Full definition
Transfer molding is a specialized rubber molding process that integrates aspects of both compression and injection molding techniques. In this process, uncured rubber is placed into a transfer pot, which is a chamber positioned above the mold. A piston mechanism applies pressure to force the rubber through sprues and into the closed mold cavities. This approach effectively mitigates the flash issue commonly associated with compression molding, where excess material can escape and create unwanted protrusions. By enclosing the mold, transfer molding enhances dimensional control and allows for the molding of complex shapes, particularly those with thin walls. The typical operational parameters for transfer molding include a transfer pressure ranging from 50 to 200 bar and temperatures between 150 to 180°C. The advantages of this method over traditional compression molding include reduced flash production and the ability to mold around metal inserts without disturbing them, making it ideal for applications where precise placement of components is critical.
Transfer molding is particularly advantageous when compared to injection molding, primarily due to lower tooling costs. The machinery required for transfer molding is simpler and more cost-effective, making it well-suited for small to medium production volumes. However, one of the trade-offs of this process is the potential for material waste in the transfer pot and sprues, which can lead to pad waste. Additionally, the cycle times for transfer molding are generally longer than those for injection molding. Despite these disadvantages, transfer molding remains a preferred choice for certain applications, particularly in producing rubber-bonded-to-metal parts like bushings and mounts, as well as for creating multi-cavity seals and complex geometries where other molding methods may result in excessive flash. The process can utilize either integral pot presses, where the pot is built into the mold, or plunger-type presses, which provide flexibility depending on the specific requirements of the production run.