Generally speaking, the overmolding process is the same as an injection molding process, except that the plastic is molded over another component. The difference lies in operation. With overmolding, the substrate is loaded into the mold on each cycle. In addition, how the substrate is loaded creates two different overmolding operations:
Manual Molding
With a manual operation, the substrate is injection molded via a traditional injection molding process. The substrates are then hand-loaded into another mold for the overmolding operation. The operator will also remove the finished part from the mold, provide an inspection, and package the parts. Manual overmolding is the most common procedure for low to mid-volume overmolding.
The advantage of manual overmolding is simplicity. The tooling required for the substrate and overmold is simple (when compared to two-shot tooling), and there is no secondary equipment required. The downside is the labor allocation and potential for inconsistent cycle times created by operators. As annual order volumes increase, the labor involved can become significant enough to justify investment in automation systems or a two-shot molding operation.
Two-Shot Molding
More advanced injection molding machines can run two different polymers at the same time. Two-shot molding uses a more complicated mold and robotics so that the substrate is molded on one side of the mold and then transferred to the other half of the mold on each cycle. The process requires a more advanced injection molding machine and mold, but it may yield a lower piece price compared to manual operations.
Deciding between the two molding operations is done on a case by case basis. There is no universal rule as to when an automated overmolding operation is justified. To provide the end-user with the best option, injection molders will look at several variables, such as: labor allocation, annual order quantities, budget, material usage, cycle time, etc.
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