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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 manufacturing cost of using Liquid Composite Molding (LCM) processes has been mitigated with the use of flow simulations. Flow simulations can predict how the resin flows in a mold containing fiber preforms and can identify possible void formation locations. Simulations have been used over the last decade for mold and process design, process optimization and even process control. The results are very dependent on the input material parameters provided to the simulation. Most important of these parameters is the fiber preform permeability. Fiber preform permeability is a second order symmetric tensor which requires the determination of six independent components in any given coordinate system. For thin parts, 2D simulation is sufficient which requires only the in-plane permeability, either two principal values and the orientation of principal axes or two normal and one "skew" component. Several methods to obtain these values have been reported. For thick parts, particularly when distribution media is used on the part surface, through the thickness permeability is needed as well and can be measured and has been reported. However, three-dimensional tensor contains not only this (normal) transverse permeability but also two additional skew components. These are, in practice, neglected as it is assumed that fabric layering produces symmetry in the through thickness direction. This assumption is somewhat questionable in the first place, but it becomes truly invalid when thick, three-dimensionally woven or braided reinforcements are used. The geometry of weave with skew terms in the through thickness direction can influence the flow behavior and hence the void formation. In this study, we present a measurement work station that will provide all the six components of the permeability tensor from one experiment. The methodology uses flow visualization data to collect the flow front motion information and then couples it with a multi-objective optimization algorithm and our flow simulation tool, LIMS, to determine the permeability tensor. The entire process is automated and experimental results are superimposed on the simulation results. Permeability values in the simulation are updated until the error between the experimental and the simulation results is minimized for all permeability components. This algorithm is utilized with 3D preforms to test its applicability. The experimental results are discussed in terms of the applicability of the developed algorithm. [ABSTRACT FROM AUTHOR]

Laminate structure of fiber preform is an important factor in determining the processing conditions of liquid composite molding as well as mechanical properties of fiber reinforced composite product. In resin transfer molding process, fiber preform deforms undesirably by the flow pressure of resin, which causes defectives in size, properties and appearance of the final composite products. Therefore, process condition should be strictly controlled in order to prevent preform deformation in the molding process. Several types of fiber deformation such as slip, wrinkle, and contraction are observed by structural and process related factors. In this study, structural factors of fiber preform affecting the flow induced fiber deformation in resin transfer molding are investigated, which include fiber volume fraction and laminate structure of fiber preform. Effects of laminate structure are investigated by measuring two important factors which are hydrodynamic friction coefficient between fiber and mold surface and bulk stiffness of fiber preform in the mold. The former is related to slip and the latter is related wrinkle and contraction of fiber preform. Several kinds of fiber mat such as unidirectional and woven fabrics are tested and the resulting flow induced deformations are predicted and compared with the observed deformations in resin transfer molding. Woven structure of the most outer layer was an important factor in friction related deformation and the overall structure of the fiber preform affected the local deformations such as wrinkle and compaction. It is expected that the unexpected fiber deformation can be prevented by optimum design of laminate structure considering fiber deformation as well as mechanical properties of composite. [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]