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Laser sintering (LS) enables cost-effective production of small batches as well as complex functional integration due to the direct build-up process without the need for specific tools. Further, geometrical restrictions are non-existent or only very limited. The combination of LS components with series components, for example, from injection molding (IM), allows to follow the growing trend of customizing and time tightening in the development process as well as the implementation of application-specific functions in small quantities. In order to exploit these potentials, reproducible and mechanically highly loadable joining processes are required for joining LS and IM components. Vibration welding represents a highly robust and stable process, which in this study is investigated for the production of LS-IM joints. Thereby, the focus is on the existing interactions between the two joining partners in the bonding zone. The investigations show that high bond strengths (in the area of the base materials) can be achieved by vibration welding. In contrast to other joining processes such as infrared welding, the bond quality is only marginally affected by the welding parameters. The characteristics of the weld seam are striking. While on the IM side a typical seam structure as known in the literature results, it deviates significantly for the LS side. Independent of the weld parameters, a highly oriented microstructure is recognizable that exhibits transcrystalline structures. In addition, less melt is generated and displaced into the weld bead for the LS component. Both aspects have been attributed to the different material properties of the joining partners.

Continuous Fiber Reinforced Thermoplastic (CFRT) hybrid parts offer interesting possibilities for lightweight application, which can exceed the capabilities of mono material metal or CFRT parts. In this case, the joining technology oftentimes is the limiting factor. This study investigates a joining operation with metal pin structures which are additively manufactured via powder bed fusion featuring different diameters and tip geometries, which are inserted into the locally infrared heated CFRT part. The resulting fiber rearrangement is assessed using transmitted light microscopy, confocal laser scanning microscopy as well as micro-computer-tomography. It could be shown that for all assessed pin variants a similar distinct fiber displacement can be seen and that the pin diameter has a significant effect on the resulting fiber orientation with smaller pin diameters being advantageous because of gentle fiber displacement and reduced undulation. The tip geometry has only minor effect on the fiber orientation. Especially in the X/Y plane no systematic influence of the tip geometry on the fiber displacement could be observed. Based on the gained insights a three-stage model of the fiber orientation processes is proposed.

A major challenge in manufacturing polymer-metal electronic systems, for example, encapsulations of metal inserts using assembly injection molding, is to create a tight sealing in order to prevent leakage. One typical reason for leakage is the formation of gaps between polymer and metal. Through labyrinth seals, which can be manufactured by structuring of the metal surface, the gap-based leakage networks can be interrupted. However, in order to use the appropriate structure in the right position, knowledge about the formation of the gaps is essential. The research covered in this paper focuses on the analysis of the formation of gap-based leakages in polymer-metal electronic systems with labyrinth seals to improve the component design of such parts. The effects of different embossed labyrinth seals, which differ in depth and features, and an electrochemically manufactured areal seal on the tightness and leakage position are investigated. Furthermore, the formation of the leakage network is presented for the investigated variants.

Regarding the necessity of lightweight construction, performance and design, composites are well established. At this moment, the joining of these composites still is often a major challenge. While suitable technologies like welding, sticking or riveting do exist, there are several drawbacks of these technologies such as damaging the fiber structure and low bonding strength. The combination of welding and sewing is a novel approach to improve the bonding of glass fibre-reinforced polypropylene and the influence of the processing parameters is not yet well understood. This study aims at analyzing the influence of parameters such as operating temperature, overlap length, needle temperature and thread material on the tensile strength of thermoplastic composites joined in the previously described hybrid approach. Furthermore, the interaction between thread and composite material is investigated by a microscopical analysis. The joint strength has been found to depend on the overlap length of the joint and the results suggest a contribution of the seam to the joint strength, especially for lower overlap lengths. Influences of the processing temperature, the thread material and needle temperature are also present, however, due to the complex interaction, no systematic conclusions could be drawn for these yet. The optical analysis confirms the findings of thermoset composites stitched before impregnation, where additional seams cause dislocations and local agglomeration of fibers. Additional investigations are necessary to determine the effect of the stitching on the joint and to further the understanding of the interaction between composite and thread material.

Forming processes of continuous fiber reinforced thermoplastic materials are oftentimes limited to high volume production due to the high costs for tooling and processing machines. This study suggests the combined use of a cold and simple tool and high forming speeds to reduce tooling and processing costs and enable the usage of common stamping machines. Half sphere samples are produced from single and two-layer polypropylene and glass fiber organo-sheets in a custom built drop tower and analyzed for their geometry, degree of re-consolidation, surface quality and potential fiber damage using a variety of microscopy techniques. While only mediocre degrees of re-consolidation and limited surface qualities can be achieved with the combination of a cold tooling and state-of-the-art forming speeds of 0–0.5 ms−1, the usage of a higher forming speed of 3 ms−1, vastly improves surface qualities and the degree of re-consolidation without any detectable fiber damage. This effect is more pronounced in the dual layer material. Extensive knowledge on the forming behavior of continuous fiber reinforced thermoplastics at high cooling rates and high speeds of deformation is required for sufficient process control and future studies need to further elaborate and quantify the influencing factors and limits of high-speed forming of continuous fiber reinforced thermoplastics.

One method to produce electronic systems with high resilience is the encapsulation of metal inserts, for example, lead frames, using assembly injection molding. Such parts are exposed to different mediums, such as water and oil, which can infiltrate and damage the electronic system, especially in automotive applications. Hence, one challenge is to ensure the tightness. The research covered in this paper focuses on the assembly injection molding of tight electronic systems using microstructured metal inserts, manufactured by a two-stage electrochemical treatment. The effects of the electrochemical treatment on the tightness and the bond between metal and polymer of the electronic system are investigated. Furthermore, the influence of the electrochemical treatment on the surface and geometry of the metal insert is evaluated.

The joining of distinct incompatible materials, like metals and polymers or fiber-reinforced polymers, is gaining in importance, especially for lightweight applications. Here, it is advantageous if the materials can be joined during the manufacturing of the hybrid component. Besides conventional technologies, like over-molding or the use of adhesive bonds, the use of micro structures is a promising approach for in-mold assembly. However, the characterization of these micro structures to assess the bond strength is difficult, especially for a load perpendicular to the joining surface. This paper deals with the assessment of the bond strength of polymer-metal hybrid structures with micro-structured metal inserts by the use of roughness parameters. The micro structures were produced by electrochemical treatments.

Due to the cost-efficient injection molding process and its high degree of freedom in design injection molded gears are widely used in actuating drives. One important functional requirement is the positioning precision of these systems. In gear applications, this precision is mostly dependent on the transmission error. Therefore, a lot of effort in mold design and construction is spent on ensuring acceptable transmission errors of injection molded plastic spur gears. To predict the transmission error of injection molded spur gears, an integrative simulation method is developed in this work. First, the injection molding process is simulated. The resulting gear geometry is transferred to the mechanical model of a flank-rolling test to evaluate the transmission error. The transmission error is mainly dependent on the local shrinkage and warpage caused in the solidification processes during injection molding, which in turn are influenced primary by tool design and process parameters. It is shown, that accurate simulation results concerning gear geometry, require a precise modeling of the process, tool and material. This includes accurate modelling of injection and temperature parameters, gate and cooling design, and behavior of the material. The simulation of the flank-rolling test has to take the specified reference torque and testing speed into account to ensure a realistic prediction of the resulting transmission errors. The research is done on gears with module 1 mm and 39 teeth. According to the model, the gate design has the highest influence on the transmission error. An increase in transmission error of 100% is predicted for gears with three symmetric pin-point gates compared to a central pin-point gate, and an increase of 50% for an eccentric pin-point gate. Therefore, if sufficiently modeled, a realistic prediction of transmission errors is possible.Due to the cost-efficient injection molding process and its high degree of freedom in design injection molded gears are widely used in actuating drives. One important functional requirement is the positioning precision of these systems. In gear applications, this precision is mostly dependent on the transmission error. Therefore, a lot of effort in mold design and construction is spent on ensuring acceptable transmission errors of injection molded plastic spur gears. To predict the transmission error of injection molded spur gears, an integrative simulation method is developed in this work. First, the injection molding process is simulated. The resulting gear geometry is transferred to the mechanical model of a flank-rolling test to evaluate the transmission error. The transmission error is mainly dependent on the local shrinkage and warpage caused in the solidification processes during injection molding, which in turn are influenced primary by tool design and process parameters. It is shown, that accurat...

In order to achieve sustainable and resource-saving products, the use of intelligent lightweight design is a current trend. One approach is the implementation of multi-material systems. However, the joining technology poses a key challenge when combining different materials like continuous fibre-reinforced thermoplastic composites (CFRTP) and metal or joining steel and aluminium. Due to different material properties and partial chemical incompatibilities, established joining techniques without auxiliary element, like welding or clinching, are reaching their limits. Joining dissimilar materials through pin structures has proven as a possible strategy to produce hybrid multi-material systems on a laboratory scale. Nevertheless, this technology is hardly used in mass production due to the currently complex, uneconomical pin manufacturing process. In this work, cold forming is presented as a promising approach for the production of such pins. In a first step, the pins are extruded from a steel sheet (DC04). In a second step, the steel sheets are joined with aluminium (EN AW-6016) or CFRTP by either pressing pins directly into the material or by caulking pins with a pre-punched joining partner. The material for the pin is extruded directly from the sheet metal thus preventing additional weight in contrast to fasteners. In addition, the direct press-fit is a suitable method to achieve a tightly sealed joint. Within this work, the extrusion of the pin, as well as the two different joining operations, are investigated showing the fundamental applicability and the potential of the new joining process. In order to analyse the applicability of the joining operation shear tensile tests are conducted.

The development towards higher individualization and functional density pushes the need towards a flexible production of multi-material and lightweight components. In this paper, extrusion based additive manufacturing was used to produce polymer-metal hybrids with polypropylene and aluminum alloy. For this purpose, a screw-driven extruder on a six-axis robot was used. Due to the adhesion incompatibility of polypropylene and untreated metals, the surface of the aluminum sheets was electrochemically micro-structured. The investigations show that this enables a mechanically stressable joint through the filling of the surface microstructures with polymer. Investigations on lap shear joints reveal a distinct influence of the contact temperature between the polymer and metal onto the lap shear strength. A sufficient contact temperature is required for filling surface microstructures. Thus, increased metal and extrusion temperatures favor higher strengths. Furthermore, the use of a consolidation roll shows beneficial influences in lower temperature ranges due to the application of higher pressures during the polymer strand deposition.

As a new and innovative processing method for carbon fiber reinforced thermoplastic composites, the In-Mould-Impregnation process (IMI) adopts carbon fibers as a heating element by electrical conduction. During heating of the dry carbon fibers in the production process, temperatures up to over 500°C can occur. However, the surface properties of carbon fibers and sizing may change under such conditions and thus affect the resulting composite. The present study is a practical approach to validate the suitability of sized carbon fibers for the IMI. The influence of a thermal treatment according to the parameters of the IMI-Process on carbon fiber-thermoplastic matrix interfacial adhesion was investigated by means of micromechanical and optical test methods. The experimental results demonstrate that the thermal treatment of carbon fibers causes a reduction of tensile strength of single fibers. It does not show an influence on the micromechanical breaking behavior in a PA 6 composite but the surface tension of carbon fibers changes. The change in surface tension can affect the wettability of the carbon fiber with a thermoplastic matrix.