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Optimizing production of multiresin, multipart plastic devices

Posted by Jenna Vogel on Aug 31, 2011 1:00:00 PM
Jenna Vogel

We have been seeing a huge increase in requests for overmolding and two-shot applications. This is particularly true of OEMs wishing to produce high-quality and aesthetically pleasing handheld gadgets and devices.

In reality, what the customer is often requesting isn’t necessarily one or the other in terms of terminology. Rather, what the customer needs is a means to produce a part or device that has both hard and soft surfaces and may have a need for color or textural variation across subcomponents. With fairly recent advances in resin engineering technology, such considerations may be accomplished via either overmolding or two-shot molding. Determining which method will be most efficient in terms of cost and production capability—especially early on in the development and design process—is key.

Overmolding is an injection molding process in which two unique resins are combined to get different textural or color combinations. This is closely related to “insert molding,” in which a premolded insert is placed into a mold and a (softer) material is shot directly over it. In either case, standard injection molding machines can be utilized via two separate operations.

With two-shot (or multishot) molding, a substrate material is molded during first part of cycle; then the platen rotates to position it for a second material to be molded over substrate. This more advanced method of injection molding requires special injection molding machines with two or more barrels.

It used to be that two-shot molding was necessary in order to get a good bond between the substrate and the overmolded material, but that is not the case anymore. With today’s engineered resins, a material can be formulated to bond well to almost any substrate. Having two options to get the same desired result opens the door to get very creative with today’s designs and allow a better evaluation of which process is the most cost effective. For example, two-shot molding has definite cycle time advantages, but tool costs are typically higher.

Not all plastic injection molders have two-shot capabilities. Having that option, and the engineering expertise to determine the best production method, is one of the advantages that my customers seem to really appreciate. Kaysun’s ability to bring that to the table is a great asset in my ability to help find solutions.

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