Proto Labs recently introduced an overmolding service to its line up of prototyping and production services. This capability can produce 25 to 10,000+ custom overmolded parts in 15 days or less. This process suits prototyping and low-volume production.

Overmolding is a two-part injection molding process where a flexible thermoplastic or thermoset material is overlaid onto a second substrate part, which is typically make of a more rigid plastic. At Proto Labs, overmolding requires the manufacture of two separate molds. A substrate part is molded in a desired material, then it is hand loaded into a second mold so that a second material can be molded onto that substrate. This is often referred to as pick-n-place overmolding.

The overmolding process allows parts to be delivered much faster than traditional molding. Proto Labs uses proprietary technology to analyze part geometry, provide design and manufacturability feedback, and produce tools in a fraction of the time that is traditionally needed.

Here are a few guidelines to keep in mind when planning to use this service:

Part Sizes

• Maximum part size of 8 in. by 16 in. by 6 in. (203 mm by 406 mm by 152mm)

*Height may be limited if using a LSR as the overmold material

• No deeper than 3 in. (72 mm) from any parting line

*Deeper parts are limited to a smaller outline

• Maximum projected mold area of 175 sq. in. (1,129 sq. cm)
• Maximum part volume of 59 cu. in. (966cc)
• Minimum part volume of 0.025 cu. in. (0.39cc) *Smaller if side-actions are required

Tolerances

• Substrate
• ±0.003 in. (0.08 mm) for machining tolerance with an included resin tolerance of no less than 0.002 in./in. (0.002 mm/mm)
• Overmold
• If LSR then 0.025 in./in. (0.025mm/mm)
• If thermoplastic then same as substrate

Adhesion

Chemical bonding between materials is possible, but close attention must be paid to material compatibility to achieve the desired bond strength. Incorporation of an adequate mechanical bond is strongly recommended if bonding is critical to your application. An undercut is a good example of a mechanical bond.

Materials

• Production grade thermoplastics and liquid silicone rubber materials available.
• Customer supplied thermoplastic material is accepted
• Customer supplied liquid silicone rubber material and customer supplied substrates are not accepted

Proto Labs Inc.
www.protolabs.com