Open-Mold Filling Method

Closed-mold filling method Open-mold filling method... 

TABLE 1.3 Cycle Time Comparison for Filling of a Dash Board Using the Open- and the Closed-Mold Filling Method... 

Molds can be of three basic types. Open molds are used to define one surface of a product. They can be of the female (indenting) or male (projecting) type. Two matched female half-molds can be used to make hollow items, and a matched female and male pair is used to form a cavity that is to be completely filled. Shaping of the polymer inside the mold is usually achieved by applying pressure to cause the fluid to conform to one or both mold surfaces. The variation in types of molding is primarily due to the type of mold used and the method of melt delivery to the mold. 

In ICM, the predosed, preplasticized mass is injected into the opened mold. When the mold is closed, the flowing mass fills the mold cavity. Items with large surface areas such as flat packing, membranes, and flat product trays are suited to the ICM method. 

When the open cavity is filled, slowly foaming mixtures are used because the mold has to have enough time to close. In the past, the so-called closing time was brought down to less than four seconds due to the use of constantly improving motion drives. Neverless, the cure times are longer than the cures time for the closed mold injection method of PUR systems. 

MIMIC represents another non-photolithographic method that forms complex microstructures on both planar and curved surfaces (Kim, 1995). In this process, the PDMS mold is placed on the surface ofa substrate and makes conformal contact with that surface. The relief structure in the mold forms continuous empty channels. When low viscosity sol-gel precursor is placed at the open ends of the channels, the precursor solution spontaneously fills the channels by capillary action. After filling the channels and curing the sol-gel precursor into a solid, the PDMS mold is removed, and a continuous sol-gel material remains on the surface of the substrates. 

On occasion the opening at the gate is smaller than the cavity thickness, and the melt no longer fills the mold by an advancing front mechanism. Rather, it snakes its way into the mold, leading to a material with a poor surface appearance and reduced physical properties. Snaking does not seem to be a common method found in the filling of molds, but it can occur. 

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