A soft-to-the-touch overmolded urethane exterior can add impressive user benefits to a die cast housing: enhanced grip and feel, added case damage protection, water resistance, and, in the case of electronic enclosures, even added heat dissipation. A die cast housing itself, of course, will provide built-in EMI/RFI shielding, plus, in thin-wall magnesium, one of the highest strength-to weight ratios of any cast material.
While die casting offers similar opportunities to plastic molding in reducing part counts and assembly time by the design of as-cast features into a housing itself, overmolding allows the additional integration of mechanical features in the overmold which would otherwise require added cost and assembly. Die cast housings can incorporate detailed features with tolerances critical to exacting shut-offs required in the overmolding process, with dimensional consistency vital to a part destined for use as a cast insert in the overmold tool. Tiny "gripper" teeth can be cast along a part’s entire perimeter, designed to attach the low durometer elastomer overmold to the die casting in precise position. Secondary machining may be required to deliver the part to final dimensions required for successful overmolding.
The tighter tolerances required for the die cast part must be reviewed carefully in order to serve as a repeatable cast insert in the overmold tool.
Overmolding can be ideal in the following situations:
Injecting rubber over a cast metal substrate (insert molding)
Injecting rigid plastic over a cast metal substrate (insert molding)
Begin with a die cast substrate. The substrate is then placed into an injection molding tool and plastic is molded onto or around the casting. Common examples of this are structural frames for consumer electronics devices, telecommunication devices and other hand-held applications.
● Eliminates the need for assembly operations like gluing and fastening.
● Increased design flexibility, Creates design functions and features that are not feasible by plastic alone.
● The encapsulating process can add strength and durability to parts.
● Increased part consistency.