Fusible core molding

This technology is also called fusible core molding, soluble core technology (SCT), lost-wax molding, loss core molding, etc. This technique is a take off and similar to the lost wax molding process used... 

Developments. A variety of process modifications aimed at improving surface finish or weld line integrity have been described. They include gas assisted, co-injection, fusible core, multiple Hve feed, and push—pull injection mol ding (46,47). An important development includes computer-aided design (CAD) methods, wherein a proposed mold design is simulated by a computer and the melt flow through it is analy2ed (48). 

The basics observed in molded products are always the same only the extent of the features varies depending on the process variables, material properties, and cavity contour. That is the inherent hydrodynamic skin-core structure characteristic of all IM products. However, the ratio of skin thickness to core thickness will vary basically with process conditions and material characteristics, flow rate, and melt-mold temperature difference. These inherent features have given rise to an increase in novel commercial products and applications via coinjection, gas-assisted, low pressure, fusible-core, in-mold decorating, etc. 

Soluble core molding The soluble core technology (SCT) is called by different names such as soluble fusible metal core technology (FMCT), fusible core, lost-core, and lost-wax techniques (3). In this process, a core [usually molded of a low melting alloy (eutectic mixture) but can also use water soluble TPs, wax formulations, etc.] is inserted into a mold such as an injection molding mold. This core can be of thin wall or solid construction. 

Lost-wax Also called RP molding, fusible-core. A bar (or any shape) of wax is wrapped with RP. After the RP is cured (bag molding, etc.) in a simplified restrictor mold to keep the RP-wax shape, the wax is removed by drilling a hole or removing the end caps by applying a low temperature so that the RP is not effected (review in this chapter INJECTION MOLDING, Modified... 

The original development was by Porsche, in 1972, but the mass-production breakthrough was by Ford Europe, molded with fusible core technology by Dunlop Automotive in the UK (subsequently taken over by Siemens). Ford s interest dates back to the 1970s, when it developed a manifold compression molded in TS polyester BMC, but... 

The fusible-core technique provides the designer with a different processing method for each different shape. Some examples of recent products produced with it include the tennis racket and automobile engine intake manifold. These designs permitted injection molding in bent or curved shapes. 

Both shape and design details are heavily process related. The ability to mold ribs, for example, may depend on material flow during a process or on the flowability of a plastic reinforced with glass. The ability to produce hollow shapes depends on the ability to use removable cores, including air, fusible or soluble solids, and even sand. Hollow shapes can also be produced using cores that remain in the product, such as foam inserts in RTM or metal inserts in IM. 

Particularly sophisticated tooling is used for major application for RTFs such as automobile air intake manifolds. These large (1.5-3 kg) moldings, in glass fiber/reinforced nylon, are IM on fusible metal cores, which are subsequently melted out, or are molded as two mirror images, which are then ultrasonically welded together. 

The core material to be used depends on the actual processing requirements, particularly temperature. It can range from a wax to different ratios of zinc-aluminum eutectic mixtures (alloys) to special fusible eutectic alloys. The core material has to melt below the melt temperature of the plastic. These shaped cores are usually inserted in a mold cavity where it is retained by the mold (such as is used with a mold core puller) or by spiders (as used in certain metal core supports for extrusion dies). After processing, the core material... 

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