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An increased awareness of sustainability among the population leads, from an industrial point of view, to efforts to act more ecologically as well as to the aim for lower production costs and an increased efficiency. With this in mind, a new process has been developed for foaming without blowing agents in rotational molding. Process related air inclusions in the polymer melt are expanded to form the cell structure by means of vacuum application. In the presented study, the influence of different particle sizes as well as the arising potential of deploying microgranules in the otherwise powder-based process is investigated with regard to the resulting foam cells. The results confirm that particle size and form greatly influence the existence and size of air inclusions in the polymer melt. It could be proven that these differences, caused by the particle characteristics, propagate during the foaming process and lead to different cell morphologies in the resultant foam. Furthermore, it is indicated that qualitative predictions of the resulting cell dimensions can be made on the basis of bulk density measurements and the analysis of the sintering behaviour of the initial particles. [ABSTRACT FROM AUTHOR]

Powder bed-based additive manufacturing has become increasingly important for industrial applications. In the light of this, qualitative considerations such as the geometrical accuracy, the resulting mechanical properties, and the surface quality of additively manufactured parts must be taken into account. Optical measuring techniques such as confocal laser scanning microscopy, fringe projection and focus variation as well as profilometers are evaluated here, to determine the surface quality of powder bed-based manufactured parts. Even though these surface evaluation methods are established commercially, no standardized measuring procedure has yet been established. Within an experimental study the validity and accuracy of surface measurement methods are evaluated below, taking the limitations of each measurement system and the comparability of areal surface textures into account. The examinations are carried out with the powder materials EN-AW2024, Ti-6V-4Al and PA12, which are processed by electron beam melting, and laser beam melting of metals and polymers. Guidance for a consistent and comparable surface evaluation is thereby provided. [ABSTRACT FROM AUTHOR]

In the product manufacturing cycle, the joining of polymers often takes a central position. Vibration welding is characterized by short cycle times, high process flexibility and stability as well as by the achievement of high bond strengths without using additives. However, the vibration welding process is clearly restricted by a necessary adhesion compatibility of the joining partners. By means of structuring one joining partner and subsequent filling of the structures by a second joining partner, the joining by form-fit using vibration welding enables the combination of adhesion incompatible polymers. Within these investigations, bonds between adhesion incompatible semi-crystalline thermoplastics were generated based on mechanical adhesion. Also semi-crystalline and amorphous polymers could be connected for the first time without any connecting elements, although they conventionally do not show mechanical resilience. The analysis of the thermomechanical material properties and the resulting multimaterial link enabled the determination of first influences on the resulting formfit connection caused by the occurring joining zone temperature. [ABSTRACT FROM AUTHOR]

Continuous fiber-reinforced thermoplastics (CFRTs) can in combination with high-strength metals offer characteristics that cannot be achieved with mono-material parts. One possible example is the combination of locally high-temperature resistance in the metal component with superior weight-related mechanical properties due to the CFRT component. This approach requires a reliable and durable joining technology, which considers the material-specific properties and allows to exploit the full potential of CFRT/metal hybrid parts. A promising approach in the field of CFRT/metal joining is the use of metallic pins, which can be embedded in the locally heated CFRT component to create a form-fitting joint. In the current state of the art, primarily single-pins are investigated and characterized: especially the distinct fiber orientation in the direct pin pressing process is only described for single-pin joints. Behind this background, the present study aims at creating an understanding of the fiber orientation mechanism for multi-pin arrays. Therefore, in the scope of this study, unidirectional reinforced glass fiber/polypropylene samples are joined via direct pin pressing and infrared heating with different 1D and 2D multi-pins arrays with different pin-diameters, spacing and pin distributions. The resulting joint morphology is consequently analyzed using micro-computer-tomography. Based on the performed investigations, a model for the fiber displacement mechanism is proposed, and the first recommendations for the design of fiber-friendly multi-pin joints with unidirectional reinforcements are given. It showed that especially pin-spacing in fiber orientation in dependency of the pin diameter is critical for a fully reconsolidated joint quality, and it is suggested that a pin-offset in the fiber direction is beneficial for a fiber-friendly joining process.

Radiation cross-linking of polyamide 66 with electron beams alters the material's characteristics. This leads to a varied relationship amongst the process, structure, and properties for infrared welding cross-linked polyamide 66. A threedimensional network of covalent bonds results in an impeded melt flow and altered welding characteristics. Compared to non-cross linked polyamide, a changed energy input in the weld during infrared heating and a reduced meltdown can be observed. Such thermal developments and a reduced meltdown affect the resulting weld strengths. Welding factors of almost 60% of base material strengths can be achieved. A clear influence of the heating time on the weld strength can be observed. The scope of this article is to investigate the influence of radiation cross-linking on the material characteristics and, by extension, the resulting processing and welding characteristics. Mechanical and optical investigations serve to highlight the influence of radiation cross-linking on the infrared welding process of polyamide 66. [ABSTRACT FROM AUTHOR]

Compared to amorphous thermoplastics, semi-crystalline thermoplastics usually have a smaller processing range for thermoforming, due to their narrow temperature window for the transition from viscoelastic to viscous material behavior. On the other hand, semi-crystalline thermoplastics offer superior properties for applications like ductility or chemical resistance. Within this article, modification of semi-crystalline polyamide 12 by radiation cross-linking with respect to its suitability for vacuum thermoforming as well as the effects of processing parameters and sheet thickness on the resulting strain distributions in thermoformed parts are shown. Experimental thermoforming processing studies in combination with digital image correlation measurements, thermo-mechanical and elongational rheometry were performed to characterize the behavior of cross-linked semi-crystalline thermoplastics in the vacuum thermoforming process. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: To mold thin-walled and micro scaled parts high flow rates and injection speeds are required. Otherwise, incomplete filling can occur due to rapid cooling of the polymer. Furthermore, high flow rates improve the molding quality of microstructures. It is well known, that high injection speeds in micro-molding can cause a melt compression. Thus, the implied flow rates are not achieved and the process becomes unstable. Expansion–injection–molding (EIM) makes use of this physical effect of melt compressibility. In a first step of the process the melt is pressurized. Due to the pressure drop after opening the compression chamber a high flow rate develops. The filling process itself is not influenced by the machine-setup or process control. This paper introduces a new modular mold design for EIM by cavity near melt compression. The great advantage for micro-molding is the reduction of the length of the flow path and consequently of the pressure loss as well as the melt volume required. The process characteristic was analyzed by molding a downscaled tensile bar using a Polyoxymethylene resin. A robust process at very high flow rates was verified. In comparison to conventional injection molding the maximum flow rates were about 10 times higher. [Copyright &y& Elsevier]

The microinjection moulding process is subject to microspecific phenomena, such as rapid cooling or high shear rates, which greatly affect part properties. While the correlations between morphology, crystallinity and the mechanical properties are well known for parts of usual macroscopic dimensions, there is less information available for microparts. In this paper, these correlations are discussed, related to the dimensions of semicrystalline thermoplastic parts. Results indicate that, if submitted to rapid cooling, microparts exhibit a fine structure, with low crystallinity, low yield strength and low elastic modulus. Experimental investigations have shown the influence of process parameters to be negligible. More important are the material's rate and ability to crystallise, which allow for properties to be significantly enhanced. Another possibility to considerably improve the performance of microparts independent of the used polymer is processing with slow cooling in thermally conductive moulds. [ABSTRACT FROM AUTHOR]

The instrumented falling weight perforation impact behavior of coinjection-molded multipolypropylene sandwich plaques of various compositions having a β-phase isotactic polypropylene (PP) homopolymer core was studied at room temperature and T=-40°C, respectively. The results were compared with those achieved on injection-molded monomaterial plaques of α- and β-polymorphs. It was found that the coinjection strategy is beneficial only if the skin-forming α-phase PP has a markedly lower molecular weight than the β-nucleated core PP. Sandwich plaques with PP copolymer skins exhibited an outstanding perforation impact resistance. The coinjection strategy for extrusion grade PPs yielded no improvement. Perforation impact at T=-40°C showed a prominent toughness reduction of the multipolypropylene plaques which became comparable with that of the monolayer plaques. [ABSTRACT FROM AUTHOR]

This paper deals with the computation, production and test results of a rotor for brushless dc motors, consisting of two different permanent magnetic materials as well as having three different magnetic field areas. The main advantage of this highly integrated system of low costs is the implementation of two additional magnetic traces for commutation and speed detection into one single unit. [ABSTRACT FROM AUTHOR]

Recently, there is rising demand of electronic systems with functional density for industrial and automotive applications. Those components, which are typically manufactured by overmoulding blanked metal inserts within an assembly injection process, are often exposed to rough operating conditions. Especially penetrating water can lead to a severe damage of electronic systems which are often crucial to safety. Leakage can be caused among other things by crack initiation within the polymer at sharp edges of the metal insert as a consequence of stress concentration. In order to reduce stress concentration the effect of metal inserts with rounded edges and the forming process to manufacture such inserts is investigated. Since typical sheet thicknesses for electronic components are 1 mm and less the dimensions of the rounded edges are on the scale of micro features. The microforming operation of rounded edges is provided by open coining. The influence of varying part dimensions is investigated using FE-simulation. Furthermore, ideal rectangular insert shapes are compared to parts with sheared edge geometry. In addition the effect of rounded edges on stress distribution of overmoulded parts is analysed by combining resulting geometries of the forming simulation with the numerical analysis of stress distribution within the polymer.