Search

A reduction of material usage of cold forged components while maintaining the functional requirements is put into effect using hollow or tubular preforms. These preforms are used to meet lightweight requirements and decreased production costs of cold formed components. In order to increase efficiency of manufacturing the combined forming process "manufacturing of hollow preforms by combining the processes backward cup extrusion and piercing" was established and will be discussed in this paper. This investigation consists of the numerical identification of substantial process input variables, process outcomes, and the process limits with regard to combined forming processes in the field of cold forging. The numerical results which are relevant for further experimental studies and the influence on the produced preforms as far as surface quality and diameter tolerance are concerned will be presented in this paper. Thus, an outlook of the experimental studies will be given. [ABSTRACT FROM AUTHOR]

This study presents a strategy to improve the quality of a dry preforms. Preforming tests were performed out with one and two-layers of interlock Carbone fabric at different configurations. Initial results leaded to preforms with several defects. A new blank holder pressure and an increase of the pressure applied on the fabric allowed to improve the quality of the preforms. For the two-layer preforming, the insertion of mat fabric in the interface to decrease the friction has significantly improved the quality of the preforms. [ABSTRACT FROM AUTHOR]

Liquid composite molding is manufacturing techniques that involve the injection or infusion of catalyzed liquid resin into a mold to impregnate a dry fiber preform. The challenges of LCM processes are related to the obtaining of a complete wetting of the reinforcement as well as a reduction of the void to obtain a final product with high mechanical properties. The heating of the resin prior the injection into the mold cavity has proven to be useful to improve the LCM processes. The increasing of temperature results in a reduction of resin viscosity and allows the resin to flow more easily through the reinforcement; the cure stage is also improved resulting in a reduction of global process time required. Besides the conventional solutions to heat up the resin based on the thermal conduction, in-line microwave heating is a suitable method to heat dielectric materials providing an even temperature distribution through the resin, thereby avoiding a thermal gradient between the surface and the core of liquid resin, which could result in a premature and uncontrolled cure. In the present work, an in-line microwave system, manually controlled, have been coupled with a VARTM apparatus to heat the resin before the infusion. In addition, parallel-plate dielectric sensors and pressure sensors, embedded into the mold, were employed to track the flow front through the fiber reinforcement in two distinct cases: unheated resin and pre-heated resin. The aim of work was to assess the effectiveness of microwave pre-heating to improve the macro and micro-impregnation of dry preform. The obtained results showed capability of in-line microwave heating to shorten the impregnation of dry fabric and provide a homogeneous wetting of fibers. [ABSTRACT FROM AUTHOR]

This paper presented that the high accuracy semisteel meridian tire molding machine structure configurations, combining tyre high precision characteristics, the original structure and parameter optimization, technology improvement innovation design period of opening and closing machine rotary shaping drum institutions. This way out of the shaft from the structure to the push-pull type movable shaping drum of thinking limit, compared with the specifications and shaping drum can smaller contraction, is conducive to forming the tire and reduce the tire deformation. [ABSTRACT FROM AUTHOR]

The difficulties in performing accurate measurements of the effect of pressure on the viscosity of the polymeric materials results in a shortage of relevant experimental data in the literature. In this work, an atactic polystyrene has been characterized to determine the effect of pressure on viscosity during the injection molding process. In particular, the nozzle of the injection molding machine has been modified to host a slit rheometer that allows obtaining in-line rheological measurements by means of two pressure transducers. Slits with two different geometries have been adopted, in order to obtain a wide range of shear rates (10²-105 s-1). Experiments have been conducted at increasing injection flow rates, corresponding to different shear rates. By analyzing the measured pressures it has been possible to determine the coefficient β which describes the effect of pressure on viscosity. Results show that the effect of pressure on viscosity decreases on increasing the shear rate until a plateau is reached at very high shear rates. [ABSTRACT FROM AUTHOR]

Microcellular injection molding process is a promising solution for products with special requirements such as weight reduction, extra thin wall, high dimensional stability, clamping force reduction, etc. Despite microcellular foaming application used in reciprocating screw injection molding machine was built more than a decade, some limitations, such as poor surface quality or poor foaming control, confine the usage of this technology. Earlier CAE simulation tool for microcellular injection molding was not successful due to insufficient physical and computational considerations, limited by complicated bubble growth mechanism; so that, an economic and efficient tool for examining foaming quality of injection foaming product was lack. In this study, a recent developed three-dimensional simulation tool is used to predict injection foaming process. Predictions are carried out with commodity polypropylene and polystyrene with nitrogen and carbon dioxide supercritical fluids (SCFs). Comparisons of simulations between microcellular injection molding with and without counter pressure are discussed to provide insights into the correlation of surface quality and cell size distribution near the surface of product. Furthermore, comparisons between simulation predictions and experimental results of molding process, which is featured with dynamic mold temperature and gas counter pressure, are given for understanding quality improvement by controlling foaming morphology, and benefit of industrial application. [ABSTRACT FROM AUTHOR]