to microclamping.

Recently, near-infrared lasers show remarkable progress in terms of output power, long running stability and cost. The development of laser precision plastic welding technology utilizing these laser sources as one of main applications has been actively conducted all over the world. The authors studied and developed brand-new laser splicing technology as a new application of laser welding for thermoplastic film material fed at roll-to-roll handling process, which showed better bonding quality compared to the conventional splicing methods such as adhesive tape method, heat sealing method, and so on. In this report, basic laser splicing method for transparent thermoplastic films, correlation between laser processing condition and bonding condition, how to measure heating situation when laser irradiated, in-process controlling method, moreover high precision and photon absorber-free laser butt splicing technology which is state-of-the-art laser welding technology is described.

In laser transmission welding of thermoplastics the optical properties of the joining parts determine the quality of the welding result. Especially, the scattering of laser radiation in the transparent welding part has an impact on weld seam properties. This scattering is caused by additives. For polycarbonate (PC) with different additives the transmittance, the reflectance and the collimated transmittance are measured with a UV-VIS-NIR spectrometer. From this data, the optical properties, such as scattering coefficient, absorption coefficient, and anisotropy factor are calculated. The calculations are made with the aid of the four-flux model of radiation transport in the diffusive approximation. The results show that the additives have a significant influence on the scattering coefficient. For most additives under consideration the scattering is forward directed, which means that most of the radiation is transmitted into the absorbing welding part. However, the power density distribution of the transmitted radiation may differ significantly from PC without additives. So, the weld seam may also differ due to different additives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 451–455, 2010

Polymeric products play an important role in almost every aspect of our lives and they can be found in a wide variety of products starting from everyday products up to high tech products in the automotive, electronics, medical and other sectors. The possibility to fabricate complex shapes in various sizes provides design flexibility and high performance at lower costs and allows designers to face today’s complex demands. Starting as an unconventional joining technology for the manufacturing of polymeric products the laser beam welding earned over the last decade through an extensive research effort a respectable place among the other available joining methods.Currently one of the main process limitations is related to the requirement of having a laser transparent and a laser absorbing joining component. One possibility to overcome this limitation is to adapt the wavelength of the laser source to the absorption characteristic of the material and to select a suitable irradiation strategy. Following this approach this paper presents the latest results and the future perspectives for the laser absorber free welding using adapted laser wavelengths and irradiation strategies. The welding results for Poly(methyl methacrylate) - PMMA transparent components with feed rates up to 100 mm/s and different laser wavelengths such as 1550 nm, 1700 nm or 1908 nm are presented and discussed.Polymeric products play an important role in almost every aspect of our lives and they can be found in a wide variety of products starting from everyday products up to high tech products in the automotive, electronics, medical and other sectors. The possibility to fabricate complex shapes in various sizes provides design flexibility and high performance at lower costs and allows designers to face today’s complex demands. Starting as an unconventional joining technology for the manufacturing of polymeric products the laser beam welding earned over the last decade through an extensive research effort a respectable place among the other available joining methods.Currently one of the main process limitations is related to the requirement of having a laser transparent and a laser absorbing joining component. One possibility to overcome this limitation is to adapt the wavelength of the laser source to the absorption characteristic of the material and to select a suitable irradiation strategy. Following this app...

The increasing use of plastics as a construction material has given rise to the problem of how to join dissimilar materials. For the production of hybrid plastic–metal components, several processes are possible. In a new joining method LIFTEC®, recently developed at the Fraunhofer Institute for Laser Technology, a part or a defined area of a part is heated by laser radiation through the plastic component with which it is to be joined. The part is held in contact with the plastic component under mechanical pressure and heated; then, further mechanical pressure is applied to press it into the plastic material. A stable positive bond is achieved during cooling, provided that a suitable component geometry has been selected. An important aspect of the process is that the part to be heated should have a higher melting point than the plastic component with which it is to be joined. The more heat resistant of the two parts/components can be metal, ceramic, or a heat-resistant plastic. The high energy density of the laser beam permits the heating stage to be accomplished very rapidly. Another approach is pursued within the Cluster of Excellence “Integrative Production Technology for High-Wage Countries” of the RWTH Aachen University. Multiple irradiation strategies in line with the choice of the material, the beam source, and the pretreatment of the samples are investigated. In a first experimental series, the influence of the surface structure on the joining process is examined. A structure in dot, line, and cross pattern is implemented on the surface of stainless-steel samples with Nd:YAG laser radiation. Afterwards, these samples are joined with transparent plastic samples. For the laser beam transmission joining process, contour or quasi-simultaneous irradiation strategies are considered while using diode laser power. The results show promising achievements, with good strength being obtained.

AbstractDank seiner Vorteile hat sich das Laserschweißen von Kunststoffen zu einem etablierten Fügeverfahren entwickelt und es ersetzt mehr und mehr die bisher üblichen Fügeverfahren. Neue Entwicklungen beim Laserdurchstrahlschweißen ermöglichen nun das Überschreiten bisheriger Grenzen und eröffnen diesem Schweißverfahren weitere Anwendungsfelder.

Main focus of this contribution is an investigation on process monitoring methods for transparent thermoplastic film laser beam welding. Target is to find feasible approaches to monitor and control the welding process in common industrial applications. The welding process is supported by an IR-absorber between the join partners. The presented work is focused on three different wavelength ranges: Starting from the visible wavelength through near infrared to mid infrared wavelength. In these areas two kinds of sensors are used. The sensors are imaging and integrating systems. The detectors for visible and near infrared are integrated into the beam path.

The laser welding of thermoplastics has been established in several industrial applications, but it has not yet been able to weld transparent thermoplastics without an IR-absorber. However, by the use of special optics in combination with a proper wavelength, absorber-free laser beam welding can be utilized in a large number of applications primarily in medical device technology or in high-tech products. The availability of high brilliance fiber lasers with new wavelengths makes these applications possible. The different wavelengths are achieved by doping the fibers with the laser-active elements ytterbium (1060 – 1080 nm), erbium (1530 – 1600 nm) or thulium (1800 – 2100 nm). Starting from 1200 nm the intrinsic absorption of several visually transparent polymers reaches a sufficient value to allow laser welding without any IR-absorber. To generate a heat source in the joining area, the intensity distribution and the wavelength of the laser must be aligned to the absorption characteristics of the polymer. The usage of special optics with high numerical aperture keeps the laser intensity on top of the material and below the melting threshold. Only in the welding area does the intensity reach the necessary value to determine the welding of the transparent components.