What are insert molding and encapsulation?


Encapsulation or insert molding is the process of adding inserts to your molded part. It is a very effective way to add strength and stiffness to the finished product without giving up any of the weight or the flexibility. Thermoset poleutharyne is a very effective choice for insert molding. The lower molding temperature and the pressure when compared to other materials get rid of the risks of inserts such as damaging the metal and wood during the whole molding process. Reaction injection molding technology provides the opportunity for a wide variety of encapsulations. It can be anything from simple additions such as metal rods and plates to complex electrical components or materials. The options can be unlimited. Adding inserts to your project can create an even better strong and durable part than ever before.

Insert molding or also known as encapsulation or multi material molding can be done in a lot of different ways. Smaller encapsulations can be placed into the mold and can be molded around through a traditional process. However special variations on the traditional molding can be used when particular large inserts, a certain high number of inserts or multiple different materials are needed for a part. The three most common and frequent varieties of insert molding are multi component injection molding, multi shot injection molding and over molding.

By multi component injection molding we understand when multiple materials such as metal and plastic, or thermostat polymer and thermoplastic are injected in a mold simultaneously. These materials mold around each other and creates a strong structure which can be compared to a sandwich and it has excellent cohesion. It is also known as co injection molding.

Multi shot injection molding is the process in which materials are injected into the mold once at a time in a selected specific sequence. This can create a structure which is aesthetically pleasing and structurally pleasing ‘layered geometry’. It also features strong bonds between materials that are similar to multi component molding. This is also known as sequential molding process.

Over molding is another molding variant in which a material, usually polymer resin is layered on top of an existing molded component.  This creates a unique design which features different geometric designs and layers around a central core structure. It can often be done by using standard injection molding or RIM equipment. In the mean time multi component and multi shot injection molding can require specialized tools.


Regardless of the process used, it is very important to properly prepare the insert before starting the molding. Hollow inserts must have the insides and ends sealed with thermoplastic (click here) and caps. All inserts should be cleaned and roughened at the same time to make way for good and proper cohesion and adhesion with the materials. In some cases, it is recommended that the insert should be treated with and insert promoter before molding.

It is recommended to observe the minimum distance between the insert and the mold wall.