In this paper, first results regarding the realization of laser-based hot-melt bonding of additive manufactured plastics parts to metal sheets for strong and tight multi-material joints are presented. Compared to earlier investigations, in which nearly solely extruded plastic materials were applied, the use of additive manufactured plastics complements the research field with a promising approach. Besides the typical advantages of multi-material joints regarding weight reduction and high strengths, such parts can meet the needs of constructional freedom and the avoiding of tool costs. Materials used for this paper are aluminum (AlMg3), stainless steel (1.4301) and polyamide 12 (PA12). The performed experiments resulting in multi-material joints between metal and polyamide. The realized specimens undergo a tensile shear test and a tightness test, in which the characteristics of the joints are determined.

The generation of multi-material components by laser beam melting (LBM) is a challenge which requires the invention of new coating devices for preparation of arbitrary powder patterns. One solution is the usage of vibration-controlled nozzles for selective deposition of polymer powders. Powder flow can be initiated by vibration enabling a start-stop function without using any mechanical shutter. In this report, the delivery of polymer powder by vibrating nozzles is investigated with respect to their application in LBM machines. Therefore, a steel nozzle attached to a piezo actor and a weighing cell is used in order to measure the stability and time-dependence of the powder mass flow upon vibration excitation with the usage of different kind of powder formulations. The results show that precompression of the powder inside the nozzle by vibration excitation is essential to realize a reliable start-stop function with reproducible discharge cyles and to prevent a initial flush of powder flow. Moreover, the use of different powder materials showed that mass flow is even possible with powders which are not optimized regarding flowability, but is readily enhanced with a factor of 2 to 3 by admixing Aerosil® fumed silica.

Due to continuous improvements in process technology additively generated components are increasingly used for prototypes and small series devices. In comparison to conventional manufacturing process chain, additive manufacturing enables in principle embedding of conductive circuits and electronic components during the part building process. However, technologies like Selective Laser Sintering (SLS) or stereolithography (SLA) imply disadvantages concerning high process temperatures or time consuming cleaning steps. In contrast, Fused Deposition Modeling (FDM) seems to be well suited for production of mechatronic integrated devices due to the use of thermoplastic materials for electronic productions (e.g. ABS, PC/ABS), a low thermal load of electronic parts and a simple process management. In this paper, additive manufacturing of mechatronic devices by means of FDM in combination with direct printing of silver ink for generating conductive circuits is investigated. The silver ink is deposited in the matrix or applied on the surface of the part by a dispensing system during the building process. The in situ sintering process of the ink is carried out by a subsequently infrared laser (IR) irradiation. In order to generate components with a high mechanical stability the adhesion of the extruded material strings is optimized considering processing temperature and flow properties of the extruded thermoplastics (ABS, PC/ABS). Furthermore, depending on the flow behavior important FDM process parameters (e.g. volume flow, hatch distance) are adjusted to minimize cavities and generate media-tight components. The conductive circuits are characterized with respect to their electrical conductivity and mechanical stability.

During the last years, several studies have been conducted to improve the laser-based heat conduction joining of thermoplastic metal hybrids. Most scientists tried to improve the joint quality by a prior surface enlargement of the metal in order to achieve a strong mechanical interlocking. Only a few authors investigated hybrids which consist of merely cleaned and not additionally enlarged metallic specimens. For merely cleaned specimens, Katayama et al. postulated the bubble theory which suggests that small bubbles near the metallic interface are very important for strong joints. The bubble formation leads to a high pressure between thermoplastic and metal so that the thermoplastic melt wets the metallic surface and an anchor effect occurs. Investigations by the author confirm the anchor effect theory, but the bubble theory itself cannot be verified since strong joints can be realized without the formation of bubbles. On the contrary, it seems rather advisable to avoid bubbles because they indicate a thermal decomposition of the plastic. However, there is still no sufficient description of the relationship between process parameters, joint morphology, and resulting joint strength. The main objective of this paper is to point out the process-structure-property relationship of laser-based joined thermoplastic metal hybrids.

The objective of this paper is to investigate how microstructures generated by ultrashort pulse laser structuring of stainless steel affect the laser-based joining of thermoplastic metal hybrids. For structuring experiments a picosecond laser (X, = 1064 nm) is used. The machined surfaces are topographically analyzed by optical microscopy. The experimental setup for the joining process consists of a disk laser (X, = 1030 nm), a scanner optic and a clamping device for lap joint. The joined specimens are mechanically analyzed by tensile shear tests and the influence of ultrashort pulse laser structuring on the mechanical properties of the dissimilar joints is evaluated. Besides, a fracture analysis of the mechanically tested specimens using scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDX) mapping is done.

Shorter production cycles and development times for molded interconnect devices (MID) result in increasing production of cost intensive injection molding tools. Thus, a manufacturing technology for a fast and flexible production of complex prototypes and small series without the use of additional tools is needed. A possible solution is the layerwise manufacturing of mechatronic components by fused deposition modeling (FDM). By additionally embedding electronical components during the additive manufacturing process, electronic functions can also be integrated. In this paper, an experimental investigation for printing of conductive circuits on FDM components by dispensing silver ink and subsequently sintering by laser irradiation is determined. To prevent infiltration of silver ink into the matrix material after application, important process parameters will be optimized getting a media-tight surface.

Thermal malleability of thermoplastics results in a high product diversity in various industry sectors. However, industrial applications require a constant and high component quality. Hence, material processing such as laser welding has to consider that, e.g., the moisture content of thermoplastics influences the mechanical properties such as the tensile strength. Moreover, water evaporates during laser welding and can form pores and defects. Thus, there is a large need for non-invasive material inspection before processing. To that end, we developed a methodology based on Raman-microscopy and multivariate data analysis (MVD) to determine the moisture content of polyamide (MCP). Further, the impact of the MCP on the mechanical properties was verified. For samples with a defined variation of the MCP, xyz-Raman-scans were carried out and analysed using MVD. For reference purposes, the samples were weighted and tensile tests were performed. An evaluation by means of partial least squares regression analysis (PLSR) resulted in a prediction of the MCP with a correlation coefficient >98%. Consequently, Raman-microscopy shows large potential for developing new techniques for inspection and quality control of plastics before processing.Dedicated to Professor Alfred Leipertz on the occasion of his 70th birthday. (C) 2016 Published by Elsevier B.V.

In future, the use of tailored multi material parts consisting of thermoplastics and metals will increase especially in the field of automotive applications based on the pursuit of lightweight design. This provides completely new demands on automated manufacturing because dissimilar materials have to be joined reliably. A promising approach is the thermal joining by laser radiation which enables a non-contact, automated and reproducible production of thermoplastic metal hybrids. Thereby, laser radiation heats the metal and through heat conduction the thermoplastic melts and wets the metal surface. The surface topography of the metallic joining partner plays an important role for the strength of the hybrid joint. In this paper, a novel approach for the fast and flexible fabrication of part-adapted surface structures by means of laser cladding with powder injection is investigated. The aim of the performed experiments is to find out how the geometry and arrangement of additive manufactured line-like metallic structures affect the strength of the dissimilar joint. Therefore, the height and width of the structures are varied. The structure geometries are investigated by microscopy of cross-sections and laser-scanning microscope measurements. As substrate and powder material stainless steel is used. Finally, the metallic samples are joined with polyamide 12 by means of laser radiation and mechanically analyzed by tensile shear tests.

In this paper, first results regarding the realization of multi-material parts by Simultaneous Laser Beam Melting (SLBM) of polymers are presented.This new approach allows the layerwise generation of parts consisting of different polymer materials within one building process.Besides the typical advantages of additive manufacturing technologies, such parts can fulfill different product requirements concomitant and therefore could enlarge the overall field of application.The powder materials used for this paper are polyethylene (PE) and a polyamide based thermoplastic elastomer (TPE).After depositing the powder materials next to each other, infrared-emitters heat the lower melting polymer and a CO 2 laser provides the preheating temperature of the higher melting polymer.In the last step, a thulium fibre laser melts the two preheated powders simultaneously.The realized specimens are characterized by cross sections and their tensile strengths are determined.Additionally, the new approach of the simultaneous energy irradiation is investigated using a Finite Element Analysis in order to gain a more profound process understanding.In that sense, the influence of the size of the exposure area on the reachable maximum temperatures inside that area was analyzed by the simulation and compared to experimental studies.

The requirements for mechatronic devices in terms of functionality, integration density and costs have risen according to the different application areas whereby a high demand for complex mechatronic modules exists. Furthermore, fast implementation of mechatronic modules in series production requires functional prototypes in the early stages of the development process. However, the manufacturing technology offers several methods which are suitable for prototype and small series production. In this context, the stereolithography (SLA) is a suitable technology, which can be used for production of functional prototypes. The layer-wise building process by means of laser polymerization of resin offers the integration of e.g. sensor functions without thermal damaging and opens up new possibilities for the realization of multifunctional components with high integration density. In addition, embedding of electronic circuits provides protection against environmental influences. The following paper presents a hybrid manufacturing technology that combines stereolithography and dispensing system technologies to fabricate mechatronic devices with embedded electronic circuits. This so-called embedding stereolithography (eSLA) requires a flexible and modular system technology which allows continuing the layer-wise process after integration of the electronic circuit. In order to fulfill this requirement, the laser sintering of silver filled conductive adhesive is an appropriate method to create conductive circuits directly after dispensing on the current surface of parts. Additionally, the placement of the electronic components could be realized by preformed cavities of SLA parts and the contacting of them could be done in situ by laser radiation. Thereby, the conductive adhesive is used like solder for fixing and contacting the components. In this paper, the laser sintering of conductive adhesive on SLA parts using UV-laser radiation (λ = 355 nm) is investigated regarding the transition resistance * Corresponding author. Tel.: +49-(0)9131-97790-27; fax: +49-(0)9131-97790-11. E-mail address:b.niese@blz.org of contacted components by four point measurement and the characterization of laser contacted components by cross sections. The investigations are intended to evaluate the beam-matter-interaction of the silver filled conductive adhesive and the UV-laser radiation by an optical analysis of the material, the curing behavior and the long-term stability of the contacting under environmental stresses.

In former works, the optical material properties of different polymer powders used for Laser Beam Melting (LBM) at room temperature have been analyzed. With a measurement setup using two integration spheres, it was shown that the optical material properties of polymer powders differ significantly due to multiple reflections within the powder compared to solid bodies of the same material. Additionally, the absorption behavior of the single particles shows an important influence on the overall optical material properties, especially the reflectance of the powder bed.Now the setup is modified to allow measurements at higher temperatures. Because crystalline areas of semi-crystalline thermoplastics are mainly responsible for the absorption of the laser radiation, the influence of the temperature increase on the overall optical material properties is analyzed. As material, conventional polyamide 12 and polypropylene as new polymer powder material, is used. By comparing results at room temperature and at higher temperatures towards the melting point, the temperature-dependent optical material properties and their influence on the beam-matter interaction during the process are discussed. It is shown that the phase transition during melting leads to significant changes of the optical material properties of the analyzed powders.

In this report, the delivery of polyamide 12 (PA 12) powder and powder layer preparation by vibrating steel nozzles is investigated and discussed with respect to its application for laser beam melting. Therefore, a setup was realized which includes a steel nozzle attached to a piezo actor as well as a positioning system. In order to investigate the mass flow characteristics in dependency on the applied vibration state, a weighing cell is used enabling time-resolved mass flow measurements. Moreover, single-layer patterns consisting of colored and uncolored polyamide 12 were created and characterized regarding surface homogeneity and selectivity before as well as after the melting of the powder layers by a hot plate.

By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam–matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.

The embedding stereolithography (eSLA) is an additive, hybrid process which combines the flexible production of 3D-components with the integration of electrical and optical conductive structures and functional components. This combination of several process steps in one manufacturing process implies a high technological potential regarding the integration density of the assemblies.To create conductive circuitsinside and on the surface of SLA-parts, the manufacturing process of these structures has to be integrated into the SLA-process and shouldnot contain disassembling of partsfrom the SLA-building platform. In this context, the production of embedded conductive circuits by means of dispensing conductive adhesivesand laser sintering is a highly promising process.The dispensing can be made during the entire SLA-process by interrupting it. In this way the conductive adhesive can be deposit inside the part and the electrical conductivity of these structures will be achieved by laser sintering in the next step.This paper shows fundamental investigations concerning the applicability of the conductive adhesive for embedding stereolithography and the laser sintering process as well.

In this report, the dry delivery of polyamide 12 powders by vibrating capillary steel nozzles is investigated and discussed regarding its potential for powder layer preparation in Laser Beam Melting. Therefore, a setup including a steel nozzle assembled on a piezoelectric actuator is presented, which enables the precise control over very small powder quantities by vibration excitation. An analysis reveals that the mass flow through the nozzle can be adjusted by the vibration modes in a certain range depending on the nozzle's specifications, whereas the vibration modes themselves show a complicated behaviour. Using a positioning system in combination with the vibrating nozzle, single-layer patterns consisting of polyamide 12 are produced and characterized regarding surface homogeneity and selectivity using a laser stripe sensor.

By simultaneous laser beam melting (SLBM), different polymer powders can be processed to multi-material parts, which offers the potential to enlarge the field of application for conventional LBM. In a SLBM process, a powder bed consisting of different polymers and therefore with different melting and crystallization temperatures is deposited. Besides the use of infrared emitters for preheating the lower melting polymer, a CO2 laser distributes the necessary preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser distributes the energy necessary for melting the two preheated powders simultaneously. In order to analyze the temperature gradients of the process on the powder surface and in deeper layers, a high-resolution thermal imaging system and thermocouples are used.

Embedding stereolithography (eSLA) is an additive, hybrid process, which provides a flexible production of 3D components and the ability to integrate electrical and optical conductive structures and functional components within parts. However, the embedding of conductive circuits in stereolithography (SLA) parts assumes usage of process technologies, which enables their direct integration of conductive circuits during the layer-wise building process. In this context, a promising method for in-situ generation of conductive circuits is dispensing of conductive adhesive on the current surface of the SLA part and its subsequent sintering. In this paper, the laser sintering (λ = 355 nm) of conductive adhesive mainly consisting of silver nanoparticles is investigated. The work intends to evaluate the curing behavior of the conductive adhesive, the beam-matter-interactions and the thermal damage of the SLA substrate. The investigations revealed a fast and flexible laser sintering process for the generation of conductive circuits with sufficient electrical conductivity and sufficient current capacity load. In this context, a characterization of the conductive structures is done by measuring their electrical resistance and their potential current capacity load.