Laser Transmission Welding (LTW) is a well-known technique for joining conventionally manufactured high-volume thermoplastic parts, such as automotive injection molded parts. When LTW is used for additively manufactured parts (typically prototypes, low-volume production, or one-offs), the technology must be developed to overcome the difficulties in welding the parts, that result from the additive manufacturing process itself. Compared to injection molding, additive manufacturing results in an inhomogeneous structure with entrapped air within the volume. Therefore, there is a change in the transmissivity behavior in the weld area due to the additive manufacturing process. In order to make LTW available for additively manufactured thermoplastic components, a process chain was developed to support manufacturing. This process chain ranges from the optimization of the additive manufacturing process to the welding process and is supported by an expert system. For the evaluation of the manufacturing process chain, welding experiments with additively manufactured samples were performed. The transparent samples were welded to black samples with varying process parameters in overlap configuration and tensile shear tests were performed. The additive manufacturing process parameters were used to predict the transmittance of the transparent sample and the weld seam strength of welded parts using the expert system.
New lightweight construction concepts should make it possible to reduce the weight of aircrafts and vehicles. This has an effect on energy consumption, in order to reduce CO2 emissions. New material combinations are used to implement these concepts, or in some cases, plastics substitute metals. The production of single-variety plastic components is particularly advantageous, as these can be returned into a recycling cycle. Thermoplastics are suitable for the production of such composites. If such parts are joined by means of adhesive bonding, the adhesive would remain on the components and prevent sorted recycling. Welding does not have this disadvantage. Wide weld seams are required for the transmission of high forces. Applying laser welding, wide weld seams could be generated using conventional beam shaping techniques using a homogeneous intensity distribution. However, such an intensity distribution is critical if the component geometry has small radii. To solve this problem, a welding system was developed as part of the MultiSpot project, which makes it possible to adapt the intensity distribution to the weld path. For the evaluation of the new welding system, different intensity distribution profiles were developed based on bead on plate welds and then transferred to the demonstrator components.
Laser transmission welding (LTW) is a known technique to join conventionally produced high volume thermoplastic parts, e.g. injected molded parts for the automotive sector. For using LTW for additively manufactured parts (usually prototypes, small series, or one-off products), this technique has to be evolved to overcome the difficulties in the part composition resulted in the additive manufacturing process itself. In comparison to the injection molding process, the additive manufacturing process leads to an inhomogeneous structure with trapped air inside the volume. Therefore, a change in the transmissivity results due to the additive manufacturing process. In this paper, a method is presented to enhance the weld seam quality of laser welded additively manufactured parts assisted by a neural network-based expert system. The designed expert system supports the user setting up the additive manufacturing process. With the results of a preliminary work, a neural network is trained to predict the transmissivity values of the transparent samples. To validate the expert system, specimen of transparent polylactide are additively manufactured with various manufacturing parameters in order to change the transmissivity. The transmissivity of the parts are measured with a spectroscope. The parameters of the additive manufacturing process are used to predict the transmissivity with the neural network and are compared to the measurements. The transparent samples are welded to black polylactide samples with different laser power in overlap configuration and shear tensile tests are performed. With these experiments, the prediction of additive manufacturing parameters with the expert system in order to use the parts for a LTW process is demonstrated.
Today, parts based on fiber reinforced thermoplastics are used in many different applications in the aerospace and automotive industry. Furthermore, the number of parts made of semicrystalline polyphenylene sulfide (PPS) or polymers belonging to the polyaryletherketone (PAEK) family are increasing due to their excellent chemical and mechanical resistance. For some applications, these parts have to be joined to more complex structures. Besides mechanical fastening or adhesive bonding, laser transmission welding can be used when one of the joining members consists of a natural or glass fiber reinforced thermoplastic. The transmissivity of the joining members for the wavelength of the laser has an influence on the welding parameters. Often, diode lasers are used emitting in a wavelength range from 808nm to 980nm. At this wavelength range, PPS and PAEK have a lower transmissivity than for example at 1530nm. Therefore, a change of the used wavelength should affect the welding process. In order to determine this influence, a study was conducted comparing the welding process with diode lasers emitting at 940nm and 1530nm focusing on welding times. In these investigations, the joining members were made of glass fiber reinforced PPS and carbon fiber reinforced PPS.
An adequate use of finite resources is one of the greatest challenges of our times. To address this, lightweight concepts based on continuously fiber reinforced composites (FRC) are already being adapted for the transportation industry, especially within the automotive and the aerospace sectors. In order to broaden the use of lightweight composite structures and components, suitable processing, monitoring and control techniques are required for a variety of materials, constituting a prerequisite for economic, flexible and automated high volume production. In this regard, photonic technologies can provide valuable solutions. In this presentation, the latest developments within the field of FRC laser machining are summarized. For the processing of large structures such as resin transfer molding parts, combinations of galvo scanners with robots or axis systems are of particular interest. For this purpose, both high brightness cw fiber lasers and pulsed systems are used. Within the repair chain for valuable FRC parts, pulsed UV and NIR lasers are used for the precise removal of fiber layers in order to generate a defined scarfing. For both applications, disintegration of the fiber matrix interconnection due to thermal impact has to be avoided. Thermoplastic composites are becoming increasingly important for many industrial applications. In contrast to thermoset systems, welding techniques are particularly applicable. In this context, laser welding is not limited to the joining of transparent-absorbing-combinations, as it is required for conventional laser transmission welding processes but can be extended to the welding of structural parts consisting of high-performance carbon fiber reinforcements.
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