In overmolding, three 3D CAD models — substrate, overmold and assembly files — must be provided. When parts are ready to be ordered, your designs move to the mold designers at Proto Labs, where we develop your models in their negative image to digitally design two halves of each mold, or the A-side and B-side. The mold designers create the shutoffs and the parting lines — which are custom to your geometry — as well as layout of the gate(s) and ejector pins. The mold designs are sent back to you for final approval, and when ready, the necessary toolpathing begins to mill your mold.
Our designers toolpath the CAD models to our CNC machines instructing the end mills where to travel on the X, Y and Z planes, so the machine can rapidly mill both sides of both molds out of aluminum blocks. Any pickouts, cams or additional mold features that need to be fitted are also created at this time. Your molds are now in a Proto Labs surface finish stage of F0, or as-milled. The molds move into our build department where a mold operator is assigned to polish them to your desired level of finish. All of the ejector pins are then cut to length, the A-side and B-side of the substrate mold are assembled to the press and final fittings are done to ensure the mold will seal properly once resin is injected.
Resin pellets — from either a stocked or customer supply — are loaded into a barrel where they will eventually be melted, compressed and injected into the substrate mold’s runner system. Hot resin is shot into the mold cavity through the gates and the part is molded. Ejector pins facilitate removal of the part from the mold where it falls into a loading bin.
When the total run of substrate parts are molded, overmold tooling is then assembled to the press. The substrate parts are placed by hand into the mold where each part is overmolded with either a thermoplastic or liquid silicone rubber material. The part is ejected and the pick-n-place process begins again. When the run is complete, parts (or the initial sample run) are boxed and shipped shortly thereafter.
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