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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-crystal-line 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., 52:884-892, 2012. © 2011 Society of Plastics Engineers, INTRODUCTION Thermoforming is one of the most important techniques in polymer processing besides injection molding, extrusion, and blow molding. With a large variety of process variants a heated thermoplastic sheet [...]

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. Index Terms--Brushless de motor, finite-element method (FEM), permanent magnetic rotor, sensor traces.

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.

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]