Mold filling structuring

Eq. (12) has commonly been used, e.g. in the analysis of mass and gas transfer in gas-filled systems. From this relationship it may be deduced that varies from 0 to 00 and that = 1 when G = 0.5. Systems for which G 4 0.5 are poorly gas-filled ( low-porous ) and those with G > 0.5 are highly gas-filled . The rule of reciprocals ( reversal rule ) facilitates the analysis of gas-filled structures such as foamed plastics by enabling the use of the so-called complementary gas-filled (porous, cellular) systems. The complementary systems relate to each other as a mold and casting or negative and positive . 

The reasons for this Include such things as reduced density to lower cost, Increased ease of mold filling, and Improved part surface apppearance. The microcellular structure which makes these benefits realizable Is achieved by nucleatlon, either with a gas such as air or nitrogen, or by Incorporating a blowing agent In the system formulation. An IMR agent must, therefore, not affect the cell structure or the stability of the nucleated froth It must... 

Scheme 1. Templating steps induding both casting and coating approaches. Schematic illustration demonstrating the casting and coating of a star-shaped template. The casting technique gives a composite in which the second material fills the area around the mold so that on removal of the mold a structured material is obtained, which is an inverse replica of the initial template. In contrast, coating of the template results in a layer of the second material aroimd the mold, resulting in a hollow replica on removal of the template...

Injection molded plaques or bars of PLC have a skin—core structure [33]. The molecular chains in the skin regions are largely aligned in the mold fill direction while the chain orientation in the core is more or less random. The high molecular alignment in the skin layer is induced by the elongational stress in the fountain flow and is immediately frozen upon contact with the mold surface. 

Permeability to resin flow To achieve the highest mechanical properties, the designers would like to have high fiber volume fraction but they should not forget that this decreases the permeability of the preform, and thus the resin flow will be more difficult. High preform permeability allows rapid mold filling under constant pressure injection, or lower injection pressure under constant flow rate injection. The permeability is dependent on the fiber structure (tex of the yarns, type of the fabric, orientations of the plies and fiber volume fraction which is dependent on the compaction of the preform in the mold cavity). 

Darcy s law describes the overall relationship between the velocity and the pressure gradient, and not the details of the velocity and pressure at each point inside the microscale fiber structure. Usually, this is sufficient to model the resin flow in RTM while designing the mold as we are interested in macroscopic variables such as mold fiU time, maximum value of the injection pressure required and locations of gates/vents to ensure complete mold filling. 

Bickerton, S., Sozer, E. M., Graham, P. J. and Advani, S. G., Fabric structure and mold curvature effects on preform permeability and mold filling in the RTM process. Part I Experiments , Composites Part A Applied Science and Manufacturing, 31(5), 423 38, 2000. 

Once a geometric model of data base is created it may be shared for many of the product development steps described earlier. The data base may be copied and scaled for shrink factors to enable a mold designer to do preliminary mold design, or an engineer can use the same data base to perform structural analysis. Numerical control tool paths may be developed concurrently with the final mold design. Such modeling tools as finite element analysis, mold fill, and mold thermal... 

Bruschke, M.V. Advani, S.G. A finite element/control volume approach to mold filling in anisotropic porous media. Polym. Compos. 1990, 11, 398-405. Bruschke, M.V. Advani, S.G. RTM Filling simulation of complex three-dimensional shell-like structures. SAMPE Q. 1991, 22, 2-11. 

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