Custom Services

Over Molding and Insert Molding

Over Molding and Insert Molding in Low Volume and Prototype Projects
Over Molding and Insert Molding in a prototyping or low volume production environment is the molding process in which one material (typically a soft material or a color accent material) is molded over a second material (typically a rigid plastic or a metal). Through thoughtful selection of materials, the over molded material will form a strong bond with the substrate material that is maintained as the product is used. One typical example of over molding is a toothbrush handle with a soft grip. Many interior parts in luxury automobiles are insert or over molded. Planet Proto can simulate overmolded soft plastics over hard plastics and hard plastics over metal components (known as insert molding). Overmolding can provide exciting features and new applications in products. By using color change in combination in an application, new finishes can work together to give a product a great look while delivering new or integrated function. Overmolding is usually associated only with higher volume injection molding. Planet Proto can deliver these options to its customers through the Planet Cast low volume and prototype production process. The Planet Cast process also molds Flex soft materials over existing injection molded parts in many cases.

Planet Proto’s plastic over plastic approach is parallel to two shot over molding in injection molding. If the need is for a soft over hard plastic, Planet Proto will use one of the Flex (elastomeric) Series materials over a rigid or Ultimate Series material. If it is not practical in the Planet Cast process to mold soft over hard material, a Planet Proto representative may recommend gluing the soft material over the hard material. This approach is not typical, but is sometimes the best approach in prototyping and low-volume manufacturing.

Insert Molding
One of the most widely used custom processes at Planet Proto is insert molding. This process is where a pre-molded insert is placed into a mold and the Flex (elastomeric) material is cast directly over it. Planet Proto has over molded antennas, cable ends and cooling features (blocks of machined aluminum) into plastic parts. Planet Proto also has over molded rigid plastics over sheet metal components in quantities of thousands. If there is a delicate antenna design that may be deformed or upset in the high pressure injection molding process, Planet Proto can offer the right approach for your production application.

Why Overmold Parts in Prototypes?
The best prototypes fully represent the production options being explored for full-scale production. Over molding also improves grip in dry conditions. Over molding helps increase the comfort level of grips on tools and handheld items. It helps eliminate vibration noises or provide vibration dampening while providing ease of assembly. Over molding also provides a water-resistant seal and sound absorption.

Overmolding considerations in Injection molding
In injection molding, insert molding is the preferred process when annual production volumes and local labor costs are low. For higher volume production programs (over 250,000 units annually) or areas with increased labor costs, multi-shot molding operations are the method of choice.

In an injection molding overmolding application, the challenge lies in achieving maximum adhesion between the Thermo Plastic Elastimer and the substrate. Material suppliers of TPEs are very helpful in defining substrate materials that have the adhesion characterizes needed.

Successful insert molding in injection molding usually requires the substrate component to be designed with mechanical features that lock once the over mold shot has been injected.