Over Molding – the lower volume answer

Published On: July 26th, 2022|Categories: Blog|

When your volumes are thousands and not millions, you can still utilize positive design characteristics like multiple colors and/or a mix of hard and flexible materials.

Historically, two shot molding was the means to utilize two different thermoplastics in a component design to create design features like grips, hinges, airtight seals, gaskets, and much more. At the same time accommodating multiple colors and making for more aesthetically desirable parts. Two shot molding evolved into the creation of specialized presses that have two barrels to accommodate the two resins and the design of complex molds. Think of two different layers of materials or colors coming from the injection molding press. The first material is injected into a mold to create the first layer. The first layer solidifies and cools before being moved — by hand, robot arm, or mold function — to a second cavity of the mold. The complexity of the mold involves the mold opening and the side with the first shot rotating 180° to meet the other injection molding nozzle. Once in place, the second material is injected and bonds with the first layer to form a firm hold. Once the second layer cools, the final part is ejected.

A common misperception is that two shot molding requires the specialized two shot press and complex mold to interface with it, and justify for only for high volume applications, e.g., consumer products, medical disposables, and the like.

Overmolding is a viable option and the positive choice for low to medium volume, batch run type parts in industrial, telecom, agricultural, HVAC and more. Utilizing two cavities in either the same mold or two separate molds, the process of applying an initial layer followed by a second layer can be utilized in two separate press runs. Either manually or through robotics to shuttle parts between the two cavities, the low to medium volume OEMs can achieve the same design and aesthetic goals of their large volume competitors. Examples here at PlastiCert include:


Medical disposable with overmolded gasket                                   Agricultural product – chemical resistant first shot with structural overmold

Interested in exploring the possibilities of overmolding your parts in two shots? Give us a call or drop us a line through our website. We would be happy to show you want we have done, and what we can do for you!

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