It can be made from a low melting point metal, such as a tin-bismuth alloy, or a polymer, such as a soluble acrylate.
[7][8] One key in casting metal cores is to make sure they do not contain any porosity as it will induce flaws into the molded part.
Another system slowly rocks the casting dies as the molding cavity fills to "shake" the air bubbles out.
[9] The metal cores can be made from a number of low melting point alloys, with the most common being a mixture of 58% bismuth and 42% tin, which is used for molding nylon 66.
The bath temperature is slightly higher than that of the core alloy's melting point, but not so high that it damages the molding.
The advantage to using a hot bath is that it is simpler than induction heating and it helps cure thermoset moldings.
The disadvantage is that it is uneconomically slow at a cycle time of 60 to 90 minutes and it poses environmental cleanup issues.
The disadvantage is that induction heating does not remove all of the core material so it must then be finished off in a hot bath or be brushed out.
[12] Traditional horizontal injection molding machines have been used since the mid-1980s, however loading and unloading 100 to 200 lb (45 to 91 kg) cores are difficult so two robots are required.
These types of machines only require one robot to load and unload cores and have a 30% shorter cycle time.
[13] The greatest advantage of this process is its ability to produce single-piece injection moldings with highly complex interior geometries without secondary operations.
Other advantages include:[4] Two of the major disadvantages of this process are the high cost and long development time.
[1][14] One of the difficulties that result from these long development times and high costs is making accurate cores repeatably.
The fusible core process finds application, for example, for injection molded passenger car engine intake manifolds.